Equivalent time-average and effective medium for periodic layers     

Alexey Stovas  Bjorn Ursin 《Geophysical Prospecting》2007,55(6):871-882

The propagation of acoustic waves through a periodic layered medium is analyzed by an eigenvalue decomposition of the propagator matrix. This reveals how the velocity and attenuation of the layered medium vary as function of the periodic structure, material parameters and frequency. There are two important parameters which control the wave propagation in the periodic medium: the reflection coefficient and the ratio between one‐way traveltimes of the two parts of the cyclic layered medium. For low frequencies (large values of wavelength to layer thickness), the layered structure behaves as an effective medium, then there is a transition zone, and for higher frequencies (small values of wavelength to layer thickness) the medium is described by the time‐average velocity. In this paper we mostly concentrate on the transition zone between an effective medium and time‐average medium regimes. The width of the transition zone increases with larger values of the reflection coefficient. The transition zone corresponds to a blocking regime for which the transmission response of the layered structure is close to zero. For even higher frequencies, the time‐average medium is replaced by a new transition zone, and then again a time‐average medium. This pattern is periodically repeated with higher frequencies. For small values of the reflection coefficient, the transition between effective medium and time‐average medium occurs around a value of wavelength to layer thickness equal to 4.  相似文献   

Assessment of concentration of radionuclides in river water and bottom sediments     

A. L. Krylov  A. V. Nosov  A. I. Kryshev  I. I. Kryshev  V. P. Kiseliev 《Russian Meteorology and Hydrology》2007,32(7):470-478

The results of modeling of ^{89, 90}Sr, ¹³⁷Cs, and ^{239, 240}Pu migration in the Techa River are compared with observed data. It is shown that taking into account of the process of mass exchange between the main stream of a river and underflow is important for adequate modeling of migration and accumulation of radiative substances in a river. It is difficult to obtain results of modeling corresponding to the observed data if the process is neglected. Taking into account the mass exchange is especially important in developing models for long enough rivers that were polluted by radionuclides during long time. Authors believe that, in future, the considered aspects of modeling radioactive substances in rivers can be generalized on chemical polluting substances with similar physical and chemical properties, for example, heavy metals, phenols, etc.  相似文献   

Causes of variations of Nd-O isotope ratios of granitoids in the Tuva-Mongolia microcontinent and its early Caledonian framing     

D. P. Krylov  I. K. Kozakov  V. A. Glebovitsky  A. M. Fedoseenko 《Doklady Earth Sciences》2006,409(1):762-764

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Generalized Problem of Two and Four Newtonian Centers     

Alexey?V.?BorisovEmail author  Ivan?S.?Mamaev 《Celestial Mechanics and Dynamical Astronomy》2005,92(4):371-380

We consider integrable spherical analog of the Darboux potential, which appear in the problem (and its generalizations) of the planar motion of a particle in the field of two and four fixed Newtonian centers. The obtained results can be useful when constructing a theory of motion of satellites in the field of an oblate spheroid in constant curvature spaces.  相似文献   

Uncertainty of Climate Response to Natural and Anthropogenic Forcings Due to Different Land Use Scenarios   总被引：1，自引：0，他引：1  

Alexey V. ELISEEV  Igor I. MOKHOV 《大气科学进展》2011,28(5):1215-1232

The A.M.Obukhov Institute of Atmospheric Physics,Russian Academy of Sciences (IAP RAS) climate model (CM) of intermediate complexity is extended by a spatially explicit terrestrial carbon cycle module.Numerical experiments with the IAP RAS CM are performed forced by the reconstructions of anthropogenic and natural forcings for the 16th to the 20th centuries and by combined SRES (Special Report on Emission Scenarios) A2-LUH (Land Use Harmonization) anthropogenic scenarios for the 21st century.Hereby,the impact of uncertainty in land-use scenarios on results of simulations with a coupled climate-carbon cycle model is tested.The simulations of the model realistically reproduced historical changes in carbon cycle characteristics.In the IAP RAS CM,climate warming reproduced in the 20th and 21st centuries enhanced terrestrial net primary production but terrestrial carbon uptake was suppressed due to an overcompensating increase in soil respiration.Around year 2100,the simulations the model forced by different land use scenarios diverged markedly,by about 70 Pg (C) in terms of biomass and soil carbon stock but they differed only by about 10 ppmv in terms of atmospheric carbon dioxide content.  相似文献   

How well do coupled models replicate ocean energetics relevant to ENSO?     

Jaclyn N. Brown  Alexey V. Fedorov  Eric Guilyardi 《Climate Dynamics》2011,36(11-12):2147-2158

Accurate replication of the processes associated with the energetics of the tropical ocean is necessary if coupled GCMs are to simulate the physics of ENSO correctly, including the transfer of energy from the winds to the ocean thermocline and energy dissipation during the ENSO cycle. Here, we analyze ocean energetics in coupled GCMs in terms of two integral parameters describing net energy loss in the system using the approach recently proposed by Brown and Fedorov (J Clim 23:1563?C1580, 2010a) and Fedorov (J Clim 20:1108?C1117, 2007). These parameters are (1) the efficiency ?? of the conversion of wind power into the buoyancy power that controls the rate of change of the available potential energy (APE) in the ocean and (2) the e-folding rate ?? that characterizes the damping of APE by turbulent diffusion and other processes. Estimating these two parameters for coupled models reveals potential deficiencies (and large differences) in how state-of-the-art coupled GCMs reproduce the ocean energetics as compared to ocean-only models and data assimilating models. The majority of the coupled models we analyzed show a lower efficiency (values of ?? in the range of 10?C50% versus 50?C60% for ocean-only simulations or reanalysis) and a relatively strong energy damping (values of ??^?1 in the range 0.4?C1?years versus 0.9?C1.2?years). These differences in the model energetics appear to reflect differences in the simulated thermal structure of the tropical ocean, the structure of ocean equatorial currents, and deficiencies in the way coupled models simulate ENSO.  相似文献   

Age and origin of the corundum-bearing rocks of Khitostrov Island, Northern Karelia     

D. P. Krylov  E. B. Sal’nikova  A. M. Fedoseenko  S. Z. Yakovleva  Yu. V. Plotkina  I. V. Anisimova 《Petrology》2011,19(1):79-86

The Chupa nappe of the Belomorian Complex contains aluminous silica-undersaturated rocks with corundum, which are characterized by extremely low ¹⁸O/¹⁶O (whole-rock δ¹⁸O up to −21‰). Revealed isotopic anomalies are explained by the influence of meteoric waters that were modified through evaporation-precipitation cycles (Rayleigh distillation) under cold climatic conditions. In order to estimate whether the decrease in δ¹⁸O occurred prior to metamorphism of the protoliths of the Chupa Sequence or during water percolation in the course of metamorphic or postmetamorphic transformations, we studied oxygen composition in the rocks and minerals and conducted U-Pb dating on single zircons from corundumbearing rocks of Khitostrov.  相似文献   

Sedimentogenesis in the Amundsen Basin from geophysical data and drilling results on the Lomonosov Ridge     

A. A. Chernykh  A. A. Krylov 《Doklady Earth Sciences》2011,440(2):1372-1376

Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this region. The horizons bounding these complexes were dated by identifying the linear magnetic anomalies. The recognized SSCs are correlated with the seismostratigraphic and lithostratigraphic units of the Lomonosov Ridge. Based on these correlations, the lithological composition of SSCs in the Amundsen Basin is suggested. The formation of SSC2 is supposed to be due to the diagenetic processes associated with the transition of opal-A to opal-CT. It is found that, generally, the rate of sedimentation in the Amundsen Basin has consistently decreased since the beginning of its formation. However, in the Chattian time, the global regression resulted in a sharp increase in the rate of sedimentation in the basin. Arguments in favor of the duration of the Middle Cenozoic sedimentary hiatus on the Lomonosov Ridge reduced to 16.3 Ma are presented. It is supposed that the decrease in the intensity of oceanic crustal accretion in the Eurasian Basin, which is identified by the slowdown in the rate of its opening in the interval from 46 to 20–23 Ma might have resulted in a gradual sea level falling in the Arctic Ocean isolated from the World Ocean. This fact probably accounts for the Lomonosov Ridge having remained in subaerial conditions over the period from 36.7 to 20.4 Ma.  相似文献   

A 96-antenna radioheliograph     

Sergey V. Lesovoi Alexander T. Altyntsev Eugene F. Ivanov Alexey V. Gubin 《中国天文和天体物理学报》2014,(7):864-868

Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The configuration of the array antenna, transmission lines and digital receivers is the main focus of this work. The radioheliograph is a T-shaped centrally condensed radiointerferometer operating in the frequency range 4–8 GHz.The justification for the choice of such a configuration is discussed. The signals from antennas are transmitted to a workroom by analog optical links. The dynamic range and phase errors of the microwave-over-optical signal are considered. The signals after downconverting are processed by digital receivers for delay tracking and fringe stopping. The required step of delay tracking and data rates are considered. Two 3-bit data streams(I and Q) are transmitted to a correlator with the transceivers embedded in Field Programmed Gate Array chips and with PCI Express cables.  相似文献   

Geological Structure of the Novaya Zemlya Archipelago (West Russian Arctic) and Peculiarities of the Tectonics of the Eurasian Arctic     

Korago  E. A.  Kovaleva  G. N.  Schekoldin  R. A.  Il’in  V. F.  Gusev  E. A.  Krylov  A. A.  Gorbunov  D. A. 《Geotectonics》2022,56(2):123-156

Geotectonics - Our study considers the structure and tectonics of the Novaya Zemlya archipelago, located in the west Russian Arctic and part of the Eurasian Arctic: (i) the age of the Pre-Paleozoic...  相似文献