脂肪酶发酵条件的统计学优化     

徐健全  郑连英 《科技通报》2007,23(4):568-573

从受油烟污染严重的土壤中分离到一株脂肪酶产量较高的菌株，通过统计实验设计的方法对发酵过程进行了优化。首先，通过Plackett-Burman设计实验，对影响产脂肪酶发酵的碳源、氮源、无机盐、pH、温度和转速等因素进行考察。通过实验，发现黄豆粉、K2HPO4和摇床转速对脂肪酶的产生影响较大。随后，利用曲面响应法中的中心点设计进行实验，以上述3个因素作为自变量。以发酵液的酶活作为响应，通过拟合最终得到了脂肪酶发酵的响应曲面函数。对该函数在一定的约束条件下求极值．得到了脂肪酶产率最大时的发酵条件。  相似文献   

Measuring knowledge integration: Validation of four‐year assessments     

Ou Lydia Liu  Hee‐Sun Lee  Marcia C. Linn 《科学教学研究杂志》2011,48(9):1079-1107

Science education needs valid, authentic, and efficient assessments. Many typical science assessments primarily measure recall of isolated information. This paper reports on the validation of assessments that measure knowledge integration ability among middle school and high school students. The assessments were administered to 18,729 students in five states. Rasch analyses of the assessments demonstrated satisfactory item fit, item difficulty, test reliability, and person reliability. The study showed that, when appropriately designed, knowledge integration assessments can be balanced between validity and reliability, authenticity and generalizability, and instructional sensitivity and technical quality. Results also showed that, when paired with multiple‐choice items and scored with an effective scoring rubric, constructed‐response items can achieve high reliabilities. Analyses showed that English language learner status and computer use significantly impacted students' science knowledge integration abilities. Students who took the assessment online, which matched the format of content delivery, performed significantly better than students who took the paper‐and‐pencil version. Implications and future directions of research are noted, including refining curriculum materials to meet the needs of diverse students and expanding the range of topics measured by knowledge integration assessments. © 2011 Wiley Periodicals, Inc. J Res Sci Teach 48: 1079–1107, 2011  相似文献   

专题征稿增强科技类学术期刊对社会热点问题的响应     

王晓飞  王少霞  邵世云  张静蓉 《编辑学报》2020,32(6):690-693

目前,科技类学术期刊对社会热点存在关注不足、响应不够的现实问题。结合《中国环境科学》对社会热点问题专题征稿的实践,总结出实施所需4方面内容:了解与期刊相关的社会热点问题、确立征稿范围、建立征稿的快速响应机制和按约定时间刊出。并对专题征稿成效及其成功与不足进行了反思和总结,以为其他科技期刊的社会热点问题征稿提供参考。  相似文献   

DNA-damage response network at the crossroads of cell-cycle checkpoints,cellular senescence and apoptosis   总被引：2，自引：0，他引：2  

Schmitt E  Paquet C  Beauchemin M  Bertrand R 《Journal of Zhejiang University. Science. B》2007,8(6):377-397

Tissue homeostasis requires a carefully-orchestrated balance between cell proliferation, cellular senescence and cell death. Cells proliferate through a cell cycle that is tightly regulated by cyclin-dependent kinase activities. Cellular senescence is a safeguard program limiting the proliferative competence of cells in living organisms. Apoptosis eliminates unwanted cells by the coordinated activity of gene products that regulate and effect cell death. The intimate link between the cell cycle, cellular senescence, apoptosis regulation, cancer development and tumor responses to cancer treatment has become eminently apparent. Extensive research on tumor suppressor genes, oncogenes, the cell cycle and apoptosis regulatory genes has revealed how the DNA damage-sensing and -signaling pathways, referred to as the DNA-damage response network, are tied to cell proliferation, cell-cycle arrest, cellular senescence and apoptosis. DNA-damage responses are complex, involving ＂sensor＂ proteins that sense the damage, and transmit signals to ＂transducer＂ proteins, which, in turn, convey the signals to numerous ＂effector＂ proteins implicated in specific cellular pathways, including DNA repair mechanisms, cell-cycle checkpoints, cellular senescence and apoptosis. The Bcl-2 family of proteins stands among ＂the mos＂t crucial regula＂tors of apop＂tosis and performs vi＂tal func＂tions in deciding whether a cell will live or die after cancer chemotherapy and irradiation. In addition, several studies have now revealed that members of the Bcl-2 family also interface with the cell cycle, DNA repair/recombination and cellular senescence, effects that are generally distinct from their function in apoptosis. In this review, we report progress in understanding the molecular networks that regulate cell-cycle checkpoints, cellular senescence and apoptosis after DNA damage, and discuss the influence of some Bcl-2 family members on cell-cycle checkpoint regulation.  相似文献   

“丝绸之路经济带”干旱-半干旱区生态环境全球变化响应的空间认知   总被引：3，自引：0，他引：3       下载免费PDF全文

李新武  张丽  郭华东  傅文学  鹿琳琳  邱玉宝  王心源  贾根锁 《中国科学院院刊》2016,31(5):559-566

在高强度人类活动和全球变化的影响下,"丝绸之路经济带"的资源环境面临严峻问题与挑战。地处"丝绸之路经济带"核心区的中亚地区的生态环境退化已经上升为全球干旱地区生态环境问题突出地区之一,严重制约了中亚及周边国家的经济与社会发展。文章针对"丝绸之路经济带"核心区的中国新疆、中亚地区及周边区域的典型生态环境要素:植被要素和水资源要素,基于长时间序列的卫星遥感数据,研究和分析了其参数时空演进格局及对气候变化的响应。研究结果表明,中亚地区近几十年的生态环境总体上呈现退化趋势,具体表现为水储量减少、湖泊面积萎缩、地表土壤水分减少和植被退化等。  相似文献   

Electronic in-class course evaluations and future directions     

Fred Kuch  Robin M. Roberts 《Assessment & Evaluation in Higher Education》2019,44(5):726-731

This study sought to determine whether an evaluator conducting electronic course evaluations in person in a classroom increased response rates. At a large public university in the United States, course evaluations were being conducted electronically, attaining a response rate of <50% over several semesters. At the end of the Spring 2015 at this university, an evaluator entered several classrooms having a total enrollment of 273 students and guided students through the process of completing course evaluations using their mobile devices. A response rate of 78.4% was achieved. The process described in this study provides evidence that response rates can be increased in similar circumstances. In addition, several ways the technology described could be used in the future for course evaluation are discussed.  相似文献   

PLC程序执行时序对控制结果的影响     

傅继军 《兰州石化职业技术学院学报》2011,11(3):23-25

可编程序逻辑控制器PLC是一种基于软件和硬件控制的工业现场计算机控制系统。在了解生产工艺和控制要求的基础上,设计系统程序时必须充分考虑到硬件的特性,编制出与硬件协调配合的程序,合理分配PLC软件程序执行时序,使控制系统能精确、稳定、快速工作。反之,则会出现一些意外故障,造成控制系统误动作。通过PLC控制电梯的部分梯形图...  相似文献   

PISA Country Rankings Valid? Results for Canada and Finland     

James McIntosh 《Scandinavian Journal of Educational Research》2019,63(5):670-678

This article examines whether the way that PISA models item outcomes in mathematics affects the validity of its country rankings. As an alternative to PISA methodology a two-parameter model is applied to PISA mathematics item data from Canada and Finland for the year 2012. In the estimation procedure item difficulty and dispersion parameters are allowed to differ across the two countries and samples are restricted to respondents who actually answered items in a mathematics cluster. Different normalizations for identifying the distribution parameters are also considered. The choice of normalization is shown to be crucial in guaranteeing certain invariance properties required by item response models. The ability scores obtained from the methods employed here are significantly higher for Finland, in sharp contrast to PISA results, which gave both countries very similar ranks in mathematics.  相似文献   

竞赛特质焦虑干扰优势反应抑制的神经准备过程:ERP的证据     

孙国晓  张力为 《天津体育学院学报》2015,30(4):307-311

竞赛焦虑对操作表现的影响是运动心理学的重要研究领域,注意控制理论对二者关系从执行功能的角度进行了新的阐释,认为焦虑干扰执 行功能中的抑制功能。近年来,运动心理学对抑制功能探讨较多,对优势反应和任务无关刺激的抑制是抑制功能的2个重要成分,但以往研究大多 集中于抑制无关刺激,对优势反应抑制的探讨相对欠缺,而后者却是竞技场上运动员时常需要面对的问题。已有行为学研究发现,竞赛特质焦虑对 优势反应抑制功能有干扰效应,但其神经机理尚待探讨。本研究采用ERP技术探讨竞赛特质焦虑干扰优势反应抑制的神经基础,假设竞赛特质焦 虑干扰前脑区域（额区和中央区）优势反应抑制的神经准备过程。招募26名研究参与者,根据《赛前情绪量表32×6》测试得分,二分法划分竞赛特质 焦虑高分组和低分组。2组均完成代表优势反应抑制功能的反向眼跳任务,分析抑制“线索”出现前-100~0 ms时程的ERP成分,发现反向眼跳的准 备期在额区和中央区诱发出一负成分,竞赛特质焦虑高分组的波幅小于低分组。以上结果部分支持了假设,竞赛特质焦虑对优势反应抑制的神经 准备期有干扰效应,且主要由前脑区域控制,此结果为注意控制理论在竞赛焦虑领域的适用性提供了神经生理学的部分证据。  相似文献   

The effect of issue obtrusiveness,issue congruence,and response strategies on the acceptance of crisis communication messages     

Heewon Cha  Jee Won Suh 《亚洲交流杂志》2015,25(3):307-326

Based on issue ownership theory, this study identifies the effects of issue obtrusiveness, issue congruence, and crisis response strategies on the level of acceptance of crisis communication messages employing 2 × 2 × 3 (issue obtrusiveness × issue congruence × response strategies: scapegoat, justification, reminder) experimental research. Two large Korean business groups (Hyundai and SK) were selected. There was a main effect in crisis response strategies and a three-way interaction effect. A crisis communication message was effective when a corporation owns congruent and unobtrusive issues. Implications for public relations research and practices were discussed.  相似文献