Suchergebnisse

Electric vehicles (EVs) have the advantages of low pollution, low energy consumption, and high energy efficiency, so they are highly valued by governments, enterprises, and consumers. However, the promotion and use of electric vehicles is restricted to a certain extent because of their limited range. This paper selects electric vehicle intercity medium- and long-distance travel as the research object, and takes the classical flow-capturing location problem as the theoretical basis for the expressway network or national highway network. This paper also considers the driver's charging choice behavior and range anxiety, studies the electric vehicle charging station location problem, establishes the charging station location model, and uses the Tabu search algorithm to solve the problem. Finally, the effectiveness of the model and algorithm is verified by empirical analysis. The results show that the charging station location model considering the driver's charging choice behavior and range anxiety performs better.

Abstract
Background
Achieving nitrogen (N) and phosphorus (P) control in sediment remediation projects by adding natural materials is receiving increasing attention. In this study, different natural materials, including iron-rich clay minerals, calcite, kaoline, sugarcane bagasse and Phragmites detritus, were applied to test their effects on N and P in a mesocosm experiment.

Results
Iron-rich clay minerals and Phragmites detritus had obvious advantages for P control; they resulted in almost undetectable levels of soluble reactive phosphorus (SRP) in the water column throughout the experiment. This finding can be explained by their strong P adsorption ability. The high level of available organic carbon in the sediment and water column after sugarcane bagasse addition provided enough electron donors for denitrification and dissimilatory nitrate reduction to ammonium (DNRA), which caused nitrate (NO3−-N) deficiency and ammonium (NH4+-N) accumulation in the water column. Additionally, this resulted in anaerobic conditions, further fuelling the release of P from iron-bound P induced by anoxia. Thus, the amount of sugarcane bagasse applied should be considered carefully in order to balance denitrification and DNRA as well as P releases. Calcite and Phragmites detritus are recommended as remediation materials for N removal based on their significant promotion of denitrification and limitation of DNRA, which resulted in low NO3−-N and NH4+-N levels. These results can be explained by the shifts in the functional microbial community composition and abundance after the addition of natural materials.

Conclusions
Iron-rich clay minerals and Phragmites detritus are promising sediment remediation materials for P immobilization due to their strong P adsorption ability. Taken together, the selection of sediment remediation materials should consider the N and P coupling relationship, to prevent NO3−-N removal from causing P leaching or NH4+-N accumulation.

Context
Wild yak (Bos grunniens), Tibetan wild ass (Equus kiang, also known as kiang) and Tibetan antelope (Pantholops hodgsoni, also known as chiru) have been sympatric on the Tibetan Plateau for numerous generations. There is concern over potential dietary competition among them, particularly in winter when their forage resources are scarcer, but little is known about their dietary interactions.

Aim
We aimed to determine diet composition and dietary overlap of the three ungulate species, and to assess the extent of potential dietary competition among them in order to enhance our understanding of mechanisms underlying their co-existence. We predicted that the three species would widen their choice of forages in winter (December) compared with summer (June–July), and that there would be diet segregation among them, particularly in winter when food resources were scarcer.

Methods
We collected fresh faecal samples of the three species and reference forage samples from the field during our transect line surveys in the summers of 2012 and 2013, and winter of 2012 in Arjin Shan National Nature Reserve (ANNR) of Xinjiang Province, China. Slides of faecal samples were prepared for microhistological analysis, and plant fragments in faecal samples were identified under microscope. Relative percentage frequency of diet plant species, diet breadth and dietary overlap were calculated.

Key results
The three species consumed similar forage plants, but varied greatly in their percentage use of the available forages. Wild yak mainly fed on sedges in summer and graminoids in winter, supplemented with forbs. Kiang consumed mainly forbs in summer and browse in winter, and chiru mainly fed on graminoids and forbs in summer. Wild yak had the widest choice of forages, and kiang had the narrowest one in summer, but both wild yak and kiang became less selective in their food choice in winter, resulting in higher diet breadth. The dietary overlaps among them, as represented by Pianka's index, were generally low, ranging from 0.26 between chiru and kiang to 0.51 between wild yak and kiang. The dietary overlap between wild yak and kiang decreased from summer (0.51) to winter (0.35), suggesting an increased dietary divergence.

Key conclusion
Our study reveals that the three species are 'opportunistic feeders', able to cope with coarse forage resources. There is dietary segregation among them as indicated by low dietary overlap, suggesting risk of potential competition for diets. We suggest that competition may have shaped their dietary divergence, contributing to their co-existence in ANNR.

Implication
Although there is dietary segregation among the three species in ANNR, it is not possible to make definitive conclusions about interspecific competition from these results. Further studies are needed to investigate if there is spatial and habitat segregation among them, which may facilitate their dietary divergence and thus contribute further to their co-existence in ANNR. Continued efforts are also needed to monitor their population dynamics and status of forage resources in order to prevent overgrazing.