小小型水电站的控制系统

如果一个小型水电站并入大的电网,则电网的频率和电压处于支配地位,在这种情况下,采用一个异步发电机是有利的.若这一小型水电站向一个自动化的电网供电,而电网的负荷在一天和一年之内都发生着变化,这样使得小小型水电站既要控制电压又要控制频率,在这种情况下就必须应用异步发电机.频率调节为了减少投资,小小型水电站中水轮机常常采用具有固定导水机构和固定叶片的水轮机.因此,水轮机的转速就不能像通常那样由改变水轮机的水力矩来进行控制,此外截流阀仅能     

用于调节交流感应电机速度的独特IC控制器

用于调节交流感应电机速度的独特ＩＣ控制器廉价的交流感应电机一向需要复杂的、昂贵的速度控制机构。廉价的ＩＣ和６个ＭＯＳＦＥＴ功率管改变了这种格局Ｆｒａｎｋ　Ｇｏｏｄｅｎｏｕｇｈ许多消费类应用和工业应用都需要变速的电机驱动器，但大多数驱动器技术存在明显的...     

紫外激光冷却镁原子

利用反向激光与原子跃迁产生共振,可使Na和Cs原子减速。与Na和Cs原子相比,Mg原子结构对于冷却更为方便。Mg原子的部分能级示于图1。从图中可以看出,区别于Na或Cs原子的是Mg原子的基态没有精细结构,因此也就避免了光泵效应。当然有一定输出功率的与Mg原子的~1S_0—~1P_1产生共振跃迁的285.2nm的激光是必要的。     

在纵波和横波数据中观察到的超临界反射

我们观察了在纵波和横波地震数据中超临界反射的有趣的例子。数据是1977—1978年间由孔诺科(Conoco)横波组合爆炸计划在得克萨斯的米德兰盆地(Midland Basin)记录到的。正如资料中所观察,纵波和横波的临界角现象十分相似。在炮检距超过大约2000英尺以后,同相轴的振幅很小或不能检测出来,但排列在2500英尺到3600英尺之间时,其振幅又高于别的同相轴。在临界距离处出现的首波是微弱的,但可以观察到。纵波和横波同相轴的超临界部份的长程多次反射以预料到的倍数和炮检距出现。借助常速度时差校正可以确定它们. 声测井与岩性知识的结合使得纵波临界角现象的模型制作成为可能。当我们假定柱面波前时,模型的结果与数据的一致性是不错的。如所预期的,基于平面波的模型与所观察到的相位和振幅情况是不能一致的。勘探与数据处理中的临界反射的许多潜在应用确实来自于这样的思想,即许多超临界反射是与不同距离的相对高振幅记录有关,这里,震源产生的噪声是低的。特别对横波而言,接近临界炮检距时,在振幅上所观察到的上跳现象是非常突然的。这样就可推之,高振幅的波跳变化对于掌握反射界面处的速度对比的变化可能是有用的。     

毫米波技术的新发展—对电子战领域的挑战

引言在历史上,毫米波技术主要是从雷达和特殊的通信应用方面去讨论的,因为雷达和通信使用毫米波似乎会获得许多明显的好处。电子战系统在应用毫米波技术方面显然落后于雷达。因为电子战领域内的许多活动都是保密的,所以对真实情况很难作出正确的评价。正如任何技术学科中的普遍规律一样,毫米波技术对电子战来说,某些方面是独特的。比如,     

苏联电子支援措施的能力

引言本文的目的是介绍苏联电子支援措施(简称ESM)的概况,从而说明苏联是怎样认真对待电子战的这个重要方面的。本文完全是以公开资料所能得到的消息为基础写成的,因为有关这个问题的详细消息本来就难得发表。尽管如此,笔者还是希望本文能使那些没有机会看到苏联ESM活动的比较详细资料的读者感兴趣。     

对医药和农药制剂有特殊参考价值的悬浮剂物理稳定性

农药和医药的悬浮剂(concentrated suspension)与粉剂相比有显著的优越性,因粉剂难于分散。悬浮剂通常由0.1～10微米大小范围的颗粒分散在液体介质(一般为水)中组成,固体体积比很高(最高达60％),为了满足制剂应用中的各项基本指标、有效期及其生物和医药活性,制剂的稳定性必须加以控制。虽然在胶体科学中“稳定”一词是常用的,可是其含     

Magnetically controllable gastrointestinal steering of video capsules

Wireless capsule endoscopy (WCE) allows for comfortable video explorations of the gastrointestinal (GI) tract, with special indication for the small bowel. In the other segments of the GI tract also accessible to probe gastroscopy and colonscopy, WCE still exhibits poorer diagnostic efficacy. Its main drawback is the impossibility of controlling the capsule movement, which is randomly driven by peristalsis and gravity. To solve this problem, magnetic maneuvering has recently become a thrust research area. Here, we report the first demonstration of accurate robotic steering and noninvasive 3-D localization of a magnetically enabled sample of the most common video capsule (PillCam, Given Imaging Ltd, Israel) within each of the main regions of the GI tract (esophagus, stomach, small bowel, and colon) in vivo, in a domestic pig model. Moreover, we demonstrate how this is readily achievable with a robotic magnetic navigation system (Niobe, Stereotaxis, Inc, USA) already used for cardiovascular clinical procedures. The capsule was freely and safely moved with omnidirectional steering accuracy of 1°, and was tracked in real time through fluoroscopic imaging, which also allowed for 3-D localization with an error of 1 mm. The accuracy of steering and localization enabled by the Stereotaxis system and its clinical accessibility world wide may allow for immediate and broad usage in this new application. This anticipates magnetically steerable WCE as a near-term reality. The instrumentation should be used with the next generations of video capsules, intrinsically magnetic and capable of real-time optical-image visualization, which are expected to reach the market soon.     

Detection of vesicoureteral reflux using microwave radiometry-system characterization with tissue phantoms

Microwave (MW) radiometry is proposed for passive monitoring of kidney temperature to detect vesicoureteral reflux (VUR) of urine that is externally heated by a MW hyperthermia device and thereafter reflows from the bladder to kidneys during reflux. Here, we characterize in tissue-mimicking phantoms the performance of a 1.375 GHz radiometry system connected to an electromagnetically (EM) shielded microstrip log spiral antenna optimized for VUR detection. Phantom EM properties are characterized using a coaxial dielectric probe and network analyzer (NA). Power reflection and receive patterns of the antenna are measured in layered tissue phantom. Receiver spectral measurements are used to assess EM shielding provided by a metal cup surrounding the antenna. Radiometer and fiberoptic temperature data are recorded for varying volumes (10-30 mL) and temperaturesg (40-46°C) of the urine phantom at 35 mm depth surrounded by 36.5°C muscle phantom. Directional receive pattern with about 5% power spectral density at 35 mm target depth and better than -10 dB return loss from tissue load are measured for the antenna. Antenna measurements demonstrate no deterioration in power reception and effective EM shielding in the presence of the metal cup. Radiometry power measurements are in excellent agreement with the temperature of the kidney phantom. Laboratory testing of the radiometry system in temperature-controlled phantoms supports the feasibility of passive kidney thermometry for VUR detection.     

Antioxidant enzyme activities in beef in relation to oxidation of lipid and myoglobin

Lipid- and oxy-free radical generation has been implicated in oxidative processes which occur during meat maturation but the importance of the antioxidant enzyme (AOE) activity in these processes is not known. It was shown that metmyoglobin (MetMb) % and lipofuscin content were higher in colour-unstable muscles such as psoas major (PM) and diaphragma (D) compared to longissimus lumborum (LL) and tensor fasciae latae (TFL). Although Superoxide dismutase (SOD) activity is higher post mortem in PM and D muscles than in LL and TFL muscles, catalase and glutathione peroxidase (GPx) activities were higher only in D muscle. The higher AOE activity in colour-unstable muscles such as PM and D was not sufficient to prevent increased formation of MetMb and lipofuscin in these muscles compared to LL and TFL muscles.