FX型相关处理机长期累加器子系统的研究

介绍了中国VLBI网FX型相关处理机的结构和功能,并着重阐述了相关处理机的长期累加器子系统(LTA),它是相关处理机的条纹数据压缩部件。通过对长期累加器子系统的研究,提出了对该子系统的改进方案,以提高硬件线路的集成度和系统的可靠性,适应了对相关处理机更快速度、更高精度及多台站测量的要求,并说明了实现方法及其改进后的特点。     

The Latest Research Progress on El Ninod

1　ＭａｔｈｅｍａｔｉｃＭｏｄｅｌｏｆＴｉｄａｌＶｉｂｒａｔｉｏｎＳｕｐｐｏｓｅｔｈａｔ 3ｓｅｍｉ -ａｘｅｓｏｆａｅｌｌｉｐｓｏｉｄａｒｅａ ,ｂａｎｄｃ (ａ >ｂ >ｃ) ,ｌａｔｉｔｕｄｅｉｓθ ,ｌｏｎｇｉｔｕｄｅｉｓψ(ｃｈａｎｇｉｎｇｆｒｏｍ 0°ｔｏ 90°) ,     

不协调决策表的规则提取

对决策表数据的性质、数据之间的关系进行了讨论,并由此对决策表进行了分类.讨论了不协调决策表的数据约简,并证明其不影响属性约简和规则提取.基于数据的协调性,对不协调决策表的属性约简进行了研究,并提出了一种规则提取方法.最后,用实例验证了方法的有效性.     

Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Dust particles in interplanetary space are expected to charge up to an electrostatic potential of about +5 V mostly by the solar UV (Horányi, 1996, Annu. Rev. Astrophys. 34, 383). Since the dynamics of charged grains may be quite different from neutral particles, the knowledge of the grain charge Q_d is highly desirable. In the last two decades, several detectors on spacecraft were flown to measure the dust charge in-situ, but the instrumentation was not capable of determining the dust charge unambiguously. The Cosmic Dust Analyser (CDA) on the Cassini spacecraft includes a charge sensitive entrance grid system (QP detector). While entering the instrument, sufficiently charged particles induce a characteristic charge feature onto the grid system, which allows a reliable determination of Q_d as well as of the impact speed v_d. Here we report the first successful in-situ measurement of charged interplanetary dust grains by CDA. Amongst 37 impacts by interplanetary grains registered between November 1999 and January 2000, we identified 6 impacts whose QP signals show a clear feature caused by charged grains, corresponding to Q_d between 1.3 and 5.4 fC. Knowledge of Q_d also allows us to estimate the grain mass m_d. Assuming a potential of φ_d≈+5 V and spheroidal grain morphologies with ratios of the maximum size to the minimum size of less than 2 the masses derived from Q_d were found to be in excess of 10⁻¹³ kg. The dynamics of such particles are dominated by the Sun's gravity. In the framework of the micro-meteoroid models of the Solar System these grains belong to the core population of interplanetary grains (Divine, 1993, J. Geophys. Res. 98, 17029). Furthermore, a rate of 6 impacts of grains with m_d?10⁻¹³ kg during 107 days is in good agreement with the predictions of the interplanetary dust environment model by Staubach et al. (1997, Adv. Space Res. 19, 301). This result demonstrates that charge detectors as the CDA QP system offer a reliable in-situ technique for determining simultaneously both the mass and velocity of big interplanetary grains. The primary CDA subsystem to determine m_d and v_d, however, is an impact ionisation detector. The majority of the 37 recorded dust impacts produced impact charges are well outside the calibrated range. Moreover, these impacts were usually characterised by impact ionisation signals which differ significantly from signals taken in calibration experiments. In this paper we took advantage of the fact that the measurement of Q_d is not affected by the subsequent impact of the grain with the detector. By relating m_d and v_d derived from Q_d of the 6 QP impactors to their corresponding ionisation signals we show that in many cases even for energetic impacts outside the calibrated range meaningful values for the dust mass can be obtained. The observed deviations of the ionisation signals from the calibration measurements are likely due to the large amount of plasma generated by such impacts. We discuss the implications of these findings on a meaningful reduction of impact ionisation signals caused by big particle impacts. A new scheme to identify and to evaluate such signals is presented. These finding are of great importance for future Cassini measurements in the saturnian system.     

含内边界非均匀材料三维FEM模型的时间逆转仿真研究

运用 3- D非线性动态有限元方法 ,针对地壳块体建立了一个材料非均匀的包含多个内部界面的三维典型模型 ,通过对模型的时间逆转效应的仿真研究 ,初步探讨了基于动力学原理人工触发地震的可能性 ,重新提出以提前触发地震、增加频度、降低震级为基本方法的消除震害原理。模拟结果表明 ,如果将地震图 (seismogram)进行时间逆转后 ,作为加载曲线 ,在地震台站点上通过一个有效的力源加载于基岩 ,利用时间逆转效应 ,可以将人工施加的能量在某一瞬间集中到以往的震源 ,引起一个强烈的冲击 ,因而可能触发地震。     

The Latest Research Progress on El Nino

Cold water in the deep Pacific can be drawn up to the surface (or west warm water drifts eastwards) because strong tide increases the mixing of seawater both in vertical and horizontal. In this way greenhouse effect is decreased or in-creased by means of absorbing (or releasing) CO2. Therefore, La Nina cold event (or El Nino warm event) may occur, which is caused by wanning - up or cooling - down air above the ocean. Volcanic action at sea bottom is also controlled by strong tide.     

Jovian satellite positions from Hubble Space Telescope images

An accurate technique has been developed for measuring planetocentric positions of Jupiter's satellites from Wide Field/Planetary Camera images. Our method of finding the centers of the satellites and planet is based upon established limb-fitting techniques, but we have adapted those techniques to astrometry. We compare our limb-fitting results with previously published work and discuss its errors. A model ellipse is generated from the physical ephemeris of the planet including its phase defect. Then the planet center coordinates are computed by fitting the model to the limb observations using the method of least squares. A satellite position is determined similarly, and its offset from the planet is calculated. A total of 76 positions of the galileans satellites, the small moon Amalthea, and the shadows of Io and Ganymede cast on Jupiter have been measured on 61 images. Comparison between the observational results and JPL satellite ephemerides demonstrates the validity of this new method of analysis. The accuracy of the galilean satellite measurements is estimated to be 0.04 arcsec in right ascension and in declination.     

地壳波浪运动机制探讨

讨论了地壳波浪运动形成的机制及其效应 ,并为地壳波浪状镶嵌构造学说提供了初步的数理模型和理论依据。     

Longitude-resolved imaging of Jupiter at λ=2 cm

We present a technique for creating a longitude-resolved image of Jupiter's thermal radio emission. The technique has been applied to VLA data taken on 25 January 1996 at a wavelength of 2 cm. A comparison with infrared data shows a good correlation between radio hot spots and the 5 μm hot spots seen on IRTF images. The brightest spot on the radio image is most likely the hot spot through which the Galileo probe entered Jupiter's atmosphere. We derived the ammonia abundance (= volume mixing ratio) in the hot spot, which is ∼3×10⁻⁵, about half that seen in longitude-averaged images of the NEB, or less than 1/3 of the longitude-averaged ammonia abundance in the EZ. This low ammonia abundance probably extends down to at least the 4 bar level.     

Experimental study on the effectiveness of TLDs under wave loading

The objective of this study is to experimentally investigate the effectiveness of Tuned Liquid Dampers (TLDs) for suppressing the dynamic response of a platform structure subjected to wave loading and to explore the applicability of TLDs for suppressing the structural vibration of fixed offshore platforms. The experimental model is scaled according to a full size platform by matching its dynamic properties. Rectangular and circular TLDs of various sizes and water depths are examined.The experiments were performed in a 2-D wave flume. The effectiveness of TLDs is evaluated based on their response reduction. By observing the performance and the behavior of TLDs through laboratory experiments, the effects of a number of parameters including container shape, container size, number of dampers, frequency ratio, mass ratio, and incident wave characteristics are investigated.