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排序方式: 共有457条查询结果,搜索用时 15 毫秒
21.
This study focuses on the statistical characterization of ice conditions (extent, sea ice occurrence probability (SIOP), and length of ice season) in the Gulf of Riga, Baltic Sea, using remote-sensing data. The optical remote-sensing data with 250 m resolution acquired by a Moderate Resolution Imaging Spectroradiometer (MODIS) during 2002–2011 were used for statistical characterization of sea ice. A method based on bimodal histogram analysis of remote-sensing reflectance data was developed to discriminate ice from water. In general, ice extent information obtained from MODIS data agrees with the official ice chart data (synthetic aperture radar (SAR) and in situ measurements) and multi-sensor product containing data from microwave and infrared instruments (R2 >0.83). However, in case of severe winters and extremely mild winters there are differences in the dates when maximum ice extent is registered. MODIS data can be used for detailed analysis of ice extent in specific basins of Baltic Sea. Depending on the year, the ice season length in the Gulf of Riga ranged from 68 to 146 days, and the maximum ice extent varied greatly from 329 to 15,350 km2. SIOP and number of ice days increased significantly in areas where the depth is less than 15 m. Based on negative-degree days and ice cover characteristics (SIOP and ice season length), three winter scenarios were defined: severe (2003, 2006, 2010, and 2011), medium (2004 and 2005), and mild (2007, 2008, and 2009). 相似文献
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A game theoretic model of six kinds of players is analyzed, i.e. countries, central banks, banks, firms, households, and financial inter-governmental organizations. Each player has a strategy set, with strategies such as setting interest rates, lending, borrowing, producing, consuming, investing, importing, exporting, defaulting, and penalizing default. Markets for goods, debt, and capital are modeled endogenously. This conceptualization of strategic opportunities for as many as six types of players is richer than anything that has been attempted earlier. 2005–2011 empirical data for Greece is used to analyze how utility is impacted by public consumption and lump sum transfers, and negative productivity shocks, and to analyze equilibrium over several time periods with and without the possibility of default. 2007–2008 empirical data for Greece and Germany is used to determine how the two countries’ utilities depend on Greece’s public 2007 consumption, with and without negative productivity shocks. Greece’s high debt burden is shown to make default optimal when productivity shocks are large and the default penalty is small. We find that Germany has limited ability, through its available strategies, to prevent a Greek default, and may need to resort to unconventional tools such as debt forgiveness and changing the default penalty. 相似文献
24.
Kjell Hausken 《Information Systems Frontiers》2014,16(2):329-336
This paper endogenizes the value of an information set which has to be produced and protected. The profit is inverse U shaped in security investment and production effort. The breach probability is commonly assumed to decrease convexly in security investment, which means that modest security investment is sufficient to deter most perpetrators. We allow the breach probability to be not only convex, but concave, which means that substantial security investment is needed to deter most perpetrators. Convexity versus concavity depends on the security environment, perpetrators, technology, and law enforcement. A firm strikes a balance between producing and protecting an information set dependent on seven model parameters for production, protection, convexity, concavity, vulnerability, and resource strength. 相似文献
25.
Climate variations affect timber structures by causing moisture induced stresses which may lead to cracks in timber members. The paper presents experimentally determined moisture induced stresses that arise perpendicular to the grain of glulam specimens during exposure to 1-dimensional drying and wetting. Although to a certain extent reduced by creep effects, the determined tensile stresses can significantly exceed the characteristic tensile strength of glulam. Additional measurements of moduli of elasticity (E) and hygroexpansion coefficients (α) revealed that these parameters are strongly affected by the geometrical configuration (pith locations) of the specimens. By means of all the parameters determined here, it can be avoided that parameters have to be selected from different literature sources, which introduces large uncertainties into the numerical simulations. 相似文献
26.
Reactions between Strontium-Substituted Lanthanum Manganite and Yttria-Stabilized Zirconia: II, Diffusion Couples 总被引:1,自引:0,他引:1
Kjersti Kleveland Mari-Ann Einarsrud Christian R. Schmidt Senem Shamsili Sonia Faaland Kjell Wiik Tor Grande 《Journal of the American Ceramic Society》1999,82(3):729-734
Formation of secondary phases and diffusion of cations in diffusion couples of yttria-stabilized zirconia and lanthanum manganite substituted with 0 to 60 mol% strontium have been studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Only the primary phases were observed after 120 h at 1200°C, while formation of secondary phases was identified already after 1 h heat treatment at 1350°C. The phase composition of the reaction layer altered from La2 Zr2 O7 to SrZrO3 at increasing Sr content in La x Sr1- x MnO3 . The thickness of the reaction layer was increasing with heat treatment time. In diffusion couples of La0.4 Sr0.6 MnO3 formation of manganese oxide was observed in the perovskite layer after 1 h heat treatment at 1350°C, while isolated grains of SrZrO3 relatively deep inside the zirconia were observed after longer heat treatment time. Diffusion of Mn into zirconia was observed preferenced along grain boundaries in the early stage of the interface reaction. 相似文献
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28.
Ove Wolfgang Arne Haugstad Birger Mo Anders Gjelsvik Ivar Wangensteen Gerard Doorman 《Energy》2009,34(10):1642
The Norwegian Energy Act that came into force in 1991 deregulated the electricity market and removed the former obligation power companies had to supply electricity to the geographical area they were responsible for. Hence producers can supply electricity on the basis of profitability. In 2007 the Energy Act was evaluated by the Government. As a part of this, a study concerning hydro reservoir handling before and after deregulation was carried out by SINTEF. Public statistics show that average hydro reservoir levels measured in per cent of reservoir capacity have been reduced after 1990. We have used the power-market model EMPS1 (EFI's Multi-area Power-market Simulator) to analyze if this reduction can be explained by natural variation in climatic variables or by structural changes that have occurred after 1990. Simulation results show that the reduced reservoir levels cannot be explained by natural variation in climatic variables. Structural changes such as increased transmission capacities can, however, explain some of the reduction. Our study does not indicate that the present reservoir handling gives reservoir levels that are too low. In this paper we also describe the stochastic dynamic optimization problem for long-term hydropower scheduling, and we explain how this problem actually is solved by the EMPS model. 相似文献
29.
Bjaerum S Torp H Kristoffersen K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(6):693-704
The quality of ultrasound color flow images is highly dependent on sufficient attenuation of the clutter signals originating from stationary and slowly moving tissue. Without sufficient clutter rejection, the detection of low velocity blood flow will be poor, and the velocity estimates will have a large bias. In some situations, e.g., when imaging the coronary arteries or when the operator moves the probe in search for small vessels, there is considerable movement of tissue. It has been suggested that clutter rejection can be improved by mixing down the signal with an estimate of the mean frequency prior to high pass filtering. In this paper, we compare this algorithm with several other adaptive clutter filtering algorithms using both experimental data and simulations. We found that realistic accelerations of the tissue have a large effect on the clutter rejection. The best results were obtained by mixing down the signal with non-constant phase increments estimated from the signal. This adapted the filter to a possibly accelerated tissue motion and produced a significant improvement in clutter rejection 相似文献
30.
A study of subthreshold leakage current in n-channel transistors on low threshold voltage CMOS circuits has been made. Redistribution of impurities at the silicon surface during thermal oxidation is shown to be the main cause of excess subthreshold leakage current. Processing techniques to minimize this leakage have been developed. 相似文献