排序方式： 共有13条查询结果，搜索用时 296 毫秒
1.
Erland M. Schulson 《Meteoritics & planetary science》2006,41(10):1497-1508
Abstract— This paper presents a short overview of the fracture of water ice Ih. Topics include the ductile‐to‐brittle transition, tensile and compressive strength, compressive failure under multiaxial loading, compressive failure modes, and brittle failure on the geophysical scale (Arctic sea ice cover, Europa's icy crust). Emphasis is placed on the underlying physical mechanisms. Where appropriate, comment is made on the formation of high‐latitude impact craters on Mars. 相似文献
2.
Large-scale thermohaline circulation cells in the world oceans exist due to horizontal density gradients. Owing to differential heating between equator and pole a north-south density gradient is present at the ocean surface. An additional mechanism for producing north-south density gradients is the heat and salinity transport by boundary currents in the upper parts of the world oceans. In the North Atlantic, high density sinking water is produced by a convergence of salt water from the south and cold water from the north.We have investigated large-scale thermohaline convection cells by time integrating a two-dimensional Boussinesq model. The flow is driven by an imposed density gradient at the upper boundary (mixed layer) and an externally prescribed, meridionally varying density flux in the interior of the model domain. We perform numerical simulations and through time integrations we determine equilibrium states of the model. By changing the forcing parameters slowly during the course of a time integration, we have identified regions in parameter space where a hysteretic behaviour may be found. For a given set of the forcing parameters the model has two stable equilibrium states which differ in the direction of the circulation.We have thus found that due to the nonlinear nature of the balance between advection, internal mixing and forcing more than one stable equilibrium circulation pattern can be found under a given set of external forcing parameters. This result may offer a potential explanation for the existing asymmetries between the thermohaline circulation patterns in the Atlantic and Pacific Oceans as well as possible implications for the climatic state of the oceans under changing external conditions. 相似文献
3.
Modelling changes in suspended sediment from forest road surfaces in a coastal watershed of British Columbia 
下载免费PDF全文
下载免费PDF全文 H. Andres Araujo Ashley Page Andrew B. Cooper Jeremy Venditti Erland MacIsaac Marwan A. Hassan Duncan Knowler 《水文研究》2014,28(18):4914-4927
Erosion from logging road surfaces, cut slopes, banks, and ditches represents a chronic source of sediment input to streams that can degrade aquatic habitats. Road surface erosion is of particular concern because the magnitude of sediment generation when traffic levels are high can be large. Current models for predicting sediment production from roads require information on area‐specific sediment delivery, which is not often available. Here, we developed a model to quantify suspended sediment concentrations (SSC) generated by forest roads surfaces under different conditions of use and density. This model is designed for a typical medium‐size coastal watershed of British Columbia or the American Pacific Northwest, and was applied to the Chilliwack River watershed as a case study. The results illustrate that intensive use of forest roads combined with high road density can increase the number of extreme sedimentation events over a predetermined threshold. A comparison of the effects of road density and the level of road use suggests that the level of road use is more important than the road density for the generation of fine sediment from road surfaces. However, the model omits the impact of roads on mass movements in a watershed, which represent a major source of sediment in steep watersheds, so the effect of road density is likely more substantial than the model predicts. The model is an attempt to overcome field data limitations by using an empirical relation between SSC and traffic variables, and presents a starting point for more intensive field studies that could be used to validate it. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
4.
Mats Leijon Cecilia Boström Oskar Danielsson Stefan Gustafsson Kalle Haikonen Olivia Langhamer Erland Strömstedt Magnus Stålberg Jan Sundberg Olle Svensson Simon Tyrberg Rafael Waters 《Surveys in Geophysics》2008,29(3):221-240
This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider? buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system. 相似文献
5.
6.
Based on high-resolution seismics, submerged terraces have been identified and mapped. They constitute two semi-continuous terrace zones that can be followed for up to about 350 km along the bank flanks, at more or less uniform depths of ca. 150 m and ca. 220 m, respectively. The features are interpreted as wave-cut platforms, and thus indicate a submergence of as much as 220 m after they formed. Several arguments suggest that they were probably not formed during glaciation maxima, but rather during interglacials or parts of glacials with restricted glaciation. Consequently, only a smaller part of their submergence may be due to glacial eustasy. A signigicant tectonic related subsidence is inferred. Relatively young ages are indicated since they are so lightly eroded by the Plio-Pleistocene ice sheets. A maximum age in the order of 0.8 Ma and a minimum age of 0.2 Ma is tentatively suggested. One implication is that subsidence rates for this part of the Barents Sea margin are in the range 0.2–0.9 m/kyr. 相似文献
7.
8.
Jonas Persson Erland Jungert 《International journal of geographical information science》2013,27(6):497-510
Abstract One motivation for the need of maps to be organized hierarchically in different resolutions is the fact that in most applications low-resolution maps require less heavy computations than maps represented at higher resolutions. Spatial data structures that permit generation of lower levels or resolution in a hierarchical fashion already exist, e.g., quad-trees and resolution pyramids. Many other spatial data structures that are non-hierarchical, and therefore do not permit the generation of resolution hierarchies, also exist. One such structure is the run-length-code (RLC), which has many powerful advantages that make the structure feasible in geographical information systems. In this article an approach to the problem of generating a resolution hierarchy from RLC is described and discussed. 相似文献
9.
10.
Late Holocene palaeoceanography in Van Mijenfjorden, Svalbard 总被引：2，自引：0，他引：2
Based on detailed stratigraphical analysis of sediment cores spanning the last ca. 4000 calendar years, we reconstruct the palaeoceanograhic changes in the fiord Van Mijenfjorden, western Svalbard. Benthic foraminiferal δ18 O indicate a gradual reduction in bottom water salinities between 2200 BC and 500 BC. This reduction was probably mainly a function of reduced inflow of oceanic water to the fiord, due to isostatic shallowing of the outer fiord sill. Stable salinity conditions prevailed between 500 BC and. 1300 AD. After the onset of a major glacial surge of the tidewater Paulabreen (Paula Glacier) system (PGS) around 1300 AD, there was a foraminiferal faunal change towards glacier proximal conditions, associated with a slight bottom water salinity depletion. During a series of glacial surges occuring from 1300 AD up the present salinity in the fiord has further decreased, corresponding to a δ18 O depletion of 0.5 %o. This salinity decrease corresponds to the period when the PGS lost an equivalent of 30 – 40 % of its present ice volume, mainly through calving in the fiord. 相似文献