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611.
The Caspian Sea is characterized in the geographic and ecological aspects, and the state of its ecosystem is estimated. The natural and anthropogenic processes that control the formation of the environmental conditions in the Caspian Sea and the distribution of principal commercial hydrobionts and their food items are analyzed. Data on modern tendencies in changes in the abiotic and biotic parameters of the ecosystem, their causes and mechanisms are summarized. Prospects of further changes related to the development of shelf fields of petroleum hydrocarbons are assessed. 相似文献
612.
Human exploration of the Moon and Mars: implications for Aurora 总被引:1,自引:0,他引:1
Ian A Crawford 《Astronomy& Geophysics》2004,45(2):2.28-2.29
613.
Specific hydrological and hydrochemical conditions in Kenozero Lake have led to changes in the morphology of fishes at a cellular level. The abnormalities in the function of the respiratory, digestive, and excretory systems were recorded. The degree of pathology depended on the ecological features of the fish. The pathological changes were most pronounced in the gills of the fish species (orfe, perch, and roach) characterized by active mode of life and sensible to oxygen deficiency. The changes in the epithelium of gill filaments had a compensatory significance and were aimed at increasing the area of the functional surface of the gills under the conditions of hypoxia. 相似文献
614.
The study of wave propagation in finite/infinite media has many applications in geotechnical and structural earthquake engineering and has been a focus of research for the past few decades. This paper presents an analysis of 2D anti- plane problems (Love waves) and 2D in-plane problems (Rayleigh waves) in the frequency domain in media consisting of a near-field irregular and a far-field regular part. The near field part may contain structures and its boundaries with the far-field can be of any shape. In this study, the irregular boundaries of the near-field are treated as consistent boundaries, extending the concept of Lysmer's vertical consistent boundaries. The presented technique is called the Condensed Hyperelements Method (CHM). In this method, the irregular boundary is limited to a vertical boundary at each end that is a consistent boundary at the far-field side. Between the two ends, the medium is discretized with hyperelements. Using static condensation, the stiffness matrix of the far-field is derived for the nodes on the irregular boundary. Examples of the application of the CHM illustrate its excellent accuracy and efficiency. 相似文献
615.
616.
G. Lanzo M. Tallini G. Milana G. Di Capua F. Del Monaco A. Pagliaroli S. Peppoloni 《Bulletin of Earthquake Engineering》2011,9(6):1855-1875
The paper focuses on the strong motion array deployed in the upper Aterno River Valley, in the immediate outskirts north-west
of the town of L’Aquila, which is part of the Italian Strong Motion Network operated by the Department of Civil Protection.
The array is composed of six accelerometric stations located along a cross section of the valley. The importance of this array
relies on the fact that a large amount of high-quality records were obtained during the 2009 L’Aquila seismic sequence, from
both the mainshock and several aftershocks. These data are especially important to investigate site effects in sediment-filled
valleys during moderate earthquakes in epicentral area because well-documented observational studies are very limited in the
literature. However, the main drawback for the study of site effects in the Aterno valley is the lack of a detailed knowledge
of the geometry of the valley, soil layering and dynamic properties of materials. The main motivation for this study stems
from the need to provide a reliable subsoil model of the valley coupled with high-quality strong motion data. Based on the
above, in the framework of S4 project, a major effort was undertaken to get a trustworthy cross section of the valley by an
ad hoc investigation, comprising geological and geotechnical surveys as well as an extensive geophysical campaign, characterized
by both active and passive measurements. These results were complemented by additional geological and geotechnical data available
in the literature. By merging all the information acquired, a 2D subsoil model of the transversal section of the upper Aterno
valley has been produced. The valley is characterised by an asymmetric shape with a shallower rock basement at the western
edge of the valley that deepens at the valley centre. Moreover, based on the results of geophysical tests, representative
Vs values were assigned to the different lithologic units forming the alluvial deposits filling the valley. Shear wave velocity
is a fundamental parameter for ground response studies and it is also effective in classifying the accelerometric station
from a seismic point of view. The 2D model may be therefore, considered a benchmark model for future studies of site effects.
It will offer the possibility to examine site effects with a complex underlying geology and to validate the results of numerical
simulations of site response analyses with the numerous observations from earthquake recordings, both for weak and strong
ground motion conditions. 相似文献
617.
Digitization of the daily prominence sketches based on data from the global observational network of visual solar spectroscopes was performed for 1922–1934. More than 55000 prominences were distinguished. The results of analysis of distributions by area, height, and prominence location are presented. In addition, the prominence characteristics were compared to those obtained from more recent observations at the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory. The distributions of prominence areas and heights are close to lognormal. The maximal height distribution corresponds to ~25–40 arcsecs. A second maximum also exists for prominence heights of ~70–90 arcsecs. 相似文献
618.
The upper crustal location of the foci of the Spitak earthquake of December 7, 1988, and its aftershocks is proved. It is demonstrated that the seismological network in Armenia and Georgia allowed unequivocal focal depth identification based on the kinematic data. The waveforms of all the Spitak earthquakes are typical of sources in the upper crust. It is noted that up to now, mantle earthquakes in the Caucasus have only been revealed in the Terek–Sunzha depression. 相似文献
619.
620.
A problem of convective cooling of both freshwater and saltwater lake is formulated. A transient one-dimensional turbulent model with variable layer depth is proposed to describe the process of freezing. The dependence of layer depth on time is determined by a universal equation describing the propagation of Deardorff convective layer. A combination of the main form of equations of Kolmogorov–Obukhov theory and available experimental data is shown to allow the construction of a universal profile of turbulent exchange coefficient, depending on the height. 相似文献