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161.
Laboratory experiments with regular waves were used to investigate wave transmission by overtopping for a smooth, impermeable breakwater with a 1-in-4 slope.A resulting relationship between the transmission coefficient and a breakwater height above mean sea level normalized with a theoretical wave run-up height is reported in this paper. 相似文献
162.
163.
Jan Vanaverbeke Maaike Steyaert Karline Soetaert Vronique Rousseau Dirk Van Gansbeke Jean-Yves Parent Magda Vincx 《Journal of Sea Research》2004,52(4):588
The response of nematode communities to the sedimentation of a spring phytoplankton bloom in a sandy, well-oxygenated sediment at a single station (station 330) in the Southern North Sea was investigated monthly from early March to July 1999. Both structural (nematode density, diversity, vertical distribution and community composition) and functional (feeding type distributions, number of species within feeding groups) characteristics showed considerable changes shortly after the arrival of fresh organic material at the sediment surface. The general increase in numerical densities and diversity was related to changes within the groups of selective deposit-feeding and epistrate-feeding nematodes. It is hypothesised that sedimentation and subsequent remineralisation of fresh organic matter during the spring phytoplankton bloom result in an increase of suitable food items (both living and dead). This, combined with the availability of oxygen, creates conditions in which many nematode species can co-exist. 相似文献
164.
van der Sloot Hans A Dirk Hoede Gert Hamburg Joost R.W Woittiez van der Weijden Cornelis H 《Marine Chemistry》1990,31(1-3)
In the anoxic hypersaline Tyro and Bannock Basins of the eastern Mediterranean, extremely high concentrations of Co (0.015%), Cu (1.35%) and Zn (0.28%) were found in suspended matter collected at the sharp interface between seawater and the anoxic brine. The high particulate Co, Cu and Zn concentrations can be explained by the sharp increase in dissolved sulphide at these interfaces, and the resultant precipitation of metal sulphides. The particulate As, Sb and Mo concentrations also showed a sharp maximum at or close to the interface. However, the contributions of As, Sb and Mo contents in suspended matter to the total concentrations in the water column are small. Scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDAX) of suspended particulate matter from the Tyro Basin revealed spherical particles strongly enriched in Fe, Cu and Zn at the seawater-brine interface. 相似文献
165.
Alexander Matul Andrea Abelmann Ralf Tiedemann Andre Kaiser Dirk Nürnberg 《Geo-Marine Letters》2002,22(1):25-32
Five radiolarian datum events have been recorded in the Late Quaternary sediment section from the Sea of Okhotsk, using age assignments based on oxygen-isotope stratigraphy: the last occurrence datum (LOD) of Stylacontarium acquilonium (at about 329 ka), the LOD of Spongodiscus sp. (at about 287 ka), the LOD of Amphimelissa setosa (at about 72 ka), the LOD of Lychnocanoma nipponica sakaii (at about 28 ka), and the L. nipponica sakaii acme event (at about 72 ka). The LODs of S. acquilonium, Spongodiscus sp. and A. setosa appear to be synchronous in comparison with those in the Subarctic North Pacific, but the LOD and the acme event of L. nipponica sakaii show an apparent diachroneity with the corresponding North Pacific events. 相似文献
166.
Knut H. Andersen Philippe Jeanjean Dirk Luger Hans Petter Jostad 《Ocean Engineering》2005,32(7):845-863
Three centrifuge model tests were performed in normally consolidated Speswhite Kaolin to study the penetration of suction anchors in soft clay. The suction anchors could be penetrated by means of underpressure to a depth of about 12.4 to a little more than 14.5 times the diameter. When the anchors were penetrated by underpressure, all clay displaced by the skirt moved into the anchor. At a penetration depth of about half the maximum penetration depth, the volume of the soil heave inside the anchor actually increased more than the volume of the displaced clay. When a material coefficient of 1.5 against plug failure was mobilized, more than the clay displaced by the skirts had accumulated inside the anchor. The penetration resistance increased by 42 and 26% during rest periods of 4.5 and 0.8 days prototype time, respectively. Some uncertainty in the shear strength of the clay beds gave some uncertainty with respect to the interpretation, but the observed behaviour generally confirmed the theoretical analyses. 相似文献
167.
We investigated long-term variations of the differential rotation of the solar large-scale magnetic field on 1024 H charts in the latitude zones from +45° to -45° in the period 1915–1990. We used the expansion in terms of Walsh functions. It turns out that the rotation of the Sun becomes more rigid than average during the cycle maximum and the rotation is more differential during minimum. From 1915 to 1990, 7 bands of faster- and 7 bands of slower-than-average rotation are revealed showing an 11-year period. These bands drift towards the equator: 45° in 2.5 to 8 years. The time span of the bands varies from 4 to 6.8 years and is in anti-phase with long-term solar activity. The latitude span of the bands of torsional oscillations varies from 0.5 R
to 1.3 R
and shows a long-term variation of about 55 years. The poloidal component of velocity, V
varies from 2 ms -1 to 6 ms -1. The maximum rate of the equatorial drift occurs in the period between 1935 and 1955 and it develops prior to the highest maximum activity. At the modern epoch from 1965 to 1985, V
does not exceed 3 ms -1, but now it has a tendency to increase. The bands of slower-than-average rotation correspond to the evolution of the magnetic activity towards the equator in the butterfly diagram. 相似文献
168.
Nwosu Ebuka C. Brauer Achim Kaiser Jérôme Horn Fabian Wagner Dirk Liebner Susanne 《Journal of Paleolimnology》2021,66(3):279-296
Journal of Paleolimnology - Since the beginning of the Anthropocene, lacustrine biodiversity has been influenced by climate change and human activities. These factors advance the spread of harmful... 相似文献
169.
170.