One of the water source areas of the South-to-North Water Diversion Project is the Danjiangkou Reservoir （DJKR）. To understand seasonal variation in phytoplankton composition, abundance and distribution in the DJKR ...One of the water source areas of the South-to-North Water Diversion Project is the Danjiangkou Reservoir （DJKR）. To understand seasonal variation in phytoplankton composition, abundance and distribution in the DJKR area before water diversion, as well as to estimate potential risks of water quality after water diversion, we conducted an investigation on phytoplankton in the DJKR from August 2008 to May 2009. The investigation included 10 sampling sites, each with four depths of 0.5, 5, 10, and 20 m. In this study, 117 taxa belonging to 76 genera were identified, consisting of diatoms （39 taxa）, green algae （47 taxa）, blue-green algae （19 taxa）, and others （12 taxa）. Annual average phytoplankton abundance was 2.01×10^6 ind./L, and the highest value was 14.72 ×10^6 ind/L （at site 3 in August 2008）. Phytoplankton abundance in front of the Danjiangkou Dam （DJKD） was higher than that of the Danjiang Reservoir Basin. Phytoplankton distribution showed a vertical declining trend from 0.5 m to 20 m at most sites in August 2008 （especially at sites of 1, 2, 4 and 10）, but no distinct pattern in other sampling months. In December 2008 and March 2009, Stephanodiseus sp. was the most abundant species, amounting to 55.23% and 72.34%, respectively. We propose that high abundance ofStephanodiscus sp. may have contributed greatly to the frequent occurrence of Stephanodiscus sp. blooms in middle-low reaches of the Hanjiang River during the early spring of 2009. In comparison with previous studies conducted from 1992 to 2006, annual average phytoplankton density, green algae and blue-green algae species, as well as major nutrient concentrations increased, while phytoplankton diversity indices declined. This indicates a gradual decline in water quality. More research should be conducted and countermeasures taken to prevent further deterioration of water quality in the DJKR.展开更多
This study focuses on the suburbanization and subcentering of population and examines the nature of spatial restructuring in terms of the population distribution in the Beijing metropolitan area.Instead of the classic...This study focuses on the suburbanization and subcentering of population and examines the nature of spatial restructuring in terms of the population distribution in the Beijing metropolitan area.Instead of the classic density function approach,we employ the nonparametric analysis to characterize the spatial pattern of population densities in the Beijing metropolitan area and identify the suburban subcenters.Our findings suggest that the population has spread with rapid urban growth in the Beijing metropolitan area,and the compact urban form has been replaced by a more dispersed polycentric spatial distribution.However,compared with the decentralization of western cities,the spatial extent of the decentralization of population in the Beijing metropolitan area is quite limited.The rapid growth of population in the near suburbs has expedited the sprawl of the central city,with a larger central agglomeration of population dominating the metropolitan area.In this sense,the spatial pattern of the Beijing metropolitan area is still characterized by the continuous compactness.However,our findings do provide the evidence that the city has been turning to a polycentric structure.We find significant population subcenters have emerged in the suburbs of Beijing since the 1980s.But the polycentricity emerged in the Beijing metropolitan area is very different by nature from that observed in Western cities.The subcenters emerged are adherent to the development scheme planned for the city,so it can be referred to as the so called 'planned polycentricity'.展开更多
The analysis of spatial mismatches in access to employment remains a very important area of labour market literature. A particular case is that of the mismatches in urban labor markets, which can result in substantial...The analysis of spatial mismatches in access to employment remains a very important area of labour market literature. A particular case is that of the mismatches in urban labor markets, which can result in substantial differences in the employment opportunities available in city centre and suburbs. This study examines the spatial mismatches present in the labour market of Santa Cruz de Tenerife. To that end, the results of a survey taken in 2003-2004 with a sample of 2000 city residents were reviewed. Results confirm the importance of transport policy for city residents; they suggest that public transport linking the different districts to the city centre should be reviewed.展开更多
Air-conditioners used in high-rise residential or office buildings often have outdoor units installed on the side-walls or roofs in the confined space of the buildings.The heat released from the outdoor units causes t...Air-conditioners used in high-rise residential or office buildings often have outdoor units installed on the side-walls or roofs in the confined space of the buildings.The heat released from the outdoor units causes the tem-perature rise in the confined installation space and leads to uncomfortable thermal environment and deteriorative performance of air-conditioners.The factors affecting the performance of air-conditioners are the heat released from the outdoor units,the solar radiation and the ventilation of the confined installation space,which are inves-tigated in this study and simulated by FLUENT using the porous model and discrete ordinates (DO) radiation model.It is proved that the porous model is more reliable than the solid model.The optimal installation distance from the supporting wall is obtained.The average temperature of the exit without wind is 1.18% higher than that with wind.The results show that the heat released from the outdoor units and the ventilation of the confined in-stallation space are the main factors affecting the thermal environment in the confined installation space.The in-fluence of the solar radiation is negligible.展开更多
In a Gaussian laser beam pumped single-photon frequency up-conversion system, the spatial distribution of the con- version efficiency is calculated, which strongly depends on the intensity distribution of the pump bea...In a Gaussian laser beam pumped single-photon frequency up-conversion system, the spatial distribution of the con- version efficiency is calculated, which strongly depends on the intensity distribution of the pump beam and leads to a spatial modulation of the output single photons. As a result, by simply varying the Gauss/an pump beam intensity and the beam size, the converted photons could be modulated spatially and exhibit a programmable distribution. This will be meaningful for the researches on quantum communication and quantum manipulation based on frequency up-conversion svstem.展开更多
基金Supported by the National Basic Research Program of China (973 Program) (No. 2008CB418006)the Knowledge Innovation Program of Chinese Academy of Sciences (No. KZCX-YW-14-1)
文摘One of the water source areas of the South-to-North Water Diversion Project is the Danjiangkou Reservoir （DJKR）. To understand seasonal variation in phytoplankton composition, abundance and distribution in the DJKR area before water diversion, as well as to estimate potential risks of water quality after water diversion, we conducted an investigation on phytoplankton in the DJKR from August 2008 to May 2009. The investigation included 10 sampling sites, each with four depths of 0.5, 5, 10, and 20 m. In this study, 117 taxa belonging to 76 genera were identified, consisting of diatoms （39 taxa）, green algae （47 taxa）, blue-green algae （19 taxa）, and others （12 taxa）. Annual average phytoplankton abundance was 2.01×10^6 ind./L, and the highest value was 14.72 ×10^6 ind/L （at site 3 in August 2008）. Phytoplankton abundance in front of the Danjiangkou Dam （DJKD） was higher than that of the Danjiang Reservoir Basin. Phytoplankton distribution showed a vertical declining trend from 0.5 m to 20 m at most sites in August 2008 （especially at sites of 1, 2, 4 and 10）, but no distinct pattern in other sampling months. In December 2008 and March 2009, Stephanodiseus sp. was the most abundant species, amounting to 55.23% and 72.34%, respectively. We propose that high abundance ofStephanodiscus sp. may have contributed greatly to the frequent occurrence of Stephanodiscus sp. blooms in middle-low reaches of the Hanjiang River during the early spring of 2009. In comparison with previous studies conducted from 1992 to 2006, annual average phytoplankton density, green algae and blue-green algae species, as well as major nutrient concentrations increased, while phytoplankton diversity indices declined. This indicates a gradual decline in water quality. More research should be conducted and countermeasures taken to prevent further deterioration of water quality in the DJKR.
基金Under the auspices of National Key Basic Research Program of China (No. 2012CB955802)National Natural Science Foundation of China (No. 41001069)Grant Program of National Social Science Foundation of China (No.10zd&022)
文摘This study focuses on the suburbanization and subcentering of population and examines the nature of spatial restructuring in terms of the population distribution in the Beijing metropolitan area.Instead of the classic density function approach,we employ the nonparametric analysis to characterize the spatial pattern of population densities in the Beijing metropolitan area and identify the suburban subcenters.Our findings suggest that the population has spread with rapid urban growth in the Beijing metropolitan area,and the compact urban form has been replaced by a more dispersed polycentric spatial distribution.However,compared with the decentralization of western cities,the spatial extent of the decentralization of population in the Beijing metropolitan area is quite limited.The rapid growth of population in the near suburbs has expedited the sprawl of the central city,with a larger central agglomeration of population dominating the metropolitan area.In this sense,the spatial pattern of the Beijing metropolitan area is still characterized by the continuous compactness.However,our findings do provide the evidence that the city has been turning to a polycentric structure.We find significant population subcenters have emerged in the suburbs of Beijing since the 1980s.But the polycentricity emerged in the Beijing metropolitan area is very different by nature from that observed in Western cities.The subcenters emerged are adherent to the development scheme planned for the city,so it can be referred to as the so called 'planned polycentricity'.
文摘The analysis of spatial mismatches in access to employment remains a very important area of labour market literature. A particular case is that of the mismatches in urban labor markets, which can result in substantial differences in the employment opportunities available in city centre and suburbs. This study examines the spatial mismatches present in the labour market of Santa Cruz de Tenerife. To that end, the results of a survey taken in 2003-2004 with a sample of 2000 city residents were reviewed. Results confirm the importance of transport policy for city residents; they suggest that public transport linking the different districts to the city centre should be reviewed.
基金supported by National Basic Research Program of China (973 Program)(No.2012CB720406)the Fundamental Research Funds for the Central Universities (No.FRF-AS-10-005B)
文摘Air-conditioners used in high-rise residential or office buildings often have outdoor units installed on the side-walls or roofs in the confined space of the buildings.The heat released from the outdoor units causes the tem-perature rise in the confined installation space and leads to uncomfortable thermal environment and deteriorative performance of air-conditioners.The factors affecting the performance of air-conditioners are the heat released from the outdoor units,the solar radiation and the ventilation of the confined installation space,which are inves-tigated in this study and simulated by FLUENT using the porous model and discrete ordinates (DO) radiation model.It is proved that the porous model is more reliable than the solid model.The optimal installation distance from the supporting wall is obtained.The average temperature of the exit without wind is 1.18% higher than that with wind.The results show that the heat released from the outdoor units and the ventilation of the confined in-stallation space are the main factors affecting the thermal environment in the confined installation space.The in-fluence of the solar radiation is negligible.
基金supported by the National Natural Science Foundation of China(Nos.61127014,61378033 and 11434005)the National Key Scientific Instrument Project(No.2012YQ150092)+2 种基金the Program of Introducing Talents of Discipline to Universities(No.B12024)the Shanghai Rising-Star Program(No.13QA1401300)the Shanghai International Cooperation Project(No.13520720700)
文摘In a Gaussian laser beam pumped single-photon frequency up-conversion system, the spatial distribution of the con- version efficiency is calculated, which strongly depends on the intensity distribution of the pump beam and leads to a spatial modulation of the output single photons. As a result, by simply varying the Gauss/an pump beam intensity and the beam size, the converted photons could be modulated spatially and exhibit a programmable distribution. This will be meaningful for the researches on quantum communication and quantum manipulation based on frequency up-conversion svstem.
