Mobile Content Distribution with Vehicular Cloud in Urban VANETs

Plenty of multimedia contents such as traffic images, surveillance video, music and movie will flood into vehicular ad hoc networks. However, content distribution over VANETs is not a easy task, due to the high mobility of vehicles and intermittent connectivity. Infrastructure-based scheme can relieve the problem, but with a large amount of investment. In this paper, we propose a mobile content distribution scheme based on roadside parking cloud(RPC), which is formed by the parked car on the roadside, and mobile cloud(MC), which is formed by moving cars on the road. According to a trip history model, a mobile car can estimate its following trajectory. When it wants to download the content, gateway node of the RPC will work out a downloading schedule, which tells it how much chunks it can download from which RPCs. Moreover, the helper of the mobile car in mobile cloud would deliver specified chunks to it when there is lack of RPC in the following trip. Simulation results show that cloud-based scheme performs better than inter-vehicle communication approach and cluster-based scheme.

Study on the Practical and Ideal Mature Age of Pinus densiflora

This study was conducted on the analytic tree and got the fitting empirical equation of tree growth, in which the tree growth rate was used as the variable and time as the independent variable. The arithmetical operation to the function got the mature age of tree growth, and the practical and ideal mature ages of Pinus densiflora were 58 and 123.5 a, respectively. In addition, the application research direction and matters needing attention were proposed.

Carbon fluxes and soil carbon dynamics along a gradient of biogeomorphic succession in alpine wetlands of Tibetan Plateau

Hydrological changes under climate warming drive the biogeomorphic succession of wetlands and may trigger substantial carbon loss from the carbon-rich ecosystems.Although many studies have explored the responses of wetland carbon emissions to short-term hydrological change,it remains poorly understood how the carbon cycle evolves with hydrology-driven wetland succession.Here,we used a space-for-time approach across hydrological gradients on the Tibetan Plateau to examine the dynamics of ecosystem carbon fluxes(carbon dioxide(CO_(2))and methane(CH4))and soil organic carbon pools during alpine wetland succession.We found that the succession from mesic meadow to fen changed the seasonality of both CO_(2) and CH4 fluxes,which was related to the shift in plant community composition,enhanced regulation of soil hydrology and increasing contribution of spring-thaw emission.The paludification caused a switch from net uptake of gaseous carbon to net release on an annual timescale but produced a large accumulation of soil organic carbon.We attempted to attribute the paradox between evidence from the carbon fluxes and pools to the lateral carbon input and the systematic changes of historical climate,given that the wetlands are spatially low-lying with strong temporal climate-carbon cycle interactions.These findings demonstrate a systematic change in the carbon cycle with succession and suggest that biogeomorphic succession and lateral carbon flows are both important for understanding the long-term dynamics of wetland carbon footprints.

Terrestrial carbon sinks in China and around the world and their contribution to carbon neutrality

Enhancing the terrestrial ecosystem carbon sink(referred to as terrestrial C sink) is an important way to slow down the continuous increase in atmospheric carbon dioxide(CO_(2)) concentration and to achieve carbon neutrality target.To better understand the characteristics of terrestrial C sinks and their contribution to carbon neutrality,this review summarizes major progress in terrestrial C budget researches during the past decades,clarifies spatial patterns and drivers of terrestrial C sources and sinks in China and around the world,and examines the role of terrestrial C sinks in achieving carbon neutrality target.According to recent studies,the global terrestrial C sink has been increasing from a source of (-0.2±0.9) Pg C yr^(-1)(1 Pg=1015g)in the 1960s to a sink of (1.9±1.1) Pg C yr^(-1) in the 2010s.By synthesizing the published data,we estimate terrestrial C sink of 0.20–0.25 Pg C yr^(-1) in China during the past decades,and predict it to be 0.15–0.52 Pg C yr^(-1) by 2060.The terrestrial C sinks are mainly located in the mid-and high latitudes of the Northern Hemisphere,while tropical regions act as a weak C sink or source.The C balance differs much among ecosystem types:forest is the major C sink;shrubland,wetland and farmland soil act as C sinks;and whether the grassland functions as C sink or source remains unclear.Desert might be a C sink,but the magnitude and the associated mechanisms are still controversial.Elevated atmospheric CO_(2) concentration,nitrogen deposition,climate change,and land cover change are the main drivers of terrestrial C sinks,while other factors such as fires and aerosols would also affect ecosystem C balance.The driving factors of terrestrial C sink differ among regions.Elevated CO_(2) concentration and climate change are major drivers of the C sinks in North America and Europe,while afforestation and ecological restoration are additionally important forcing factors of terrestrial C sinks in China.For future studies,we recommend the necessity for intensive and long-term ecosystem C monitoring over broad geographic scale to improve terrestrial biosphere models for accurately evaluating terrestrial C budget and its dynamics under various climate change and policy scenarios.

Mapping the vertical distribution of maize roots in China in relation to climate and soil texture

Aims Optimizing water and fertilizer management for crops requires an understanding of root distribution.Maize(Zea mays L.)is currently the most widely planted cereal crop in China,yet the vertical dis-tribution of maize roots across different regions remains unknown.The aims of this work were(i)to quantify the effects of climate and soil texture on the vertical distribution of maize roots,and(ii)to show the depth distribution of root biomass in China.Methods We used data of maize root biomass from 11 Chinese ecological stations with discontinuous observations from 2004 to 2014 to fit the regression coefficientβfor an asymptotic equation Y=1-βd,where d is the soil depth and Y is the proportion of root biomass from the surface to depth d.A statistical model was then developed to quantify the effects of climate and soil texture on the fittedβval-ues.Using the statistical model,we map the depth distribution of maize root biomass in China.Important Findings Maize root biomass in the 0-100 cm soil depth varied by an order of magnitude at different stations,from 64 to 268 g m−2.Maize planted in sandy soils and/or maize with high accumu-lated temperature for development had higher root biomass and deeper rooting systems.The fittedβvalues ranged from 0.785 to 0.977,which can be modeled by an integration of the accu-mulated temperature during the maize growing period and the soil clay and sand fractions(R2=0.66,n=50,P<0.001).Up to 82%of maize planting regions in China showed shallower rooting systems where more than 90%and 95%of the root bio-mass occurred in the top 20 and 30 cm soil layers,respectively.Deeper rooting systems occurred in some temperate arid and temperate semi-arid regions,with less than 80%of the root bio-mass in the top 20 cm soil.Our findings highlighted the vertical distribution of maize roots,and underlined the spatial variability in the vertical distribution of roots across China’s planting areas of maize.