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21.
Svetlana A. Suleymanova Joanna M. Rankin 《Monthly notices of the Royal Astronomical Society》2009,396(2):870-877
This paper reports new observations of pulsar B0943+10 carried out at the Pushchino Radio Astronomy Observatory (PRAO) at the low radio frequencies of 42, 62 and 112 MHz. B0943+10 is well known for its exquisitely regular burst-mode (B-mode) drifting subpulses as well as its weaker and chaotic quiescent mode. Earlier Arecibo investigations at 327 MHz have identified remarkable, continuous changes in its B-mode subpulse drift rate and integrated-profile shape with durations of several hours. These PRAO observations reveal that the changes in profile shape during the B-mode lifetime are strongly frequency dependent – namely the measured changes in the component amplitude ratio are more dramatic at 327 and 112 MHz as compared with those at 62 and 42 MHz. The differences, however, are most marked during the first several tens of minutes after B-mode onset; after an hour or so the profile shape changes tend to be more similar at all four frequencies. We also have found that the linear polarization of the integrated profile increases continuously throughout the lifetime of the B mode, going from hardly 10 per cent just after onset to some 40–50 per cent after several hours. Pulsar B0943+10's B mode thus provides a unique new opportunity to investigate continuous systematic changes in the plasma flow within the polar flux tube. While refraction in the pulsar's magnetosphere may well play some role, we find that the various frequency-dependent effects, both between and within the two modes, can largely be understood geometrically. If the modes and B-mode decay reflect systematic variations in the carousel-'spark' radius and emission height then a specific set of profile and linear polarization changes would be expected. 相似文献
22.
Svetlana S. Kostrova Hanno Meyer Hannah L. Bailey Anna V. Ludikova Raphael Gromig Gerhard Kuhn Yuri A. Shibaev Anna V. Kozachek Alexey A. Ekaykin Bernhard Chapligin 《Boreas: An International Journal of Quaternary Research》2019,48(2):361-376
This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (δ18Odiatom) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8 cal. ka BP. The δ18Odiatom values range from +29.8 to +35.0‰, and relatively higher δ18Odiatom values around +34.7‰ between c. 7.1 and 5.7 cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in δ18Odiatom since c. 6.1 cal. ka BP accelerates after c. 4 cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8–0.2 cal. ka BP, corresponding to the Little Ice Age. Lake‐level rises result in lower δ18Odiatom values, whereas lower lake levels cause higher δ18Odiatom values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4–4.0 cal. ka BP. Generally, overall high δ18Odiatom values around +33.5‰ characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga δ18Odiatom record is roughly in line with the 60°N summer insolation, a linkage to broader‐scale climate change is likely. 相似文献
23.
Sea level variability along the US West Coast is analyzed using multi-year time series records from tide gauges and a high-resolution regional ocean model, the base of the West Coast Ocean Forecast System (WCOFS). One of the metrics utilized is the frequency of occurrences when model prediction is within 0.15 m from the observed sea level, F. A target level of F?=?90% is set by an operational agency. A combination of the tidal sea level from a shallow water inverse model, inverted barometer (IB) term computed using surface air pressure from a mesoscale atmospheric model, and low-pass filtered sea level from WCOFS representing the effect of coastal ocean dynamics (DYN) provides the most straightforward approach to reaching levels F>80%. The IB and DYN components each add between 5 and 15% to F. Given the importance of the DYN term bringing F closer to the operational requirement and its role as an indicator of the coastal ocean processes on scales from days to interannual, additional verification of the WCOFS subtidal sea level is provided in terms of the model-data correlation, standard deviation of the band-pass filtered (2–60 days) time series, the annual cycle amplitude, and alongshore sea level coherence in the range of 5–120-day periods. Model-data correlation in sea level increases from south to north along the US coast. The rms amplitude of model sea level variability in the 2–60-day band and its annual amplitude are weaker than observed north of 42 N, in the Pacific Northwest (PNW) coast region. The alongshore coherence amplitude and phase patterns are similar in the model and observations. Availability of the multi-year model solution allows computation and analysis of spatial maps of the coherence amplitude. For a reference location in the Southern California Bight, relatively short-period sea level motions (near 10 days) are incoherent with those north of the Santa Barbara Channel (in part, due to coastal trapped wave scattering and/or dissipation). At a range of periods around 60 days, the coastal sea level in Southern California is coherent with the sea surface height (SSH) variability over the shelf break in Oregon, Washington, and British Columbia, more than with the coastal SSH at the same latitudes. 相似文献
24.
Jan-Michael Frahm Marc Pollefeys Svetlana Lazebnik David Gallup Brian Clipp Rahul Raguram Changchang Wu Christopher Zach Tim Johnson 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(6):538-549
This paper presents a system approaching fully automatic 3D modeling of large-scale environments. Our system takes as input either a video stream or collection of photographs obtained from Internet photo sharing web-sites such as Flickr. The system achieves high computational performance through algorithmic optimizations for efficient robust estimation, the use of image-based recognition for efficient grouping of similar images, and two-stage stereo estimation for video streams that reduces the computational cost while maintaining competitive modeling results. In addition to algorithmic advances, we achieve a major improvement in computational speed through parallelization and execution on commodity graphics hardware. These improvements lead to real-time video processing and to reconstruction from tens of thousands of images within the span of a day on a single commodity computer. We demonstrate modeling results on a variety of real-world video sequences and photo collections. 相似文献
25.
26.
Vitaly Salnikov Galina Turulin Svetlana Polyakov Marat Moldahmetov Lyazzat Mahmudova 《寒旱区科学》2013,5(1):0109-0113
Methods of calculating the basic hydrological characteristics of a water resource assessment, as well as the planning and management
of their long-term use are based upon the concept of stationarity of long-term flow fluctuations. However, data of researches
by hydrologists and climatologists clearly indicate that there are long-period changes in the characteristics of precipitation and river
flow. This article discusses the variations of annual precipitation and river flow in the Ishim River Basin in Kazakhstan, based
on the W, C and E classification developed by G.Y. Vangengeim who analyzed the long-term variability of anomalies by the number
of days with some form of atmospheric circulation. From this study, the largest anomaly of the macro-circulation processes
was revealed, and a comparative analysis of the number of days with various forms of atmospheric circulation and precipitation
anomalies was made. It was demonstrated that the nature of atmospheric circulation depends on the distribution of precipitation;
however, precipitation is also highly dependent on local physiographic conditions. The analysis of anomalous precipitation during
the maximum number of days of positive anomalies with various forms of atmospheric circulation was also carried out. This study
presents some results from the preliminary analysis of annual river flow linked with forms of atmospheric circulation. 相似文献
27.
Dmitry A. Ruban Svetlana O. Zorina Clinton P. Conrad Nadezhda I. Afanasieva 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(1):7-18
Chronostratigraphically-justified records of regional transgressions and regressions are important for understanding the nature of the Paleocene shoreline shifts on a global scale. Review of previously synthesized data from 7 tectonically “stable” regions, namely the eastern Russian Platform, Northwestern Europe, Northwestern Africa, Northeastern Africa, the Arabian Platform, the northern Gulf of Mexico, and Southern Australia, allows a comparison of transgressions and regressions interpreted in these regions. No common patterns are found in the early Danian and late Selandian, which reflects small or zero eustatic fluctuations that are overwhelmed locally on coastlines by regional tectonic motions and local changes in dynamic support of surface topography by mantle flow. Sea level was stabilized during these stages by a warm climate and a lack of planetary-scale tectonic changes. We have detected a middle–late Danian regression that occurred in 5 of 7 study regions, and can be explained by glacial advance at ~62–63 Ma or by concurrent subduction of the Izanagi–Pacific ridge beneath eastern Asia. An early–middle Selandian transgression also occurred in 5 regions, probably, as a result of a hyperthermal at ~61 Ma that coincided with emplacement of large igneous provinces in the oceanic domain. Both events are characterized by significant diachroneity, which can also be explained by the influence of regional tectonic subsidence or uplift. Results of the present study permit us to propose a tentative framework for a new Paleocene eustatic curve that is constrained globally using available records of transgressions and regressions. 相似文献
28.
Oleg G. Safonov Elizaveta I. Kovaleva Svetlana A. Kosova H.M. Rajesh Georgy A. Belyanin Maria A. Golunova Dirk D. Van Reenen 《地学前缘(英文版)》2012,3(6):829-841
Reaction textures and fluid inclusions in the~2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses(Central Zone of the Limpopo Complex) suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750—800℃and 5.5—6.2 kbar.partial melting,and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650—700℃.These processes caused local variations of water and alkali activity in the fluids,resulting in various mineral assemblages within the dehydration zone.The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO-2-(K,Na)Cl fluids at 750 and 800℃and 5.5 kbar.It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-(K.Na)Cl fluids is accompanied by partial melting at 750—800℃.Orthopyroxene-bearing assemblages are characteristic for temperature 800℃and are stable in equilibrium with fluids with low salt concentrations,while salt-rich fluids produce clinopyroxene-bearing assemblages.These observations arc in good agreement with the petrological data on the dehydration zones within the Sand River orthoeneisses. 相似文献
29.
Comparison of Synchrotron Radiation X-Ray Fluorescence with Conventional Techniques for the Analysis of Sedimentary Samples 总被引:3,自引:0,他引:3
Michael A. Phedorin Vladislav A. Bobrov Evgeny P. Chebykin Evgeny L. Goldberg Michael S. Melgunov Svetlana V. Filippova Konstantin V. Zolotarev 《Geostandards and Geoanalytical Research》2000,24(2):205-216
A comparison is made of elemental analyses of sediment samples (lake bottom sediments and sediments from the petroliferous Bazhenovka Formation) by five competitive methods (synchrotron radiation X-ray fluorescence (SR-XRF), INAA, ICP-MS, AAS and traditional XRF). The object of this study was to identify the most suitable analytical techniques for applications in sedimentary geochemistry. Advantages and shortcomings of the five techniques were considered with respect to applications related to studies of palaeo-climate changes recorded in sedimentary cores from Lake Baikal and the geochemical stratigraphy of the Bazhenovka Formation, which is rich in organic material. We have concluded that SR-XRF was the best technique for producing extensive analytical data series, from the point of view of its speed, ease of application, cost, non-destructive nature and sensitivity, which allowed for the simultaneous determination of more than twenty elements of geochemical interest in small samples of sediments. An additional benefit of the method was demonstrated when used for the independent certification of geological reference materials. International reference samples BIL-1 and SDO-1 were certified by means of this method without use of reference materials. Analyses were based on the physics of the theory of energy transport. 相似文献
30.
Bruno P. Besser Mikhail I. Pudovkin Valentina V. Lebedeva Svetlana A. Zaitseva Claudia-Veronika Meister 《Astrophysics and Space Science》2000,274(1-2):399-405
Variations of the magnetic field and plasma parameters across the Earth's magnetosheath are calculated for an anisotropic
plasma in the Chew-Goldberger-Low approximation. Additionally, proton pitch-angle diffusion is taken into account as the energy
transfer mechanism between the direction perpendicular and parallel to the magnetic field. We discuss the main characteristics
of the magnetic barrier for different temperature relaxation times and their dependence on the interplanetary magnetic field
orientation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献