Heterotrophic microbial communities on the water-sediment boundary in the Kara Sea

The qualitative and quantitative characteristics of the heterotrophic microbial communities (bacteria, flagellates, and ciliates) in the thin water-sediment layer in the Kara Sea are analyzed. The bacterial abundance correlated with the concentration of organic matter, whereas their size depended on the abundance of heterotrophic flagellates. The number of species of heterotrophic flagellates increased with the increase in the bacterial number. A positive relationship between the bacterial abundance and the ration of heterotrophic flagellates was observed at the offshore stations, probably due to the grazing pressure. The density of the ciliates on the soft silty and sandy-silty sediments was extremely low. The share of upstream filter feeding ciliate species increased with the increase in the abundance of the flagellates, probably due to the shift to less selective feeding strategies at higher values of the food concentrations. The classification of the heterotrophic microbial communities in the surface sediment layer has revealed two distinct types of the communities. The river communities are rich in species and are characterized by the high abundance of microorganisms. They are gradually replaced by marine communities at the salinity of 9%.     

Landscape–biogeochemical factors of transformation of the Cs-137 contamination field in the Bryansk region

Data are presented on the distribution of Chernobyl-derived ^137Cs in different landscapes of the Bryansk region. The role of different landscape-biogeochemical factors in the transformation of the ^137Cs contamination field is examined. The distribution of ^137Cs in the typical soil catenary junction of predpolessie, predopolje, and opolje landscapes is analyzed. The role of biogeochemical barriers in the ^137Cs accumulation is considered. It is revealed that the slope exposure affects the intensity of geochemical migration. In particular, the intensity of lateral migration of ^137Cs on the slopes of the southern and southwestern exposure is much higher than that on the slopes of the northern and northeastern exposure. The different types of geochemical lateral structure of landscape are analyzed on the basis of the catenary ^137Cs distribution.     

Evolution of latitude zonal structure of the large-scale magnetic field in solar cycles

Properties of a latitude zonal component of the large-scale solar magnetic field are analyzed on the basis of H charts for 1905–1982. Poleward migration of prominences is used to determine the time of reversal of the polar magnetic field for 1870–1905. It is shown that in each hemisphere the polar, middle latitude and equatorial zones of the predominant polarity of large-scale magnetic field can be detected by calculating the average latitude of prominence samples referred to one boundary of the large-scale magnetic field. The cases of a single and three-fold polar magnetic field reversal are investigated. It is shown that prominence samples referred to one boundary of the large-scale magnetic field do not have any regular equatorward drift. They manifest a poleward migration with a variable velocity up to 30 m s^-1 depending on the phase of the cycle. The direction of migration is the same for both low-latitude and high-latitude zones. Two different time intervals of poleward migration are found. One lasts from the beginning of the cycle to the time of polar magnetic field reversal and the other lasts from the time of reversal to the time of minimum activity. The velocity of poleward migration of prominences during the first period is from 5 m s^-1 to 30 m s^-1 and the second period is devoid of regular latitude drift.     

Viscous overstability and eccentricity evolution in three-dimensional gaseous discs

We investigate the growth or decay rate of the fundamental mode of even symmetry in a viscous accretion disc. This mode occurs in eccentric discs and is known to be potentially overstable. We determine the vertical structure of the disc and its modes, treating radiative energy transport in the diffusion approximation. In the limit of very long radial wavelength, an analytical criterion for viscous overstability is obtained, which involves the effective shear and bulk viscosity, the adiabatic exponent, and the opacity law of the disc. This differs from the prediction of a two-dimensional model. On shorter wavelengths (a few times the disc thickness), the criterion for overstability is more difficult to satisfy because of the different vertical structure of the mode. In a low-viscosity disc a third regime of intermediate wavelengths appears, in which the overstability is suppressed as the horizontal velocity perturbations develop significant vertical shear. We suggest that this effect determines the damping rate of eccentricity in protoplanetary discs, for which the long-wavelength analysis is inapplicable and overstability is unlikely to occur on any scale. In thinner accretion discs and in decretion discs around Be stars overstability may occur only on the longest wavelengths, leading to the preferential excitation of global eccentric modes.     

Reflection of equatorial Kelvin waves at eastern ocean boundaries Part I: hypothetical boundaries

A baroclinic shallow-water model is developed to investigate the effect of the orientation of the eastern ocean boundary on the behavior of equatorial Kelvin waves. The model is formulated in a spherical polar coordinate system and includes dissipation and non-linear terms, effects which have not been previously included in analytical approaches to the problem. Both equatorial and middle latitude response are considered given the large latitudinal extent used in the model. Baroclinic equatorial Kelvin waves of intraseasonal, seasonal and annual periods are introduced into the domain as pulses of finite width. Their subsequent reflection, transmission and dissipation are investigated. It is found that dissipation is very important for the transmission of wave energy along the boundary and for reflections from the boundary. The dissipation was found to be dependent not only on the presence of the coastal Kelvin waves in the domain, but also on the period of these coastal waves. In particular the dissipation increases with wave period. It is also shown that the equatorial β-plane approximation can allow an anomalous generation of Rossby waves at higher latitudes. Nonlinearities generally have a small effect on the solutions, within the confines of this model.     

Post-earthquake investigation on several geosynthetic-reinforced soil retaining walls and slopes during the Ji-Ji earthquake of Taiwan

This paper gives an overview on the application of geosynthetic-reinforced soil structures in Taiwan. Taiwan has an unique topography and geotechnical conditions that rendered a less conservative and more challenging design compared to that of North America, Europe and Japan. The Ji-Ji (Chi-Chi) earthquake of 1999 gave an opportunity to examine the behavior of reinforced soil structures. The performance of several modular-block reinforced soil retaining walls and reinforced slopes at the vicinity of the fault was evaluated. Reinforced structures performed better than unreinforced soil retaining walls. The failure cases were highlighted and the cause of failure was identified. The lack of seismic design consideration could be a major cause of failure. The compound failure mode, the inertia force of the blocks, and the connection stiffness and strength relative to the large dynamic earth pressure, were among major items that would warrant further design consideration.     

The August 27, 2008, M w = 6.3 Kultuk earthquake (South Baikal): The stress-strain state of the source area from the aftershock data

We consider the results of reconstructing the stress-strain state of the Earth’s crust in South Baikal from the focal mechanism data for the Kultuk earthquake of August 27, 2008 (M _w = 6.3) and its aftershocks. The source parameters of the main shock were determined by calculating the seismic moment tensor. The focal mechanism solutions of 32 aftershocks (M _w ≥ 2.3) were obtained through the deployment of a local seismic network at South Baikal. It is found that the main shock and first aftershocks (August–September) gave rise to the activation of latitudinal fragments of the segmented near-edge fault, and the sources of the consequent aftershocks were dominated by the NW-striking planes related to the small intrabasin structures. The calculations of seismotectonic deformations based on the data on the focal mechanisms of the earthquakes show that the area of activation is dominated by the transtension regime (with deformation in the form of extension with shear). The epicentral and hypocentral fields of the aftershocks and the mechanisms of their sources reflect the complex tectonic structure of the source zone of the Kultuk earthquake, which exhibits a clear subvertical zonality of the local seismically active volume and a wedge-shaped area of crustal destruction.     

The Solar Flare of November 4, 2001, and Its Manifestations in Energetic Particles from Coronas-F Data

Based on X-ray, gamma-ray, and charged-particle measurements with several instruments onboard the Coronas-F satellite and on ACE and GOES experimental data presented on the Internet, we investigate the parameters of the solar flare of November 4, 2001, and the energetic-particle fluxes produced by it in circumterrestrial space. The increase in relativistic-electron fluxes for about 1.5 days points to a moving source (shock front). The structure of the energetic-particles fluxes in the second half of November 5, 2001, can be explained by the passage of the coronal mass ejection that was ejected on November 1, 2001, and that interacted with the shock wave from the flare of November 4, 2001.