共查询到20条相似文献，搜索用时 703 毫秒
1.
The experiment in which a candle is burned inside an inverted vessel partially immersed in water has a history of more than
2,200 years, but even nowadays it is common that students and teachers relate the change in volume of the enclosed air to
its oxygen content. Contrary to what many people think, Lavoisier concluded that any change in volume in this experiment is
negligible; moreover, the explanation relating oxygen consumption in the air with its change in volume is known to be wrong.
In this work we briefly review the history behind the candle experiment and its relationship with some typical erroneous explanations.
One of the key factors behind Lavoisier’s success was the use of experiments carefully designed to test different hypotheses.
Following these steps, we performed several closed volume experiments where the candle wick was replaced by a capillary stainless
steel cylinder supported and heated by a nichrome filament connected to an external power supply. Our recorded experiments
are displayed as web pages, designed with the purpose that the reader can easily visualize and analyze modern versions of
Lavoisier’s experiments. These experiments clearly show an initial phase of complete combustion, followed by a phase of incomplete
combustion with elemental carbon or soot rising to the top of the vessel, and a final phase where the hot artificial wick
only evaporates a white steam of wax that cannot ignite because no oxygen is left in the closed atmosphere. After either a
complete or incomplete combustion of the oxygen, our experiments show that the final gas volume is nearly equal to the initial
air volume. 相似文献
2.
This article studies how the height of water varies with time when water flows out through a horizontal tube at the bottom of a cylindrical bottle. As an extension of the study, this article also studies the flow through two bottles. This experiment is exciting as well as thought-provoking. 相似文献
3.
李杰 《新乡师范高等专科学校学报》2007,21(5):23-25
分析了一种根据毛细现象原理设计的永动机的错误原因。指出,由于毛细管顶部表面层接触角大于零导致表面层面积减小、表面层张力减小,致使毛细管内液体实际上升高度减小,故而此第一类永动机的设计是不可能实现的。 相似文献
4.
张国钧 《华中科技大学学报(社会科学版)》2010,24(1)
市场德性,作为市场发育中自下而上、由外而内生成,保障市场健康发展,有道德意义的价值,经两种途径发育:内生,从民间自下而上、由内而外自发演进,包括主体自治、行业自律等;外赋,自上而下、由外而内人为建构,包括政府施为、法律规制等。其中,内生是基本途径,外赋须基于内生才起作用;若缺乏甚至没有内生,任何外赋都无效。市场德性和习用的市场道德有同有异:若指市场内在的道德性或道德价值,则同;若指市场须有、须受道德规范,则该道德规范在市场德性中主要是内生的自我范导,在市场道德中则除此之外更可能是外赋的规制。以自由、公平、诚信为例,有助于讨论内生的市场德性。 相似文献
5.
To figure out the distribution of temperature gradient along the girder height of steel-concrete composite box girder, combined with the mechanical characteristics of prestressed concrete composed box girder with corrugated steel webs, the calculation formulas of cross-sectional temperature stress along the span in a simply-supported beam bridge with composite section were derived under the conditions of static equilibrium and deformation compatibility of the beam element. The methods of calculating the maximum temperature stress value were discussed when the connectors are assumed rigid or flexible. Theoretical and numerical results indicate that the method proposed shows better precision for the calculation of temperature self-stress in both the top and the bottom surfaces of the box girder. Moreover, the regularity of temperature stress distribution at different locations along the girder span is that the largest axial force of the top or the bottom plate of the box girder is located in the midspan and spreads decreasingly until zero at both supported ends, and that the greatest longitudinal shear density in steel-concrete interface appears at both supported ends and then reduces gradually to zero in the midspan. 相似文献
6.
INTRODUCTION Vertical cylindrical steel tanks widely used for fluid storage generally consist of a thin bottom plate, a cylindrical shell, and a fixed or floating roof. Large tanks constructed on soft foundations are susceptible to various types of settlement deflections. The set-tlement components are: uniform settlement, planar tilt and differential settlement. The uniform settle-ment and planar tilt cause rigid-body deflection or rotation of the tank, and so, are of relatively little i… 相似文献
7.
李伟涛 《天津师范大学学报(基础教育版)》2004,5(4):18-22
在中小学，校内管理制度的产生方式有两种：自上而下制定与内生。首先指出了自上而下制定制度的缺陷，然后在哈耶克“自生自发”秩序论的启示下，提出了一种与自上而下制定制度相对应的制度产生方式——内生，最后则着重对两种产生方式进行了辩证思考，论述了两者的互补性与实现两者有机融合的关键。 相似文献
8.
HUANG Wei-jun DENG Xian-he ZHOU Shui-hong 《重庆大学学报(英文版)》2006,5(1):8-12
1 Introduction A well known method to increase heat transfer from a surface is to roughen the surface by use of regular geometric roughness elements, such as transversely-ridged tube, spirally-ridged tube or converging-diverging tube, etc., on the surface… 相似文献
9.
以北海穗丰金湾小区1#楼为例,针对85m相对悬空高度、3.8m大悬挑砼圆形构件施工过程中模板及支撑系统的设计和施工,介绍高空大悬挑砼构件模板与支撑系统的施工方案。该支模承重体系主要利用下部结构为剪力墙的受力支撑点搭设出一个钢桁架承重平台,以此来支撑上部结构施工过程中的荷载。该体系具有较高的安全性和较强的可操作性,设计思路可供建筑工程技术人员参考和借鉴。 相似文献
10.
“can’t hold a candle to”是一个很流行的表达，它起源于电还没有被发明的时期，当时人们都用蜡烛照明。住在大房子里的人通常会让仆人拿着一根蜡烛在前面照明引路。这一表达的原意是指不能拿着蜡烛给你带路的人不配当你的仆人。现在，它的意思是“远远比不上……”。比如，“辛迪唱歌远远比不上她的姐姐。” 相似文献
11.
The top‐down approach to designing a multistage test is relatively understudied in the literature and underused in research and practice. This study introduced a route‐based top‐down design approach that directly sets design parameters at the test level and utilizes the advanced automated test assembly algorithm seeking global optimality. The design process in this approach consists of five sub‐processes: (1) route mapping, (2) setting objectives, (3) setting constraints, (4) routing error control, and (5) test assembly. Results from a simulation study confirmed that the assembly, measurement and routing results of the top‐down design eclipsed those of the bottom‐up design. Additionally, the top‐down design approach provided unique insights into design decisions that could be used to refine the test. Regardless of these advantages, it is recommended applying both top‐down and bottom‐up approaches in a complementary manner in practice. 相似文献
12.
13.
Reformed at the turn of the century toward top‐down, centralized administration, city school systems are frequently being reorganized today toward a bottom‐up, decentralized construction. The most radical of these is Chicago. But Chicago, in a condition shared widely throughout the USA, is a city school system experiencing serious budgetary and infrastructure decline ‐ a condition tending anew toward organizational centralization. Such political forces may not mesh well ‐ as a new politics of adaptive realignment at the grassroots encounters renewed strength in an ‘old politics’ of bureaucratic centralization. Largely unstudied and unknown at this time are the effects on the internal politics of the organization in city schooling ‐ a politics that may adapt in some unforeseen way to new battles between top‐down and bottom‐up. 相似文献
14.
This study examined how Chinese children acquire the untaught positional constraints of stroke patterns that are embedded in left–right structured and top–bottom structured characters. Using an orthographic regularity pattern elicitation paradigm, 536 Hong Kong Chinese children at different levels of reading (kindergarten, 2nd, and 5th grades) were asked to produce invented characters with left–right and top–bottom stroke pattern pairs. Even kindergartners were aware of the positional constraints of stroke patterns and were able to produce orthographically legal pseudocharacters with different stroke pattern pairs. This ability improved across grade level. Moreover, there was a production asymmetry in which children produced more top–bottom structured pseudocharacters than left–right structured pseudocharacters. The error pattern analysis further revealed that more positional errors were observed in producing left–right structured noncharacters than in the top–bottom structured noncharacters. This production asymmetry seemed to reflect children’s experience with a distribution asymmetry observed between left–right (59.19%) and top–bottom structured characters (23.46%) in a corpus of school Chinese. These results are discussed within the framework of statistical learning of orthographic regularity in Chinese. 相似文献
15.
1）万圣节前夜点燃放在南瓜灯里的蜡烛可以使妖魔鬼怪远离。2）万圣节前夜如果蜡烛突然自然熄灭,看上去是被人或是被风吹灭,其实都意味着鬼魂来了。3）在万圣节前夜为了保证好运气,一定要点新的蜡烛。一年中除万圣节前夜外点燃那种蜡烛可不是一个好主意,可能会带来坏运气,或引发奇怪的事情,而你对此却没有丝毫控制能力。 相似文献
16.
尹湘兵 《韩山师范学院学报》2003,24(1):12-18
史学界对戊戌变法“自上而下”的变法道路颇多微词，认为正是由于走了“自上而下”的变法道路才导致了变法的失败。该文并非是探讨变法失败的主要原因，而是旨在说明康梁等维新派走“自上而下”变法道路的历史合理性。他们之所以走这条道路，不仅仅是由于这种“自上而下”的改革道路已经在中国和世界的历史上都有一些成功的范例，更是由康梁等维新派在戊戌之前所承继的历史前提所决定的。 相似文献
17.
梁桂芳 《新疆师范大学学报(哲学社会科学版)》2001,22(4):60-65
唐代有近七百篇写到蜡烛的诗，由于当时蜡烛价值不菲，且它的出现是在夜晚这一特殊时空，其本身形态，光线等又具有某些特色，所以在诗中蜡烛意象产生了宝贵化，女性化，温情化，悲情化等倾向。同时，蜡烛意象蕴含了越来越强烈的主观情感，至中晚唐，烛意象的表现趋于成熟，出现人格化意象。 相似文献
18.
王书艳 《洛阳师范学院学报》2012,31(1):63-67
灯烛从照明用具走向生活娱乐和情感寄托,成为一种文化和生命的精神载体。唐代女子在灯烛的折射下呈现出不同的生活情态,歌舞、化妆、劳作、游戏构成其夜间生活的主要内容。"花烛"和"烛泪"寓含的生命情感象征了女子人生的两个不同阶段,共同构成女子的人生经历。 相似文献
19.
在有效质量和有限高势垒近似下,变分研究了在双电子柱形GaN/Al0.2Ga0.8N量子点中掺入不同类型杂质时,杂质电子体系的基态能随杂质电荷、量子点的高度及杂质位置的变化规律。结果表明,随量子点高度增加,杂质电子体系的基态能单调递减;杂质带负电时,体系的基态能量都比较大,不易形成稳定的束缚态。随着杂质由量子点下界面沿z轴上移至上界面,对于类氢施主杂质,体系的基态能先减小后增大,在z0=1.0 nm处取得极小值;而受主杂质,变化趋势相反：体系的基态能先增大后减小,在z0=1.0 nm处取得极大值;若掺入中性杂质,杂质电子体系的基态能不变。 相似文献
20.
Mark Stubbs John Pal 《British journal of educational technology : journal of the Council for Educational Technology》2003,34(5):651-661
theRetailGame.com is a web‐based package of e‐learning materials designed to support students on retailing courses. It uses the focal point of a ‘store opening’ to draw attention to key operational variables. The web‐based package allows students to explore the impacts of variable combinations in a risk‐free environment. This paper outlines the rationale for developing this new package; explains the design principles underlying its construction; and describes the delivery and assessment mechanisms in which it has been embedded. The case history of the project is reviewed, and actor‐network theory is used to characterise the alignment of requisite time and expertise as a feat of engineering, facilitated by top‐down support but dependent upon the creative manoeuvrings of the bottom‐up enthusiast. 相似文献