In order to have a comprehensive eco-efficiency measure which can incorporate productivity, resource efficiency, environmental efficiency, and inter-temporal comparability and circularity, the paper ...proposes an extended data envelopment analysis model, named GB-US-SBM model, which combines global benchmark technology, undesirable output, super efficiency and slacks-based measure. Using the GB-US-SBM model, this paper investigates the dynamics of regional eco-efficiency in China from 2000 to 2010. The empirical results show that the movement of average eco-efficiency of China presents a “V” shape from 2000 to 2010 with the trough occurred in 2005, but there are big differences of eco-efficiency among the regions. For the growth of eco-efficiency, technological progress contributes 56.87%, 58.21%, 18.27%, 62.19%; scale efficiency contributes 40.01%, 61.14%, 167.43%, 39.12%; efficiency change contributes 3.82%, −19.99%, −63.40%, −2.16% to the eastern, middle, western and northeastern regions of China respectively. These imply that there is a big space for western region to enhance its technological progress, and huge space for the whole country to promote its management ability.
Gas drilling technologies play an increasingly important role in oil and gas exploitation. The modern gas drilling method minimizes reservoir damage and increases the efficiency of oil and gas ...exploration. The practical use and the development of the gas drilling technology are limited by the ineffectiveness of migration and control of the cuttings bed, which is unavoidable in horizontal sections during gas drilling. In this paper, the author applies the chemical initiation theory to study the initiation of the cuttings bed migration in a horizontal well in the process of gas drilling. Then, the author deducts the formula to calculate the cuttings bed initial velocity by considering characteristics of the cuttings in a horizontal well during gas drilling. The calculation results show that the initial velocity gradually increases with an increase in the size of cuttings, decrease in the cuttings sphericity, and increase in the degree of exposure in the cuttings window. The results are coherent with the field engineering data. The study can also provide a useful reference for the cuttings bed control in gas drilling of horizontal wells.
•This paper presents a mixed integer linear programming (MILP) model to optimize vehicle trajectories and traffic signals in a unified framework at isolated signalized intersections in a CAV ...environment.•Phase sequences, green start and duration of each phase, and cycle lengths are optimized together with vehicle lane-changing behaviors and vehicle arrival times for delay minimization.•Vehicle trajectories are determined by optimal control models and car-following models on the basis of optimized arrival times with the objective to minimize fuel consumption and emission.•Simulation results validate the advantages of the proposed control method over vehicle actuated control in terms of intersection capacity, vehicle delays, and CO2 emissions.
Existing traffic signal control systems only allocate green time to different phases to avoid conflicting vehicle movements. With advances in connected and automated vehicle (CAV) technologies, CAV trajectories not only provide more information than existing infrastructure-based detection systems, but also can be controlled to further improve mobility and sustainability. This paper presents a mixed integer linear programming (MILP) model to optimize vehicle trajectories and traffic signals in a unified framework at isolated signalized intersections in a CAV environment. A new planning horizon strategy is applied to conduct the optimization. All vehicle movements such as left-turning, right-turning and through are considered. Phase sequences, green start and duration of each phase, and cycle lengths are optimized together with vehicle lane-changing behaviors and vehicle arrival times for delay minimization. Vehicles are split into platoons and are guaranteed to pass through the intersection at desired speeds and avoid stops at stop bars. Exact vehicle trajectories are determined based on optimized vehicle arrival times. For the trajectory planning of platoon leading vehicles, an optimal control model is implemented to minimize fuel consumption/emission. For following vehicles in a platoon, Newell's car-following model is applied. Simulation results validate the advantages of the proposed control method over vehicle-actuated control in terms of intersection capacity, vehicle delays, and CO2 emissions. A sensitivity analysis is conducted to show the potential benefits of a short minimum green duration as well as the impacts of no-changing zones on the optimality of the proposed model.
The North China Plain (NCP) is the most important agricultural production area in China. Crop production in the NCP is sensitive to changes in both climate and management practices. While previous ...studies showed a negative impact of climatic change on crop yield since 1980s, the confounding effects of climatic and agronomic factors have not been separately investigated. This paper used 25 years of crop data from three locations (Nanyang, Zhengzhou and Luancheng) across the NCP, together with daily weather data and crop modeling, to analyse the contribution of changes in climatic and agronomic factors to changes in grain yields of wheat and maize. The results showed that the changes in climate were not uniform across the NCP and during different crop growth stages. Warming mainly occurred during the vegetative (preflowering) growth stage of wheat and maize, while there was a cooling trend or no significant change in temperatures during the postflowering stage of wheat (spring) or maize (autumn). If varietal effects were excluded, warming during vegetative stages would lead to a reduction in the length of the growing period for both crops, generally leading to a negative impact on crop production. However, autonomous adoption of new crop varieties in the NCP was able to compensate the negative impact of climatic change. For both wheat and maize, the varietal changes helped stabilize the length of preflowering period against the shortening effect of warming and, together with the slightly reduced temperature in the postflowering period, extend the length of the grain-filling period. The combined effect led to increased wheat yield at Zhengzhou and Luancheng; increased maize yield at Nanyang and Luancheng; stabilized wheat yield at Nanyang, and a slight reduction in maize yield at Zhengzhou, compared with the yield change caused entirely by climatic change.
In this paper, by taking full consideration of distributed delay, demographics and contact heterogeneity of the individuals, we present a detailed analytical study of the Susceptible-Infected-Removed ...(SIR) epidemic model on complex population networks. The basic reproduction number Formula: see text of the model is dominated by the topology of the underlying network, the properties of individuals which include birth rate, death rate, removed rate and infected rate, and continuously distributed time delay. By constructing suitable Lyapunov functional and employing Kirchhoff's matrix tree theorem, we investigate the globally asymptotical stability of the disease-free and endemic equilibrium points. Specifically, the system shows threshold behaviors: if Formula: see text, then the disease-free equilibrium is globally asymptotically stable, otherwise the endemic equilibrium is globally asymptotically stable. Furthermore, the obtained results show that SIR models with different types of delays have different converge time in the process of contagion: if Formula: see text, then the system with distributed time delay stabilizes fastest; while Formula: see text, the system with distributed time delay converges most slowly. The validness and effectiveness of these results are demonstrated through numerical simulations.
An extensive dataset on rice phenology in China, including 202 series broadly covering the past three decades (1980s–2000s), was compiled. From these data, we estimated the responses of growth ...duration length to temperature using a regression model based on the data with and without detrending. Regression coefficients derived from the detrended data reflect only the temperature effect, whereas those derived from data without detrending represent a combined effect of temperature and confounding cultivar shifts. Results indicate that the regression coefficients calculated from the data with and without detrending show an average shortening of the growth duration of 4.1–4.4 days for each additional increase in temperature over the full growth cycle. Using the detrended data, 95.0% of the data series exhibited a negative correlation between the growth duration length and temperature; this correlation was significant in 61.9% of all of the data series. We then compared the difference between the two regression coefficients calculated from data with and without detrending and found a significantly greater temperature sensitivity using the data without detrending (−2.9 days °C−1) than that derived from the detrended data (−2.0 days °C−1) in the period of emergence to heading for the late rice, producing a negative difference in temperature sensitivity (−0.9 days °C−1). This implies that short‐duration cultivars were planted with increase in temperature and exacerbated the undesired phenological change. In contrast, positive differences were detected for the single (0.6 days °C−1) and early rice (0.5 days °C−1) over the full growth cycle, which might indicate that long‐duration cultivars were favoured with climate warming, but these differences were insignificant. In summary, our results suggest that a major, temperature induced change in the rice growth duration is underway in China and that using a short‐duration cultivar has been accelerating the process for late rice.
Northeast China (NEC) accounts for about 30% of the nation's maize production in China. In the past three decades, maize yields in NEC have increased under changes in climate, cultivar selection and ...crop management. It is important to investigate the contribution of these changing factors to the historical yield increases to improve our understanding of how we can ensure increased yields in the future. In this study, we use phenology observations at six sites from 1981 to 2007 to detect trends in sowing dates and length of maize growing period, and then combine these observations with in situ temperature data to determine the trends of thermal time in the maize growing period, as a measure of changes in maize cultivars. The area in the vicinity of these six sites accounts for 30% of NEC's total maize production. The agricultural production systems simulator, APSIM‐Maize model, was used to separate the impacts of changes in climate, sowing dates and thermal time requirements on maize phenology and yields. In NEC, sowing dates trended earlier in four of six sites and maturity dates trended later by 4–21 days. Therefore, the period from sowing to maturity ranged from 2 to 38 days longer in 2007 than it was in 1981. Our results indicate that climate trends alone would have led to a negative impact on maize. However, results from the adaptation assessments indicate that earlier sowing dates increased yields by up to 4%, and adoption of longer season cultivars caused a substantial increase in yield ranging from 13% to 38% over the past 27 years. Therefore, earlier sowing dates and introduction of cultivars with higher thermal time requirements in NEC have overcome the negative effects of climate change and turned what would have otherwise been a loss into a significant increase in maize yield.
In the North China Plain, the grain yield of irrigated wheat-maize cropping system has been steadily increasing in the past decades under a significant warming climate. This paper combined regional ...and field data with modeling to analyze the changes in the climate in the last 40 years, and to investigate the influence of changes in crop varieties and management options to crop yield. In particular, we examined the impact of a planned adaptation strategy to climate change -“Double-Delay” technology, i.e., delay both the sowing time of wheat and the harvesting time of maize, on both wheat and maize yield. The results show that improved crop varieties and management options not only compensated some negative impact of reduced crop growth period on crop yield due to the increase in temperature, they have contributed significantly to crop yield increase. The increase in temperature before over-wintering stage enabled late sowing of winter wheat and late harvesting of maize, leading to overall 4–6% increase in total grain yield of the wheat-maize system. Increased use of farming machines and minimum tillage technology also shortened the time for field preparation from harvest time of summer maize to sowing time of winter wheat, which facilitated the later harvest of summer maize.
•The stock return of oil sales sector responds to all shocks most significantly.•Before and after 2012, the impacts of oil price shocks change structurally.•The stock returns are mostly affected by ...oil supply and precautionary demand shocks.•The contribution of China’s oil stock returns to oil price shocks is increasing.
Based on a Structural Vector Autoregression (SVAR) model, this paper decomposes oil price changes into four components: oil supply shocks, global demand shocks, domestic demand shocks and precautionary demand shocks. Then, this paper investigates the impacts of these oil price shocks on the stock returns of China’s listed companies in the oil industrial chain using data from 2009 to 2014. The empirical results show that the returns of the listed companies in the whole oil industrial chain benefit from appreciation in the oil price, the impacts of oil supply shocks and precautionary demand shocks are the most significant, and there is a structural change in the impacts of oil price shocks in 2012. Among the four oil price shocks, the impacts of oil supply shocks and precautionary demand shocks are the most significant. Moreover, there is a gradual increase in the aggregate contributions of oil price shocks to the changes in stock returns. A robustness check with different global crude oil prices and a different industry classification standard confirms that the above empirical results are robust. The empirical results of the paper imply that stock investors, oil-related companies and the government need pay close attention to sudden changes that may affect current and future oil availability and pay greater attention to the stocks at the two ends of the oil industrial chain.
The objective of the present paper was to review the consumption status of meat and dairy products among Chinese residents. The research topics included production, consumption and health ...implications of dairy and meat, and the data sources included reports of national surveys, research papers and data from the National Bureau of Statistics of China. The average intake of meat, especially pork, has continued to increase in China. Pork intake increased from 37·1 g/d in 1992 to 64·3 g/d in 2012. There was a much higher margin in rural regions; pork intake of rural residents increased from 25·0 g/d in 1992 to 59·9 g/d in 2012, which resulted in a narrowed gap between urban and rural areas. Although the average intake of dairy products increased from 14·9 g/d in 1992 to 24·7 g/d in 2012, the overall level was still lower. There was a significant difference of dairy consumption between urban and rural residents. The gap of per capita consumption of milk between urban and rural households was 3·5 kg/year in 1990, reached the maximum of 16·9 kg/year in 2003, then decreased to 8·7 kg/year in 2012. In conclusion, the finding of this review sheds light on some problems with food consumption patterns in China. Effective strategies need to be adopted in order to change the consumption patterns. The consumption of milk and replacing pork with poultry or fish or other health foods should be encouraged.
PDF
