人造石英晶体不同生长区的热致发光

许多采用石英晶体的电子器件都工作在容易受到辐照的环境中。因此,研究辐照对石英晶体的影响是很重要的。我们在本文中指出,热致发光技术可以作为研究这个问题的一种好方法。我们将介绍在15—300°K温度范围内测量到的热致发光。已经分别获得Y切石英片各生长区(即+X、-X、+Z、-Z)的测量结果。该石英片是从未经扫描处理的电子级人造石英Y切生长棒上切割下来的。在这项工作中,我们首次发现在72°K、80°K、87°K和104°K时有很清晰的辉光峰。我们认为,在室温下经过X射线(50千伏、17毫安的白辐射)予辐照之后,仅仅出现在+X生长区(即135°K、162°K、178°K)的辉光峰可能与[Al_e_+]°中心有关。在+Z区样品中高于104°K的辉光峰完全不同于在+X区样品中看到的情况。在这个温度范围的所有辉光峰都随着室温下予辐照剂量的增大而逐渐减弱。从本文介绍的测量结果可以看出,一个或多个辉光峰相应于各个生长区存在的某种缺陷,而且它们的热致发光强度比例于石英中所含缺陷的密度。     

一种用于波长测量的数字式干涉仪

本文介绍了一种用来测量激光波长的简单的条纹计数式干涉仪,给出了几种激光谱线波长的测定值.它们是氦—氖、氩和氪激光谱线,由饱和吸收的碘蒸气所稳定,不准确性为2×10~(-8)(可信度99%)。     

Domain evolution and functional diversification of sulfite reductases

Sulfite reductases are key enzymes of assimilatory and dissimilatory sulfur metabolism, which occur in diverse bacterial and archaeal lineages. They share a highly conserved domain "C-X5-C-n-C-X3-C" for binding siroheme and iron-sulfur clusters that facilitate electron transfer to the substrate. For each sulfite reductase cluster, the siroheme-binding domain is positioned slightly differently at the N-terminus of dsrA and dsrB, while in the assimilatory proteins the siroheme domain is located at the C-terminus. Our sequence and phylogenetic analysis of the siroheme-binding domain shows that sulfite reductase sequences diverged from a common ancestor into four separate clusters (aSir, alSir, dsr, and asrC) that are biochemically distinct; each serves a different assimilatory or dissimilatory role in sulfur metabolism. The phylogenetic distribution and functional grouping in sulfite reductase clusters (dsrA and dsrB vs. aSiR, asrC, and alSir) suggest that their functional diversification during evolution may have preceded the bacterial/archaeal divergence.     

Trojans in habitable zones

With the aid of numerical experiments we examined the dynamical stability of fictitious terrestrial planets in 1:1 mean motion resonance with Jovian-like planets of extrasolar planetary systems. In our stability study of the so-called "Trojan" planets in the habitable zone, we used the restricted three-body problem with different mass ratios of the primary bodies. The application of the three-body problem showed that even massive Trojan planets can be stable in the 1:1 mean motion resonance. From the 117 extrasolar planetary systems only 11 systems were found with one giant planet in the habitable zone. Out of this sample set we chose four planetary systems--HD17051, HD27442, HD28185, and HD108874--for further investigation. To study the orbital behavior of the stable zone in the different systems, we used direct numerical computations (Lie Integration Method) that allowed us to determine the escape times and the maximum eccentricity of the fictitious "Trojan planets."     

Toward optimizing lighting as a countermeasure to sleep and circadian disruption in space flight

Light is being used as a pre-launch countermeasure to circadian and sleep disruption in astronauts. The effect of light on the circadian system is readily monitored by measurement of plasma melatonin. Our group has established an action spectrum for human melatonin regulation and determined the region of 446-477 nm to be the most potent for suppressing plasma melatonin. The aim of this study was to compare the efficacy of 460 and 555 nm for suppressing melatonin using a within-subjects design. Subjects (N=12) were exposed to equal photon densities (7.18 x 10(12) photons/cm2/s) at 460 and 555 nm. Melatonin suppression was significantly stronger at 460 nm (p<0.02). An extension to the action spectrum showed that 420 nm light at 16 and 32 microW/cm2 significantly suppressed melatonin (p<0.04 and p<0.002). These studies will help optimize lighting countermeasures to circadian and sleep disruption during spaceflight.     

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.     

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。     

Status and efficacy of countermeasures to physiological deconditioning from space flight

The recent biomedical investigations conducted on the Space Shuttle and Spacelab have provided a wealth of biomedical information, including the ability to test the efficacy of proposed countermeasures. This achievement was made possible by the ability to conduct mechanistic and control-interventive studies simultaneously with a large number of individuals over a relatively brief period and to compare these data with results obtained from the Skylab missions. Comparisons between short- and long-duration results were limited to establishing trends or extrapolating from short-duration missions. To date, we have evaluated several protocols involving the lower-body negative pressure (LBNP) device, the bicycle-ergometer, the treadmill and preparations for body-fluid replenishment. In many instances, the traditional means of applying these protocols were not sufficient to protect against space-related deconditioning. This paper will review current countermeasures and compare their efficacy to that of existing protocols. Results from in-flight and ground-based experiments will be presented to illuminate the recommended protocols and procedures.     

The second generation of the incubator hardware for studying avian embryogenesis under microgravity conditions

This paper describes a technical device, INCUBATOR 1M, which enables incubation of Japanese quail eggs aboard the piloted orbital station.