The β Cephei instability strip

We carried out a series of linear stability analyses of the radial and low-degree non-radial p modes for stellar models with initial masses of     . The stellar models were computed by using convective overshoot distance     , 0.25 and 0.40  H _P. Our numerical results show that the β Cephei instability strip forms a horn-shaped region pointing upwards near the main sequence on the Hertzsprung–Russell diagram (HRD). The lower part of the instability strip for the radial modes join the zero-age main-sequence (ZAMS) at     , while the top of the instability strip extends up to     . The instability strip for the non-radial modes is even wider. The overall instability strip is dominated by the radial and non-radial fundamental modes. The first overtone (the radial-order index     is also pulsationally unstable. We have shown that the β Cephei stability is almost independent of the overshoot parameter d _over used for the stellar models, while it depends critically on the metal abundance. With decreasing metal abundance, the instability region shrinks and eventually disappears for     .     

A Note on the Mixing Length Theory and Massive Star Evolution

1 INTRODUCTIONThe mixing length theory (MLT) for stellar convection originally developed by Vitense(1953, 1958) has been the most popularly used local convection theory in the studies of stellarstructure and evolution. The theory was later modified and revised by many investigators,who suggested some different expressions. In fact, MLT is not a real hydrodynamic theory,rather, it is a simple "ballistic" theory which traces the motion of imaginary convective elements. In reality j stell…     

Environmental dependence of stellar mass,SFR, and SSFR for the Luminous Red Galaxy (LRG) sample of the SDSS DR7

Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we investigate the environmental dependence of stellar mass, star formation rate (SFR) and specific star formation rate (SSFR) of LRGs. It is found that stellar mass of LRGs nearly is independent of local environments, and that the environmental dependence of SFR and SSFR in the LRG sample is much weaker than the one in the Main galaxy sample. One possible explanation is that galaxy color and morphology are a pair of galaxy properties most predictive of local environments, while LRGs are a group of galaxies that are likely to be luminous, red and of early types (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the correlation between morphology and luminosity for two classes of main galaxies

Using an apparent-magnitude limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 7(SDSS DR7), we investigate the correlation between morphologies and luminosity for the Main galaxy sample. Our Main galaxy sample is divided into two classes: Main galaxies only with TARGET_GALAXY flag (bestPrimtarget = 64), and ones also with other flags. It is found that for the second class Main galaxies, the early-type proportion monotonously increases with increasing luminosity nearly in the whole luminosity region. But for the first class Main galaxies, the early-type proportion increases with increasing luminosity only within a certain luminosity region (−22.2 < M _r  < −19.8). In the high luminosity region (M _r  < −22.2), the early-type proportion of the first class Main galaxies even decreases dramatically with increasing luminosity. We also analyze the correlation between morphologies and luminosity of galaxies around the peak of the redshift distribution ( 0.07 ≤ z ≤ 0.08 ). In such a narrow redshift region, we still observe strong correlation between morphologies and luminosity, which shows that this correlation is fundamental.     

江西萍乡杨家湾2号洞哺乳动物化石及其时代探讨

2015年11月和2016年10月先后对杨家湾2号洞化石点进行发掘。目前已出土哺乳动物化石1000多件,主要为单个牙齿化石,骨骼较少且较为破碎。初步鉴定出31个哺乳动物属种,其中偶蹄类数量最为丰富,野猪所占比例最大;灵长类和食肉类较为丰富;啮齿类、长鼻类及奇蹄类较少;尚未发现食虫类和翼手类。大部分属种为现生类群,少量灭绝属种如巴氏大熊猫、东方剑齿象及华南巨貘等。从动物群组成来看,该动物群与杨家湾1号洞、湖南道县福岩洞等动物群较为相似,属于我国南方典型的晚更新世大熊猫-剑齿象动物群,但是其所包含的动物属种相对后两个化石点都较少,尤其是小哺乳动物属种单调。杨家湾2号洞的堆积物颗粒比1号洞的较粗,且含较多角砾,缺少红色粘土;据初步判断,该洞的堆积物是由洞口进入。动物群组合指示该地区晚更新世气候较为温暖湿润。

     

广西国土空间格局演变特征与形成机理

国土空间格局演化与形成机理是人地系统交互关系研究的科学问题和国土空间规划的关键前提。采用地学图谱、标准差椭圆和空间自相关方法,分析2000—2018年广西国土空间格局演变特征,并运用地理探测器揭示其形成机理。结果表明：① 广西城镇空间加速挤占农业、生态空间形成了“一增双减”的面积变化特征,国土空间动态变化速度加快;② 广西国土空间相互转化频繁,转移轨迹多样性特征明显,农业空间与生态空间加速互换以及生态空间内部结构加快重组;③ 城镇空间与农业空间互竞主导了广西国土空间的迁移路径,城镇、农业空间存在“南高北低”和生态空间存在“北高南低”的集聚特征;④ 广西国土空间格局演变受自然地理与社会经济因素的共同作用影响,自然环境条件的限制作用减弱,社会经济发展水平驱动力增强,政策调控力度驱动作用深远。下一步可通过国土空间规划、调整产业布局和引导生产生活方式优化国土空间格局。     

Degrading river network due to urbanization in Yangtze River Delta

Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s–2010s in the Yangtze River Delta (YRD) were investigated based on streams derived from the topographic maps in the 1960s, 1980s and 2010s. A list of indices, drainage density (Dd), water surface ratio (WSR), ratio of area to length of main streams (R), evolution coefficient of tributaries (K) and box dimension (D), were classified into three types (quantitative, structural, and complex indices) and used to quantify the variations of stream structure. Results showed that: (1) quantitative indices (Dd, WSR) presented decreasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan have decreased most, about 20%. Structurally, the Qinhuai River basin was characterized by significant upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s–2010s. Decreasing tendency in D was found dominating across the YRD, and decreasing magnitude in Wuchengxiyu and Hangjiahu peaks for 7.8% and 6.5%, respectively in the YRD. (2) Urbanization affected the spatial pattern of river system, and areas with high level of urbanization exhibited least Dd (2.18 km/km²), WSR (6.52%), K (2.64) and D (1.42), compared to moderate and low levels of urbanization. (3) Urbanization also affected the evolution of stream system. In the past 50 years, areas with high level of urbanization showed compelling decreasing tendency in quantitative (27.2% and 19.3%) and complex indices (4.9%) and trend of enlarging of main rivers (4.5% and 7.9% in periods of the 1960s–1980s and the 1980s–2010s). In the recent 30 years, areas with low level of urbanization were detected with significant downward trend in Dd and K. (4) Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means which degraded the river system in the YRD.     

The 1786 earthquake-triggered landslide dam and subsequent dam-break flood on the Dadu River, southwestern China — Reply

A short reply to discussion by Chanson.