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51.
Lars Danielsson 《Astrophysics and Space Science》1969,5(1):53-58
The distribution of asteroid orbits in space is studied and a detailed investigation for Hirayama's Flora family is presented. Some tendencies to (5-dimensional) clustering are found by means of comparing actual with random distribution simulated on a computer. 相似文献
52.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
53.
Olga V. Sidorova Matthias Saurer Vladimir S. Myglan Anja Eichler Margit Schwikowski Aleksander V. Kirdyanov Marina V. Bryukhanova Oksana V. Gerasimova Ivan A. Kalugin Andrey V. Daryin Rolf T. W. Siegwolf 《Climate Dynamics》2012,38(1-2):175-188
For the first time we present a multi-proxy data set for the Russian Altai, consisting of Siberian larch tree-ring width (TRW), latewood density (MXD), δ13C and δ18O in cellulose chronologies obtained for the period 1779–2007 and cell wall thickness (CWT) for 1900–2008. All of these parameters agree well between each other in the high-frequency variability, while the low-frequency climate information shows systematic differences. The correlation analysis with temperature and precipitation data from the closest weather station and gridded data revealed that annual TRW, MXD, CWT, and δ13C data contain a strong summer temperature signal, while δ18O in cellulose represents a mixed summer and winter temperature and precipitation signal. The temperature and precipitation reconstructions from the Belukha ice core and Teletskoe lake sediments were used to investigate the correspondence of different independent proxies. Low frequency patterns in TRW and δ13C chronologies are consistent with temperature reconstructions from nearby Belukha ice core and Teletskoe lake sediments showing a pronounced warming trend in the last century. Their combination could be used for the regional temperature reconstruction. The long-term δ18O trend agrees with the precipitation reconstruction from the Teletskoe lake sediment indicating more humid conditions during the twentieth century. Therefore, these two proxies could be combined for the precipitation reconstruction. 相似文献
54.
The occurrence of a thin band of marine limestone (Graua Limestone) within a thick succession of fluviatile sandstones in south-eastern Ethiopia is direct evidence of flooding of part of the East African craton (Horn of Africa). According to the presence of abundant orbitolinid foraminifers (Palorbitolina lenticularis Blumenbach andPraeorbitolina cormyi Schroeder), the age of the Graua Limestone can be referred to the Early Aptian. Stratigraphy and palaeogeographic reconstructions for the Early Cretaceous in the surrounding regions (Kenya, Somalia, Yemen, Socotra, Oman, Syria, Lebanon, Israel, Egypt and Libya) show that the Early Aptian transgression was of regional extent. Our data seem to confirm that this transgression was of relatively short duration. This pulse cannot be related to tectono-eustatic mechanisms, which are too slow. A short-lived event should be invoked: either a regional tectonic pulse or the desiccation of the proto-South Atlantic. 相似文献
55.
Recent data from exposures of terrestrial Pleistocene sediments in the Fraser Lowland of southwestern British Columbia reveal at least two ‘Bond cycles’ within Oxygen Isotope Stage 2. The maximum of the Coquitlam Stade coincides with the timing of Heinrich event H2, the Port Moody Interstade with Dansgaard–Oeschger (D–O) interstade 2, the maximum of the Vashon Stade with H1, and the Fort Langley interval with D–O interstade 1. The Sumas Stade apparently preceded H0 (Younger Dryas) but could have been in response to the same climatic signal. The timing of Sumas advances may be explained by a combination of glacio-isostatic rebound, destabilisation of the ice margin, and rapid movement over a short distance on soft muddy beds of a rising sea floor, thereby leading the timing of North Atlantic events by hundreds of years. In contrast, Coquitlam and Vashon advances were mainly over permeable glaciofluvial sediments and because of this their maxima probably did not precede the timing of H2 and H1. The Port Moody Interstade coincided with the global Last Glacial Maximum, due in part to the moderating effect of moist summer storms in a southward-shifted jet stream that influenced the Fraser Lowland at that time. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
56.
Rolf Köster 《International Journal of Earth Sciences》1959,46(2):564-571
Zusammenfassung Die wichtigsten glazialen Stauchungsvorgänge wurden experimentell nachgeahmt. Als Versuchsmaterial fanden erwärmte Sand-Paraffin-Gemenge mit eingelegten Schichten von Modellgips Verwendung. Bei Temperaturen über dem Schmelzpunkt des Paraffins besitzen sie ähnlich günstige Eigenschaften wie der meist bevorzugte Tonschlamm, bei Zimmertemperatur sind sie erhärtet und erlauben, im Gegensatz zum Tonschlamm, beliebige Profilschnitte und damit Einblicke in den inneren Bau.Die Experimente ergaben Zusammenhänge zwischen Veränderungen im Versuchsansatz und verschiedenen Störungstypen. Es entstanden:Schuppen bei Stauchung vor dem Modell einer Eiszunge,Falten bei Stauchung unter Belastung,Horizontal eingeschlichtete Streifen bei Bewegung des Modelles unter seiner Sohle.Die Beobachtungen stimmen weitgehend überein mit den Lagerungsstörungen in eisentstandenen Formen entsprechender Bildungsbedingungen. 相似文献
57.
Hans J. Lippolt Rolf S. Wernicke Werner Boschmann 《Physics and Chemistry of Minerals》1993,20(6):415-418
In order to test the chronometer qualities of speculante for the (U + Th)/He dating method, 4He release experiments by stepwise heating of two specularites from the Rimbach mineralization locality in the southern Vosgues (France) have been carried out. The diffusion coefficients define linear Arrhenius plots within a temperature interval of 250 to 830 °C, which is suggestive of volume diffusion. Extrapolation of the diffusion behavior to 20° C yields diffusion coefficients (D20 values) smaller than 10?26 [cm2 s?1] for both hematites with activation energies at 116 [kJ/mole]. The results of our study suggest that specularite is a very helium retentive hematite variety which is capable of quantitatively retaining radiogenic helium over geologic periods of time. 相似文献
58.
Sujay V. Kumar Rolf H. Reichle Christa D. Peters-Lidard Randal D. Koster Xiwu Zhan Wade T. Crow John B. Eylander Paul R. Houser 《Advances in water resources》2008
The Land Information System (LIS) is an established land surface modeling framework that integrates various community land surface models, ground measurements, satellite-based observations, high performance computing and data management tools. The use of advanced software engineering principles in LIS allows interoperability of individual system components and thus enables assessment and prediction of hydrologic conditions at various spatial and temporal scales. In this work, we describe a sequential data assimilation extension of LIS that incorporates multiple observational sources, land surface models and assimilation algorithms. These capabilities are demonstrated here in a suite of experiments that use the ensemble Kalman filter (EnKF) and assimilation through direct insertion. In a soil moisture experiment, we discuss the impact of differences in modeling approaches on assimilation performance. Provided careful choice of model error parameters, we find that two entirely different hydrological modeling approaches offer comparable assimilation results. In a snow assimilation experiment, we investigate the relative merits of assimilating different types of observations (snow cover area and snow water equivalent). The experiments show that data assimilation enhancements in LIS are uniquely suited to compare the assimilation of various data types into different land surface models within a single framework. The high performance infrastructure provides adequate support for efficient data assimilation integrations of high computational granularity. 相似文献
59.
Aleksandre Kandilarov Rolf Mjelde Rolf-Birger Pedersen Bjarte Hellevang Cord Papenberg Carl-Joerg Petersen Lars Planert Ernst Flueh 《Marine Geophysical Researches》2012,33(1):55-76
The Jan Mayen microcontinent was as a result of two major North Atlantic evolutionary cornerstones—the separation of Greenland
from Norway (~54 Ma), accompanied by voluminous volcanic activity, and the jump of spreading from the Aegir to the Kolbeinsey
ridge (~33 Ma), which resulted in the separation of the microcontinent itself from Eastern Greenland (~24 Ma). The resulting
eastern and western sides of the Jan Mayen microcontinent are respectively volcanic and non-volcanic rifted margins. Until
now the northern boundary of the microcontinent was not precisely known. In order to locate this boundary, two combined refraction
and reflection seismic profiles were acquired in 2006: one trending S–N and consisting of two separate segments south and
north of the island of Jan Mayen respectively, and the second one trending SW–NE east of the island. Crustal P-wave velocity
models were derived and constrained using gravity data collected during the same expedition. North of the West Jan Mayen Fracture
Zone (WJMFZ) the models show oceanic crust that thickens from west to east. This thickening is explained by an increase in
volcanic activity expressed as a bathymetric high and most likely related to the proximity of the Mohn ridge. East of the
island and south of the WJMFZ, oceanic Layers 2 and 3 have normal seismic velocities but above normal average crustal thickness
(~11 km). The similarity of the crustal thickness and seismic velocities to those observed on the conjugate M?re margin confirm
the volcanic origin of the eastern side of the microcontinent. Thick continental crust is observed in the southern parts of
both profiles. The northern boundary of the microcontinent is a continuation of the northern lineament of the East Jan Mayen
Fracture Zone. It is thus located farther north than previously assumed. The crust in the middle parts of both models, around
Jan Mayen island, is more enigmatic as the data suggest two possible interpretations—Icelandic type of oceanic crust or thinned
and heavily intruded continental crust. We prefer the first interpretation but the latter cannot be completely ruled out.
We infer that the volcanism on Jan Mayen is related to the Icelandic plume. 相似文献
60.
Andreas Macrander Rolf H. Käse Uwe Send Héðinn Valdimarsson Steingrímur Jónsson 《Ocean Dynamics》2007,57(2):75-89
In spite of the fundamental role the Atlantic Meridional Overturning Circulation (AMOC) plays for global climate stability,
no direct current measurement of the Denmark Strait Overflow, which is the densest part of the AMOC, has been available until
recently that resolve the cross-stream structure at the sill for long periods. Since 1999, an array of bottom-mounted acoustic
instruments measuring current velocity and bottom-to-surface acoustic travel times was deployed at the sill. Here, the optimization
of the array configuration based on a numerical overflow model is discussed. The simulation proves that more than 80% of the
dense water transport variability is captured by two to three acoustic current profilers (ADCPs). The results are compared
with time series from ADCPs and Inverted Echo Sounders deployed from 1999 to 2003, confirming that the dense overflow plume
can be reliably measured by bottom-mounted instruments and that the overflow is largely geostrophically balanced at the sill. 相似文献