Sand casting and die casting processes have been used widely for complex automotive products such as knuckle, arm, etc.Usually, a part fabricated by casting has limited strength due to manufacturing defects such as th...Sand casting and die casting processes have been used widely for complex automotive products such as knuckle, arm, etc.Usually, a part fabricated by casting has limited strength due to manufacturing defects such as the dendrite structure, segregation and porosities.As an attempt to offer a solution to these problems, forging has been used as an alternative process.However, the forging process provides limited formability for complex shape products.Rheo-forging of metal offers not only superior mechanical strength but also requires significantly lower machine loads than solid forming processes.In order to produce semi-solid materials of the desired microstructure, a stirring process is applied during solidification of molten metal.The results of an A356 aluminum alloy sample, which are obtained by experiment and by simulation using DEFORM 3D, are present.展开更多
Knowledge and management of soil pH, particularly soil acidity across spatially variable soils is important, although this is greatly ignored by farmers. The objective of the study was to evaluate in-field spatial var...Knowledge and management of soil pH, particularly soil acidity across spatially variable soils is important, although this is greatly ignored by farmers. The objective of the study was to evaluate in-field spatial variability of soil pH, and compare the efficiency of managing soil pH through site-specific method vs. uniform lime application. The study was conducted on three sites with study sites I and II （23°50＇ S; 29°40＇ E）, and study sites IIl （23°59＇ S; 28°52＇ E） adjacent to each other in the semi-arid regions of the Limpopo Province, South Africa. Soil samples were taken in four replicates from geo-referenced locations on a regular grid of 30 m. Soils were analyzed for pH, and SMP buffer pH. Soil maps were produced with Geographic Information System （GIS） software, and soil pH datasets were interpolated using a geostatistical tool of inverse distance weighing （IDW）. Soil pH in the fields varied from 3.93 to 7.00. An excess amount of lime as high as 30 t/ha under uniform lime application were recorded. These recommendations were in excess on field areas that needed little or no lime applications. Again, there was an under applications of lime as much as 35 t/ha for uniform liming applications. This under- and over-recommendations of lime based on average soil pH values suggests that uniform soil acidity correction and soil pH management strategy is not an appropriate strategy to be adopted in these fields with spatially variable soils. The field can be divided into lime application zones of （1） high rates of lime, （2） low rates of lime and （3） areas that requires no lime at all so that lime rates are applied per zone. A key to site-specific soil acidity correction with lime is to reach ideal soil pH for the crop in all parts of the field.展开更多
Centrifugal pumps are being widely used in many industrial and commercial applications.Many of these pumps are being operated at constant speed but could provide energy savings through adjustable speed operations.The ...Centrifugal pumps are being widely used in many industrial and commercial applications.Many of these pumps are being operated at constant speed but could provide energy savings through adjustable speed operations.The purpose of this study was to get the energy saving rates of the multistage centrifugal pump with variable speed conditions.For this investigation an experimental set up of variable flow and pressure system was made to get energy saving rates and numerical analyses are applied to validate the pump performance.The energy saving and therefore the cost saving depends on the specific duty cycle of which the machine operates.Duty cycle is the proportion of time during which a component,device and system is operated.The duty cycle segmented into different flow rates and weighting the average value for each segment by the interval time.The system was operated at 50%or less of the pump capacity.The input power of the system was carried out by pump characteristics curve of each operating point.The energy consumption was done by the product of specific duty cycle and the input power of the system for constant speed and variable speed drive operation.The total energy consumed for constant speed drive pump was 75,770 k W.hr and for variable speed drive pump was 31,700 k W.hr.The total energy saving of the system was 44,070 k W.hr or 58.16%annually.So,this paper suggests a method of implementing an energy saving on variable-flow and pressure system of the multistage centrifugal pump.展开更多
Understanding the response of ecosystems to past climate is critical for evaluating the impacts of future climate changes.A large-scale abrupt shift of vegetation in response to the Holocene gradual climate changes ha...Understanding the response of ecosystems to past climate is critical for evaluating the impacts of future climate changes.A large-scale abrupt shift of vegetation in response to the Holocene gradual climate changes has been well documented for the Sahara-Sahel ecosystem. Whether such a non-linear response is of universal significance remains to be further addressed. Here,we examine the vegetation-climate relationships in central Asia based on a compilation of 38 high-quality pollen records. The results show that the Holocene vegetation experienced two major abrupt shifts, one in the early Holocene(Shift I, establishing shift) and another in the late Holocene(Shift II, collapsing shift), while the mid-Holocene vegetation remained rather stable. The timings of these shifts in different regions are asynchronous, which are not readily linkable with any known abrupt climate shifts,but are highly correlated with the local rainfalls. These new findings suggest that the observed vegetation shifts are attributable to the threshold effects of the orbital-induced gradual climate changes. During the early Holocene, the orbital-induced precipitation increase would have first reached the threshold for vegetation "establishment" for moister areas, but significantly later for drier areas. In contrast, the orbital-induced precipitation decrease during the late Holocene would have first reached the threshold, and led to the vegetation "collapse" for drier areas, but delayed for moister areas. The well-known 4.2 kyr BP drought event and human intervention would have also helped the vegetation collapses at some sites. These interpretations are strongly supported by our surface pollen-climate analyses and ecosystem simulations. These results also imply that future climate changes may cause abrupt changes in the dry ecosystem once the threshold is reached.展开更多
The ecological and environmental effects caused by land use change have attracted global attention.Huaihai Economic Zone, as the core of the Huaihe River ecological economic belt, has experienced a reciprocal evolutio...The ecological and environmental effects caused by land use change have attracted global attention.Huaihai Economic Zone, as the core of the Huaihe River ecological economic belt, has experienced a reciprocal evolution of land use, ecological security and regional economic development. Based on multi-stage land use data extracted by Google Earth Engine(GEE), the spatio-temporal differentiation characteristics of ecosystem service value(ESV) evolution in Huaihai Economic Zone from 1998 to 2018 were analyzed with the help of ESV assessment and a minimum accumulated resistance model(MCR), and the regional ecological security pattern(ESP) was optimized. The results show that ESV intensity has obvious spatial differentiation, which is higher in northeastern China and lower in southwestern China. The median ESV area accounted for the largest proportion, while the high and low ESV areas accounted for a small proportion. The characteristics of EVS temporal and spatial differentiation show decreasing and increasing grades. From the perspective of development period, the ESV grade changes show a positive trend. In the optimization of the ecological security pattern, 26 important ecological sources, 22main landscape ecological corridors, and 65 ecological strategic nodes were optimized and identified, and the middle-level ecological security zone accounted for the largest proportion. The main reasons for the changes in the ESV and ESP are closely related to the changes in local natural resources and the changes and adjustments in government protection policies. These research results can provide a reference for inter-provincial territorial space protection and the formulation of a sustainable development strategy.展开更多
基金Project(2009-0081077) supported by the National Research Foundation (NRF) by Korea Government
文摘Sand casting and die casting processes have been used widely for complex automotive products such as knuckle, arm, etc.Usually, a part fabricated by casting has limited strength due to manufacturing defects such as the dendrite structure, segregation and porosities.As an attempt to offer a solution to these problems, forging has been used as an alternative process.However, the forging process provides limited formability for complex shape products.Rheo-forging of metal offers not only superior mechanical strength but also requires significantly lower machine loads than solid forming processes.In order to produce semi-solid materials of the desired microstructure, a stirring process is applied during solidification of molten metal.The results of an A356 aluminum alloy sample, which are obtained by experiment and by simulation using DEFORM 3D, are present.
文摘Knowledge and management of soil pH, particularly soil acidity across spatially variable soils is important, although this is greatly ignored by farmers. The objective of the study was to evaluate in-field spatial variability of soil pH, and compare the efficiency of managing soil pH through site-specific method vs. uniform lime application. The study was conducted on three sites with study sites I and II （23°50＇ S; 29°40＇ E）, and study sites IIl （23°59＇ S; 28°52＇ E） adjacent to each other in the semi-arid regions of the Limpopo Province, South Africa. Soil samples were taken in four replicates from geo-referenced locations on a regular grid of 30 m. Soils were analyzed for pH, and SMP buffer pH. Soil maps were produced with Geographic Information System （GIS） software, and soil pH datasets were interpolated using a geostatistical tool of inverse distance weighing （IDW）. Soil pH in the fields varied from 3.93 to 7.00. An excess amount of lime as high as 30 t/ha under uniform lime application were recorded. These recommendations were in excess on field areas that needed little or no lime applications. Again, there was an under applications of lime as much as 35 t/ha for uniform liming applications. This under- and over-recommendations of lime based on average soil pH values suggests that uniform soil acidity correction and soil pH management strategy is not an appropriate strategy to be adopted in these fields with spatially variable soils. The field can be divided into lime application zones of （1） high rates of lime, （2） low rates of lime and （3） areas that requires no lime at all so that lime rates are applied per zone. A key to site-specific soil acidity correction with lime is to reach ideal soil pH for the crop in all parts of the field.
基金supported by the Korea government through the Korea institute of Energy Technology Evaluation and Planning(KETEP)The grant number is 20132010101870 for the Promotion of Science
文摘Centrifugal pumps are being widely used in many industrial and commercial applications.Many of these pumps are being operated at constant speed but could provide energy savings through adjustable speed operations.The purpose of this study was to get the energy saving rates of the multistage centrifugal pump with variable speed conditions.For this investigation an experimental set up of variable flow and pressure system was made to get energy saving rates and numerical analyses are applied to validate the pump performance.The energy saving and therefore the cost saving depends on the specific duty cycle of which the machine operates.Duty cycle is the proportion of time during which a component,device and system is operated.The duty cycle segmented into different flow rates and weighting the average value for each segment by the interval time.The system was operated at 50%or less of the pump capacity.The input power of the system was carried out by pump characteristics curve of each operating point.The energy consumption was done by the product of specific duty cycle and the input power of the system for constant speed and variable speed drive operation.The total energy consumed for constant speed drive pump was 75,770 k W.hr and for variable speed drive pump was 31,700 k W.hr.The total energy saving of the system was 44,070 k W.hr or 58.16%annually.So,this paper suggests a method of implementing an energy saving on variable-flow and pressure system of the multistage centrifugal pump.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41330105, 41690113 and 41430531)the National Key Research and Development Program of China (Grant No. 2016YFA0600501)the Chinese Academy of Sciences Strategic Priority Research Program (Grant No. XDB03030000)
文摘Understanding the response of ecosystems to past climate is critical for evaluating the impacts of future climate changes.A large-scale abrupt shift of vegetation in response to the Holocene gradual climate changes has been well documented for the Sahara-Sahel ecosystem. Whether such a non-linear response is of universal significance remains to be further addressed. Here,we examine the vegetation-climate relationships in central Asia based on a compilation of 38 high-quality pollen records. The results show that the Holocene vegetation experienced two major abrupt shifts, one in the early Holocene(Shift I, establishing shift) and another in the late Holocene(Shift II, collapsing shift), while the mid-Holocene vegetation remained rather stable. The timings of these shifts in different regions are asynchronous, which are not readily linkable with any known abrupt climate shifts,but are highly correlated with the local rainfalls. These new findings suggest that the observed vegetation shifts are attributable to the threshold effects of the orbital-induced gradual climate changes. During the early Holocene, the orbital-induced precipitation increase would have first reached the threshold for vegetation "establishment" for moister areas, but significantly later for drier areas. In contrast, the orbital-induced precipitation decrease during the late Holocene would have first reached the threshold, and led to the vegetation "collapse" for drier areas, but delayed for moister areas. The well-known 4.2 kyr BP drought event and human intervention would have also helped the vegetation collapses at some sites. These interpretations are strongly supported by our surface pollen-climate analyses and ecosystem simulations. These results also imply that future climate changes may cause abrupt changes in the dry ecosystem once the threshold is reached.
基金The National Natural Science Foundation of China (41971175)。
文摘The ecological and environmental effects caused by land use change have attracted global attention.Huaihai Economic Zone, as the core of the Huaihe River ecological economic belt, has experienced a reciprocal evolution of land use, ecological security and regional economic development. Based on multi-stage land use data extracted by Google Earth Engine(GEE), the spatio-temporal differentiation characteristics of ecosystem service value(ESV) evolution in Huaihai Economic Zone from 1998 to 2018 were analyzed with the help of ESV assessment and a minimum accumulated resistance model(MCR), and the regional ecological security pattern(ESP) was optimized. The results show that ESV intensity has obvious spatial differentiation, which is higher in northeastern China and lower in southwestern China. The median ESV area accounted for the largest proportion, while the high and low ESV areas accounted for a small proportion. The characteristics of EVS temporal and spatial differentiation show decreasing and increasing grades. From the perspective of development period, the ESV grade changes show a positive trend. In the optimization of the ecological security pattern, 26 important ecological sources, 22main landscape ecological corridors, and 65 ecological strategic nodes were optimized and identified, and the middle-level ecological security zone accounted for the largest proportion. The main reasons for the changes in the ESV and ESP are closely related to the changes in local natural resources and the changes and adjustments in government protection policies. These research results can provide a reference for inter-provincial territorial space protection and the formulation of a sustainable development strategy.
