The circumstellar shells of carbon miras     

Martin Groenewegen 《Astrophysics and Space Science》1995,224(1-2):321-324

The relation between mass loss rate and pulsation period in carbon Miras is discussed. The dust mass loss rate is very low (about 2 × 10^–10 M/yr) up to aboutP = 380 days, where there is a sudden increase. ForP > 400 days there is a linear relation between logM andP. The change in the mass loss rate near 380 days may be related to radiation pressure on dust becoming effective in driving the outflow.  相似文献   

Engineering geological studies and tunnel support design at Sulakyurt dam site, Turkey   总被引：2，自引：0，他引：2  

H. Basarir 《Engineering Geology》2006,86(4):225-237

This paper presents the results of engineering geological investigations and tunnel support design studies, carried out at the Sulakyurt dam site, northeast of Ankara, Turkey. The Sulakyurt dam will be used for flow control and water storage for irrigation projects. Studies were carried out both in the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, core drilling and sampling for laboratory testing. The diversion tunnel will be driven in rock mass, consisting of granite and diorite. Empirical, analytical and numerical methods were combined for safe tunnel design. Rock mass rating (RMR), Rock mass quality (Q) and Geological strength index (GSI) systems were used for empirical rock mass quality determination, site characterization and support design. The convergence–confinement method was used as analytical method and software called Phase², a 2D finite element program, was utilized as numerical method. According to the results acquired from the empirical, analytical and numerical methods, tunnel stability problems were expected in both granite and diorite rock masses. The support system, suggested by empirical methods, was applied and the performance of suggested support system was evaluated by means of numerical modelling. It was concluded that the suggested support systems were adequate, since after applying the suggested support system to granite and diorite, tunnel deformation and the yielded elements around the tunnel decreased significantly. Thus, it is suggested that for more reliable support design empirical, numerical and analytical methods should be combined.  相似文献   

湿地功能快速评价中的若干理论问题   总被引：9，自引：5，他引：9  

殷书柏  吕宪国 《湿地科学》2006,4(1):1-6

针对目前湿地功能快速评价中存在的不足之处,分析了产生这些不足的原因及湿地功能快速评价过程中存在的一些基本理论问题。分析表明:湿地功能快速评价方法是为了达到“湿地功能无净损失”目的,是在需要评价的湿地如此之多而从事湿地功能评价的专业人员又极其缺乏的情况下发展起来的。它对于湿地恢复与重建以及湿地受人类活动干扰程度的评价是非常有效的;在湿地功能快速评价过程中,把相对未受人类干扰的参照湿地的功能指数规定为1,这就使得快速评价方法不能对参照湿地的功能进行评价,而目前最需要评价其功能的湿地往往就是这些相对未受人类活动干扰的湿地;在相同水文地貌的湿地类型内评价湿地功能之间的差异,这使得快速评价方法不能评价湿地的水文地貌功能;由于快速评价的结果都是相对的功能指数,并不能说明湿地所提供的功能量是否满足人们的需求,因而在决策中不能单独使用;快速评价都是“一次调查就获得结果”,同时由于快速评价过程中指标选择的主观性、指标赋值的主观性、采样点空间设置的主观性以及采样时间的主观性,对于具有时空变化特征的湿地功能的评价结果的可重复性和科学性是很低的。为了使湿地功能评价的结果对管理和决策具有指导意义,基于湿地功能量计算的、定量的评价湿地功能的方法必须开发出来。针对不同的评价目的,湿地功能评价可采用双重参照标准:一是以自然为参照来评价湿地功能受人类活动影响的程度以及湿地恢复与重建成功与否;二是以人类需要为标准来评价湿地提供的功能量是否满足了我们的期望,以便采取措施改进湿地功能来满足人类的需求。  相似文献   

Comparative Seismic Risk Studies for German Earthquake Regions on the Basis of the European Macroseismic Scale EMS-98     

Jochen Schwarz  Mathias Raschke  Holger Maiwald 《Natural Hazards》2006,38(1-2):259-282

Within the framework of recent research projects, basic tools for GIS-based seismic risk assessment technologies were developed and applied to the building stock and regional particularities of German earthquake regions. Two study areas are investigated, being comparable by the level of seismic hazard and the hazard-consistent scenario events (related to mean return periods of 475, 2475 and 10000 years). Significant differences exist with respect to the number of inhabitants, the grade and extent of urbanisation, the quality and quantity of building inventory: the case study of Schmölln in Eastern Thuringia seems to be representative for the majority of smaller towns in Germany, the case study of Cologne (Köln) stands for larger cities. Due to the similarities of hazard and scenario intensities, the considerable differences do not only require proper decisions concerning the appropriate methods and acceptable efforts, they enable conclusions about future research strategies and needs for disaster reduction management. Not least important, results can sharpen the focus of public interest. Seismic risk maps are prepared for different scenario intensities recognising the scatter and uncertainties of site-dependent ground motion and also of the applied vulnerability functions. The paper illustrates the impact of model assumptions and the step-wise refinements of input variables like site conditions, building stock or vulnerability functions on the distribution of expected building damage within the study areas. Furthermore, and in contrast to common research strategies, results support the conclusion that in the case of stronger earthquakes the damage will be of higher concentration within smaller cities like Schmölln due to the site-amplification potential and/or the increased vulnerability of the building stock. The extent of damage will be pronounced by the large number of masonry buildings for which lower vulnerability classes have to be assigned. Due to the effect of deep sedimentary layers and the composition of building types, the urban centre of Cologne will be less affected by an earthquake of comparable intensity.  相似文献   

A Connectivity Index for Discrete Fracture Networks     

C. Xu  P. A. Dowd  K. V. Mardia  R. J. Fowell 《Mathematical Geology》2006,38(5):611-634

Connectivity is an important measure for assessing flow transport in rock, especially through fractures. In this paper, rock fracture systems are modelled by a discrete fracture model simulated by a marked point process. A connectivity index is then introduced to quantify the connectivity between any two points in space. Monte Carlo simulation is used to evaluate the connectivity index for stationary cases and relationships between the connectivity index and the parameters of the discrete fracture model are analysed. The average number of intersections per fracture, X_f, and the fracture intensity, P12 (P32), are calculated and the relationships between these parameters and the connectivity index are investigated, concluding that X_f is the more suitable parameter for the classification of rock mass flow properties. The relationships between the connectivity index and the percolation state of the fractured medium are also discussed. An edge correction is briefly discussed and a practical example is used to demonstrate the method of computing the connectivity index.  相似文献   

A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss Alps   总被引：3，自引：0，他引：3  

Anne Hormes  Jürg Beer  Christian Schlüchter 《Geografiska Annaler: Series A, Physical Geography》2006,88(4):281-294

We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid‐latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon‐dated periods defined with less extensive glaciers coincide with periods of reduced radio‐production, pointing to a connection between solar activity and glacier melting processes. Measured long‐term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long‐term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances.  相似文献   

Retrieval of stratospheric O3 and NO2 vertical profiles using zenith scattered light observations     

G. S. Meena  C. S. Bhosale  D. B. Jadhav 《Journal of Earth System Science》2006,115(3):333-347

Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to retrieve vertical profiles of ozone (O₃) and nitrogen dioxide (NO₂) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured and recalculated slant column densities (SCDs) and they are found to be well matching. O₃ and NO₂ vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡ SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities (TCDs) of O₃ and NO₂ along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003. The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer and minimum in the winter season. Increasing trend is found in column density of NO₂ in stratospheric, tropospheric and surface layers, but no trend is observed in O₃ columns for above layers during the period 2000–2003  相似文献