不同标度震级关系和台基影响问题探讨

利用近年中国数字地震台网观测报告中的中国及邻区地震目录资料,取能够同时计算面波震级MS和近震震级ML的地震,拟合出2种震级之间的关系,发现与过去使用30余年的换算公式存在系统差别。考虑现代化地震数字观测系统有动态范围大、频带宽、台站多、覆盖区域广、测定精度高的特点,由此拟合的关系应当更可靠。考虑不同误差因素统计面波震级MS和近震震级ML的关系表明,2种震级之间换算和不换算的差别并不大,因此建议MS和ML震级之间不换算为宜。分析地震台站的场地响应发现:一些基岩台的放大因子在1附近,场地响应不随频率变化;处于沉积土层的台站,放大因子在低频段大于1,高频段小于1;还有一些台站在某个频段范围大于1,或者小于1。另外,沉积土层台站的单台震级和台网平均震级差也随周期增大,呈现由负到正的增长趋势。看来并不存在固定的台站校正系数,因此不能把台站校正作为提高震级测定精度的方法。     

Modeling thermal deformation of VLBI antennas with a new temperature model

Temperature variations at very long baseline interferometry (VLBI) sites cause thermal deformations of the VLBI antennas and corresponding displacements of the VLBI reference points. The thermal deformation effects typically contain seasonal and daily signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending on the design of the antenna structure, on the material, and on the environmental effects such as global station position, station height and climatology effects. Simple methods to correct this effect use the difference of the environmental temperature with respect to a defined reference temperature, the antenna dimensions, the elevation of the antenna, the material of antenna structure. Applying these simple models for thermal deformation in the VLBI data analysis improves the baseline length repeatability by 3.5%. A comparison of these simple models with local thermal deformation measurements at the antennas in Onsala and Wettzell show that the local measurements and the modeled corrections agree well when the temperature of the antenna structure is used, but agree less good when the surrounding air temperatures are used. To overcome this problem we present a method to model temperature penetration into the antenna structures, that allows to model thermal deformation effects that agree with the observed vertical deformation of the Onsala and Wettzell radio telescopes with a root mean square deviation of 0.07 and 0.13 mm, respectively. Possible implementations in the VLBI analysis are presented, and the definition of an adequate reference temperature is discussed.     

HST UV measurements of wind structure and velocities in Local Group OB stars

Archival HST FOS and GHRS data sets have been used to collect ultraviolet evidence for large- and small-scale stellar wind structure in extragalactic Local Group OB stars (i.e. SMC, LMC including R136, M31, M33 and NGC 6822). By comparison with previous studies of Galactic OB stars, wind activity is principally diagnosed in individual spectrograms via the presence of 'narrow absorption components' and saturated 'black' absorption troughs in the resonance line doublets. Their characteristics broadly suggest that these stars share the same physical mechanisms for perturbing the winds as those that act in Galactic stars. Both of these spectral indicators are also used to provide reliable measures of wind terminal velocities. These velocities are directly compared with previously published Galactic values, without reliance on model profile fitting. Relative to Galactic OB stars, the most discrepant terminal velocities (and wind line profiles) result from main-sequence early O-type stars in the SMC.     

SAR图像保留边缘多窗口相干斑滤除方法

在处理合成孔径雷达（ＳＡＲ）图像中,精确地估计图像的局部统计特性和尽可能多地滤除相干斑都需要较大的窗口尺寸,而这与图像边缘和纹理结构的检测需要较小的窗口尺寸相矛盾。一般滤波器都是二者窗口尺寸的均衡,这必然导致二者都不能取得很好的效果。本文提出的新方法有效的解决了这一矛盾。此方法使处理后的ＳＡＲ图像既保存了边缘和纹理结构,避免了以往滤波器中使边缘变模糊的问题,又有效地滤除了相干斑噪声。     

The globular cluster system of the Sagittarius dwarf spheroidal galaxy: the age of Terzan 8

We present deep V - and I -band CCD photometry of the globular cluster Terzan 8, recently found to be a member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. We accurately estimate the metallicity of Terzan 8, and provide the first direct determination of the colour excess toward this cluster. Our robust age estimate confirms that this cluster is indeed coeval with typical Galactic globulars of comparable metal content, and thus it is probably significantly older than at least two other Sagittarius clusters, Terzan 7 and Arp 2. The implications of this result on the star formation history of the Sagittarius galaxy are briefly discussed.     

多维标度法在矿产预测中的应用

在矿产预测中常涉及一些定性变量,对这些变量的分析和应用,必须将定性描述的地质特征转化为用数值表示的变量,这就需要处理此问题的方法——多维标度法。笔者介绍了计量性的Ｔｏｒｇｅｒｓｏｎ法、准计量性的林知已夫数量化理论和非计量性多维标度法,并列举了其在矿产预测中的应用实例。     

Comparison of Large-Scale Flows on the Sun Measured by Time-Distance Helioseismology and Local Correlation Tracking

We present a direct comparison between two different techniques: time-distance helioseismology and a local correlation tracking method for measuring mass flows in the solar photosphere and in a near-surface layer. We applied both methods to the same dataset (MDI high-cadence Dopplergrams covering almost the entire Carrington rotation 1974) and compared the results. We found that, after necessary corrections, the vector flow fields obtained by these techniques are very similar. The median difference between directions of corresponding vectors is 24°, and the correlation coefficients of the results for mean zonal and meridional flows are 0.98 and 0.88, respectively. The largest discrepancies are found in areas of small velocities where the inaccuracies of the computed vectors play a significant role. The good agreement of these two methods increases confidence in the reliability of large-scale synoptic maps obtained by them.     

双多普勒雷达风场反演对一次后向传播雷暴过程的分析

利用常规观测、雷达和加密自动站资料,对2013年9月13日上海地区的一次以后向传播为主要特征、伴有强降水和大风的强对流过程进行了分析,并采用双多普勒雷达风场反演等技术,对其形成的环境条件及后向传播机制进行了研究。由于上海连续多日处在副热带高压(副高)西北侧边缘,具备了充足的水汽和较强的不稳定条件,地面辐合线在上海北部触发了初始对流,其出流与地面风场的辐合在西南侧不断触发出新的对流单体,出现了与引导气流相反、指向西南方向的雷暴传播矢量,当单体的新生传播速率大于引导流速率时,雷暴整体产生了与引导气流相反的后向移动。针对该后向传播机制的研究表明:对流单体强下沉运动形成的阵风锋在其西南方向与环境西南风辐合,并与该处原有的地面辐合线碰撞造成更强烈的上升气流,触发新的单体生成,新单体发展成熟后产生强降水和强下沉运动,加强和维持了其西南侧的阵风锋,使得阵风锋向西南方向推进并继续触发新单体生成;风场反演的垂直运动分布和演变也显示了多个对流单体从东北向西南依次表现出消散、成熟和新生阶段的特征。因此,本次过程中形成了"雷暴单体新生发展—成熟后缓慢东北向移动—产生强降水、下沉运动和大风在其西南侧触发新单体"的循环;向西南方向推进的地面阵风锋与原有的地面辐合线共同形成了雷暴西南侧局地锋生区,与新生对流区的位置一致,是该次过程后向传播的主要原因。