All the underground coal mines in China are gassy mines. The gas emission at coal face increasingly grows with the increase of working depth and coal output, for example, the gas emission at a full mechanized coal fac...All the underground coal mines in China are gassy mines. The gas emission at coal face increasingly grows with the increase of working depth and coal output, for example, the gas emission at a full mechanized coal face of mine No. 2 at Yongquan with a daily output of 2. 000t/d is up to 66-72m2/min. Special gas emission phenomena such as gas blowout, gas and coal outburst etc. have occurred at some faces, which threatens the safe production of face. obstructs the growth of productivity and limits the full play of mechanized equipment.In this paper, gas at face is divided, according to its origin, into three constituents, namely , coming from the coal wall, mined coal and goaf;and a formula for calculation is given. Also , the characteristics of the variation of gas emission at coal face, and the influence of mining sequence of a group of seams and supplied air quantity on the gas emission are discussed. Furthermore . based on the regularity of gas emission at coal face from the above three sources, and on the experiences of years, three principles on controlling gas emission at coal face are presented, that are managing the gas on classification basis, harnessing each source separately and comprehensive prevention and control. Finally, technical measures for prevention and treatment of the accumulation of gas in the upper corner of face, at the working place of coal-winning machine and in the bottom trough of conveyor are introduced.展开更多
A quantitative assessment method is proposed to sense the specific effects of atmospheric icing conditions on flight safety. A six degree-of-freedom computational flight dynamics model is used to study the effects of ...A quantitative assessment method is proposed to sense the specific effects of atmospheric icing conditions on flight safety. A six degree-of-freedom computational flight dynamics model is used to study the effects of ice accretion on aircraft dynamics, and a pilot model is also involved. In order to investigate icing severity under different icing conditions, support vector regression is applied in establishing relationship between aircraft icing parameter and weather conditions. Considering the characteristics of aircraft icing accidents, a risk probability assessment model optimized by the particle swarm method is developed to measure the safety level. In particular, angle of attack is chosen as a critical parameter in this method. Results presented in the paper for a series of simulation show that this method captures the basic effects of atmospheric icing conditions on flight safety, which may provide an important theoretical reference for icing accidents avoidance.展开更多
Water plays an important role in food production especially rice. Rice productivity depends greatly on sufficient water to meet evaporative demand and soil moisture. It is certain thalL rice, the most important crop o...Water plays an important role in food production especially rice. Rice productivity depends greatly on sufficient water to meet evaporative demand and soil moisture. It is certain thalL rice, the most important crop of Thailand and Vietnam, is vulnerable to climate change. This paper proposes an analysis on the impact of climate on rice water requirement and food security in Thailand and Vietnam. Water demand, yield and production of rice were computed under the changed surface air temperature for three time slices, namely 2020s, 2050s and 2080s. Food security was analyzed from rice supply （calculated milled-rice product, rice stock, and imports） and demand （domestic uses from population growth, exports to world market, domestic seed and other uses）. The result showed that, under the higher surface air temperature scenario, water requirement office in Thailand and Vietnam could increase by 1.8 times in the end of the 21 st century. Production of rice dropped by declined yield. Thailand and Vietnam which is the world largest rice exporter in last decades will face the rice shortage in 2080s and 2030s respectively.展开更多
文摘All the underground coal mines in China are gassy mines. The gas emission at coal face increasingly grows with the increase of working depth and coal output, for example, the gas emission at a full mechanized coal face of mine No. 2 at Yongquan with a daily output of 2. 000t/d is up to 66-72m2/min. Special gas emission phenomena such as gas blowout, gas and coal outburst etc. have occurred at some faces, which threatens the safe production of face. obstructs the growth of productivity and limits the full play of mechanized equipment.In this paper, gas at face is divided, according to its origin, into three constituents, namely , coming from the coal wall, mined coal and goaf;and a formula for calculation is given. Also , the characteristics of the variation of gas emission at coal face, and the influence of mining sequence of a group of seams and supplied air quantity on the gas emission are discussed. Furthermore . based on the regularity of gas emission at coal face from the above three sources, and on the experiences of years, three principles on controlling gas emission at coal face are presented, that are managing the gas on classification basis, harnessing each source separately and comprehensive prevention and control. Finally, technical measures for prevention and treatment of the accumulation of gas in the upper corner of face, at the working place of coal-winning machine and in the bottom trough of conveyor are introduced.
文摘A quantitative assessment method is proposed to sense the specific effects of atmospheric icing conditions on flight safety. A six degree-of-freedom computational flight dynamics model is used to study the effects of ice accretion on aircraft dynamics, and a pilot model is also involved. In order to investigate icing severity under different icing conditions, support vector regression is applied in establishing relationship between aircraft icing parameter and weather conditions. Considering the characteristics of aircraft icing accidents, a risk probability assessment model optimized by the particle swarm method is developed to measure the safety level. In particular, angle of attack is chosen as a critical parameter in this method. Results presented in the paper for a series of simulation show that this method captures the basic effects of atmospheric icing conditions on flight safety, which may provide an important theoretical reference for icing accidents avoidance.
文摘Water plays an important role in food production especially rice. Rice productivity depends greatly on sufficient water to meet evaporative demand and soil moisture. It is certain thalL rice, the most important crop of Thailand and Vietnam, is vulnerable to climate change. This paper proposes an analysis on the impact of climate on rice water requirement and food security in Thailand and Vietnam. Water demand, yield and production of rice were computed under the changed surface air temperature for three time slices, namely 2020s, 2050s and 2080s. Food security was analyzed from rice supply （calculated milled-rice product, rice stock, and imports） and demand （domestic uses from population growth, exports to world market, domestic seed and other uses）. The result showed that, under the higher surface air temperature scenario, water requirement office in Thailand and Vietnam could increase by 1.8 times in the end of the 21 st century. Production of rice dropped by declined yield. Thailand and Vietnam which is the world largest rice exporter in last decades will face the rice shortage in 2080s and 2030s respectively.
