The train plan of urban rail transit under multi-routing mode can be divided into three parts： train formation, train operation periods and corresponding train counts of each routing in each period. Based on the anal...The train plan of urban rail transit under multi-routing mode can be divided into three parts： train formation, train operation periods and corresponding train counts of each routing in each period. Based on the analysis of passen- ger＇s general travel expenses and operator＇s benefits, the constraints and objective functions are defined and the multiobjective optimization model for the train plan of urban rail transit is presented. Factors considered in the multi- objective optimization model include transport capacity, the requirements of traffic organization, corporation benefits, passenger demands, and passenger choice behavior under multi-train-routing mode. According to the characteristics of this model and practical planning experience, a three-phase solution was designed to gradually optimize the train formarion, train counts as well as operation periods. The instance of Changsha Metro Line 2 validates the feasibility and efficiency of this approach.展开更多
Climate change and ozone depletion are topics challenging the world over and are both attributed mainly to human activities,particularly emissions of ozone depleting substances.One such substance is chlorodifluorometh...Climate change and ozone depletion are topics challenging the world over and are both attributed mainly to human activities,particularly emissions of ozone depleting substances.One such substance is chlorodifluoromethane(HCFC-22),a cheap,widely used refrigerant with a high global warming potential and a chemical target for phase-out under the Montreal protocol.Botswana like all signatory countries to the Montreal Protocol is required to develop and implement a country-level Hydrochlorofluorocarbon Phase-out Management Plan(HPMP).This study focused on evaluating the environmental and socioeconomic implications of phasing out HCFC-22 in Botswana.A census of nine HCFC-22-importing companies was conducted and probability sampling proportional to company size was used to select a sample of 159 respondents from the Department of Meteorological Services,Customs officers and HCFC-22 Industrial consumers.Annual HCFC-22 importation figures for Botswana in 2009-2017 from the National Ozone Unit were analysed.It emerged that HCFC-22 phase-out had reduced HCFC-22 consumption by approximately 510,400 kg in 2011-2017,translating to 28,072 ozone depleting potential(ODP)saved.Also,the HCFC-22 phase-out plan saved the country 128 kW h of electricity for 2009-2017.While decreasing demand for HCFC-22,the HPMP had correspondingly occasioned the higher replacement and servicing costs of HCFC-22-compliant equipment,as HCFC-22 substitutes cost more.To deter use of HCFC-22 and promote phase-out,the price of substitute refrigerants can be made less expensive than HCFC-22.Participating stakeholders attest that HCFC-22 phase-out has positive social benefits such as raising community awareness of the ozone depleting phase-out.As a recommendation,the government of Botswana could offer a number of incentives towards HCFC-22 substitutes uptake in order to give impetus to technology transfer.展开更多
Objective:To evaluate the dose uncertainty in stereotactic body radiation therapy induced by respiratory motion using a 4D dynamic dose(4DDD)reconstruction method.Methods:A retrospective analysis was conducted on five...Objective:To evaluate the dose uncertainty in stereotactic body radiation therapy induced by respiratory motion using a 4D dynamic dose(4DDD)reconstruction method.Methods:A retrospective analysis was conducted on five lung cancer patients who received static intensitymodulated radiation therapy.The 4DDD was constructed using beam delivery log files,four-dimensional computed tomography(4DCT)scans,and treatment plans.To evaluate the impact of respiratory motion,4DDD calculations were performed with 10 starting phases for each field.A total of 270 field doses were simulated and calculated.The differences between the cumulative volume histogram in whole-course treatment and the field doses'gamma passing rate(GPR)were compared.The correlations between plan complexity metrics and the dose deviation caused by respiratory motion were evaluated independently.The phase distributions of 398 subfields were calculated and evaluated for the influence of dose rate and breathing frequency.Results:The GPRs of all fields were different among various starting phases,with the highest range from 62.20% to 76.87% for 2 mm/3%GPR.The deviation of mean point dose was(5.42±5.21)%,and the deviation in the mean dose and D98% within the internal gross tumor volume were(0.97±0.71)% and(0.77±0.53)%,respectively.There was a significant correlation between the beam aperture-to-volume(BA2V)ratio and the average 2 mm/2%GPR(R?0.601,P<0.01).Lower dose rates led to a more homogeneous distribution of phases among subfields(t?44.100,P<0.001).Conclusions:Different beam starting phases had a limited impact on the overall treatment evaluation.However,the respiratory motion could be observed to induce dose deviations using the 4DDD reconstruction model,particularly for fields with small BA2V.展开更多
基金supported by the National Natural Science Foundation of China (No. 70901076)Research Fund for the Doctoral Program of Higher Education of China (No. 20090162120021)Natural Science Foundation of Hunan Province (No. 10JJ4046)
文摘The train plan of urban rail transit under multi-routing mode can be divided into three parts： train formation, train operation periods and corresponding train counts of each routing in each period. Based on the analysis of passen- ger＇s general travel expenses and operator＇s benefits, the constraints and objective functions are defined and the multiobjective optimization model for the train plan of urban rail transit is presented. Factors considered in the multi- objective optimization model include transport capacity, the requirements of traffic organization, corporation benefits, passenger demands, and passenger choice behavior under multi-train-routing mode. According to the characteristics of this model and practical planning experience, a three-phase solution was designed to gradually optimize the train formarion, train counts as well as operation periods. The instance of Changsha Metro Line 2 validates the feasibility and efficiency of this approach.
文摘Climate change and ozone depletion are topics challenging the world over and are both attributed mainly to human activities,particularly emissions of ozone depleting substances.One such substance is chlorodifluoromethane(HCFC-22),a cheap,widely used refrigerant with a high global warming potential and a chemical target for phase-out under the Montreal protocol.Botswana like all signatory countries to the Montreal Protocol is required to develop and implement a country-level Hydrochlorofluorocarbon Phase-out Management Plan(HPMP).This study focused on evaluating the environmental and socioeconomic implications of phasing out HCFC-22 in Botswana.A census of nine HCFC-22-importing companies was conducted and probability sampling proportional to company size was used to select a sample of 159 respondents from the Department of Meteorological Services,Customs officers and HCFC-22 Industrial consumers.Annual HCFC-22 importation figures for Botswana in 2009-2017 from the National Ozone Unit were analysed.It emerged that HCFC-22 phase-out had reduced HCFC-22 consumption by approximately 510,400 kg in 2011-2017,translating to 28,072 ozone depleting potential(ODP)saved.Also,the HCFC-22 phase-out plan saved the country 128 kW h of electricity for 2009-2017.While decreasing demand for HCFC-22,the HPMP had correspondingly occasioned the higher replacement and servicing costs of HCFC-22-compliant equipment,as HCFC-22 substitutes cost more.To deter use of HCFC-22 and promote phase-out,the price of substitute refrigerants can be made less expensive than HCFC-22.Participating stakeholders attest that HCFC-22 phase-out has positive social benefits such as raising community awareness of the ozone depleting phase-out.As a recommendation,the government of Botswana could offer a number of incentives towards HCFC-22 substitutes uptake in order to give impetus to technology transfer.
基金supported by National Key R&D Program of China.(No.2016YFC0105311)National Natural Science Foundation of China(No.81803047)the Fundamental Research Funds for the Central Universities of China(No.2019kfyXKJC061).
文摘Objective:To evaluate the dose uncertainty in stereotactic body radiation therapy induced by respiratory motion using a 4D dynamic dose(4DDD)reconstruction method.Methods:A retrospective analysis was conducted on five lung cancer patients who received static intensitymodulated radiation therapy.The 4DDD was constructed using beam delivery log files,four-dimensional computed tomography(4DCT)scans,and treatment plans.To evaluate the impact of respiratory motion,4DDD calculations were performed with 10 starting phases for each field.A total of 270 field doses were simulated and calculated.The differences between the cumulative volume histogram in whole-course treatment and the field doses'gamma passing rate(GPR)were compared.The correlations between plan complexity metrics and the dose deviation caused by respiratory motion were evaluated independently.The phase distributions of 398 subfields were calculated and evaluated for the influence of dose rate and breathing frequency.Results:The GPRs of all fields were different among various starting phases,with the highest range from 62.20% to 76.87% for 2 mm/3%GPR.The deviation of mean point dose was(5.42±5.21)%,and the deviation in the mean dose and D98% within the internal gross tumor volume were(0.97±0.71)% and(0.77±0.53)%,respectively.There was a significant correlation between the beam aperture-to-volume(BA2V)ratio and the average 2 mm/2%GPR(R?0.601,P<0.01).Lower dose rates led to a more homogeneous distribution of phases among subfields(t?44.100,P<0.001).Conclusions:Different beam starting phases had a limited impact on the overall treatment evaluation.However,the respiratory motion could be observed to induce dose deviations using the 4DDD reconstruction model,particularly for fields with small BA2V.
