Productivity at the berth is one from the group of port productivity measures which is closely tied to ship turnaround times.Net berth productivity is value of productivity related to the operational time at the berth...Productivity at the berth is one from the group of port productivity measures which is closely tied to ship turnaround times.Net berth productivity is value of productivity related to the operational time at the berth.Based on the facts identified from available literature about minor share of researches related to the net berth productivity in the handling operations with dry bulk cargoes in a seaport,it was decided to take this port productivity metrics as an object of a research.After a detailed analysis of different categories of the net berth productivity in the handling operations with dry bulks,key groups of influential factors which determine values of the net berth productivity are identified and systematized.Some principal elements related to improving net berth productivity are taken into consideration,too.Concrete results shown in this paper are related to the Dry Bulk Cargo Terminal in the Port of Bar(Montenegro).展开更多
Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal con...Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal conductivity variation of compacted backfill soil,10 typical soils sampled in Zhejiang Province of China with moisture contents of 0%–25%were fully compacted according to the Proctor compaction test method and then subjected to thermal conductivity measurement using the thermal probe method at 20℃.The particle size distribution and the chemical composition of the soil samples were characterized to analyze their effects on thermal conductivity.The results showed that the maximum thermal conductivity of fully compacted soils generally exceeds 1.9 W/(m·K)and is 20%–50%higher than that of uncompacted soils.With increasing moisture content,soil thermal conductivity and dry bulk density first increase and then remain unchanged or decrease slowly;the critical moisture content is greater than 20%in most cases.Overall,the critical moisture content of soils with large particle size is lower than that of those with small particle size.Quartz has the highest thermal conductivity in the soil solid phase,and the mass percentage of quartz for most soils in this study is more than 50%,while that for yellow soil is less than 30%,which leads to the thermal conductivity of the former being nearly twice as great as that of the latter in most circumstances.Based on regression analysis,with moisture content and dry bulk density as the independent parameters,the prediction formulae for the thermal conductivity of two categories of compacted backfill soils are proposed for practical applications.展开更多
Global dry bulk shipping market is an important element of global economy and trade. Since newbuilding and secondhand vessels are often traded as assets and the freight rate is the key determinant of vessel price, it ...Global dry bulk shipping market is an important element of global economy and trade. Since newbuilding and secondhand vessels are often traded as assets and the freight rate is the key determinant of vessel price, it is important for shipping market participants to understand the market dynamics and price transmission mechanism over time to make suitable stra- tegic decisions. To address this issue, a mulfi-variate GARCH model was applied in this paper to explore the volatility spillover effects across the vessel markets （including newbuilding and secondhand vessel markets） and freight market. Specifically, the BEKK parameterizafion of the multi-variate GARCH model （BEKK GARCH） was proposed to capture the volatility transmission effect from the freight market, newbuilding and secondhand vessel markets in the global dry bulk shipping industry. Empirical results reveal that significant volatility transmission effects exist in each market sector, i.e. capesize, panamax, handymax and handysize. Besides, the market volatility transmission mechanism varies among different vessel types. Moreover, some bilateral effects are found in the dry bulk shipping market, showing that lagged variances could affect the current variance in a counterpart market, regardless of the volatility transmission. A simple ratio is proposed to guide investors optimizing their portfolio allocations. The findings in this paper could provide unique insights for investors to understand the market and hedge their portfolios well.展开更多
The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical b...The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components （β-carotene, lutein, neoxanthin, and violaxthin） decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing （T1） were relatively higher than the rapid heating curing （T2） accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments （P〉 0.05）. The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes＇ activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma.展开更多
The mass and heat transfer mechanisms during radio frequency/vacuum （RF/V） drying of square-edged timber were analyzed and discussed in detail, and a new one-dimensional mathematical model to describe the transport ...The mass and heat transfer mechanisms during radio frequency/vacuum （RF/V） drying of square-edged timber were analyzed and discussed in detail, and a new one-dimensional mathematical model to describe the transport phenomena of mass and heat during continuous RF/V drying was derived from conservation equations based on the mass and heat transfer theory of porous materials The new model provided a relatively fast and efficient way to simulate vacuum drying behavior assisted by dielectric heating. Its advantages compared with the conventional models include： （1） Each independent vari- able has a separate control equation and is solved inde- pendently by converting the partial differential equation into a difference equation with the finite volume method; （2） The calculated data from different parts of the specimen can be displayed in the evolution curves, and the change law of the,parameters can be better described. After analyzing the calculated results, most of the important phenomena observed during RF/V drying were adequately described by this model.展开更多
文摘Productivity at the berth is one from the group of port productivity measures which is closely tied to ship turnaround times.Net berth productivity is value of productivity related to the operational time at the berth.Based on the facts identified from available literature about minor share of researches related to the net berth productivity in the handling operations with dry bulk cargoes in a seaport,it was decided to take this port productivity metrics as an object of a research.After a detailed analysis of different categories of the net berth productivity in the handling operations with dry bulks,key groups of influential factors which determine values of the net berth productivity are identified and systematized.Some principal elements related to improving net berth productivity are taken into consideration,too.Concrete results shown in this paper are related to the Dry Bulk Cargo Terminal in the Port of Bar(Montenegro).
基金supported by the National Key Research and Development Program of China(No.2019YFC1805701)。
文摘Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal conductivity variation of compacted backfill soil,10 typical soils sampled in Zhejiang Province of China with moisture contents of 0%–25%were fully compacted according to the Proctor compaction test method and then subjected to thermal conductivity measurement using the thermal probe method at 20℃.The particle size distribution and the chemical composition of the soil samples were characterized to analyze their effects on thermal conductivity.The results showed that the maximum thermal conductivity of fully compacted soils generally exceeds 1.9 W/(m·K)and is 20%–50%higher than that of uncompacted soils.With increasing moisture content,soil thermal conductivity and dry bulk density first increase and then remain unchanged or decrease slowly;the critical moisture content is greater than 20%in most cases.Overall,the critical moisture content of soils with large particle size is lower than that of those with small particle size.Quartz has the highest thermal conductivity in the soil solid phase,and the mass percentage of quartz for most soils in this study is more than 50%,while that for yellow soil is less than 30%,which leads to the thermal conductivity of the former being nearly twice as great as that of the latter in most circumstances.Based on regression analysis,with moisture content and dry bulk density as the independent parameters,the prediction formulae for the thermal conductivity of two categories of compacted backfill soils are proposed for practical applications.
基金supported by State Key Laboratory of Ocean Engineering,Shanghai Jiao Tong University(GKZD010056)Project of Humanities and Social Sciences, Ministry of Education,China(12YJCGJW001)
文摘Global dry bulk shipping market is an important element of global economy and trade. Since newbuilding and secondhand vessels are often traded as assets and the freight rate is the key determinant of vessel price, it is important for shipping market participants to understand the market dynamics and price transmission mechanism over time to make suitable stra- tegic decisions. To address this issue, a mulfi-variate GARCH model was applied in this paper to explore the volatility spillover effects across the vessel markets （including newbuilding and secondhand vessel markets） and freight market. Specifically, the BEKK parameterizafion of the multi-variate GARCH model （BEKK GARCH） was proposed to capture the volatility transmission effect from the freight market, newbuilding and secondhand vessel markets in the global dry bulk shipping industry. Empirical results reveal that significant volatility transmission effects exist in each market sector, i.e. capesize, panamax, handymax and handysize. Besides, the market volatility transmission mechanism varies among different vessel types. Moreover, some bilateral effects are found in the dry bulk shipping market, showing that lagged variances could affect the current variance in a counterpart market, regardless of the volatility transmission. A simple ratio is proposed to guide investors optimizing their portfolio allocations. The findings in this paper could provide unique insights for investors to understand the market and hedge their portfolios well.
基金supported by the Key Project of State Tobacco Monoply Administration of China(3300806156)
文摘The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components （β-carotene, lutein, neoxanthin, and violaxthin） decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing （T1） were relatively higher than the rapid heating curing （T2） accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments （P〉 0.05）. The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes＇ activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma.
基金National Natural Science Foundation of China,Grant No.30972306 and 31270595
文摘The mass and heat transfer mechanisms during radio frequency/vacuum （RF/V） drying of square-edged timber were analyzed and discussed in detail, and a new one-dimensional mathematical model to describe the transport phenomena of mass and heat during continuous RF/V drying was derived from conservation equations based on the mass and heat transfer theory of porous materials The new model provided a relatively fast and efficient way to simulate vacuum drying behavior assisted by dielectric heating. Its advantages compared with the conventional models include： （1） Each independent vari- able has a separate control equation and is solved inde- pendently by converting the partial differential equation into a difference equation with the finite volume method; （2） The calculated data from different parts of the specimen can be displayed in the evolution curves, and the change law of the,parameters can be better described. After analyzing the calculated results, most of the important phenomena observed during RF/V drying were adequately described by this model.
