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41.
Olav Fjær 《Norsk geografisk tidsskrift. Norwegian journal of geography》2013,67(3):135-141
The author, an upper secondary teacher in geography, has conducted various surveys and questionnaires among pupils every year, for 30 years. The article examines his pupils' knowledge of geography when they start upper secondary school. During their first lesson in geography they are presented with a questionnaire designed to test their knowledge of concepts, places, and causal relationships. In addition, they are asked about their perceptions of geography and expectations when they start to study a new subject. The author finds it valuable and important as a teacher to know what his pupils have learned during their lower secondary education because such information could be used to adapt upper secondary education in geography to the pupils' abilities. Further, it is important to motivate, create expectations, and develop awareness of geography. In addition to discussing pupils' knowledge of geography, the article shows briefly how school curricula and geography teaching have changed in Norwegian lower secondary schools since the early 1970s. 相似文献
42.
Dynamics of grains falling on a sloping granular medium: application to the evolution of a talus
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Numerous field surveys have provided quantitative information on the characteristics of talus deposits. Much less has been done to quantify the basic dynamics processes of blocks involved in talus evolution. In this work, we perform a set of experiments at the reduced scale of some metres using an inclined board covered with a loose granular medium. The complexity of the processes forming a talus is simplified by studying the interaction of only two kinds of grain sizes at a time. Grains of one class size are dropped from a fixed height onto the board covered by a layer of grains of a different class size, and their final distribution is recorded. We find that when small grains fall on large grains, the granular abundance decreases rapidly as a function of the distance from the fall point, which is explained by the effect of multiple bouncing on the irregular surface. In contrast, large grains falling on a bed of smaller grains lose much more energy at impact. They may stop at once, or roll down slope, often reaching the whole board length; as a consequence, their abundance peaks in the fall zone and at the change of slope. Experiments also show that grains travel longer with increasing fall height and sloping angle. The results clarify in a physical manner one mechanism that might explain why large blocks are typically found in the distal part of a talus slope, while smaller blocks remain near the fall zone. Based on these and previous experiments, a schematic view of talus evolution is discussed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
43.
A modelling study of the effects of land management and climatic variations on groundwater inflow to Lake St Lucia, South Africa 总被引:1,自引:0,他引:1
Over the past few years groundwater has been recognized as an important contributor of freshwater to Lake St Lucia, South Africa during periods of prolonged drought. This has led to a management strategy aiming at increasing the groundwater recharge and minimizing groundwater use through active manipulation of the vegetation. For the Eastern Shores on the edge of Lake St Lucia, the replacement of vast areas of pine (Pinus elliottii) plantations with grassland over the past decade, combined with a strict burning regime, has led to a general rise of the water table, which has increased the groundwater seepage to Lake St Lucia. A numerical groundwater model has been applied to assess the effects of local management strategies on the mass balance of a shallow aquifer and these are compared to the effects of predicted climate and sea-level change for this area. The simulations indicate that local management actions that are being applied to the Eastern Shores have positive effects on the groundwater flux into Lake St Lucia and that they outweigh potential negative effects of future climate and sea-level change predicted for this area. 相似文献
44.
The HIRHAM regional climate model suggests an increase in temperature in Denmark of about 3 °C and an increase in mean annual precipitation of 6–7%, with a larger increase during winter and a decrease during summer between a control period 1961–1990 and scenario period 2071–2100. This change of climate will affect the suspended sediment transport in rivers, directly through erosion processes and increased river discharges and indirectly through changes in land use and land cover. Climate‐change‐induced changes in suspended sediment transport are modelled for five scenarios on the basis of modelled changes in land use/land cover for two Danish river catchments: the alluvial River Ansager and the non‐alluvial River Odense. Mean annual suspended sediment transport is modelled to increase by 17% in the alluvial river and by 27% in the non‐alluvial for steady‐state scenarios. Increases by about 9% in the alluvial river and 24% in the non‐alluvial river were determined for scenarios incorporating a prolonged growing season for catchment vegetation. Shortening of the growing season is found to have little influence on mean annual sediment transport. Mean monthly changes in suspended sediment transport between ? 26% and + 68% are found for comparable suspended sediment transport scenarios between the control and the scenario periods. The suspended sediment transport increases during winter months as a result of the increase in river discharge caused by the increase in precipitation, and decreases during summer and early autumn months. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
45.
In the monitoring of earthquakes and nuclear explosions using a sparse worldwide network of seismic stations, it is frequently
necessary to make reliable location estimates using a single seismic array. It is also desirable to screen out routine industrial
explosions automatically in order that analyst resources are not wasted upon detections which can, with a high level of confidence,
be associated with such a source. The Kovdor mine on the Kola Peninsula of NW Russia is the site of frequent industrial blasts
which are well recorded by the ARCES regional seismic array at a distance of approximately 300 km. We describe here an automatic
procedure for identifying signals which are likely to result from blasts at the Kovdor mine and, wherever possible, for obtaining
single array locations for such events. Carefully calibrated processing parameters were chosen using measurements from confirmed
events at the mine over a one-year period for which the operators supplied Ground Truth information. Phase arrival times are
estimated using an autoregressive method and slowness and azimuth are estimated using broadband f{-}k analysis in fixed frequency bands and time-windows fixed relative to the initial P-onset time. We demonstrate the improvement
to slowness estimates resulting from the use of fixed frequency bands. Events can be located using a single array if, in addition
to the P-phase, at least one secondary phase is found with both an acceptable slowness estimate and valid onset-time estimate.
We evaluate the on-line system over a twelve month period; every event known to have occured at the mine is detected by the
process and 32 out of 53 confirmed events were located automatically. The remaining events were classified as “very likely”
Kovdor events and were subsequently located by an analyst. The false alarm rate is low; only 84 very likely Kovdor events
were identified during the whole of 2003 and none of these were subsequently located at a large distance from the mine. The
location accuracy achieved automatically by the single-array process is remarkably good, and is comparable to that obtained
interactively by an experienced analyst using two-array observations. The greatest problem encountered in the single array
location procedure is the difficulty in determining arrival times for secondary phases, given the weak Sn phase and the complexity
of the P-coda. The method described here could be applied to a wide range of locations and sources for which the monitoring
of seismic activity is desirable. The effectiveness will depend upon the distance between source and receiver, the nature
of the seismic sources and the level of regional seismicity. 相似文献
46.
E. C.?HicksEmail author T.?Kv?rna S.?Mykkeltveit J.?Schweitzer F.?Ringdal 《Pure and Applied Geophysics》2004,161(1):1-19
A database containing 45 events in the Barents Sea region has been compiled and analyzed with the aim of evaluating crustal models, travel-times and attenuation relations in the context of performing regional detection threshold monitoring of this region. The 45 events are mostly located around the circumference of the study area due to the virtually aseismic nature of the Barents Sea itself. Regional P
n
and S
n
phases were observable for most events in the database, while P
g
and L
g
phases were only observable for events with raypaths that do not cross the tectonic structures in the Barents Sea. This corroborates a number of previous observations of L
g
-wave blockage within the Barents Sea. Three existing velocity models were evaluated, with a model having slightly lower S velocities than earlier assumed in the upper mantle giving the overall best fit to the observed arrivals. In order to estimate magnitudes, short-term average (STA) and spectral amplitude values were calculated in several frequency bands for all phase arrivals in the database. There were no significant differences between spectral and STA amplitudes, so the latter were used as this parameter is more efficient to calculate in real-time processing. An inversion was performed in order to determine an attenuation relation specific for this region. The resulting magnitudes based on P
n
, P
g
, S
n
and L
g
phases gave an internally consistent, reasonably stable set of values, which can be calibrated towards any existing global or regional scale. 相似文献
47.
Angela Lundberg Pertti Ala‐Aho OleMartin Eklo Björn Klöve Jens Kværner Christine Stumpp 《水文研究》2016,30(8):1230-1250
Vast regions of the northern hemisphere are exposed to snowfall and seasonal frost. This has large effects on spatiotemporal distribution of infiltration and groundwater recharge processes as well as on the fate of pollutants. Therefore, snow and frost need to be central inherent elements of risk assessment and management schemes. However, snow and frost are often neglected or treated summarily or in a simplistic way by groundwater modellers. Snow deposition is uneven, and the snow is likely to sublimate, be redistributed and partly melt during the winter influencing the mass and spatial distribution of snow storage available for infiltration, the presence of ice layers within and under the snowpack and, therefore, also the spatial distribution of depths and permeability of the soil frost. In steep terrain, snowmelt may travel downhill tens of metres in hours along snow layers. The permeability of frozen soil is mainly influenced by soil type, its water and organic matter content, and the timing of the first snow in relation to the timing of sub‐zero temperatures. The aim with this paper is to review the literature on snow and frost processes, modelling approaches with the purpose to visualize and emphasize the need to include these processes when modelling, managing and predicting groundwater recharge for areas exposed to seasonal snow and frost. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
48.
The EU has developed the first and largest international emissions trading system in the world. This development is puzzling due to the EU's scepticism to international emissions trading in greenhouse gases (GHGs) in the run-up to the 1997 Kyoto Protocol. This article analyses how the EU ETS was initiated in the first place mainly from the perspectives of Liberal intergovernmentalism (LI) and multi-level governance (MLG). LI emphasises change in the positions of the EU member states as the key to understand what happened and why, whereas MLG opens up for change in the position of supranational entrepreneurial leaders as the key explanation. The main conclusion is that entrepreneurial epistemic leadership exercised by the European Commission was crucial for making the EU ETS. The principal means of leadership involved building up independent expertise on how an EU ETS could be designed, and mobilizing support from state and non-state actors at various levels of decision-making. This type of leadership may be needed more generally to deal with challenges characterized by high scientific uncertainty and social complexity in which learning is pertinent, such as climate change. 相似文献
49.
Jaap J.M. van der Meer K.H. Kjær J. Krüger J. Rabassa A.A. Kilfeather 《Quaternary Science Reviews》2009,28(7-8):708-720
Clastic dykes are widespread in glacial settings, and we provide examples from Switzerland, Patagonia, Iceland and the Antarctic, ranging in age from Tertiary to recent. On the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds. Micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply. Clastic dykes act like safety valves in the subglacial hydraulic system. Their development depends on specific subglacial conditions like water volume and pressure, the nature of the bed, sediments or bedrock, and the hydraulic properties of the bed. A number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form. Development of clastic dykes affects glaciodynamics, like velocity and surging and landform formation, like till thickness and bedrock disruption. 相似文献
50.
Johan Striberger Svante Björck Ívar Örn Benediktsson Ian Snowball Cintia B. Uvo Ólafur Ingólfsson Kurt H. Kjær 《第四纪科学杂志》2011,26(6):561-565
Surging outlet glaciers are important in draining large ice caps, but the mechanisms controlling surge periodicities are poorly known. We investigated a sediment sequence from the glacier‐fed Lake Lögurinn in eastern Iceland, and our unique annually resolved data, based on sedimentary varves, imply that Eyjabakkajökull, an outlet glacier of Vatnajökull, began surging about 2200 cal a BP (before 1950 AD). Approximately 1700 cal a BP, the glacier started to surge at a uniform 34‐ to 38‐year periodicity that prevailed until the coldest part of the Little Ice Age when the periodicity almost halved to 21–23 years. Since the late 1800 s the surge periodicity of Eyjabakkajökull has returned to a longer period of 35–40 years. We suggest that surge periodicities of Eyjabakkajökull are forced by climatically driven mass balance changes, which may be a common forcing factor for similar surge‐type outlet glaciers. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献