The star formation histories of low surface brightness galaxies

We have performed deep imaging of a diverse sample of 26 low surface brightness galaxies (LSBGs) in the optical and the near-infrared. Using stellar population synthesis models, we find that it is possible to place constraints on the ratio of young to old stars (which we parametrize in terms of the average age of the galaxy), as well as the metallicity of the galaxy, using optical and near-infrared colours. LSBGs have a wide range of morphologies and stellar populations, ranging from older, high-metallicity earlier types to much younger and lower-metallicity late-type galaxies. Despite this wide range of star formation histories, we find that colour gradients are common in LSBGs. These are most naturally interpreted as gradients in mean stellar age, with the outer regions of LSBGs having lower ages than their inner regions. In an attempt to understand what drives the differences in LSBG stellar populations, we compare LSBG average ages and metallicities with their physical parameters. Strong correlations are seen between an LSBG's star formation history and its K -band surface brightness, K -band absolute magnitude and gas fraction. These correlations are consistent with a scenario in which the star formation history of an LSBG primarily correlates with its surface density and its metallicity correlates with both its mass and its surface density.     

Spectroscopy of globular cluster candidates in the Sculptor group galaxies NGC 253 and 55

We have obtained spectra for 103 published globular cluster candidates in the Sculptor group galaxies NGC 253 and 55. On the basis of radial velocities and digitized plate images, 14 globular clusters are identified in NGC 253 and one probable globular cluster is identified in NGC 55. The majority of the objects in the sample appear to be background galaxies. We have obtained and analysed COSMOS plate scans of NGC 253 and 55 and use these along with the spectroscopically identified clusters to define new samples of globular cluster candidates in the two galaxies which should have reduced contamination.     

三维旋涡星系的动力学研究

在三维对数螺线型密度扰动的引力Poisson方程严格解基础上,导出了对称平面(z=0)上三维混合盘密度波的色散关系,并以此讨论了对于不同类型扰动盘的局域稳定性,同时还计算了盘面上密度波的群速度．数值计算表明对数螺线型密度扰动,能比较好地满足扰动密度与扰动势反相位的关系;厚度和旋臂数目的增加有利于盘的稳定,而气体成分将导致盘不稳定;考虑厚度效应,银河系密度波传播的动力学时标与Toomre估计的数值相比将大大延长,至少需要4．17×109年,约占宇宙年龄的三分之一,从而可使以往密度波理论中得出的群速度太大的问题得到缓解．     

Effects of data incompleteness on the results of Fourier analysis of line-of-sight velocity fields in spiral-galaxy disks

Our main goal is to investigate the effects of data incompleteness on the results of Fourier analysis of line-of-sight velocity fields in the disks of spiral galaxies. We have carried out a number of numerical experiments, first with an artificially created simple velocity field and then with the velocity fields of two real galaxies, which qualitatively differ in data filling: NGC 157 and NGC 3631 with good and bad data filling, respectively. The field of purely circular velocities is chosen as the simplest artificial velocity field, because the circular velocities of spiral galaxies are much high than the residual (noncircular) velocities. Superimposing a “mask” simulating blank spots (holes) in the map of observational data on this artificial field has no effect on the results of Fourier analysis of this simplest field. A similar result is obtained for real galaxies with good data filling of the observed velocity fields. Superimposing arbitrarily shaped masks on the observed velocity field of NGC 157 in such a way that the field was filled by a mere 50% (at each radius) could not change appreciably the radial variations of large-scale Fourier harmonics. The situation qualitatively changes in attempting to fill the holes in the observed velocity field of NGC 3631 in some way. When missing velocities are artificially introduced by using the simplest model of purely circular gas rotation, the amplitudes and phases of the principal Fourier harmonics are distorted. In particular, a substantial distortion of the third harmonic also causes an increase in the error when determining the corotation radius from data of the filled field. When the filling of the velocity field is increased by degrading the spatial resolution, the amplitudes of most harmonics decrease throughout the entire disk region; as a result, their radial variations are smoothed out and the behavior of harmonic phases in the range of moderately high initial amplitudes can be distorted. An abnormal enhancement of the highest Fourier harmonics in the regions of low filling of the initial field is also possible. At the same time, despite the above distortions, the corotation radius determined from the smoothed fields matches that for the initial velocity fields.     

中国食管癌与土壤环境中元素的相关性

利用土壤元素资料 2 0 6 94 4 8个数据 ,食管癌死亡调查资料 1750 80例 ,研究了食管癌死亡率与人群生存的土壤环境中元素的相关性。结果表明 ,铅、硒、铷、铯、镁、钙、镓、铊、钍、铀、锡、铪、铋、钼、溴、碘元素与食管癌死亡率有相关性     

台风“利奇马”不同区域降水极端性特征及成因分析

利用常规气象观测资料、卫星及雷达拼图以及NCEP分辨率为1°×1°的再分析资料,对浙江和山东两个区域不同的极端降水特征及其成因进行诊断对比分析。结果表明:浙江极端降水表现出“高效”的热带降水系统特征,山东极端降水是一次长时间,中等强度的“大陆锋面型”降水。台风近海对称性和对流明显增强;同时,其西北行移速较同期台风偏慢,导致行进方向上长时间受螺旋雨带影响;受超强台风厚实云墙影响,登陆前后浙江等地风雨激增;另外,双台风及沿海山地地形对浙江降水有增幅作用。而山东地区主要受台风北侧稳定维持倒槽和西风槽结合影响,出现极端降水。敏感性分析发现山东降水和台风“第一象限”低层偏南急流强度相关性好,而台风环流持续维持、高度场的密集梯度及降水的潜热反馈共同导致低层急流(>20 m·s-1)长时间维持;同时,西风带高空槽和台风倒槽势力相当,形成稳定“锋区”;锋前多条带状对流持续向北发展,形成“列车效应”;后期冷空气侵入台风中心后山东北侧依然维持较好环流配置。上述条件共同维持了山东地区持续性的较强“锋面降水”。副高、西风槽及台风环流的强度对比是本轮台风降水预报的关键因素。     

Effect of tropical cyclone intensity and instability on the evolution of spiral bands

The evolution of spiral-band-like structures triggered by asymmetric heating in three tropical-cyclone-like vortices of different intensities is examined using the Three-Dimensional Vortex Perturbation Analyzer and Simulator （3DVPAS） model. To simulate the spiral bands, asymmetric thermal perturbations are imposed on the radius of maximum wind （RMW） of vortices, which can be considered as the location near the eyewall of real tropical cyclones （TCs）. All the three vortices experience a hydrostatic adjustment after the introduction of thermal asymmetries. It takes more time for weaker and stable vortices to finish such a process. The spiral-band-like structures, especially those distant from the vortex centers, form and evolve accompanying this process. In the quasi-balance state, the spiral bands are gradually concentrated to the inner core, the wave behavior of which resembles the features of classic vortex Rossby （VR） waves. The unstable vortices regain nonhydrostatic features after the quasi-balance stage. The spiral bands further from the vortex center, similar to distant spiral bands in real TCs, form and maintain more easily in the moderate basic-state vortex, satisfying the conditions of barotropic instability. The widest radial extent and longest-lived distant bands always exist in weak and stable vortices. This study represents an attempt to determine the role of TC intensity and stability in the formation and evolution of spiral bands via hydrostatic balance adjustment, and provides some valuable insights into the formation of distant spiral rainbands.     

沈阳“06．2”暴雪天气过程诊断分析

本文针对2006年2月24日到25日沈阳地区出现的暴雪天气进行了天气诊断分析，发现本次暴雪是在高空横槽转竖、低空锋区扰动、地面倒槽发展东移北上这样几个高低空系统相互作用的结果。水汽条件、垂直速度场和K指数等多个物理量场的条件分析，发现本次暴雪出现在强烈上升的饱和湿区和K指数大值区之中。通过卫星云图图像分析，再现本次暴雪过程的表象特征。同时通过实况天气图与日本气象厅的预报传真图之间的对比，肯定了数值预报产品在实际预报工作中的重要参考作用。     

1223号台风“山神”转向成因分析

利用micaps常规观测资料、ncep再分析资料,分析台风“山神”后期东北转向的原因,分析表明：500hPa副高东退南落是“山神”转向的关键;台风沿假相当位温高值轴线方向移动;环境风场的变化、200hPa高空辐散场中心偏离台风中心、卫星云图特征变化等都可能引起台风的转向;台风的内部特征（散度场、垂直速度场）的分布特点对台风移向有一定的关系.     

基于大型无人机的气象探测系统设计应用

利用高空高速大型无人机自身优势,设计一种基于大型无人机的新型气象探测系统,旨在丰富气象探测技术手段,提高气象探测的准确性.为了实现高空远距气象探测功能,对系统的组成、接口、控制逻辑等进行逐一设计优化,并创新地采用螺旋运转结构,大幅增加气象任务载荷数量,使单个吊舱可装载24枚探空仪.作为一项军民融合的典型应用,本气象探测...