共查询到20条相似文献，搜索用时 46 毫秒
1.
INTRODUCTION The use of plastic greenhouses is rapidly ex-panding in China with multi-span greenhouses being the most common type. For all these greenhouses, ventilation performance is a major factor in produc-tion, influencing both climatic control and yield quality over much of the year. Natural ventilation uses very little external energy as compared with forced ventilation, but it increases the complexity ofgreenhouse structures and makes climate control more difficult. Natural venti… 相似文献
2.
We assessed undergraduates’ representations of the greenhouse effect, based on student-generated concept sketches, before and after a 30-min constructivist lesson. Principal component analysis of features in student sketches revealed seven distinct and coherent explanatory models including a new Molecular Details model. After the lesson, which described the invisible molecular behaviour of gases, this group (n = 164) produced significantly more expert-like representations of the greenhouse effect, and included fewer novice ideas. The key behaviour that greenhouse gases emit radiation in random directions is new to most students and directly counters common explanations involving reflection and ‘trapping’ of radiation in the atmosphere. Thus, learning molecular behaviour of greenhouse gases may help students replace non-expert explanatory models. This Molecular Details model has not been previously identified, and is unlikely to have emerged from human evaluation of student sketches alone. When teaching the greenhouse effect, we propose that interventions explicitly incorporate greenhouse gas behaviour. 相似文献
3.
控制环境作物生产的相关管理决策问题主要包括资金预算分配决策、环境控制决策、以及作物生产经济最优决策等.针对解决这些管理问题的需要,设计了基于决策支持的控制环境作物生产管理系统,系统以MS Access数据库的方式表示模型,并在试验温室中运行此系统,验证了相关模型. 相似文献
4.
提出一种基于变指数型扩散方程的向量值图像(例如RGB图像或多谱图像)恢复模型。在新的模型中,我们利用光滑后向量值图像的几何流形特征来判断图像的真假边缘,利用P(x)-Laplace型扩散系数来控制扩散量和扩散方向。由于扩散系数具有良好的自适应判断边缘能力,新的模型在图像恢复的同时良好地保持了图像边缘。通过数值实验,对比以往的全变差模型,所提模型具有更好的图像恢复效果,明显减少了"块状"效应。 相似文献
5.
饶钻万 《中国教育技术装备》2011,(12)
随着人们生活水平的提高,各种热水器的使用已相当普及.与之相配套的控制仪也相继问世.然而,目前市场上的各种热水器控制电路还与理想要求相差甚远.消费者需要真正的"自动"控制,以实现使用的最简单化.就像家用电视机、电冰箱一样,接通电源、设定完毕就不用再操心了.太阳能热水器作为三大热水器之一,因其无污染、使用方便、长期投入成本低等特点,而越来越受到人们的青睐,但与之配套的控制器却还一直处于研究和开发阶段,为解决水温水位的自动控制问题,本电路专门设计水温的实时监测,并在设计中将水位多级化,实现更精确的测量.本次设计运用AT89C52单片机,设计一种自动控制电路,该电路用于太阳能热水器.当使用热水器时,可以自动进行温度检测和液位检测,使太阳能自动补水或排水,真正做到最简单化.并且该电路易于扩展,可实现多点的温度检测,或者更多点的液位检测.文章详细介绍基于单片机的太阳能热水器自动控制系统组成、硬件设计. 相似文献
6.
对欧盟民航业碳排放收费问题的透视 总被引：2，自引：0，他引：2
欧盟排放交易体系是温室气体排放配额的主要交易市场,也是全球利用经济手段遏制温室气体排放的最重要的力量之一。目前欧盟正通过相关议案欲将民航业纳入该排放体系,引起了各方强烈的反响。此方案对全球温室气体减排无疑是好事,但也必将对各国、各地区民航业及经济的发展带来深远影响,同时欧盟排放体系的扩张也必将引起全球碳市场格局的变化。 相似文献
7.
采用生产取样与室内分析相结合的方法,对模拟冬棚养殖的生产模式进行了施用酵素菌对南美白对虾水质综合调控影响的研究。通过和对照组同时进行实验,结果如下：（1）酵素菌对各项水质指标的处理性能存在差异,亚硝酸盐氮、氨氮、COD等的处理性能良好,而pH、DO等处理效果相对较差。（2）施用酵素菌在10~12d内可以很好的调控南美白对虾养殖水体中的pH值、DO、亚硝酸盐氮、氨氮、COD等效果,使南美白对虾养殖池达到良好的生长水质标准;（3）实验组虾种身体清亮,大小整齐,生长速度增快,虾池水清亮。 相似文献
8.
9.
In this paper, a nonlinear dynamic MIMO model of a 6-DOF underactuated quad rotor rotorcraft is derived based on Newton-Euler formalism. The derivation comprises determining equations of motion of the quad rotor in three dimensions and seeking to approximate the actuation forces through modeling of the aerodynamic coefficients and electric motor dynamics. The derived model is dynamically unstable, so a sequential nonlinear control strategy is implemented for the quad rotor. The control strategy includes exact feedback linearization technique, using the geometric methods of nonlinear control. The performance of the nonlinear control algorithm is evaluated using simulation and the results show the effectiveness of the proposed control strategy for the quad rotor rotorcraft near quasi-stationary flight. 相似文献
10.
Simos Ikonomidis Dimitris Papanastasiou Dimitris Melas Stavros Avgoloupis 《Journal of Science Education and Technology》2012,21(6):768-779
This study explores the ideas of Greek prospective primary teachers about the anthropogenic greenhouse effect, particularly about its causes, consequences and cures. For this purpose, a survey was conducted: 265 prospective teachers completed a closed-form questionnaire. The results showed serious misconceptions in all areas (causes, consequences and cures). The most prominent misconception found by this survey is the conflation between the greenhouse effect and the ozone layer depletion, which is widely reported in the literature. There is also the notion that ??good things?? (like clean beaches) can help ameliorate the greenhouse effect, whereas ??bad things?? (like insecticides) can enhance it. One of the secondary results of the survey is that prospective teachers?? main source of information about the greenhouse effect is school. This calls for educational interventions to fight misconceptions at the source. Some suggestions are presented in this paper. The results of this study are compared with the results of two similar studies conducted in the UK and in Turkey. 相似文献
11.
Xiaoxi DONG Lilia C. DIBELLO Mehmet TÜREGÜN Ruth A. BAN 《Frontiers of Education in China》2020,15(3):403
College students experience great stress due to many factors, such as an uncertain future, academic responsibilities, and pressures imposed by social communication. Many institutions of higher education are focusing on how to mediate stressful situations and increase the subjective well-being (SWB) of students to sustain a lifestyle focused on wellness. The online survey used for this study focused on testing an exploratory SWB model by implementing partial least squares structural equation modeling (PLS-SEM) techniques. The participants were 470 college-aged students enrolled in seven different institutions in six cities across China. Findings yielded a good model fit (the Standardized Root Mean Squared Residual [SRMR] = .054) with the validity of manifest variables, reliability of the latent variables (LVs), and overall SWB model indicating moderate predictiveness (GoF R2 = .476) by the LVs. Additionally, all of the direct path coefficients and indirect path coefficients that consisted of four partial mediators and one full mediator yielded statistically significant results via bootstrapping. Furthermore, path coefficients for utilization of emotion to life satisfaction for the cognitive exercise group were significantly higher than for the non-cognitive exercise group. The findings illustrated a good model fit for an exploratory SWB model that can predict an individual’s SWB, and cognitive and non-cognitive exercises had different effects on the individuals’ SWB. 相似文献
12.
Cluster sampling results in response variable variation both among respondents (i.e., within-cluster or Level 1) and among clusters (i.e., between-cluster or Level 2). Properly modeling within- and between-cluster variation could be of substantive interest in numerous settings, but applied researchers typically test only within-cluster (i.e., individual difference) theories. Specifying a between-cluster model in the absence of theory requires a specification search in multilevel structural equation modeling. This study examined a variety of within-cluster and between-cluster sample sizes, intraclass correlation coefficients, start models, parameter addition and deletion methods, and Type I error control techniques to identify which combination of start model, parameter addition or deletion method, and Type I error control technique best recovered the population of the between-cluster model. Results indicated that a “saturated” start model, univariate parameter deletion technique, and no Type I error control performed best, but recovered the population between-cluster model in less than 1 in 5 attempts at the largest sample sizes. The accuracy of specification search methods, suggestions for applied researchers, and future research directions are discussed. 相似文献
13.
国际社会和我国政府对温室气体,尤其是二氧化碳(CO2)的排放非常重视。运用卡亚公式能找出影响CO2排放量的主要因素,为了解各因素对我国CO2排放量变化的具体影响,运用完全分解模型对CO2排放量变化的影响进行分解分析,结果发现:在1990—2006年,对我国CO2排放量增大起正作用的依次是人均GDP、人口数量、密度,起副作用的是能源强度;要减少我国的CO2排放量,必须控制人口规模、改善产业结构、能源结构和推动节能减排技术的发展。 相似文献
14.
好的大棚环境对提高大棚蔬菜产量具有积极的指导作用．文章提出了一种自动调节大棚环境的监控系统．该套系统分别对大棚的温度、湿度、含氧量以及光照度进行检测．根据这些数据实时控制空气加湿器、空气烘干器、空调、草帘等设备,使大棚环境达到理想的状态．该套系统可以避免人为控制设备运行时间过长而导致的人力、能源等的浪费,从而达到节能的目的,同时达到理想的控制目标．整个设备都是基于PLC和触摸屏组态软件的自动控制,基本无需人为操作． 相似文献
15.
近年来温室白粉虱虫害大量发生,对蔬菜、花卉等造成很大危害.为控制发生,减轻危害,现就其生物学特性和防治措施加以探讨. 相似文献
16.
林路 《邵阳学院学报(社会科学版)》1994,(5)
本文首次讨论了回归系数随机化对影响曲率的影响问题。通过比较随机化和非随机化线性模型在方差扰动,均值漂移等情况下的影响曲率,证明了线性模型的回归系数随机化后,回归系数的影响曲率缩小了。回归系数的随机化程度越小,影响曲率变化越小。当回归系数的随化程度趋于零时,随机化线性模型的影响曲率等于非随机化模型的影响曲率。最后,本文提出了一个描述影响程度的统计量。 相似文献
17.
Vaille Dawson 《International Journal of Science Education》2013,35(7):1024-1043
Climate change is one of the most significant science issues facing humanity; yet, teaching students about climate change is challenging: not only is it multidisciplinary, but also it is contentious and debated in political, social and media forums. Students need to be equipped with an understanding of climate change science to be able to participate in this discourse. The purpose of this study was to examine Western Australian high school students’ understanding of climate change and the greenhouse effect, in order to identify their alternative conceptions about climate change science and provide a baseline for more effective teaching. A questionnaire designed to elicit students’ understanding and alternative conceptions was completed by 438 Year 10 students (14–15 years old). A further 20 students were interviewed. Results showed that students know different features of both climate change and the greenhouse effect, however not necessarily all of them and the relationships between. Five categories of alternative conceptions were identified. The categories were (1) the greenhouse effect and the ozone layer; (2) types of greenhouse gases; (3) types of radiation; (4) weather and climate and (5) air pollution. These findings provide science educators a basis upon which to develop strategies and curriculum resources to improve their students’ understanding and decision-making skills about the socioscientific issue, climate change. 相似文献
18.
Ilkka Johannes Ratinen 《International Journal of Science Education》2013,35(6):929-955
The greenhouse effect is a reasonably complex scientific phenomenon which can be used as a model to examine students' conceptual understanding in science. Primary student-teachers' understanding of global environmental problems, such as climate change and ozone depletion, indicates that they have many misconceptions. The present mixed method study examines Finnish primary student-teachers' understanding of the greenhouse effect based on the results obtained via open-ended and closed-form questionnaires. The open-ended questionnaire considers primary student-teachers' spontaneous ideas about the greenhouse effect depicted by concept maps. The present study also uses statistical analysis to reveal respondents' conceptualization of the greenhouse effect. The concept maps and statistical analysis reveal that the primary student-teachers' factual knowledge and their conceptual understanding of the greenhouse effect are incomplete and even misleading. In the light of the results of the present study, proposals for modifying the instruction of climate change in science, especially in geography, are presented. 相似文献
19.
Daniel P. Shepardson Anita Roychoudhury Andy Hirsch Dev Niyogi Sara M. Top 《Environmental Education Research》2014,20(3):333-353
Although many environmental and science educators have explored students’ conceptual understandings, misconceptions, and knowledge of the greenhouse effect, global warming, and climate change, few have investigated the ways students conceptualize climate as a system or how components of the system influence climate. Therefore, the purpose of this study was to begin the process of understanding how US students conceptualize a climate system. A total of 42 seventh grade students (ages 12–13) from the Midwest completed an open-response task. From the inductive analysis of student written responses, 22 codes emerged that reflected students’ conceptions of the climate system. From these codes, three path diagrams were constructed that illustrate these students’ conceptions about how a climate system influences climate and how greenhouse gases and global warming impact the climate system. A generalized model of students’ conception of a climate system was generated. Students in this study conceptualized a climate system in a unidirectional, linear, cause and effect relationship that emphasized the atmospheric component of the climate system. 相似文献
20.
A model-based estimator design and implementation is described in this paper to undertake combined estimation of vehicle states
and tire-road friction coefficients. The estimator is designed based on a vehicle model with three degrees of freedom (3-DOF)
and the dual extended Kalman filter (DEKF) technique is employed. Effectiveness of the estimation is examined and validated
by comparing the outputs of the estimator with the responses of the vehicle model in CarSim in three typical road adhesion
conditions (high-friction, low-friction, and joint-friction roads). Simulation results demonstrate that the DEKF estimator
algorithm designed is able to obtain vehicle states (e.g., yaw rate and roll angle) as well as road friction coefficients
with reasonable accuracy. 相似文献