The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have ...The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have been proved to be troublesome and less intuitive. Analytical solutions based on loss-less tube model and average friction tube model are found respectively by using fluid net theory, and they fit the experimental results well. The research work shows that： Fluid net theory can be used to solve the analytical solution of filling and exhausting processes of pneumatic system, and the result of loss-less tube model is close to that of average friction model, so loss-less tube model is recommended since it is simpler, and the difference between filling time and exhausting time is determined by initial and final pressures, the volume of container and the section area of tube, and has nothing to do with the length of the tube.展开更多
The problem with fixed valve timing that the valve train is set by the automaker for peak efficiency running at a specific point in the engine’s operating range. When the vehicle is moving slower or faster than this ...The problem with fixed valve timing that the valve train is set by the automaker for peak efficiency running at a specific point in the engine’s operating range. When the vehicle is moving slower or faster than this ideal operating point the engine’s combustion cycle fails to properly burn the air/fuel mixture leading to considerably compromised engine performance and wastes fuel. Variable Valve Timing (VVT) is a solution developed to overcome this engine deficiency, dynamically altering the valve's opening and closing for optimal performance at any speed. The intension in this work is to contribute towards pursuing the development of variable valve timing (VVT) for improving the engine performance. This investigation covers the effect of exhaust valve opening (EVO), and closing (EVC) angle on engine performance and emissions. The aim is to optimize engine power and brake specific fuel consumption (BSFC) where the effect of engine speed has also been considered. Power, BMEP, BSFC, NO, and CO were calculated and presented to show the effect of varying valve timing on them for all the valve timing cases. The calculations of engine performance were carried out using the simulation and analysis engineering software: LOTUS”, and engine emissions were calculated using “ZINOX” program. Sensitivity analysis shows that the reduction of 10% of (EVO) angle gave a reduction of around 2.5% in power and volumetric efficiency, also a slight increase in nitrogen oxide (NO) and carbon monoxide (CO), while a 10% decrease in (EVC) causes around 1% improvement in Power. The effects of different (VVT) from the simulations are analyzed and compared with those in the reviewed literature.展开更多
There are few papers in the literature focusing on the issue of the optimal depletion of exhaustible resources in the framework of variable time preference. This paper attempts to analyze the pure consumption of exhau...There are few papers in the literature focusing on the issue of the optimal depletion of exhaustible resources in the framework of variable time preference. This paper attempts to analyze the pure consumption of exhaustible resource under hyperbolic time preference, and to discuss the optimal depletion rate and the effect of the protection of the exhaustible resource under different commitment abilities. The results of model show that the case of the hyperbolic discount with the full commitment of the government is equivalent to the case of constant discount of the social planner problem. In that case, the optimal depletion rate and the initial consumption of exhaustible resource are the slowest. On the contrary, they are the highest and the myopic behaviors lead to excessive consumption of exhaustible resources inevitably without commitment. Otherwise, in the case of partial commitment, the results are between the cases of full commitment and of no commitment. Therefore, with the hyperbolic time preference, the optimal depletion rate of resource depends on the commitment ability. Higher commitment ability leads to lower effective rate of time preference, and consequently, lower depletion rate and lower initial depletion value. The improvement of commitment ability can decrease the impatience and myopia behaviors, and contribute to the protection of the exhaustible resources.展开更多
目的探讨经脐单孔腹腔镜大子宫切除术的临床可行性、安全性及优势。方法选取行腹腔镜大子宫切除术的患者82例为研究对象。其中,行经脐单孔腹腔镜手术患者41例为单孔组,行传统多孔腹腔镜手术患者41例为多孔组。比较2组患者的手术时间、...目的探讨经脐单孔腹腔镜大子宫切除术的临床可行性、安全性及优势。方法选取行腹腔镜大子宫切除术的患者82例为研究对象。其中,行经脐单孔腹腔镜手术患者41例为单孔组,行传统多孔腹腔镜手术患者41例为多孔组。比较2组患者的手术时间、术中出血量、术后24 h视觉模拟评分(VAS)、术后排气时间、术后病率、术后住院时间、切口美容评分、术后第1天炎症指标、中性粒细胞与淋巴细胞比值(NLR)、并发症发生情况及术前和术后的血红蛋白差值。结果2组患者手术均顺利完成,无中转开腹,且未发生严重手术并发症,单孔组未添加辅助孔。单孔组术后排气时间短于多孔组,术后24 h VAS评分、术后第1天NLR低于多孔组,术后切口美容度评分高于多孔组,差异有统计学意义(P<0.05)。结论在严格把握手术适应证的情况下,经脐单孔腹腔镜大子宫切除术安全性较好,可行性较高,其具有术后排气快、术后疼痛轻、免疫抑制轻以及切口美观等优势。展开更多
基金This project is supported by National Natural Science Foundation of China(No.50575209).
文摘The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have been proved to be troublesome and less intuitive. Analytical solutions based on loss-less tube model and average friction tube model are found respectively by using fluid net theory, and they fit the experimental results well. The research work shows that： Fluid net theory can be used to solve the analytical solution of filling and exhausting processes of pneumatic system, and the result of loss-less tube model is close to that of average friction model, so loss-less tube model is recommended since it is simpler, and the difference between filling time and exhausting time is determined by initial and final pressures, the volume of container and the section area of tube, and has nothing to do with the length of the tube.
文摘The problem with fixed valve timing that the valve train is set by the automaker for peak efficiency running at a specific point in the engine’s operating range. When the vehicle is moving slower or faster than this ideal operating point the engine’s combustion cycle fails to properly burn the air/fuel mixture leading to considerably compromised engine performance and wastes fuel. Variable Valve Timing (VVT) is a solution developed to overcome this engine deficiency, dynamically altering the valve's opening and closing for optimal performance at any speed. The intension in this work is to contribute towards pursuing the development of variable valve timing (VVT) for improving the engine performance. This investigation covers the effect of exhaust valve opening (EVO), and closing (EVC) angle on engine performance and emissions. The aim is to optimize engine power and brake specific fuel consumption (BSFC) where the effect of engine speed has also been considered. Power, BMEP, BSFC, NO, and CO were calculated and presented to show the effect of varying valve timing on them for all the valve timing cases. The calculations of engine performance were carried out using the simulation and analysis engineering software: LOTUS”, and engine emissions were calculated using “ZINOX” program. Sensitivity analysis shows that the reduction of 10% of (EVO) angle gave a reduction of around 2.5% in power and volumetric efficiency, also a slight increase in nitrogen oxide (NO) and carbon monoxide (CO), while a 10% decrease in (EVC) causes around 1% improvement in Power. The effects of different (VVT) from the simulations are analyzed and compared with those in the reviewed literature.
基金Funding of Humanities and Social Science Fundation of Education Ministry (Grant No.11YJC790308)
文摘There are few papers in the literature focusing on the issue of the optimal depletion of exhaustible resources in the framework of variable time preference. This paper attempts to analyze the pure consumption of exhaustible resource under hyperbolic time preference, and to discuss the optimal depletion rate and the effect of the protection of the exhaustible resource under different commitment abilities. The results of model show that the case of the hyperbolic discount with the full commitment of the government is equivalent to the case of constant discount of the social planner problem. In that case, the optimal depletion rate and the initial consumption of exhaustible resource are the slowest. On the contrary, they are the highest and the myopic behaviors lead to excessive consumption of exhaustible resources inevitably without commitment. Otherwise, in the case of partial commitment, the results are between the cases of full commitment and of no commitment. Therefore, with the hyperbolic time preference, the optimal depletion rate of resource depends on the commitment ability. Higher commitment ability leads to lower effective rate of time preference, and consequently, lower depletion rate and lower initial depletion value. The improvement of commitment ability can decrease the impatience and myopia behaviors, and contribute to the protection of the exhaustible resources.
文摘目的探讨经脐单孔腹腔镜大子宫切除术的临床可行性、安全性及优势。方法选取行腹腔镜大子宫切除术的患者82例为研究对象。其中,行经脐单孔腹腔镜手术患者41例为单孔组,行传统多孔腹腔镜手术患者41例为多孔组。比较2组患者的手术时间、术中出血量、术后24 h视觉模拟评分(VAS)、术后排气时间、术后病率、术后住院时间、切口美容评分、术后第1天炎症指标、中性粒细胞与淋巴细胞比值(NLR)、并发症发生情况及术前和术后的血红蛋白差值。结果2组患者手术均顺利完成,无中转开腹,且未发生严重手术并发症,单孔组未添加辅助孔。单孔组术后排气时间短于多孔组,术后24 h VAS评分、术后第1天NLR低于多孔组,术后切口美容度评分高于多孔组,差异有统计学意义(P<0.05)。结论在严格把握手术适应证的情况下,经脐单孔腹腔镜大子宫切除术安全性较好,可行性较高,其具有术后排气快、术后疼痛轻、免疫抑制轻以及切口美观等优势。
