45 research outputs found

    Periodic variability in Active Galactic Nuclei

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    In this doctoral thesis, multi-frequency very long baseline interferometry observations together with multi-frequency total flux-density variability data of compact relativistic jets in active galactic nuclei are presented and analyzed. The main goal of the thesis is to investigate the physical mechanisms in relativistic jets responsible for such phenomena as the co-existence of moving and stationary jet components, jet wiggling and precession. We also aim to study the connection between the structural changes in the relativistic jets and flares in the total flux-density light curves and to find observational evidences for the appearance of a primary perturbation in the base of the jet and its further propagation. In this thesis we also investigate which physical mechanisms are responsible for periodical total flux-density variability and to search for periodicities as a sign of jet precession. In order to study the jet physics we used the multi-frequency very long baseline interferometry technique which gives the highest possible in astronomy resolution. We also compared jet structural changes with single-dish multi-frequency observations spanning more than 30 years together with optical and gamma-ray data. In particular, analysis of the long-term kinematics of two active galactic nuclei S5 1803+784 and 0605-085 shows evidence for jet precession. The jet is precessing with a timescale similar to a period in the total flux-density light curves. Moreover, I show that jet structural changes are correlated with the total flux-density variability. Analyzing the long-term kinematics of S5 1803+784 I found for the first time that its jet consists of seven ``oscillating'' jet features which were observed for more than 20 years. We found five blazars and quasars (3C 454.3, 3C 446, CTA 102, 0133+476, and 0605-085) which show clear periodical total flux-density radio variability. Moreover, in the case of 3C 454.3 and 3C 446 the predicted flares were meanwhile observed. In this thesis I propose a new physical approach for searching periodicities and calculating flaring activity cycles in radio total flux-density variability. I use the separation of the flares into "core" and "jet" outbursts. I found that for the sources 3C 454.3 and 3C 446 optically thick "core" outbursts appear periodically

    Spatial variations in the Caspian Sea wave climate in 2002-2013 from satellite altimetry

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    The core properties of the wave climate and its changes in the Caspian Sea are established in terms of the annual mean significant wave height and its regional changes in 2002-2013 based on the outcome of the satellite altimetry mission JASON-1. Remotely estimated wave heights are validated against properties of the empirical distribution of instrumentally measured wave heights in the southern Caspian Sea and monthly averages of visually observed wave heights at three locations. A correction for systematic differences leads to very good correspondence between monthly averaged in situ and satellite data with a typical root mean square difference of 0.06 m. The average significant wave height in the Caspian Sea is 0.5-0.7 m in the northern basin of the sea, around 1.2 m in large parts of the central and southern basins and reaches up to 1.8 m in the northern segment of the central basin. The basin-wide average wave intensity varied insignificantly in the range of 1.02-1.14 m in 2002-2013. These estimates overestimate the wave heights by about 30% because low wave conditions are ignored. Substantial and statistically significant changes in the wave height occurred in certain areas. The wave height decreased by 0.019 +- 0.007 m/yr in the eastern segment of the central basin and by 0.04 +- 0.04 m/yr in the western segment of the southern basin. These changes can be explained by an increase in the frequency of westerly winds at the expence of southerly winds. Both basin-wide and regional extreme wave heights exhibit large interannual variations but do not show any significant trend. The patterns of changes in mean and extreme wave height are different. The average wave height has increased while the extreme wave height has decreased in the eastern segment of the southern basin.Comment: 16 pages, 10 figure

    МЕТОДИЧЕСКИЕ ПОДХОДЫ К ИЗУЧЕНИЮ АНТРАКОСИЛИКОЗА КАК ФАКТОРА РИСКА МОРФОЛОГИЧЕСКИХ НАРУШЕНИЙ СОСУДОВ

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    In work the correct method of modeling the experimental anthracosilicosis (AS) is presented. Results of the scanning electron microscopy of samples of abdominal aorta walls of white laboratory rats testify about morphological diseases of blood vessels. These diseases are associated with chronization of pneumoconiotic process in dynamics of AS progression.В работе представлена корректная методика моделирования экспериментального антракосиликоза (АС). Результаты сканирующей электронной микроскопии образцов стенки брюшной аорты белых лабораторных крыс свидетельствуют о морфологических нарушениях сосудов, ассоциированных с хронизацией пневмокониотического процесса в динамике развития АС

    Differential expression of alternatively spliced transcripts related to energy metabolism in colorectal cancer

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    DIFFUSION SURFACE ALLOYING OF TOOL STEEL

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    Subject of investigation: tool steel, grades 4OH, UD, 9HS, 5HNM. Purpose of the work: study of the peculiarities of the structure and physicomechanical and technological properties of multicomponent diffusion coatings on the toolsteel, development of recommendations on the diffusion alloying. The investigations deals with the peculiarities of the formation, structure and phase composition of hardened surface layers of the tool steel during one-, two- and three-component diffusion alloying in the titanium, chromium, vanadium and molybdenum powders. The best combination of the hardness and wear resistance of carbide coatings is attained when the mixture composition is titanium - chromium - vanadium (1:1:1). Technological instructions are developed on carrying out the process of the diffusion alloying in powder mixtures. The results of the work provide for the enhancement of wear resistance of parts of the tooling 2-2,5 timesAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

    Heavy Metal Content in Macroalgae as a Tool for Environmental Quality Assessment: The Eastern Gulf of Finland Case Study

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    Macroalgae are widely used for bioindication and assessment; however, in the case of pollutants of different origin, it is still unclear which contaminants in thalli can be regarded as indicative because too many factors influence the ability of algae to uptake them. The present study is a part of an international HAZLESS project and was conducted in the eastern Gulf of Finland (GoF). The main goal of our study was the application of metal concentrations in macroalgae as a tool for environmental quality assessment. To achieve this goal, we calculated the threshold metal concentrations in macroalgae (Cladophora glomerata) and compared our obtained values with actual concentrations. We found significant Spearman correlations in May between metals in sediments and pore water (−0.73 for Zn, −0.62 for Cd, 0.85 for Pb) and also between metals in algae and metals in pore water (1 for Cu and Cd, 0.98 for Zn and Pb). In July, Pb in algae were significantly correlated with Pb in pore water (0.88). The application of the calculated environmental quality standard (EQSMPC) for macroalgae has shown moderate pollution by Cu and Pb in the coastal zone of the eastern GoF. This was confirmed by an assessment based on the comparisons of metal concentrations in water with Environmental Quality Standards for water (EQSw). However, differences in the bioaccumulation factor and EQSMPC between May and July have shown that it is necessary to compare samples taken during the same period every year for adequate results in long-term monitoring. Considering the sensitivity of accumulating processes to the surrounding environment, we believe that in the case of habitats with diverse conditions, even for the same species of algae, threshold values should be calculated and used individually for every habitat. Our results have shown that this approach can be widely used for an assessment of environmental quality via metal concentrations in opportunistic macroalgae and can be recommended for further use

    Sea Ice as a Factor of Primary Production in the European Arctic: Phytoplankton Size Classes and Carbon Fluxes

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    The seasonally ice-covered marine region of the European Arctic has experienced warming and sea ice loss in the last two decades. During expeditions in August 2020 and 2021, new data on size-fractioned primary production (PP), chlorophyll a concentration, phytoplankton biomass and composition and carbon fixation rates in the dark were obtained in the marginal ice zone (MIZ) of the Barents Sea, Nansen Basin and Greenland Sea to better understand the response of Arctic ecosystems to ongoing climate changes. Four different situations were observed in the study region: (i) a bloom of the large-cell diatom Podosira glacialis, whose biomass was trapped in a strong halocline at the edge of a dense ice cover; (ii) a bloom of the chain-like colonies of Thalassiosira diatoms on the shelf in mixed waters in fields of shallow ice that could be supported by “fresh” elements in the polynya condition, as well as by terrestrial run-off and drifting ices; at the late stage, this bloom was accompanied by intensive growth of Phaeocystis pouchetti; (iii) dominance of small-cell phytoplankton under weakened stratification and the significant influence of the Atlantic water, depleted of microelements and silicates; (iv) dominance of dinoflagellates of eutrophic water in the contact zone between the water masses of Arctic origin and Atlantic origin in clear water under conditions of increased light intensity. The >10 µm phytoplankton cell size group increased its relative contribution to PP as a response to stratification, light and nutrient load associated with sea ice conditions. Small phytoplankton with sizes < 2 µm formed the basis of total PP in the MIZ regardless of the state of the sea ice
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