Testate amoebae are important components of benthic communities in freshwater lakes, where they play an essential role in decomposer food webs. They are used widely in paleoecological investigations because of their high taxonomic diversity, well-defined ecological preferences and decay-resistant tests. Studies of testate amoeba assemblages in lake surface sediments are necessary to better understand lake ecosystem function and improve the use of these organisms as bio-indicators in paleoecology. This study explored the use of testate amoebae as proxies for inferring past water level in freshwater lakes, and expanded upon the limited body of research into lake testate amoebae in Russia. Our results indicate that species composition of testate amoeba assemblages in the lakes was typical for such biotopes, with most of the species belonging to the genera Difflugia, Centropyxis, Arcella and Euglypha. Analysis of variation of testate amoebae along a water-depth gradient showed that three assemblage types could be distinguished: shallow-water (0–4.5 m), intermediate-water-depth (4.5–20.5) and deep-water (20.5–33 m). Deep-water assemblages did not contain any unique taxa and were dominated by eurybiotic and planktonic species. Species diversity was highest in the intermediate-water-depth assemblages and lowest in deep-water ones. Although variations in testate amoeba assemblages across water depth in freshwater lakes are complex and context-dependent, there are clear patterns in species composition and diversity, which can be used to infer past lake water levels. Future studies on the effect of water depth on testate amoeba assemblages in diverse types of freshwater lakes should increase the utility of the method.
Fifty-two species and intraspecific taxa of testate amoebae have been detected in 24 different habitats in the Belaya River basin (Northwestern Caucasus). Four types of communities are distinguished which differ in the composition of the complex of dominating species: freshwater species from bottom sediments in water bodies and water courses, soil-dwelling species from inundated parts of floodplains, a mixture of soildwelling and freshwater species in different littoral biotopes, and eurybiontic species in moss hummocks along the banks.
The process of biological wastewater treatment in a mixing aeration tank for the purpose of its intensification is studied. Two variants of intensification are consideredhydraulic partitioning of aeration volume of the mixing aeration tank and use of a vortex aerator. It is proposed a calculation method of partitioning of aeration volume of the mixing aeration tank, and it is shown that partitioning can increase its performance by 1.8 times and reduce power consumption of the aeration system. The new design of the vortex aerator is described, and it is shown that its use will significantly increase the efficiency of the tank aeration system and intensify the process of biological treatment due to the increased turbulence of the activated sludge flow. In this case, the quantity of oxygen utilization rate is =0.14-0.18, the relative concentration of organic contaminants is reduced to 0.20 at oxygen deficit 10% during the first aeration hour.
We consider the solution of boundary value problems of mathematical physics with neural networks of a special form, namely radial basis function networks. This approach does not require one to construct a difference grid and allows to obtain an approximate analytic solution at an arbitrary point of the solution domain. We analyze learning algorithms for such networks. We propose an algorithm for learning neural networks based on the method of trust region. The algorithm allows to significantly reduce the learning time of the network.
We investigated how the land-use change from rainforest into jungle rubber, intensive rubber and oil palm plantations affects decomposers and litter decomposition in Sumatra, Indonesia. Litterbags containing three litter types were placed into four land-use systems and harvested after 6 and 12 months. Litter mass loss and litter element concentrations were measured, and different microbial groups including bacteria, fungi and testate amoebae were studied. After 12 months 81, 65, 63 and 53% of litter exposed in rainforest, jungle rubber in oil palm and rubber plantations was decomposed. In addition to land use, litter decomposition varied strongly with litter type and short-term effects differed markedly from long-term effects. After 6 months, oil palm and rubber litter decomposed faster than rainforest litter, but after 12 months, decomposition of rainforest litter exceeded that of oil palm and rubber litter, reflecting adaptation of bacteria and fungi to decompose structural compounds in rainforest litter but not (or less) in rubber and oil palm litter. Bacterial and fungal community composition and testate amoeba species number and density varied strongly with litter type, but little with land use. However, community composition of testate amoebae was mainly affected by land use. Generally, changes in bacteria, fungi and testate amoebae were linked to changes in litter element concentrations, suggesting that element ratios of litter material as basal resource for the decomposer food web shape the structure of decomposer communities and decomposition processes via bottom-up forces. Overall, changing rainforest to monoculture plantations shifts the decomposer community structure and negatively affects litter decomposition.
We consider a nonlinear eigenvalue problem of the Sturm–Liouville type on an interval with boundary conditions of the first kind. The problem describes the propagation of polarized electromagnetic waves in a plane two-layer dielectric waveguide. The cases of a homogeneous and an inhomogeneous medium are studied. The existence of infinitely many positive and negative eigenvalues is proved.
The problem of diffraction of a polarized electromagnetic wave by a layer filled with a nonlinear medium is considered. The layer is located between two half-spaces with constant permittivities. Two widely used types of nonlinearities: saturation nonlinearity and Kerr nonlinearity are considered. It is proved that the results on the solvability of the problems in these cases are qualitatively different: in the case of saturation nonlinearity, there are conditions under which the diffraction problem has a unique solution and, in the case of Kerr nonlinearity, the diffraction problem always has an infinite set of solutions. Analytical and numerical methods for solving this kind of problems are developed. Numerical results are presented.