Vorontsov-Velyaminov rows: Straight segments in the spiral arms of galaxies     

A. D. Chernin  A. V. Zasov  V. P. Arkhipova  A. S. Kravtsova 《Astronomy Letters》2000,26(5):285-296

The phenomenon of rows—straight features in the spiral patterns of galaxies, which was discovered by Vorontsov-Velyaminov, is investigated. The rows are not artifacts; in several cases, they outline regular spiral arms almost over their entire lengths. The galaxies M 101, M 51, and a number of more distant spirals are used as examples to demonstrate major geometrical and physical properties of these structures. It is shown that the row lengths increase nearly linearly with distance from the disk center, and that the angle between adjacent rows is almost always close to 2π/3. The galaxies with rows generally belong to moderate-luminosity Sbc-Sc systems with low rotational velocities, regular spiral patterns (Grand Design), and an H I content normal for these types of galaxies. Two types of rows are shown to exist, which differ in thickness and appear to be evolutionarily related. The formation mechanism of the rows should probably be sought in the peculiar behavior of the gas-compression wave in spiral density waves.  相似文献   

Mapping of the Natural and Anthropogenic Landscapes of River Deltas in Different Regions of the World Using Satellite Imagery     

Kravtsova  V. I. 《Water Resources》2022,49(5):901-911

Water Resources - The article suggests a method of mapping the natural and anthropogenic landscapes of river deltas based on satellite imagery in the publicly accessible information system Google...  相似文献   

Radiocarbon-dating of transitions between marine and lacustrine sediments and their relation to the development of lakes     

PETER EMIL KALAND  KNUT KRZYWINSKI  BJØRG STABELL 《Boreas: An International Journal of Quaternary Research》1984,13(2):243-258

In three different areas in western Norway, large errors are obtained in the radiocarbon dates from lacustrine sediments close to marine/lacustrine sediment boundaries. Differences occur between radiocar-bon and pollenanalytic dates and between dates at isolation/ingression contacts for lakes of the same altitude above the present sea level. Younger radiocarbon dates are also obtained below older ones in undisturbed sediments. When divergent dates occur, the radiocarbon dates always seem to be the youngest. Large differences are also found between NaOH soluble and insoluble fractions of the same sediment samples. Insoluble fractions generally yield younger dates than the soluble. Differences are not found, however, for dates younger than about 8,000 B.P. The dating errors are connected to periods with more oligotrophic conditions with isoetides. Their roots penetrate older sediments. Due to contamination of the organic part of the sediment from partly decomposed roots, some radiocarbon dates will be too young. The isoetide vegetation and the dating errors disappear when the lakes become dystrophic.  相似文献   

A ROBUST PLS PROCEDURE   总被引：1，自引：0，他引：1  

I.N.WAKELING  H.J.H.MACFIE 《地理学报(英文版)》1992,(4)

A robust partial least squares(PLS)regression algorithm is developed.This is achieved by substitutionof the univariate regression steps in the iterative PLS2 algorithm by a robust alternative.The anglebetween loading vectors from both perturbed and unperturbed solutions is used as a measure ofrobustness.By means of a perturbation study on a structure-activity data set,it is demonstrated thatthe stability of the robust method is superior to standard PLS.  相似文献   

Environmental influence on phytoplankton production during summer on the KwaZulu-Natal shelf of the Agulhas ecosystem     

T Lamont  RG Barlow 《African Journal of Marine Science》2015,37(4):485-501

During February 2010, studies of primary production (PP) and physiology were conducted at five selected sites in the KwaZulu-Natal (KZN) Bight of the Agulhas ecosystem as part of a programme to elucidate the influence of major physical driving forces and nutrient inputs on the structure and functioning of biological communities. These sites were located in the vicinity of the Durban lee eddy, in the midshelf region of the central part of the bight, off the Thukela Mouth, and to the north and south of Richards Bay. At four of the sites, chlorophyll a ranged from 0.10 to 1.44?mg m–3 and integrated PP ranged between 0.35 and 2.58?g C m–² d–1. The highest biomass and PP, which were comparable to those observed in a wind-driven upwelling system, were associated with a diatom community observed at the midshelf site, and varied between 0.26 and 4.27?mg m–³ and 7.22 and 9.89?g C m–² d–1, respectively. Environmental conditions at each of the sites differed substantially and appeared to be influential in initiating and controlling the development and distribution of phytoplankton biomass and production. Phytoplankton adaptation to variable environmental conditions was characterised by a decreased light-limited slope (αB) and increased rate of photosynthesis (P_m ) and light saturation (Ek) with elevated temperatures. The converse (increased α^B and decreased P_m and Ek) was observed as irradiance levels declined. Generalised additive models indicated that irradiance, temperature and biomass were important variables influencing photosynthetic parameters and photosynthetic rates.  相似文献   

Modes of Ag occurrence in the loose deposits of dispersal trains at Au-Ag mineral deposits     

R. G. Kravtsova  L. A. Pavlova  Yu. I. Rogozina 《Geochemistry International》2010,48(7):731-736

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First data on forms of gold occurrence in lithochemical sedimental streams of the Gold-Silver Dukat deposit (Northeastern Russia)     

R. G. Kravtsova  L. A. Pavlova  Yu. I. Rogozina  A. S. Makshakov 《Doklady Earth Sciences》2010,434(1):1184-1191

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Upstream development in idealized baroclinic wave experiments     

HEINI WERNLI  MELVYN A. SHAPIRO  JÜRG SCHMIDLI 《地球，A辑:动力气象学与海洋学》1999,51(5):574-587

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Specific Features of Development of the Modern Sulak River Delta     

Mikhailov  V. N.  Kravtsova  V. I.  Magritskii  D. V. 《Water Resources》2004,31(2):117-132

The development of the Sulak River Delta in the 19th and 20th centuries is discussed. It is shown that a drastic reduction in sediment runoff after the establishment of river flow regulation, anthropogenic restructuring of the river channel system in the delta area, and large-scale variations in the Caspian Sea level had an impact on the delta evolution. The processes of delta degradation over the period of the recent sea level rise are analyzed. The dynamics of the Sulak Delta in recent decades is studied using space photographs.  相似文献   

Hydrological and Morphological Processes in the Kura River Delta   总被引：1，自引：0，他引：1  

V. N. Mikhailov  V. I. Kravtsova  D. V. Magritskii 《Water Resources》2003,30(5):495-508

Peculiarities of the development of the Kura Delta over the last 200 years are discussed. As shown, changes in the delta were greatly affected by the Caspian Sea level drop during 1929–1977 and its rise during 1978–1995 as well as by natural and human-induced variations in the water and sediment runoff of the river. It was noted that the delta area decreased by nearly 40% as a result of the sea level rise. The following significant changes in the Kura Delta were revealed in recent years using space images: river water rushed through the right mouth spit and, hence, the main Southeastern Branch was devoid of its flow and a new sea spit began its formation in the branch mouth using wave-cut products.  相似文献