Comment on "Lévy walks evolve through interaction between movement and environmental complexity"

de Jager et al. (Reports, 24 June 2011, p. 1551) concluded that mussels Lévy walk. We confronted a larger model set with these data and found that mussels do not Lévy walk: Their movement is best described by a composite Brownian walk. This shows how model selection based on an impoverished set of candidate models can lead to incorrect inferences.     

谱负Lévy过程位势测度的推广

位势测度在占位时的求解过程中是一个重要的工具,对谱负Lévy过程的位势测度进行了推广.在目前已有位势测度结论的基础上运用维纳-霍夫分解方法,求出了谱负Lévy过程X在0＜a＜b时,形式为Ex∫τ+bτ+ae－qt1{Xt∈dy,t＜τ－0}dt的位势测度.其表达式用谱负Lévy过程的尺度函数和拉普拉斯的逆函数表示.这些表达式可以应用到一些Lévy风险过程相关的破产时间问题的研究中.     

广义Lévy单的Markov性的注记

本文用较简单的方法和简短的篇幅证明了文献［１］及更一般形式的广义　　单及相关的某些其它过程具有＊－Ｍａｒｋｏｖ性．     

Characterizing historical(1992–2010) transitions between grassland and cropland in mainland France through mining land-cover survey data

Grassland, as one of the largest ecosystems on the earth, supports various goods and services to humanity.Historically, humans have increased agricultural output primarily by cropland expansion and agricultural intensification.The cropland area was primarily gained at the expense of grassland and forests.Apart from grassland conversion, increasing consumption of calorie- and meat-intensive diets drives the intensification of livestock systems, which is shifting steadily from grazing to feeding with crops.To cope with the environmental degradation due to agriculture, various forms of ‘green payment' were implemented to promote the adoption of sustainable farming practices over the last two decades in the European Union.The aim of this study is to monitor the recent transitions(1992–2010) between grassland and cropland during two Common Agricultural Policy(CAP) reforms at the French mainland scale.We proposed an innovative approach to link grassland conversion to agricultural commodities and farming systems practices.We first assessed the grassland-to-cropland conversion and further investigated the crop sequence patterns that were observed to be dominant after the conversion through mining land-cover survey data Teruti and Teruti-Lucas.We found the trends of the transitions between grassland and cropland over the two time intervals: The loss of grassland(1992–2003) and restoration or re-expansion of grassland(2006–2010) in mainland France.Our finding on the crop sequence patterns after the grassland conversion reveals two notable evolutions of agricultural production systems.These evolutions were related to the increase in the proportion of cropland in the total agricultural land use.One evolution was most likely influenced by the demand for fodder: The conversion from grazing livestock to feeding livestock.Another evolution was the conversion from livestock production to field crop production.Our results indicate that the intensification of livestock farming systems continued over the last two decades in France.We conclude that, the approach developed in this study can be considered as a generic method for monitoring the transitions between grassland and cropland and further identifying the crop sequence patterns after the grassland conversion from time-series land cover data.