Simulations of deep pencil-beam redshift surveys

We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω₀=0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130  h ⁻¹ Mpc observed by Broadhurst et al. has a priori probability well below 10⁻³.     

基于上市公司网络的长三角城市网络空间结构研究

公司内部网络研究是当前城市经济网络研究的重要内容.本文利用2005、2010年长三角A股上市公司企业网络数据库,运用社会网络分析方法、位序—规模分析法等,分析了2005、2010年长三角城市网络空间结构演变及其主要影响因素.研究发现:①长三角上市公司总部沿沪宁—沪杭—杭甬Z字形轴线集聚,从一主(上海)二副(杭州、南京)三中心向一主(上海)三副(杭州、苏州、南京)四中心空间结构演变;苏州超过南京成为第三大企业总部集聚中心.②长三角城市网络核心—边缘结构整体延续,Z字形轴线城市维持核心地位,具备强大的网络权力与威望.③长三角城市网络除等级扩散、邻近扩散等特征之外.还具有明显的行政地域性.主要体现在省会南京、杭州分别成为江苏、浙江省内外上市公司子公司的重要据点;尤其是南京凭借省会优势,中心度仍然高于总部职能较强的苏州.④在长三角经济一体化背景下,跨行政地域性的联系有所加强,特别是上海、苏南向苏中、苏北的扩散明显;浙西南仍是网络相对封闭、孤立的地带,中心度相对较低.⑤行政等级和区划,市场容量等是长三角城市网络空间结构的主要影响因素,而到上海高速公路时间距离、劳动力成本和土地成本的影响在统计上未通过显著性检验.     

湍流相干结构在中蒙中区一次沙尘暴起沙中的作用

起沙机制是沙尘暴天气研究中一个重要问题.本文基于中蒙中区一次沙尘暴天气过程,通过提取沙尘源地涡动相关数据中的湍流相干结构（Coherent structure,简称为CS）,研究了CS在起沙中的作用.结果发现：（1）起沙期间存在CS,其典型特征表现为上扬—下扫循环,即暖空气的辐合上升与冷空气的辐散下沉相伴;（2）起沙期间,CS具有频次高、持续时间短、间歇性适中、连发频繁、速度切变大、水平尺度远大于垂直尺度和尺度变化比较大的特点;（3）CS是重要的起沙机制,它可起动粒径在0.1~156 μm之间的各种沙粒,起动最多的是粒径低于8 μm的粉粒与粘粒,但CS不是唯一的起沙机制;（4）CS的上扬与下扫两过程均可引起起沙,区别在于前者通过暖空气的上升将沙粒向上空输送,后者则是将上空高速冷空气拖带下来引起地表沙粒的起动;（5）CS起沙分为单起式和连发配合式两种形式.单起式是单发CS产生的起沙形式,连发配合式是连发的CS产生的跃移—上扬的配合起沙形式.其中,连发配合式为主要形式;（6）下扫过程对起沙的贡献是上扬过程的1.8~15倍,上扬过程可将下扫过程中起动沙粒的1/3左右向上输送到空中;（7）一般情况下,CS对起沙具有稳定的贡献,其贡献率为51%,当临界起沙风速大于13 m·s^-1时,其贡献急剧降低.

     

收缩情境下城市用地结构时空格局演变及动力机制——以中国东北地区为例

构建城市用地结构时空格局演变分析框架,引入信息熵和偏移份额模型定量剖析2000-2017年中国东北地区城市用地结构时空格局演变特征,通过计量经济模型分阶段对比分析收缩情境下东北地区城市用地结构演变的动力机制.结果表明:东北地区城市用地总面积持续增长,用地结构信息熵整体呈现先上升、后下降的趋势.2011年以后,城市用地结...     

First evidence of IMF control of Jovian magnetospheric boundary locations: Cassini and Galileo magnetic field measurements compared

The Cassini spacecraft, en route to Saturn, passed close to Jupiter while the Galileo spacecraft was completing its 28th and 29th orbits of Jupiter, thus offering a unique opportunity for direct study of the solar wind-Jovian interaction. Here evidence is given of response of the Jovian magnetopause and bow shock positions to changes of the north-south component of the solar wind magnetic field, a phenomenon long known to occur in equivalent circumstances at Earth. The period analyzed starts with the passage over Cassini of an interplanetary shock far upstream of Jupiter. The shock's arrival at Galileo on the dusk-flank of the magnetosphere caused Galileo to exit into the solar wind. Using inter-spacecraft timing based on the time delay established from the shock arrival at each spacecraft, we point out that Galileo's position with respect to the Jovian bow shock appears to correlate with changes in the disturbed north-south reversing field seen behind the shock. We specifically rule out the alternative of changes in the shape of the bow shock with rotations of the interplanetary magnetic field as the cause.     

基于兴趣点（POI）大数据的东北城市空间结构分析

以东北三省36个城市为研究区,利用400余万条兴趣点行业分类大数据,采用核密度估计、标准差椭圆、区位熵等方法分析城市空间结构及其行业构成机制。研究发现,东北城市要素显著集聚,城市内部空间结构呈现集中团块型、分散组合型、线型、放射型特征以及多元复合类型;第二产业和房地产业呈现郊区化特征,各行业发展方向与东北大区域的经济轴线一致,多数行业尚未形成专业化功能区;第二产业与房地产业的离心发展对集中团块型城市的塑造作用不强,但对分散组合型城市空间结构的贡献较大。线型城市通常兼具多中心特征,放射型城市各行业仍偏向于向心聚集。     

Paleoproterozoic Extensional Structure and Its Controlling on Mineralization in the East of Liaoning Province

IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z…     

The stellar content of a spiral arm of NGC 4321

The effects of the passage of a spiral arm through the disc of the giant Virgo Sc galaxy NGC 4321 are investigated with Hubble Space Telescope WFPC2 images in two colours. Concentrating on a portion of the southern spiral arm of NGC 4321, we have applied a new program to solve for the star formation histories in the arm and interarm regions separately. The observational uncertainties and the variable crowding across the spiral arm are taken into account using the results of artificial star tests. In the interarm regions the data are consistent with a constant star formation rate for the last 50 Myr while the stars in the arm region show a star formation rate four times larger than in the interarm regions in the last 5 Myr.