Lifetime Data Analysis - Assessing the potential of surrogate markers and surrogate outcomes for replacing a long term outcome is an active area of research. The interest in this topic is partly... 相似文献
The increasing expansion of the urban environment has been considered one of the causes of biodiversity loss. Due to the decrease of the quantity and quality of habitats, this process causes the restriction of organisms to sometimes-specific microhabitats. The patterns of variation of the biodiversity along the environmental gradients, however, are still poorly understood. This study evaluated how urban gradients affect the diversity, specific composition and frequency of guild of the community of butterflies. Butterflies were collected in three transects continuously traversing the urban, rural and preserved habitats using baited traps and by active sampling. We found that the urban gradient acts as an environmental filter in the butterfly communities, reducing the richness and frequency of guilds of frugivorous butterflies, structuring the community through turnover, but without effects in the abundance. This study shows the importance of the urban gradients approach in the butterfly community and its applicability in the management of urban areas in order to include native vegetation along the gradients, aiming at increasing environmental heterogeneity, to preserve butterflies and maintain the ecosystem services and network interactions in altered landscapes.
The objective of the Interconnecting Highways problem is to construct roads of minimum total length to interconnect n given highways under the constraint that the roads can intersect each highway only at one point in a designated interval which is a line segment. We present a polynomial time approximation scheme for this problem by applying Arora's framework (Arora, 1998; also available from http:www.cs.princeton.edu/~arora). For every fixed c > 1 and given any n line segments in the plane, a randomized version of the scheme finds a
-approximation to the optimal cost in O(nO(c)log(n) time. 相似文献