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41.
42.
Maintenance and development of the Ural high and its contribution to severe cold wave activities in winter 2020/21 下载免费PDF全文
2020年底至2021年初,连续两次强寒潮入侵中国东部地区,导致大范围强降温.本文研究这两次寒潮的特征和形成机理.主要结果如下:从2020年12月中旬到2021年1月中旬,乌拉尔山地区维持一宽阔的高压脊.脊前北风的维持和加强导致局地斜压性增加,导致下游横槽槽底等高线梯度加大,冷平流加强,西伯利亚高压加强和向南扩张.准定... 相似文献
43.
The Tully-Fisher (TF) or the luminosity-linewidth relations of the galaxies in the Eridanus group are constructed using the
HI rotation curves and the luminosities in the optical and in the near-infrared bands. The slopes of the TF relations (absolute
magnitudevs log2V
flat) are −8.6 ± 1.1, −10.0 ±1.5, −10.7 ±2.1, and −9.7 ±1.3 in the R, J, H, and K bands respectively for galaxies having flat
HI rotation curves. These values of the slopes are consistent with those obtained from studies of other groups and clusters.
The scatter in the TF relations is in the range 0.5-1.1 mag in different bands. This scatter is considerably larger compared
to those observed in other groups and clusters. It is suggested that the larger scatter in the TF relations for the Eridanus
group is related to the loose structure of the group. If the TF relations are constructed using the baryonic mass (stellar
+HI + Helium mass) instead of the stellar luminosity, nearly identical slopes are obtained in the R and in the near-infrared
bands. The baryonic TF (baryonic massvs log2V
flat) slope is in the range 3.5–4.1. 相似文献
44.
We analyze the encounters of the neutron star (pulsar) Geminga with open star clusters in the OB association Ori OB1a through the integration of epicyclic orbits into the past by taking into account the errors in the data. The open cluster ASCC21 is shown to be the most probable birthplace of either a single progenitor star for the Geminga pulsar or a binary progenitor system that subsequently broke up. Monte Carlo simulations of Geminga-ASCC21 encounters with the pulsar radial velocity V r = ?100±50 km s?1 have shown that close encounters could occur between them within ≤10 pc at about t = ?0.52 Myr. In addition, the trajectory of the neutron star Geminga passes at a distance of ≈25 pc from the center of the compact OB association λ Ori at about t = ?0.39 Myr, which is close to the age of the pulsar estimated from its timing. 相似文献
45.
This series of high quality elemental abundance analyses of mostly main‐sequence band normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with the analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (≥ 200) spectrograms obtained with CCD detectors at the long camera of the Coudé spectrograph of the 1.22‐m Dominion Astrophysical Observatory telescope. Here we reanalyze 21 Aql with better quality spectra and increase the number of stars consistently analyzed in the spectral range B5 to A2 by analyzing three new stars for this series. In the early A stars the normal and non‐mCP stars have abundances with overlapping ranges. But more stars are needed especially in the B5 to B9 range. ξ2 Cet on average has a solar composition with a few abundances outside the solar range while both 21 Aql and ι Aql have abundances marginally less than solar. The abundances of ι Del are greater than solar with a few elements such as Ca being less than solar. It is an Am star (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
46.
走向21世纪的矿床学 总被引:10,自引:2,他引:10
文章简要回顾了百年来矿床学取得的重要进展,包括:(1)矿床成因分类的建立;(2)层控矿床研究与矿床多成因理论的兴起;(3)板块构造与区域成矿规律;(4)矿床模型;(5)型矿床研究;(6)海洋现代热液成矿作用的发现;(7)成矿演化的不可逆性与节律性等。针对21世纪中人类社会可持续发展的需要,矿床学研究出现了两个新趋势;(1)全球化;(2)矿业开发与环境保护一体化。面临着三个主要研究领域;(1)成矿理论的推陈出新;(2)研究开发新型矿产资源,建立广义的矿产资源地质学;(3)建立绿色矿业体制所需的矿床学基础研究。 相似文献
47.
Michael D. Smith Jochen Eislöffel & Christopher J. Davis 《Monthly notices of the Royal Astronomical Society》1998,297(3):687-691
We demonstrate that a wide range of molecular hydrogen excitation can be observed in protostellar outflows at wavelengths in excess of 5 μm. Cold H2 in DR 21 is detected through the pure rotational transitions in the ground vibrational level (0–0). Hot H2 is detected in pure rotational transitions within higher vibrational levels (1–1, 1–2, etc.). Although this emission is relatively weak, we have detected two 1–1 lines in the DR 21 outflow with the ISO SWS instrument. We thus investigate molecular excitation over energy levels corresponding to the temperature range 1015–15 722 K, without the uncertainty introduced by differential extinction when employing near-infrared data.
This gas is thermally excited. We uncover a rather low H2 excitation in the DR 21 West Peak. The line emission cannot be produced from single C-shocks or J-shocks; a range of shock strengths is required. This suggests that bow shocks and/or bow-generated supersonic turbulence is responsible. We are able to distinguish this shock-excited gas from the fluoresced gas detected in the K band, providing support for the dual-excitation model of Fernandes, Brand & Burton. 相似文献
This gas is thermally excited. We uncover a rather low H
48.
49.
中心商务区的建设是城市经济水平的折影。中心商务区的3个发展演化阶段:前现代主义的中心商务区、现代主义的中心商务区、后现代主义的中心商务区。从发展战略角度出发,广州市以珠江新城为中心的中心商务区应致力于后现代主义的中心商务区建设,与传统中心商务区形成系列化、互补协调的中心商务区系统。根据广州市建设后现代主义中心商务区的条件并参照国内外中心商务区建设的经验,广州以珠江新城为中心的中心商务区建设应在增强自身吸引力的同时,导入后现代主义开发意识,以适合新世纪新经济、新文化等新形势的发展需要。 相似文献
50.
中国地理学如何面对21世纪 总被引:1,自引:0,他引:1
面对 2 1世纪 ,如何进一步发展我国地理学 ,已成为全国地理学界和有关人士最为关注的问题。文章在简单概括回顾了 2 0世纪后期取得的巨大成绩基础上 ,初步探讨了 2 1世纪初叶中国地理学如何发展的问题。 相似文献