Analytical solutions for saturated P cygni type profiles II: General case     

A. Sapar  L. Sapar  R. Poolamäe 《Astrophysics and Space Science》2003,286(3-4):333-345

As in the first part of the present study (Sapar et al., 2002) we use the β-law for velocity of stellar wind and the Sobolev approximation for radiative transfer. Here we have succeeded to derive general and relatively simple analytical formulae in elementary functions for saturated P Cygni type line profiles if parameter 2β is arbitrary positive integer (in the first part we studied the cases 2β ≤ 4). The four terms obtained describe contributions to the line profile due to isotropic and anisotropic parts of optical thickness in the source function of the light-scattering layer followed by isotropic and anisotropic parts of multiple scattering. The limits of acceptability of the Sobolev approximation for β-law have been discussed and specified. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

长江三峡阶地的成因机制   总被引：15，自引：0，他引：15  

杨达源 《地理学报》1988,(2)

根据对长江三峡阶地堆积物进行的野外调查与室内分析发现三峡阶地的成因具有以下特点:构成阶地上部的河漫滩相堆积、中部的冲积砾石层与作为阶地基座的基岩平台是在不同时期形成的;阶地上部河漫滩相堆积是在中全新世气候温暖、长江三峡高水位条件下形成的.因此,长江三峡阶地是在构造上升的基础上由于气候及长江三峡流量及水位变化而形成的,并非一定是间歇性构造上升的标志.  相似文献   

Doppler shift measurements on the green coronal line—evidence for largescale macroscopic mass motion     

J. N. Desai  T. Chandrasekhar  P. D. Angreji 《Journal of Astrophysics and Astronomy》1982,3(1):69-77

Fabry-Perot interferometric observations on the green coronal line (λ 5303 å) carried out during the total solar eclipse of 1980 February 16 have yielded relative Doppler shift velocities with an accuracy of ± 7 km s^-1. The values show a peak in the 30–50 km s^-1 range indicating largescale macroscopic mass motion in the solar maximum corona.  相似文献   

哈雷彗星的羟基射电谱线观测     

罗先汉  周体健  姚德一  杜声孚  钱志瀚  季德盛  张卫民 《中国天文和天体物理学报》1988,(3)

本文主要论述用25米射电望远镜和自相关频谱仪于1986年4月13—17日(UT)期间在我国陕西眉县首次对哈雷彗星羟基分子1667 MHz射电话线的观测及归算结果。由谱线轮廓的幅度、宽度、形状和面积相继导出的谱线强度为-2.4Jy,膨胀速度为0.92kms~(-1),速度的一级矩为0.20kms~(-1),以及羟基的母分子产生率为1.7×10~(29)mols~(-1)。文中所给出的宇宙羟基源W3和W12的观测结果,分别用来检验设备系统探测射电谱线的功能及对哈雷彗星的羟基谱线进行强度定标。这些结果均同理论预期或以往的有关观测相符合。  相似文献   

Geotechnical characterisation of pyroclastic soils involved in huge flowslides   总被引：1，自引：0，他引：1  

Eduardo?Bilotta  Leonardo?Cascini  Vito?Foresta  Giuseppe?SorbinowEmail author 《Geotechnical and Geological Engineering》2005,23(4):365-402

Landslides of the flow type involving granular geo-materials frequently result in casualties and damage to property because of the long travel distance and the high velocities that these may attain. This was true for the events that took place in Campania Region (Southern Italy) in May 1998, involving pyroclastic soils originating from explosive activities of the Somma-Vesuvius volcano. Although these phenomena have frequently affected various areas of the Campania region over the last few centuries, there were no useful geological and geotechnical references available in the aftermath of the May 1998 events. For this reason Salerno University, which was involved in the scientific management of the emergency, addressed the issue of acquiring data on the geological, geomorphological and hydrogeological features of the slopes where the landslides had taken place. The information acquired made it possible to set up a slope evolution model that is able to interpret, from a geological point of view, past and more recent landslides that had occurred in the same area. As preliminary geotechnical analyses had already validated the above model, more detailed investigations were performed both on the pore pressure regimen of the covers still in place as well as on the physical and mechanical properties of pyroclastic soils, in saturated and unsaturated conditions. The present paper begins by discussing the data acquired during the .rst phase of the studies and then goes on to illustrate the laboratory results so far obtained with the aid of approximate procedures. These help advance our knowledge of pyroclastic soils within a reasonable time frame, thus improving landslide triggering analysis.  相似文献   

Optimum design of nailed soil slopes   总被引：12，自引：0，他引：12  

C.?R.?PatraEmail author  P.?K.?Basudhar 《Geotechnical and Geological Engineering》2005,23(3):273-296

In this paper, a generalized method of computer based optimum design of soil-nailed slopes is reported. A limit equilibrium formulation satisfying overall and internal equilibrium and considering the effect of tensile resistance of the reinforcement has been used in computing the stability of nailed slopes. The quantity of steel requirement for raising the factor of safety to a desired value is estimated. The location, size (length and diameter) and orientation of the nails and the location and shape of the critical shear surface have been treated as variables. The solutions have been isolated by formulating the problem as one of non-linear programming. The applicability of the developed method has been verified by comparing the predicted failure surfaces with those observed in model tests as well as in the field and also reported theoretical results.  相似文献   

Stochastic data in astronomy: Fourier analysis of highly nonuniform time series     

A. F. Kholtygin  A. B. Shneiwais 《Astrophysics》2005,48(1):68-78

The features of the CLEAN algorithm for Fourier analysis of time series with data separated by long pauses are analyzed in detail. Estimates are obtained for the limits of variability of the parameters of harmonic components that can be determined on a specified time grid. This analysis are used to search for harmonic components in the spectral line profile variations of the star Ori A (O8III) obtained in 2001 with the 1 m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences.Translated from Astrofizika, Vol. 48, No. 1, pp. 87–100 (February 2005).  相似文献   

Geochemistry of coral from Papua New Guinea as a proxy for ENSO ocean–atmosphere interactions in the Pacific Warm Pool     

Linda K. Ayliffe  Michael I. Bird  Michael K. Gagan  Peter J. Isdale  Heather Scott-Gagan  Bruce Parker  David Griffin  Michael Nongkas  Malcolm T. McCulloch 《Continental Shelf Research》2004,24(19):2343-2356

A Porites sp. coral growing offshore from the Sepik and Ramu Rivers in equatorial northern Papua New Guinea has yielded an accurate 20-year history (1977–1996) of sea surface temperature (SST), river discharge, and wind-induced mixing of the upper water column. Depressions in average SSTs of about 0.5–1.0 °C (indicated by coral Sr/Ca) and markedly diminished freshwater runoff to the coastal ocean (indicated by coral δ¹⁸O, δ¹³C and UV fluorescence) are evident during the El Niño – Southern Oscillation (ENSO) events of 1982–1983, 1987 and 1991-1993. The perturbations recorded by the coral are in good agreement with changes in instrumental SST and river discharge/precipitation records, which are known to be diagnostic of the response of the Pacific Warm Pool ocean–atmosphere system to El Niño. Consideration of coastal ocean dynamics indicates that the establishment of northwest monsoon winds promotes mixing of near-surface waters to greater depths in the first quarter of most years, making the coral record sensitive to changes in the Asian–Australian monsoon cycle. Sudden cooling of SSTs by 1°C following westerly wind episodes, as indicated by the coral Sr/Ca, is consistent with greater mixing in the upper water column at these times. Furthermore, the coral UV fluorescence and oxygen isotope data indicate minimal contribution of river runoff to surface ocean waters at the beginning of most years, during the time of maximum discharge. This abrupt shift in flood-plume behaviour appears to reflect the duration and magnitude of northwest monsoon winds, which tend to disperse flood plume waters to a greater extent in the water column when wind-mixing is enhanced. Our results suggest that a multi-proxy geochemical approach to the production of long coral records should provide comprehensive reconstructions of tropical paleoclimate processes operating on interannual timescales.  相似文献   

粉煤灰湿陷变形的三轴试验和计算     

明经平  赵维炳 《岩土力学》2004,25(Z2):32-38

采用双压力室三轴仪对粉煤灰试样进行了单线法湿陷试验,研究了在静水压力作用以及在不同应力状态和应力水平下粉煤灰湿陷变形的规律,得出了粉煤灰湿陷变形的经验计算公式.提出了计算粉煤灰地基湿陷变形的"全应变曲线"增量有限元法.基于本文的试验结果,对一个粉煤灰地基的湿陷变形进行了有限元计算.  相似文献   

江西金山金矿田东蒋金矿床地质特征及找矿远景   总被引：3，自引：0，他引：3  

林忠良 《矿产与地质》2004,18(6):567-570

阐述了东蒋金矿床的成矿地质背景,通过对该金矿区地质特征的分析和总结,认为东蒋韧性剪切带为一卓具规模的控矿、容矿构造,其具有构造岩分带、蚀变分带及金矿化强度分带“三位一体”的规律性分布特点。指出该区业已发现韧性剪切带中的似层状金矿体和陡倾斜断裂带(F1)中的脉状金矿体,而该带目前无矿的东段分布有物探激电、航磁、重力异常及化探异常,这些都显示该区尚具有良好的找矿前景。  相似文献