具有应变梯度的复合推进剂中裂纹扩展的特性

本文研究在具有应变梯度、填充密度大的复合推进剂中裂纹扩展的特性。采用中心有楔形裂纹的双轴试样。在室温、恒定十字头速度下进行试验。考虑了两种裂纹长度。通过分析试验数据来研究初始裂纹长度和非均匀总应变场对推进剂裂纹扩展特性的影响,还研究了测量裂纹长度所用时间间隔对裂纹扩展速率计算精度的影响。     

军用精密声表面波振荡器的研制

近年来,美国雷声公司已经有研制300～600MHz可军用的声表面波振荡器的课题;此种振荡器在频率调节能力和稳定性两方面均达当代最高水平。本文不讨论这种振荡器的详细用途。对它的要求一般为:(1)噪声本底必需至少为-160dBc/Hz;(2)振动灵敏度至少应与AT切体波器件一样好;(3)振荡器频率应能在大致±10ppm频率窗内进行调节并加以保持。在某些情况还要求加热时间小于3分钟。在满足这些要求方面,雷声公司已取得明显进展。本文将对这种进展加以讨论。在频谱纯度方面,文中讨论了二个题目:其一是低噪声放大器。实验证明,当它与310MHz声表面波谐振器联用时,噪声本底可达-176dBc/Hz。其二主要讨论了外部振动对噪声边带的影响。研制声表面波振荡器最重要的方面之一就是它的频率调节能力。利用金衬微调技术被证实既适用于延迟线也适用于谐振器。文中给出了实验结果,也讨论了在焊封过程中产生频移(约100ppm数量级)这一复杂情况。但已提出一种外部牵引频率技术来重调频率。在很多应用场合要求用恒溫箱以保持常温,于是就要求快速加热,而给出的数据要能显示出3分钟加热周期的频率稳定度。最后,除上述要求外,还要求声表面波振荡器的长稳保持在～1ppm/年的水平。利用提供的数据来确定冷焊密封在TO-8型外壳中的器件的基本老化率,同时也示出微调器件以及低振动灵敏度器件的变化率。     

分时移相调制的多路光纤陀螺仪

本文提出一上实现多路多轴光纤陀螺仪的新方法。Ｎ个Ｓａｇｎａｃ干涉仪通过一个２×Ｎ个耦合器共用一个光源。这些干涉仪都以通常的方法相位调制来进行调制然而，这些调制都在时间上有τ／Ｎ的延尺，τ是进入光纤环圈的平均传输时间。     

A status report on the characterization of the microgravity environment of the International Space Station

A primary objective of the International Space Station is to provide a long-term quiescent environment for the conduct of scientific research for a variety of microgravity science disciplines. Since continuous human presence on the space station began in November 2000 through the end of Increment-6, over 1260 hours of crew time have been allocated to research. However, far more research time has been accumulated by experiments controlled on the ground. By the end of the time period covered by this paper (end of Increment-6), the total experiment hours performed on the station are well over 100,000 hours (Expedition 6 Press Kit: Station Begins Third Year of Human Occupation, Boeing/USA/NASA, October 25, 2002). This paper presents the results of the on-going effort by the Principal Investigator Microgravity Services project, at NASA Glenn Research Center, in Cleveland, Ohio, to characterize the microgravity environment of the International Space Station in order to keep the microgravity scientific community apprised of the reduced gravity environment provided by the station for the performance of space experiments. This paper focuses on the station microgravity environment for Increments 5 and 6. During that period over 580 Gbytes of acceleration data were collected, out of which over 34,790 hours were analyzed. The results presented in this paper are divided into two sections: quasi-steady and vibratory. For the quasi-steady analysis, over 7794 hours of acceleration data were analyzed, while over 27,000 hours were analyzed for the vibratory analysis. The results of the data analysis are presented in this paper in the form of a grand summary for the period under consideration. For the quasi-steady acceleration response, results are presented in the form of a 95% confidence interval for the station during "normal microgravity mode operations" for the following three attitudes: local vertical local horizontal, X-axis perpendicular to the orbit plane and the Russian torque equilibrium attitude. The same analysis was performed for the station during "non-microgravity mode operations" to assess the station quasi-steady acceleration environment over a long period of time. The same type of analysis was performed for the vibratory, but a 95th percentile benchmark was used, which shows the overall acceleration magnitude during Increments 5 and 6. The results, for both quasi-steady and vibratory acceleration response, show that the station is not yet meeting the microgravity requirements during the microgravity mode operations. However, it should be stressed that the requirements apply only at assembly complete, whereas the results presented below apply up to the station's configuration at the end of Increment-6.     

A viable microbial community in a subglacial volcanic crater lake, Iceland

We describe a viable microbial community in a subglacial lake within the Grímsv?tn volcanic caldera, Iceland. We used a hot water drill to penetrate the 300-m ice shelf and retrieved lake water and volcanic tephra sediments. We also acquired samples of borehole water before and after penetration to the lake, overlying glacial ice and snow, and water from a nearby subaerial geothermal lake for comparative analyses. Lake water is at the freezing point and fresh (total dissolved solids = 260 mg L(-1)). Detectable numbers of cells were found in samples of the lake water column and tephra sediments: 2 x 10(4) ml(-1) and 4 x 10(7) g(-1), respectively. Plate counts document abundant cold-adapted cultivable organisms in the lake water, but not in the borehole (before penetration) or glacial ice. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from genomic DNA extracted from Grímsv?tn samples indicates that the lake community is distinct from the assemblages of organisms in borehole water (before penetration) and the overlying ice and snow. Sequencing of selected DGGE bands revealed that many sequences are highly similar to known psychrophilic organisms or cloned DNA from other cold environments. Significant uptake of 14C-labeled bicarbonate occurred in dark, low-temperature incubations of lake water samples, indicating the presence of autotrophs. Acetylene reduction assays under similar incubation conditions showed no significant nitrogen fixation potential by lake water samples. This may be a consequence of the inhibition of diazotrophy by nitrogen in the lake.     

A hydrothermal system associated with the Siljan impact structure, Sweden--implications for the search for fossil life on Mars

The Siljan ring structure (368 +/- 1.1 Ma) is the largest known impact structure in Europe. It isa 65-km-wide, eroded, complex impact structure, displaying several structural units, including a central uplifted region surrounded by a ring-shaped depression. Associated with the impact crater are traces of a post-impact hydrothermal system indicated by precipitated and altered hydrothermal mineral assemblages. Precipitated hydrothermal minerals include quartz veins and breccia fillings associated with granitic rocks at the outer margin of the central uplift, and calcite, fluorite, galena, and sphalerite veins associated with Paleozoic carbonate rocks located outside the central uplift. Two-phase water/gas and oil/gas inclusions in calcite and fluorite display homogenization temperatures between 75 degrees C and 137 degrees C. With an estimated erosional unloading of approximately 1 km, the formation temperatures were probably not more than 10-15 degrees C higher. Fluid inclusion ice-melting temperatures indicate a very low salt content, reducing the probability that the mineralization was precipitated during the Caledonian Orogeny. Our findings suggest that large impacts induce low-temperature hydrothermal systems that may be habitats for thermophilic organisms. Large impact structures on Mars may therefore be suitable targets in the search for fossil thermophilic organisms.     

Effects of repeated long duration +2Gz load on man's cardiovascular function

Usefulness of a short-arm human centrifuge is expected when it is used in space as a countermeasure against cardiovascular deconditioning, problem of bone-calcium metabolism, etc. However, nothing is solidly established regarding the most desirable program for artificial G application. Accordingly, this study was designed to analytically evaluate the effects of repeated long duration +Gz load on human cardiovascular function. Recently heart rate spectral analysis has been recognized as a powerful tool for quantitatively evaluating parasympathetic and sympathetic activity separately in human. It is reported that power of the high frequency component (HF-p) is mediated selectively by parasympathetic activity and the power ratio of low to high frequency components(LF/HF) is indicative of cardiac sympathetic activity or cardiac sympathovagal balance. Sequence method is developed to examine spontaneous baroreceptor reflex sensitivity (BRS). We studied cardiovascular control function by using these methods in 9 healthy men before and after 7 days of daily repeated 1hour +2Gz load. When compared with the data of pre-G load period, post-G load period, decrease of HR, increases of HF-p and BRS were statistically significant. SBP, DBP and LF/HF tended to decrease, however, these changes were not statistically significant. This results indicate that repeated +2Gz load increases parasympathetic activity and arterial baroreceptor-cardiac reflex sensitivity. In recent years, many investigators suggest that space flight and head-down bedrest leads to impaired baroreceptor-cardiac reflex responses and decrease of parasympathetic activity, which may contribute to orthostatic intolerance. So our results suggest that daily repeated 1hour +2Gz load would be useful in preventing post-flight orthostatic intolerance.     

Arm end-point trajectories under normal and micro-gravity environments

The purpose of the present experiment was to study the way in which the CNS represents gravitational force during vertical arm pointing movements. Movements in upward and downward directions were executed by two cosmonauts in normal-gravity and weightlessness. Analyses focused upon finger kinematics in the sagittal plane. In normal-gravity, downward direction movements showed smaller curvatures and greater relative times to peak velocity (AT/MT) when compared with upward direction movements. Data from the weightlessness experiments showed that whilst downward movements decreased their curvature during space flight, curvatures of upward movements changed slightly. Furthermore, AT/MT was modified during the first days in micro-gravity for both directions, recovering, however, to pre-flight values after 18 days in space. Results from the present study, provide evidence that gravitational force is centrally treated constituting an important component of the motor plan for vertical arm movements.     

随机子阵阵列的旁瓣电平和宽带特征

本文扩展了随机天线阵列的概念。介绍了三种新型的阵列几何图形，它们既具有随机阵列的宽带宽性能，几何图形也更简单，因而更适宜于低成本应用。对随机子阵的周期阵列、周期旋转随机子阵阵列和随机旋转随机子阵阵列的性能都进行了统计性的表征。结果表明子阵旋转能够降低天线阵排列因子的旁瓣电平。文中给出了一个设计过程的例子来说明天线阵排列因子的计算。     

舰队弹道导弹计划（2）“北极星”蜕变

是的，在舰队弹道导弹计划发展进程中．那种高昂的士气贯穿始终。无论是一个技术难点，还是一次政府攻关；是在实验室的操作台前．还是会议上的每次讨论。那种团结是推动计划的原动力。