海滩养护动力地貌基础理论与关键技术研究述评     

郑金海  张弛 《海洋与湖沼》2022,53(4):791-796

海滩养护是砂质海岸最重要的自然防护手段之一,也是我国海岸带保护修复工程最重要的建设内容之一。围绕强波浪动力、弱波浪动力、强潮等不同条件下的养护海滩动力适应性与滩肩、沙坝等地貌稳定性及其模拟预测三个主要方面,总结近年来我国海滩养护基础理论和关键技术研究中的一些新认识和新思考,并提出亟需深入研究的重点内容。  相似文献   

Risk assessment of soil erosion in semi-arid mountainous watershed in Saudi Arabia by RUSLE model coupled with remote sensing and GIS     

Javed Mallick  Yasser Alashker  Shams Al-Deen Mohammad  Mohd Ahmed  Mohd Abul Hasan 《国际地球制图》2013,28(8):915-940

Soil erosion is the most important factor in land degradation and influences desertification in semi-arid areas. A comprehensive methodology that integrates revised universal soil loss equation (RUSLE) model and GIS was adopted to determine the soil erosion risk (SER) in semi-arid Aseer region, Saudi Arabia. Geoenvironmental factors viz. rainfall (R), soil erodibility (K), slope (LS), cover management and practice factors were computed to determine their effects on average annual soil loss. The high potential soil erosion, resulting from high denuded slope, devoid of vegetation cover and high intensity rainfall, is located towards the north western part of the study area. The analysis is investigated that the SER over the vegetation cover including dense vegetation, sparse vegetation and bushes increases with the higher altitude and higher slope angle. The erosion maps generated with RUSLE integrated with GIS can serve as effective inputs in deriving strategies for land planning/management in the environmentally sensitive mountainous areas.  相似文献   

A NOTE ON THE GEOGRAPHY OF SPORT     

Richard Perkins  Eric Neumayer 《The Professional geographer》2013,65(1):55-72

The recent phenomenon of relative metropolitan decline and non-metropolitan growth is set into two broader frameworks: first, decentralization is an expected consequence of earlier industrialization and metropolitanization; and, second, the change follows a parallel shift in power, industrialization, and urbanization from the core to the periphery of the country. Evidence is found for both. The older industrial states thus exhibit non-metropolitan growth, whereas many newly industrializing states continue to show vigorous metropolitanization.  相似文献   

大口径离轴非球面镜预应力环抛方法研究     

李新南  章海鹰  崔向群  姜自波  郑奕  刘星涛  倪厚坤 《天文学报》2012,53(2):161-170

提出了一种加工离轴非球面的预应力环抛方法,基于预应力加工方法的基本原理,利用环抛机来磨制离轴非球面.设计了一套专门的加载装置,将拼接镜面中具有不同离轴量的非球面子镜转化成曲率半径相同的球面子镜进行磨制,可以在同一台环抛机上进行抛光.利用这种方法,花费连续40 h的时间,磨制了一块按照中国30 m极大口径望远镜(CFGT)主镜参数比例缩小的离轴抛物面,顶点曲率半径21.6 m,离轴量3.6 m,离轴口径为330 mm,最大非球面度为16μm.试验表明该方法效率高,适用于批量加工,特别是极大口径天文望远镜拼接主镜的大批量非球面子镜研制.  相似文献   

Relative flux calibration for the Guoshoujing Telescope （LAMOST）     

Yi-Han Song  A-Li Luo  Georges Comte  Zhong-Rui Bai  Jian-Nan Zhang  Wei Du  Hao-Tong Zhang  Jian-Jun Chen  Fang Zuo  Yong-Heng Zhao 《天体物理学报》2012,(4):453-464

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The LEGUE input catalog for dark night observing in the LAMOST pilot survey     

Fan Yang  Jeffrey L. Carlin  Chao Liu  Yue-Yang Zhang  Shuang Gao  Yan Xu  Li-Cai Deng  Heidi Jo Newberg  Sebastien Lepine  Jin-Liang Hou  Xiao-Wei Liu  Norbert Christlieb  Hao-Tong Zhang  Hsu-Tai Lee  Kai-Ke Pan  Zhan-Wen Han  Hong-Chi Wang 《天体物理学报》2012,(7):781-791

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Second‐order error propagation in the Mueller matrix of a spectropolarimeter     

I. Ilyin 《Astronomische Nachrichten》2012,333(3):213-229

Accurate measurements of Stokes IQUV in spectral lines is required for precise reconstruction of stellar magnetic field geometries with Zeeman‐Dopper imaging. Spectral Zeeman features are intrinsically weak and subjected to a number of instrumental uncertainties. The aim of this work is to study the details of the instrumental uncertainties in the Stokes IQUV measurements in spectral lines and ways of their reduction. We make a practical comparison of the polarimetric performances of two high‐resolution échelle spectropolarimeters, namely SOFIN at the NOT, and HARPS at ESO. We show the residual spectra for both instruments to characterize the cross‐talk between the observed Stokes parameters. We employ a self‐calibrating least‐squares fit to eliminate some of the polarization uncertainties to derive the full Stokes vector from stellar spectra (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Measuring the mass accretion rates of Herbig Ae/Be stars with X‐shooter     

M.A. Pogodin  S. Hubrig  R.V. Yudin  M. Schller  J.F. Gonzlez  B. Stelzer 《Astronomische Nachrichten》2012,333(7):594-612

We present the results of our observations of eight magnetic Herbig Ae/Be stars obtained with the X‐shooter spectrograph mounted on UT2 at the VLT. X‐shooter provides a simultaneous, medium‐resolution and high‐sensitivity spectrum over the entire wavelength range from 300 to 2500 nm. We estimate the mass accretion rates (Ṁ_acc) of the targets from 13 different spectral diagnostics using empiric calibrations derived previously for T Tauri‐type stars and brown dwarfs. We have estimated the mass accretion rates of our targets, which range from 2 × 10^–9 to 2 × 10^–7 M_⊙ yr^–1. Furthermore, we have found accretion rate variability with amplitudes of 0.10–0.40 dex taking place on time scales from one day to tens of days. Additional future night‐to‐night observations need to be carried out to investigate the character of Ṁ_acc variability in details. Our study shows that the majority of the calibration relations can be applied to Herbig Ae/Be stars, but several of them need to be re‐calibrated on the basis of new spectral data for a larger number of Herbig Ae/Be stars (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Rotation,activity, and lithium abundance in cool binary stars     

K. G. Strassmeier  M. Weber  T. Granzer  S. Jrvinen 《Astronomische Nachrichten》2012,333(8):663-705

We have used two robotic telescopes to obtain time‐series high‐resolution optical echelle spectroscopy and VI and/or by photometry for a sample of 60 active stars, mostly binaries. Orbital solutions are presented for 26 double‐lined systems and for 19 single‐lined systems, seven of them for the first time but all of them with unprecedented phase coverage and accuracy. Eighteen systems turned out to be single stars. The total of 6609 R = 55000 échelle spectra are also used to systematically determine effective temperatures, gravities, metallicities, rotational velocities, lithium abundances and absolute Hα‐core fluxes as a function of time. The photometry is used to infer unspotted brightness, V – I and/or b – y colors, spot‐induced brightness amplitudes and precise rotation periods. An extra 22 radial‐velocity standard stars were monitored throughout the science observations and yield a new barycentric zero point for our STELLA/SES robotic system. Our data are complemented by literature data and are used to determine rotation‐temperature‐activity relations for active binary components. We also relate lithium abundance to rotation and surface temperature. We find that 74% of all known rapidly‐rotating active binary stars are synchronized and in circular orbits but 26% (61 systems) are rotating asynchronously of which half have P_rot > P_orb and e > 0. Because rotational synchronization is predicted to occur before orbital circularization active binaries should undergo an extra spin‐down besides tidal dissipation. We suspect this to be due to a magnetically channeled wind with its subsequent braking torque. We find a steep increase of rotation period with decreasing effective temperature for active stars, P_rot α T^–7_eff, for both single and binaries, main sequence and evolved. For inactive, single giants with P_rot > 100 d, the relation is much weaker, P_rot α T^‐1.12_eff. Our data also indicate a period‐activity relation for Hα of the form R_Hα α P_0.24^rot for binaries and R_Hα α P_‐0.14^rot for singles. Its power‐law difference is possibly significant. Lithium abundances in our (field‐star) sample generally increase with effective temperature and are paralleled with an increase of the dispersion. The dispersion for binaries can be 1–2 orders of magnitude larger than for singles, peaking at an absolute spread of 3 orders of magnitude near T_eff ≈ 5000 K. On average, binaries of comparable effective temperature appear to exhibit 0.25 dex less surface lithium than singles, as expected if the depletion mechanism is rotation dependent. We also find a trend of increased Li abundance with rotational period of form log n (Li) α –0.6 log P_rot but again with a dispersion of as large as 3‐4 orders of magnitude (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Recent photometry of symbiotic stars     

A. Skopal  S. Shugarov  M. Va&#x;ko  P. Dubovský  S.P. Peneva  E. Semkov  M. Wolf 《Astronomische Nachrichten》2012,333(3):242-255

We present new multicolour (UBVR_CI_C) photometric observations of classical symbiotic stars, EG And, Z And, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, Draco C1, AG Peg, and AX Per, carried out between 2007.1 and 2011.9. The aim of this paper is to present new data of our monitoring programme, to describe the main features of their light curves (LC) and to point problems for their future investigation. The data were obtained by the method of the classical photoelectric and CCD photometry (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献