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Search Results: 1 - 10 of 2754 matches for " Andrey Alekseev "
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Evidence for a risk of tick-borne infection in the city parks of Vilnius, Lithuania
Milda ygutien , Andrey Alekseev , Helen Dubinina , Rita Kazlauskien
Ekologija , 2008, DOI: 10.2478/V10055-008-0008-y
Abstract: Thirty-six adult ticks collected in the parks of the Lithuanian capital Vilnius in the spring of 2005 were identified as Ixodes ricinus (L.) and studied for the presence of live pathogens by darkfield microscopy, of exoskeleton anomalies by light stereomicroscopy, and of several tickborne pathogens by PCR. One of the ticks was positive for three pathogens simultaneously: Ehrlichia muris (monocitic ehrlichiosis agent), Borrelia afzelii, and Borrelia garinii; one was dually infected by both species of Borrelia. In addition, ticks positive for several species of Borrelia were detected: B. afzelii (n = 5), B. garinii (n = 2), some other species of B. burgdorferi sensu lato (n = 2), Ehrlichia muris (n = 1). The total proportion of infected ticks was 27.8% (10 of 36), of which 20% (2 of 10) were multiply infected; 47.2% of ticks had exoskeleton anomalies, and such specimens had more multiple infections (35.3% versus 21%). One triply infected tick was found only among the anomalous specimens. Live spirochaetes prevailed among the anomalous specimens: 35.3% (6/17) vs. 5.3% (1/19). The difference was statistically significant: chi square was equal 5.166, P < 0.05. In conclusion, even this small sample size reveals several important tick-borne pathogens in the newly detected focus in the centre of Vilnius, transmitted by I. ricinus. It suggests that people visiting these parks are exposed to the risk of tick-borne infection, especially when resting on the grass.
Assessment and Inventory of Forest Ecosystems Biodiversity: Case Study for Karelian Isthmus of Leningrad Region, Russia  [PDF]
Alexander S. Alekseev
Open Journal of Ecology (OJE) , 2018, DOI: 10.4236/oje.2018.85019
Abstract: Regular grid of permanent sample plots (PSP) of ICP-Forests monitoring system was used for forest ecosystems biodiversity assessments and inventory. The supplementary features were added to the PSP structure to conduct biological diversity census: eight sample plots 1 × 1 m for geo-botanical description; two sample plots of 5 × 5 m each for description of the PSP’s undergrowth; one 25 × 25 m plot for coarse woody debris estimations; four soil inventory pits. The total number of PSP amounted to 248. Total data used are as following: 1) 1984 geo-botanical descriptions of vegetation belonging to ground cover layers made on 1 × 1 m sample plots; 2) 496 descriptions of undergrowth on 5 × 5 m sample plots; 3) 178 descriptions of woody debris on 25 × 25 m sample plots; 4) 496 descriptions of soil inventory pits. General statistical indicators characterizing forest land cover diversity were calculated. Statistic indicators of α-diversity for the Karelian Isthmus forest vegetation cover have the following values: 1) m (mean number of species per PSP) = 26 species; 2) σ (standard deviation) = 9.5 species; 3) v (variation coefficient) = 36.5%; 4) Р (deviation amplitude) = 60 – 7 = 53 species. β – diversity of forest ecosystems as well as γ – diversity also was studied on the base of information collected on the same regular grid of sample plots. It appears that sample plots distribution by species diversity gradation is well described by the standard curve of normal distribution for the entire Karelian Isthmus forest (determination coefficient of the curve being 95.2%) as well as for each type of forest. Hence, the criterion (standard) of biodiversity for forest ecosystems can be defined as the mean value of alpha diversity for each forest type group – m; and the standard deviation – σ, as a tool for assessing deviations from the standard. PSP locations are fixed using GPS technology, this allows biodiversity assessments at the same place in the next years for biodiversity trends estimations and consist the frame for systematic biodiversity inventory.
Effects of diel vertical migration on ephippia production in Daphnia
Victor ALEKSEEV
Journal of Limnology , 2004, DOI: 10.4081/jlimnol.2004.s1.1
Abstract: Fish presence in experimentally simulated temperature conditions (limno-towers) led to diel vertical migration and resulted in a decrease of ephippia production in Daphnia pulicaria. Diel fluctuation of food, temperature and day length similar to those experienced by migrating Daphnia were tested in laboratory experiments with flow-through-systems. Daphnids were kept under these conditions for 15 days and the proportions of females producing an ephippium were determined. In addition, maturation time, survival to maturation, size of the first clutch and female dry weight (without eggs) on day 15 were traced. The most important factor affecting ephippia production in migrating Daphnia was photoperiod change, and when mother and embryo are exposed to alternating light conditions, these are thought to have the effect on the mother of acting as a signal to stop ephippia production. Such effects might be explained by the different sensitiveness to light intensity in females carrying an embryo and an embryo itself in broods. Fish presence forced Daphnia to stay in low-light conditions during daytime hours, to avoid attacks by fish. The Daphnia were able to check light intensity constantly by short vertical jumps above a light-threshold that was confirmed experimentally in limno-towers. The dim conditions were possibly light enough for adults to check day length, but were too dark for embryos shaded by the mother's body. Food conditions played a relatively small role in the process, and no effects of temperature on ephippia production were found. As expected, food affected the size of the first clutch, and temperature controlled the time to maturation. Photoperiod had a marginally significant influence on the time to maturation in Daphnia. A hypothesis on the role of photoperiod as the key factor for Daphnia life cyclic recurrence and other seasonal adaptations is proposed.
Optimal quantum pumps have a vanishing transmission coefficient
A. Alekseev
Physics , 2002,
Abstract: In a recent Letter, Avron et. al (math-ph/0105011) introduced a notion of optimal quantum pumps. These are adiabatic quantum pumps which work without dissipation. In particular, they produce neither entropy nor noise. In the present Comment we show that in the absence of magnetic field optimal quantum pumps always have a vanishing transmission coefficient. Such `quantum pumps' do not make use of Quantum Mechanics since all tunneling or interference effects are banned by vanishing of the transmission coefficient. We leave it as an outstanding question whether genuine optimal quantum pumps with nonvanishing transmission coefficient can be constructed by making use of the magnetic field.
Basics of Low-temperature Refrigeration
A. Alekseev
Physics , 2015, DOI: 10.5170/CERN-2014-005.111
Abstract: This chapter gives an overview of the principles of low temperature refrigeration and the thermodynamics behind it. Basic cryogenic processes - Joule-Thomoson process, Brayton process as well as Claude process - are described and compared. A typical helium laboratory refrigerator based on Claude process is used as a typical example of a low-temperature refrigeration system. A description of the hardware components for helium liquefaction is an important part of this paper, because the design of the main hardware components (compressors, turbines, heat exchangers, pumps, adsorbers, etc.) provides the input for cost calculation, as well as enables to estimate the reliability of the plant and the maintenance expenses. All these numbers are necessary to calculate the economics of a low temperature application.
Travelling waves in the expanding spatially homogeneous space-times
George Alekseev
Physics , 2014, DOI: 10.1088/0264-9381/32/7/075009
Abstract: Some classes of the so called "travelling wave" solutions of Einstein and Einstein - Maxwell equations in General Relativity and of dynamical equations for massless bosonic fields in string gravity in four and higher dimensions are presented. Similarly to the well known pp-waves, these travelling wave solutions may depend on arbitrary functions of a null coordinate which determine the arbitrary profiles and polarizations of the waves. However, in contrast with pp-waves, these waves do not admit the null Killing vector fields and can exist in some curved (expanding and spatially homogeneous) background space-times, where these waves propagate in certain directions without any scattering. Mathematically, some of these classes of solutions arise as the fixed points of Kramer-Neugebauer transformations for hyperbolic integrable reductions of the mentioned above field equations, or, in the other cases, -- after imposing of the ansatz that these waves do not change the part of spatial metric transversal to the direction of wave propagation. It is worth to note that strikingly simple forms of all presented solutions make possible a consideration of nonlinear interaction of these waves with the background curvature and singularities as well as a collision of sandwiches of such waves with solitons or with each others in the backgrounds where such travelling waves may exist.
Form factors of descendant operators in the Bullough-Dodd model
Oleg Alekseev
Physics , 2012,
Abstract: We propose a free field representation for the form factors of descendant operators in the Bullough-Dodd model. This construction is a particular modification of Lukyanov's technique for solving the form factors axioms. We prove that the number of proposed solutions in each level subspace of the chiral sectors coincide with the number of the corresponding descendant operators in the Lagrangian formalism. We check that these form factors possess the cluster factorization property. Besides, we propose an alternative free field representation which allows us to study analytic properties of the form factors effectively. In particular, we prove that the form factors satisfy non trivial identities known as the "reflection relations". We show the existence of the reflection invariant basis in the level subspaces for a generic values of the parameters.
Nonparametric Estimation in the Model of Moving Average
Alexander Alekseev
Mathematics , 2003,
Abstract: The subject of robust estimation in time series is widely discussed in literature. One of the approaches is to use GM-estimation. This method incorporates a broad class of nonparametric estimators which under suitable conditions includes estimators robust to outliers in data. For the linear models the sensitivity of GM-estimators to outliers have been studied in the work by Martin and Yohai [5], and influence functionals for this estimator were derived. In this paper we follow this direction and examine the asymptotical properties of the class of M-estimators, which is narrower than the class of GM-estimators, but gives more insight into asymptotical properties of such estimators. This paper gives an asymptotic expansion of the residual weighted empirical process, which allows to prove asymptotic normality of these estimators in case of non-smooth objective functions. For simplicity MA(1) model is considered, but it will be shown that even in this case mathematical techniques used to derive these asymptotic properties appear to be rather complicated.However, the approach used in this paper could be applied to GM-estimators and to more realistic models.
On the first continuous $L^2$-cohomology of free group factors
Vadim Alekseev
Mathematics , 2013,
Abstract: We prove that the first continuous $L^2$-cohomology of free group factors vanishes. This answers a question by Andreas Thom regarding continuity properties of free difference quotients and shows that one can not distinguish free group factors by means of first continuous $L^2$-Betti number.
An Electrostatic Catastrophe Machine as an Attosecond Pulse Generator  [PDF]
Andrey Gitin
Optics and Photonics Journal (OPJ) , 2014, DOI: 10.4236/opj.2014.412034
Abstract: The generation of an attosecond pulse in the ultraviolet range is described in the terms of the catastrophe theory. A simple criterion of tunneling is proposed. The criterion allows constructing the quasiclassical model of the generator of attosecond laser pulses based on the interaction of an electric field of extremely powerful femtosecond pulse with the valence electron in the potential well of the gas atom.
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