Seismic records of late Pleistocene aridity in Lake Tanganyika,tropical East Africa

New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika’s central basin capture dramatic evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences (A–D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32–14 ka) aridity. Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged aridity.     

长江上游退耕还林工程的农业生产和水环境效益评价——以四川省为例

退耕还林工程是我国大规模的土地利用方式的改变.以四川省为例,基于退耕还林工程实施后粮食产量、粮食作物播种面积、化肥用量以及水质和水土流失状况变化的分析,讨论了退耕还林工程对环境保护的贡献和可能存在的问题.退耕还林工程导致粮食作物播种面积、粮食产量和化肥用量的减少,在退耕还林工程实施前,这三者之间有很好的相关性,但自工程实施后,这三者的下降幅度与退耕还林面积的增加幅度有较大的差异.几种原因可能造成这种不一致性,值得进一步研究.退耕还林工程实施后河流径流量、泥沙含量以及输沙量的下降充分证实了退耕还林工程对长江上游水土保持的重要贡献,同时进一步证实长江上游的泥沙主要来源于坡耕地的耕作.     

Investigation of the coordinate system of irreversible astronomical instruments

Based on an analysis of the coordinate information obtained from positional observations of stars with an irreversible cine-theodolite (KT-50), we have developed an algorithm and investigated this instrument. We have determined the parameters characterizing the coordinate system of KT-50: zero points of the azimuth and altitude scales, collimation, inclination of the horizontal axis, inclination of the vertical axis, and its azimuth. An algorithm for calculating the azimuth and altitude corrections has been developed by processing the frames of CCD observations.     

The rectilinear three-body problem

The rectilinear equal-mass and unequal-mass three-body problems are considered. The first part of the paper is a review that covers the following items: regularization of the equations of motion, integrable cases, triple collisions and their vicinities, escapes, periodic orbits and their stability, chaos and regularity of motions. The second part contains the results of our numerical simulations in this problem. A classification of orbits in correspondence with the following evolution scenarios is suggested: ejections, escapes, conditional escapes (long ejections), periodic orbits, quasi-stable long-lived systems in the vicinity of stable periodic orbits, and triple collisions. Homothetic solutions ending by triple collisions and their dependence on initial parameters are found. We study how the ejection length changes in response to the variation of the triple approach parameters. Regions of initial conditions are outlined in which escapes occur after a definite number of triple approaches or a definite time. In the vicinity of a stable Schubart periodic orbit, we reveal a region of initial parameters that corresponds to trajectories with finite motions. The regular and chaotic structure of the manifold of orbits is mostly defined by this periodic orbit. We have studied the phase space structure via Poincaré sections. Using these sections and symbolic dynamics, we study the fine structure of the region of initial conditions, in particular the chaotic scattering region.     

Reversal of the polarization of cyclotron radiation in a hot coronal loop

Spectropolarimetric features of thermal cyclotron radiation of solar coronal loops and the possibility of interpretation of the observed reversal of the sense of polarization of centimeter and decimeter waves are discussed. To this end, thermal cyclotron radiation is computed in terms of the simplest model of a three-dimensional hot loop (a half-torus). Such a loop is shown to be capable of changing appreciably the properties of the radiation of a solar active region at centimeter and decimeter wavelengths. A detailed analysis is performed to determine the conditions under which the radiation spectrum of an active region containing a coronal loop may have a complex pattern with several maxima or relatively narrow-band cyclotron lines, and the sense of polarization may change several times in the wavelength interval considered. These conditions are modelled by such parameters as the structure of the magnetic field, electron density, and size of the loop. The results of the computations of two-dimensional brightness temperature distributions at different wavelengths for ordinary and extraordinary waves at fixed points of the loop and the integrated parameters of the flux and polarization of radiation in terms of the model discussed are reported. Cases are considered where the line of sight is crossed by one or two loops. The expected distribution of polarization across the source in the model considered is compared to the results of RATAN-600 observations of the solar active region AR 7962 made on May 12–14, 1996.     

Anisotropic models of dark halos

An iterative approach is used to construct spherically symmetric equilibrium models with an anisotropic velocity distribution. The potentialities of the method have been tested on models with known distribution functions, the Osipkov-Merritt models. It is shown that models that differ significantly from the Osipkov-Merritt models can be constructed. An N-body model of a dark halo with a density distribution that approximates the results of cosmological simulations (the Navarro-Frenk-White model) has been constructed. The anisotropy profile has been taken to be similar to that yielded by cosmological simulations. The constructed models can serve as direct input data for investigating the dynamics and stability of such systems in N-body simulations.     

The effect of atmospheric circulation on the evolution and radiative forcing of smoke aerosol over European Russia during the summer of 2010

The evolution of smoke plume over European Russia (ER) during the massive forest and peatbog fires of summer 2010 has been studied using observations of aerosol optical depth (AOD) from MODIS instruments (both Aqua and Terra platforms), objective analysis of meteorological fields performed at the Russian Hydrometeorological Research Center, NCEP/NCAR reanalysis, as well as upper air data. A relation between the structure inhomogeneities of the AOD field and regional atmospheric circulation has been found. It is shown that, on August 5–9, 2010, the maximum of smoke pollution did complete turn around Moscow, while remaining at a distance of 200 to 650 km from the megacity. Both regionally averaged shortwave aerosol radiative forcings (ARFs) at the top and the bottom of the atmosphere are estimated for the period of extreme smoke pollution over ER. The spatial distributions of ARF values over the territory of the region and the estimates of the local and spatially distributed thermal effects of smoke aerosol are given. It is shown that, on August 5–9, 2010, the spatial distribution of AOD and the calculated thermal effects of smoke aerosol were in agreement with the spatial distributions of air-temperature anomalies observed in the lower 1.5-km layer of the atmosphere. MODIS’s AOD data obtained during the wildfires were validated by AOD observations from the CIMEL sun photometer operated at the AERONET station Zvenigorod.     

Environmental predictors of decapod species richness and turnover along an extensive Australian continental margin (13–35° S)

The use of environmental data in biogeographic studies of the deep sea is providing greater insight into the processes underlying large‐scale patterns of diversity. Recent surveys of Australia's western continental margin (~100–1100 m) provide systematic sampling of invertebrate megafauna along a gradient of 22° of latitude (13–35° S). Diversity patterns of decapod crustaceans were examined and we investigated the relative importance of environmental and spatial predictor variables on both species richness (alpha diversity) and species turnover. Distance‐based linear models (DistLM) indicated a suite of variables were important in predicting species turnover, of which temperature and oxygen were the most influential. These reflected the oceanographic features that dominate distinct depth bathomes along the slope. The numbers of species within samples were highly variable; a small but significant increase in diversity towards the tropics was evident. Replicated sampling along the margin at ~100 m and ~400 m provided an opportunity to compare latitudinal patterns of diversity at different depths. On the shallow upper slope (~400 m) temperature was disassociated from latitude and the latter proved to be the best predictor of sample species richness. The predictive power of latitude over other variables indicates that proximity to the highly diverse Indo‐West Pacific (IWP) may be important, especially considering that almost 40% of species in this study had a wide IWP distribution. In the management of Australia's marine environments, geomorphic surrogates have been emphasised when defining areas for protection. We found sea‐floor characteristics were relatively less important in predicting richness or community composition.     

The hydrological foundations of landscape planning of the Lake Sevan basin

The main stages of elaborating the landscape master plan for the Lake Sevan basin with reference to the water component are highlighted. Scientific basis for investigating the hydrological organization of the territory is provided by the landscape-hydrological approach determining the interrelationship of quantitative-qualitative characteristics of the runoff with landscape elements. The focus is on the selection of criteria and on the theoretical substantiation of the factors of assessment of the water potential; a number of recommendations for targeted utilization and improvement of the water-ecological situation of the territory are made.