共查询到20条相似文献，搜索用时 312 毫秒
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全日制普通高级中学教科书（必修加选修）物理第二册第52页,有一个利用空气柱测声波波长的实验：在盛有水的容器中插入一根两端开口的粗玻璃管,玻璃管上端放一正在发音的音叉,然后慢慢向上一同提玻管与音叉,当管内空气柱达到一定长度时,可以听到较强的声音,这时,从音叉发出进入玻管的声波和经水面反射回来的反射波相叠加,在空气柱内产生驻波。玻璃管开口处为波腹,水面处为波节,空气柱的长度为声波的1／4λ,如下图。 相似文献
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对白磷燃烧前后质量的测定进行了改进实验,选用铜片和医用注射器,分别替代教材中使用的细沙和气球,以温热锥形瓶点燃白磷代替玻璃管灼烧至红热点燃白磷：改进实验操作简单,成功率高,克服了教材申白磷燃烧前后质量测定的不足,能更好地达到预期教学效果。 相似文献
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X-射线的发现是一件很有趣味的事情。在一个玻璃管中装上两个电极,接上高电压,然后把管中的空气抽去,空气稀薄到了一定的程度,电子就可以由陰極飞射到陽極上去。这就是所謂陰極射線。陰極射線實際上是一般电子流。在平常的情况下,空气是不导电的,因为空气中的分子阻碍着电子的通行;当空气極为稀薄而兩个电極 相似文献
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本文研究飞机航电仿真器技术是针对飞机空气管理系统、风挡加热系统、旅客氧气系统等与航电系统存在输入输出交联关系以及通过航电网络传输信号相关方面仿真器技术的设计方案。飞机航电系统仿真器主要通过试验网络、仿真系统、输入/输出系统、数据监控/记录系统、虚拟面板和虚拟航电显示系统几个方面的技术来实现的。该仿真器可以仿真航电系统与空气管理系统、风挡加热系统和氧气系统之间的交联信号、数据信息以及逻辑关系,为空气管理系统、风挡加热控制器以及氧气系统提供正常工作所需的输入激励,并能够对上述系统的工作参数进行采集、传输、处理,完成系统的状态显示及控制。 相似文献
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《大科技．科学之谜》1998,(12)
普通的水在一个大气压的环境中加热至100℃时就会沸腾,并转变为水蒸汽,这是人所共知的。然而,如果在压力锅之类的密闭容器中水蒸汽不能外泄的条件下加热,那么会出现什么情况呢?这时容器内的压力会增大,沸点也会相应地升高。当温度上升到大约347℃,压力达到220个大气压时,因高温膨胀的水的密度与因高压而被压缩的水蒸汽的密度正好相同,此时的气体和液体已变得毫无区别,均为同样的气体。这一温度和压力被称为"临界点",超过临界点的状态就是超临界水。那么这种超临界水有什么特性和作用呢? 相似文献
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木薯淀粉生产厂气流干燥过程会产生静电,无接地导线泄放,成为淀粉燃爆破的点火源。粉尘泄漏,与空气混合,浓度达到爆炸极限,便会引起燃爆。加强静电防护,提高员工粉尘防爆意识与能力是预防淀粉燃爆的措施。 相似文献
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Roi Blanco Gianmarco De Francisci Morales Fabrizio Silvestri 《Information processing & management》2015
We present IntoNews, a system to match online news articles with spoken news from a television newscasts represented by closed captions. We formalize the news matching problem as two independent tasks: closed captions segmentation and news retrieval. The system segments closed captions by using a windowing scheme: sliding or tumbling window. Next, it uses each segment to build a query by extracting representative terms. The query is used to retrieve previously indexed news articles from a search engine. To detect when a new article should be surfaced, the system compares the set of retrieved articles with the previously retrieved one. The intuition is that if the difference between these sets is large enough, it is likely that the topic of the newscast currently on air has changed and a new article should be displayed to the user. In order to evaluate IntoNews, we build a test collection using data coming from a second screen application and a major online news aggregator. The dataset is manually segmented and annotated by expert assessors, and used as our ground truth. It is freely available for download through the Webscope program.1 Our evaluation is based on a set of novel time-relevance metrics that take into account three different aspects of the problem at hand: precision, timeliness and coverage. We compare our algorithms against the best method previously proposed in literature for this problem. Experiments show the trade-offs involved among precision, timeliness and coverage of the airing news. Our best method is four times more accurate than the baseline. 相似文献
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主要采用了系统学的思想,运用社会网络分析和统计学方法,分析了集群知识系统的内部结构,区分了集群知识系统中几种不同的认知角色。实证结果显示,虽然知识在空气中"均匀地扩散",但主要在一部分具有较强吸收能力的核心企业之间流动。在集群企业不同的认知角色中,技术的守门人对集群知识的获取、创造和扩散的作用最大,其他角色在认知上相对封闭。要提高集群的知识创新和学习能力,根本在于增强集群内企业的吸收能力。 相似文献
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随着数控线切割机床在实习教学中的广泛应用,在快走丝线切割加工中存在着两个常见的问题：一个是下丝轮处的穿丝和上丝麻烦的问题;另一个是水嘴由于出水孔小而容易被电蚀污物堵塞的问题。而一款自制的两用钩针可方便地解决这两个问题。 相似文献
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John Zeleny 《Journal of The Franklin Institute》1938,226(1):35-65
Several matters pertaining to the part played by tube walls, and surface and space charges in electrical discharges through rarefied gases, are briefly discussed, and experiments are described which throw light on some of the processes involved in such discharges. Measurements made under identical conditions of the falls of potential between striæ in the positive columns of discharges in hydrogen at various pressures in two glass tubes of different diameters showed that for pressures above 1.1 mm. these falls were increasingly greater in the larger tube. The results of experiments done with discharges produced under unusual conditions and bearing on the radial and axial fields present in the positive columns of discharges are described, and photographs of some of the discharges are reproduced in a part of which the positive column was made to pass through a long metal tube placed inside of the glass discharge tube, the two ends of the metal tube being at times both open and at other times both closed with wire gauzes of fine mesh. The potential assumed by the metal tube and the current flowing through its walls were measured, and special experiments were done to elucidate the process by which the current manages to penetrate the more or less field-free space inside the metal cylinder. The distributions of the space and surface charges along the length of a glass discharge tube were measured separately, at least roughly, and the nature of these distributions was found to depend markedly upon whether the anode or the cathode of the discharge tube was connected to earth, although the combined effects of the two charges of necessity produced the same field distribution within the discharge tube in both cases. The gases used in the experiments were air and hydrogen. 相似文献
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开展气候变化与空气污染之间的反馈响应研究对于有效控制大气污染与温室气体排放、应对气候变化具有十分重要的意义。本文将区域气候模型和空气质量模型有机结合,提出模型互馈集成框架结构,描述了集成中空间与时间尺度问题。将互馈集成系统总体逻辑结构划分为五个层次,即数据层、模型层、集成层、应用层和结果层。介绍了区域气候模型与空气质量模型之间的数据集成接口和功能集成接口。设计并开发了气候变化与空气污染的互馈集成系统,利用该系统可以有效模拟和预估未来区域气候变化的情况,发现空气污染与区域气候变化之间的关系。 相似文献
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介绍了SIMADYN D全数字控制系统在高线生产线上的应用,实践证明,该系统能有效提高交流调速传动控制系统的设计、调试效率,具有控制精度高、响应快速、操作可靠及易于维护的优良品质。 相似文献
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Gang Li Yahui Luo Qiang Chen Lingying Liao Jianlong Zhao 《Biomicrofluidics》2012,6(1):014118-014118-16
This paper presents an easy-to-use, power-free, and modular pump for portable microfluidic applications. The pump module is a degassed particle desorption polydimethylsiloxane (PDMS) slab with an integrated mesh-shaped chamber, which can be attached on the outlet port of microfluidic device to absorb the air in the microfluidic system and then to create a negative pressure for driving fluid. Different from the existing monolithic degassed PDMS pumps that are generally restricted to limited pumping capacity and are only compatible with PDMS-based microfluidic devices, this pump can offer various possible configures of pumping power by varying the geometries of the pump or by combining different pump modules and can also be employed in any material microfluidic devices. The key advantage of this pump is that its operation only requires the user to place the degassed PDMS slab on the outlet ports of microfluidic devices. To help design pumps with a suitable pumping performance, the effect of pump module geometry on its pumping capacity is also investigated. The results indicate that the performance of the degassed PDMS pump is strongly dependent on the surface area of the pump chamber, the exposure area and the volume of the PDMS pump slab. In addition, the initial volume of air in the closed microfluidic system and the cross-linking degree of PDMS also affect the performance of the degassed PDMS pump. Finally, we demonstrated the utility of this modular pumping method by applying it to a glass-based microfluidic device and a PDMS-based protein crystallization microfluidic device. 相似文献
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输电线路避雷线的感应电压利用 总被引：1，自引：0，他引：1
本文通过对输电线路避雷线上感应电压和感应电流的产生机理,提出了多种利用方式.加装电流检测装置,可及时监测线路断线,进行维修,保障恶劣天气时避雷线有效防雷;通过并联方式,在输电线路中途借用避雷线感应电压提供电能,添加整流装置和稳压措施,为保护和控制系统提供直流操作电源;为去污装置提供驱动,利于绝缘予去污,提高系统的酎雷水平;同时补充了避雷线防盗,提供线路照明的功能.这些多元化的功能实现,将为电力系统带来更多便利和实效. 相似文献