Perch larvae (Perca fluviatilis L.) survive better in dilute sea water     

Georg Ribi 《Aquatic Sciences - Research Across Boundaries》1992,54(1):85-90

Larvae of perch (Perca fluviatilis L.) reared in tanks for 27 days survived better in lake water to which 2% of artificial sea water had been added (46.6% average survival rate) than in lake water only (13.5% survival). One week after hatching, over 90% of the larvae had their guts filled in all tanks. During the following week the populations divided into floaters (fish with an inflated swimbladder) and sinkers (fish apparently lacking a functional swim-bladder). Although they continued feeding, sinkers remained smaller than floaters and most of them died.  相似文献   

Multicriteria assessment of water dynamics reveals subcatchment variability in a seemingly homogeneous tropical cloud forest catchment          下载免费PDF全文

Edison Timbe  Jan Feyen  Luis Timbe  Patricio Crespo  Rolando Célleri  David Windhorst  Hans‐Georg Frede  Lutz Breuer 《水文研究》2017,31(7):1456-1468

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Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time     

Patricio Crespo  Amelie Bücker  Jan Feyen  Kellie B. Vaché  Hans‐Georg Frede  Lutz Breuer 《水文研究》2012,26(25):3896-3910

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km²) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub‐páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C‐horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Discharge experiments simulating chemical evolution on the surface of Titan     

Kristof Plankensteiner  Bernd M. Rode  Tomas Mikoviny  Armin Hansel  Georg Fischer  Helmut O. Rucker 《Icarus》2007,187(2):616-619

Saturn's moon Titan has been considered as one of the few places in our Solar System, where atmospheric and surface conditions could have produced organic compounds essential as precursors for an evolution of life. The Cassini-Huygens mission has provided new data on Titan's atmosphere and surface, which enabled us to simulate the chemical processes occurring under these conditions. Possible lightning events on Titan cannot only produce higher hydrocarbons, but also allow surface water ice to participate in the reaction scenario, resulting in CHO, CHN, and CHON compounds including several molecules relevant for the formation of amino acids and nucleic acids.  相似文献   

A model of sand transport in Treporti channel: northern Venice lagoon     

Georg Umgiesser  Francesca De Pascalis  Christian Ferrarin  Carl L. Amos 《Ocean Dynamics》2006,56(3-4):339-351

The origin of the sands in the Venice lagoon has been the subject of an extensive field survey in parallel with numerical modelling. Four transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths. The modelling study consists of three parts: the sediment transport model sedtrans96 was used with a finite-element hydrodynamic model (Shyfem) and an empirical wave model (US Army Corps of Engineering) to simulate sand transport in the Treporti canal. A type of link box model was created where finite elements of the hydrodynamic model have been combined to macro-boxes on which the water and sediment flux over the sections, and a mass balance has been computed. Several grain size classes were simulated; the distributions before and after the simulation were examined. Idealised wind and tidal values were initially used to force 12 h simulations to test the sediment transport sensitivity. Finally, a full-year simulation (1987) has been carried out using measured tidal and wind data. Only a part of Venice lagoon was covered by the simulation: a major channel (Treporti) running from Lido inlet towards the northern lagoon. The total sand transport through all of the sections was computed for 1 year. Sediment mass balance was determined, and the resulting trends of erosion and deposition were computed. There were no trends in the median grain diameter and sorting of bottom samples from the Treporti canal; all sands were fine (120 μm, one outlier of 300 μm was removed). The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some centimeters per year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s, which hold fine sand in suspension and thus prevent sedimentation.  相似文献   

Landscape evolution and glaciation of the Rwenzori Mountains, Uganda: Insights from numerical modeling     

Georg Kaufmann  Douchko Romanov 《Geomorphology》2012,138(1):263-275

The Rwenzori Mountains are a high alpine mountain chain, about 40 × 80 km in size, just north of the equator in the western branch of the East African Rift System in Africa. The central part of the mountain chain is located in Uganda, and the highest peak, the Margherita Peak with 5119 m, lies on the border to the Democratic Republic of Congo. Topography is very pronounced, with steeply incised valleys and clear glacial landforms in the upper part of the mountain chain. The Rwenzori Mountains are an unusually high mountain chain located in the extensional setting of the East African Rift System, and the large elevation poses a challenging problem for geodynamists to explain.We have used the landscape evolution model ULTIMA THULE, which combines hillslope diffusion, fluvial erosion, and glacial abrasion and is driven by a climate driver, simulating the variations in temperature, precipitation, and relief over several glacial cycles. With a simulation time of 800 ka, we test the hypothesis of climate-tectonic interactions on the uplift of the Rwenzori Mountains.Our results show that a moderate cooling of around 6° causes widespread glaciation of the high mountain regions as observed during the peak glacial phases, and that morphological processes degrading the landscape allow for a tectonic uplift rate of around 0.5 mm a^− 1.  相似文献   

Effects of seed particle size and composition on heterogeneous nucleation of n-nonane     

Paul M. Winkler  Anca Hienola  Gerhard Steiner  Gerard Hill  Aron Vrtala  Georg P. Reischl  Markku Kulmala  Paul E. Wagner 《Atmospheric Research》2008,90(2-4):187-ICNAA07

Heterogeneous nucleation of supersaturated n-nonane vapour on seed particles of different size and composition has been investigated using a fast expansion chamber. Monodisperse seed particle sizes were ranging from about 4 nm up to about 24 nm in diameter. By using different types of particle generators WO_x, Ag and (NH₄)₂SO₄ particles were generated. For direct comparison between different particle compositions overlapping sizes have been generated for WO_x and Ag at about 7 nm particle diameter as well as for Ag and (NH₄)₂SO₄ at about 15 nm. Nucleation temperature was kept constant at about 278 K. Experimental data were compared to Kelvin equation and Fletcher theory including the effect of line tension. It was found that heterogeneous nucleation of n-nonane seems to be independent of seed particle composition and starts well below the Kelvin curve. Good agreement was achieved with Fletcher theory including the effect of line tension.  相似文献   

Electronic and magnetic structure of pyroxenes: II. Orthoferrosilite     

Danylo Zherebetskyy  Georg Amthauer  Michael Grodzicki 《Physics and Chemistry of Minerals》2010,37(7):455-464

The electronic and magnetic structure of the chain silicate orthoferrosilite Fe ₂ ²⁺ Si₂O₆ has been investigated by electronic structure calculations in the local spin density approximation. All calculations are based on experimentally determined geometrical data at room temperature. The calculated spin-allowed d–d excitation energies and hyperfine parameters are in quantitative agreement with the respective experimental data from optical absorption and Mössbauer spectroscopy. Inside one ribbon that is parallel to the crystallographic c axis and contains two non-equivalent M1 and M2 sites, all iron spins are ferromagnetically coupled with coupling constants of about +16 cm^?1. Between these ribbons within the (b, c)-plane a weak ferromagnetic coupling of about +2 cm^?1 is obtained. Neighboured (b, c)-planes are coupled antiferromagnetically via chains of Si ^B -tetrahedra but ferromagnetically via chains of Si ^A -tetrahedra. Such a theoretically determined "double-plane antiferromagnetic" spin structure is at variance with an experimentally derived magnetic structure. This discrepancy is attributed to differences between the geometry at room temperature and at temperatures below the Néel temperature currently not available.  相似文献   

Quaternary glaciations in the Verkhoyansk Mountains, Northeast Siberia   总被引：1，自引：0，他引：1  

Georg Stauch  Frank Lehmkuhl 《Quaternary Research》2010,74(1):145-196

Geomorphological mapping revealed five terminal moraines in the central Verkhoyansk Mountains. The youngest terminal moraine (I) was formed at least 50 ka ago according to new IRSL (infrared optically stimulated luminescence) dates. Older terminal moraines in the western foreland of the mountains are much more extensive in size. Although the smallest of these older moraines, moraine II, has not been dated, moraine III is 80 to 90 ka, moraine IV is 100 to 120 ka, and the outermost moraine V was deposited around 135 ka. This glaciation history is comparable to that of the Barents and Kara ice sheet and partly to that of the Polar Ural Mountains regarding the timing of the glaciations. However, no glaciation occurred during the global last glacial maximum (MIS 2). Based on cirque orientation and different glacier extent on the eastern and western flanks of the Verkhoyansk Mountains, local glaciations are mainly controlled by moisture transport from the west across the Eurasian continent. Thus glaciations in the Verkhoyansk Mountains not only express local climate changes but also are strongly influenced by the extent of the Eurasian ice sheets.  相似文献   

A comparison of community and trophic structure in five marine ecosystems based on energy budgets and system metrics   总被引：1，自引：1，他引：0  

Sarah Gaichas  Georg Skaret  Jannike Falk-Petersen  Jason S. Link  William Overholtz  Bernard A. Megrey  Harald Gjster  William T. Stockhausen  Are Dommasnes  Kevin D. Friedland  Kerim Aydin 《Progress in Oceanography》2009,81(1-4):47

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