带有补片电极的矩形AT切石英片的厚度切变、厚度扭转和弯曲振动

本文研究了补片《矩形》电极尺寸和质量对镀膜矩形晶体片的振动和能陷的影响。文中采用晶体片振动的Mindlin二维近似方程来保留厚度切变、厚度扭转和弯曲的耦合膜。通过采用位移公式以有限元法获得数值解,此解满足晶体片的边缘静止条件和在晶体片镀膜与非镀膜交界处的应力和位移的连续条件。文內对位置对称的补片电极矩形AT切石英片进行了数值计算,获得了晶体片和电极不同尺寸和不同质量时的谐振频率及其相应的二维振动膜。Mindlin和Lee,Lee和Spencer及Tiersten把计算结果同现有的分析结果做了比较,而Curran和Koneval把计算结果与实验数据进行了比较。所得二维Bechmann数基本上取决于三个参数:电极长度与晶体片厚度之比;电极宽度与晶体片厚度之比;以及电极质量与晶体单位面积质量之比。     

卫星通信系统的现状与动向

CCC——卫星通信系统——星上等效全向辐射功率 BPK——(地面频道信号)时分——脉码调制——二重相位键控——(卫星转发器通道信号)频分多     

航天飞机的表面磨削

航天飞机提出一系列从未遇到过的工程技术问题。在许多问题中首先考虑的是表面的研制和表面的材质问题——需能够经得住重返大气层时的热量。 现请作者(加工工程师协会副会长)谈谈它是如何制做的……。 对于外层空间研究的下一个阶段将由航     

1968年国际实用温标的展望

自68国际实用温标正式通过以来,巳将近二十年了。这段时间内一直围绕继68国际实用温标之后的温标可能形式展开讨论。的确,在相当一段时间里认为1987年可能为通过新温标的日期。在70年代末期,有关计温学方面大量新工作已经取得成果。从0.5K 至金点1337K 整个范围内,热力学温度的测量已基本上完成或取得很大的进展。我们发现,热力学温度与国际实用温标明显不同,其差值比原来所估计的要大得多,特别是在0℃至460℃范围内。在0℃以下,铂电阻温度计内插方程的新工作表明,可建设一个新方程,比68温标中所使用的更精确更简单,此外还大大     

现代表面分析——俄歇电子谱(AES)和X-射线光电子谱(XPS)在冶金学中的应用

Ⅰ 前言 关于腐蚀的一个简单而直接的定义可以是:通过与周围环境作用,材料发生变质。这种变质可以表现为失去承载能力,电性能变差,尺寸改变,触媒作用变差以及表面装饰性能变坏等。我们周围有很多腐蚀的例子,本讲中我     

Evaluation of various cleaning methods to remove bacillus spores from spacecraft hardware materials

A detailed study was made of the biological cleaning effectiveness, defined in terms of the ability to remove bacterial spores, of a number of methods used to clean hardware surfaces. Aluminum (Al 6061) and titanium (Ti 6Al-4V) were chosen for the study as they were deemed the two materials most likely to be used in spacecraft extraterrestrial sampler construction. Metal coupons (1 cm x 2.5 cm) were precleaned and inoculated with 5.8 x 10(3) cultivable Bacillus subtilis spores, which are commonly found on spacecraft surfaces and in the assembly environments. The inoculated coupons were subsequently cleaned using: (1) 70% isopropyl alcohol wipe; (2) water wipe; (3) multiple-solvent flight-hardware cleaning procedures used at the Jet Propulsion Laboratory (JPL); (4) Johnson Space Center-developed ultrapure water rinse; and (5) a commercial, semi-aqueous, multiple-solvent (SAMS) cleaning process. The biological cleaning effectiveness was measured by agar plate assay, sterility test (growing in liquid media), and epifluorescent microscopy. None of the cleaning protocols tested completely removed viable spores from the surface of the aluminum. In contrast, titanium was capable of being cleaned to sterility by two methods, the JPL standard and the commercial SAMS cleaning process. Further investigation showed that the passivation step employed in the JPL standard method is an effective surface sterilant on both metals but not compatible with aluminum. It is recommended that titanium (Ti 6Al-4V) be considered superior to aluminum (Al 6061) for use in spacecraft sampling hardware, both for its potential to be cleaned to sterilization and for its ability to withstand the most effective cleaning protocols.     

Initial characterization of the microgravity environment of the international space station: increments 2 through 4

The primary objective of the International Space Station (ISS) is to provide a long-term quiescent environment for the conduct of scientific research for a variety of microgravity science disciplines. This paper reports to the microgravity scientific community the results of an initial characterization of the microgravity environment on the International Space Station for increments 2 through 4. During that period almost 70,000 hours of station operations and scientific experiments were conducted. 720 hours of crew research time were logged aboard the orbiting laboratory and over half a terabyte of acceleration data were recorded and much of that was analyzed. The results discussed in this paper cover both the quasi-steady and vibratory acceleration environment of the station during its first year of scientific operation. For the quasi-steady environment, results are presented and discussed for the following: the space station attitudes Torque Equilibrium Attitude and the X-Axis Perpendicular to the Orbital Plane; station docking attitude maneuvers; Space Shuttle joint operation with the station; cabin de-pressurizations and the station water dumps. For the vibratory environment, results are presented for the following: crew exercise, docking events, and the activation/de-activation of both station life support system hardware and experiment hardware. Finally, a grand summary of all the data collected aboard the station during the 1-year period is presented showing where the overall quasi-steady and vibratory acceleration magnitude levels fall over that period of time using a 95th percentile benchmark.     

SC切石英晶体谐振器在甚高频低噪声振荡器中的应用

晶体控制的甚高频振荡器广泛应用于具有优良短期频率稳定度和低相位噪声的信号发生器中。这种振荡器均采用工作在泛音模的 AT 切晶体。由于 AT 切晶体谐振器的幅频效应,使相位噪声难以进一步减小。双旋转切晶体(例如 SC 切晶体)的幅频效应较 AT 切的小得多。因此,可使 SC 切晶体工作在较 AT 切晶体所允许的更大的激励电流上。如果能使振荡器固有的相位起伏不随晶体电流的增大而显著增大,则采用 SC 切晶体元件可以改善晶体控制甚高频信号发生器的短期频率稳定度和噪声。曾用三次泛音 SC 切晶体(而不是用五次泛音 AT 切晶体)进行过100MHz 低噪声振荡器的实际可行性试验。对 SC 切和 AT 切晶体元件的相频特性进行了测量。测量结果表明,晶体元件的功耗能够比使用 AT 切晶体增加6-10dB。对用双极结型晶体管振荡器的噪声源的检查表明,二次及三次失真是造成实际振荡器呈现显著相位闪变的原因。从解凡得堡(微分)方程中出现的频率校正项可了解到减小频率闪变的要求。桥式 T 形振荡器适合于作 SC 切甚高频晶体振荡维持电路。曾研究过这种电路的噪声源(包括调幅闪变噪声的幅相变换),并得到了对上述振荡器所预期的 L(f)的估算值。对相同的一对振荡器进行了测量,预计的 L(f)和所测得的 L(f)很一致。结果表明,和 AT 切甚高频晶体控制振荡器相比较,SC 切晶体控制的甚高频振荡器的L(f)得到了显著改善。     

远站跟踪转换方程的推导

托诺帕试验靶场需要一种可以用小型计算机在很短时间完成跟踪数据精确视差修正的方法。本文推导了一种球面变换方程,用于地球表面上的一定范围内时,可以给出非常精确的结果。在16位小型计算机上,计算速度很快,因为它不需要浮点计算,并且几乎不需要双倍字长处理。结果表明,计算的目标位置与用地心变换公式计算的位置相比较,精确度在一荚尺以内。     

铯束管电子倍增器的工作特性

本文介绍一种用可拆卸的测试系统来测定和铯束管中使用的电子倍增器的工作特性。测试时输入电子信号,由测出的这些数据计算电子倍增器的增益和倍增器电极的二次电子发射系数。对环境因素(敞露在空气中和真空烘烤)的影响也进行了测定。