The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys (x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%), produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and agin...The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys (x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%), produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al3(Sc,Zr) particles formed during solidification as heterogeneous nuclei. Secondary Al3(Sc,Zr) precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al-Zn-Mg-Cu-Zr alloy with 0.05%Sc and 0.15%Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.展开更多
To identify genetic loci controlling grain weight, an elite indica rice variety, Baodali, with large grains was identified and used in this study. Its derived F2, F3 and BC2 F2 with another japonica rice variety Zhong...To identify genetic loci controlling grain weight, an elite indica rice variety, Baodali, with large grains was identified and used in this study. Its derived F2, F3 and BC2 F2 with another japonica rice variety Zhonghua 11 were used as mapping populations. Linkage analyses demonstrated that two genes controlling grain weight, designated as GW3 and GW6, were mapped to chromosome 3 and chromosome 6, respectively. Fine mapping delimited GW3 to a 122 kb physical distance between two sequence tagged site markers (WGWt6 and WGW19) containing 16 open reading frames annotated by The Institute for Genomic Research (http://www.tigr.org). GW6 was further mapped between two simple sequence repeat markers (RM7179 and RM3187). These results are useful for both marker assisted selection of grain weight, and for further cloning of GW genes, which will contribute to the dissection of the molecular mechanism underlying grain weight in rice.展开更多
The spatio-temporal characteristics of net primary productivity(NPP) since implementation of the Grain to Green Program(GTGP) are important for understanding ecological restoration of the Loess Plateau in China. H...The spatio-temporal characteristics of net primary productivity(NPP) since implementation of the Grain to Green Program(GTGP) are important for understanding ecological restoration of the Loess Plateau in China. Here, we conduct spatio-temporal analysis of NPP using MODIS datasets(500 m, 8-day intervals) and VPM(Vegetation Photosynthesis Model) from 2000–2015. We found that NPP on the Loess Plateau increased significantly from 2000 to 2015(p0.05). Significant increases in NPP were observed in core areas of the GTGP, including northern Shaanxi and Lüliang Mountain in Shanxi. NPP in alluvial plains decreased due to urban expansion into cropland. Significant increases in NPP from 2006–2010 were located north of the area of change in 2000–2005. NPP increased across three vegetation types and four slope gradients. In hilly-gully regions prone to soil erosion, such as central and southeastern parts of the Loess Plateau, obvious vegetation restoration was detected.展开更多
The response of grain yield, biomass yield and harvest index of maize to the application of commercial organic ameliorants was inconsistent and poor. Hence it was hypothesized that the supply of N and P to maize plant...The response of grain yield, biomass yield and harvest index of maize to the application of commercial organic ameliorants was inconsistent and poor. Hence it was hypothesized that the supply of N and P to maize plants was inadequate during vegetative growth, resulting in low concentrations of the two nutrients in maize biomass. The effects of nine ameliorants on the N and P concentrations of maize plants at ninth leaf (V9) and silking (R1) stages of maize were studied over three years at Bothaville (8% clay), Ottosdal (12% clay) and Potchefstroom (34% clay). All ameliorants were applied as prescribed by manufacturers. The N and P concentrations in maize biomass of the ameliorants at V9 and R1 were lower, comparable or higher, showing that the inconsistent and poor response of yield parameters can not be ascribed to inadequate uptake of N and P. A matter of concern that justifies thorough investigation, is the prescribed use of Crop care and Growmor with partial and of Montys and Promis with no NPK fertilization, an unsustainable practice over the long term. Characterization of the active ingredient(s) of the ameliorants is deemed also of importance for better insight.展开更多
Oat (Avena sativa L.) and wheat (Triticum aestivum L.) vary in the structure of their inflores-cences and also in how pollination proceeds within the inflorescence. In both species the grain position in the spikelet d...Oat (Avena sativa L.) and wheat (Triticum aestivum L.) vary in the structure of their inflores-cences and also in how pollination proceeds within the inflorescence. In both species the grain position in the spikelet determines grain weight potential. Primary grains in oat and proximal grains in wheat weigh more than secondary and distal grains. This variation in grain weight can potentially result from differences in post-pollination cell division in the grain. In this study pollination duration and dynamics were analyzed from head samples collected at two-day intervals, starting from the pollination of the most advanced floret. The number of grain cells was determined for individual grains throughout the inflorescence, starting from the pollination event. When mature, grain position in the spikelet and spike was noted and grain weight assessed. Pollination advance in oat proceeded from the uppermost primary floret towards the basal spikelets in ten to eleven days. Within the spikelet, the primary floret was pollinated on average one day earlier than the secondary floret. In wheat, pollination duration was four to five days, starting from the proximal florets in the mid-section of the inflorescence progressing towards the apical and basal spikelets. Proximal florets were pollinated one to two days earlier than distal florets. Maximum cell number in primary grains exceeded that of secondary grains in two oat cultivars. Similarly, primary grains were heavier than secondary grains. Cell number and single grain weight were correlated in terms of grain position in the spikelet (primary – secondary) and cultivar. Oat cultivar Belinda had a higher single grain weight than Fiia, which was also expressed as larger grain cell number. In wheat, proximal grains had higher maximum cell numbers and were also heavier than distal grains. This grain weight gradient was apparent throughout the inflorescence. Consequently, grain cell number is one of the possible regulators of grain-filling capacity in both cereal crops.展开更多
The influence of ageing time on microstructure and mechanical properties of low-cost beta (LCB) titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstruc...The influence of ageing time on microstructure and mechanical properties of low-cost beta (LCB) titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstructure and fatigue crack initiation and growth was also studied. Increasing ageing time tended to increase the volume fraction of the secondary α-precipitates, β-grain size and partial spheroidization of primary α-phase. The maximum tensile strength (1565 MPa) and fatigue limit (750 MPa) were obtained for the samples aged at 500 °C for 0.5 h, while the minimum ones of 1515 MPa and 625 MPa, respectively, were reported for the samples aged at 500 °C for 4 h. The samples aged at 500 °C for 4 h showed a transgranular fracture mode. However, the samples aged at 500 °C for 0.5 h revealed a mixture fracture mode of transgranular and intergranular. The formed cracks on the outer surface of the fatigue samples were found to propagate through the β-grains connecting the primary α-particles existing at the β-grain boundaries.展开更多
AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the m...AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the morphologies of AlP crystals were studied comprehensively by experimental observation and theorical prediction.It is found that AlP collected from an Al-0.03 P melt could be divided into two categories:spinel twin crystals and non-twin crystals.During the nucleation process,these two kinds of AlP crystals triggered morphologically templated nucleation of primary Si phase,resulting in the formation of hexagonal primary Si twin and octahedral non-twin crystals,respectively.As such,the percentage of primary Si twin crystals in the experimental Al-18 Si alloy was also increased obviously after the morphologically templated nucleation via Al P.The morphologically templated nucleation also eliminated the dendritic growth of primary Si phase and the formation of hopper structures inside primary Si,forcing primary Si to maintain to be faceted solid crystals through layer-by-layer growing mechanism.The insight into morphologically templated nucleation offers a new view in understanding the mechanism of heterogeneous nucleation of primary Si phase on AlP nuclei.展开更多
The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si com...The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.展开更多
Studies were conducted with rice varieties developed in recent years in Liaoning Province of China as test materials. Results showed that the varieties tested could be divided into three types: (1) the high-yieldi...Studies were conducted with rice varieties developed in recent years in Liaoning Province of China as test materials. Results showed that the varieties tested could be divided into three types: (1) the high-yielding (HYV), (2) the mediumyielding (MYV), and (3) the low-yielding (LYV). The panicle population was in the order of HYV〈 MYV 〈 LYV, while the grain number per panicle and seed-setting rate were just opposite. There was no significant difference in the 1 000-grain weight. Biomass was higher in HYV than in MYV and LYV, while the harvest index was higher in HYV and MYV than in LYV. Yield was inversely correlated with panicle population, but positively correlated with the grain number per panicle, seed-setting rate, the number of primary and secondary branch grains, seed density and harvest index. Yield was most closely linked with the grain number per panicle which was determined chiefly by the number of secondary branch grains and to a lesser degree by seed density and the number of primary branch grains. The seed-setting rate of the secondary branches was positively correlated with that of the whole panicle and yield. The peak value of primary branches for HYV, MYV and LYV was 12-14, 10-13 and 8-12, respectively. LYV had fewer secondary branch grains, while MYV and HYV had more. Such grains distributed mainly in the middle and lower parts of panicle axis for LYV and in the middle and upper parts for MYV and HYV.展开更多
基金Project(0211002605132)supported by Institute of Multipurpose Utilization of Mineral Resources,Chinese Academy of Geological Sciences,ChinaProject(0211005303101)supported by the Fundamental Research Funds for the Central Universities,China+1 种基金Project(2010BB4074)supported by Natural Science Foundation Project of CQ CSTC,ChinaProject(2010ZD-02)supported by State Key Laboratory for Advanced Metals and Materials,China
文摘The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys (x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%), produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al3(Sc,Zr) particles formed during solidification as heterogeneous nuclei. Secondary Al3(Sc,Zr) precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al-Zn-Mg-Cu-Zr alloy with 0.05%Sc and 0.15%Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.
基金Supported by the National Natural Science Foundation of China (30771317)the State Key Basic Research and Development Plan of China(2005CB120807).
文摘To identify genetic loci controlling grain weight, an elite indica rice variety, Baodali, with large grains was identified and used in this study. Its derived F2, F3 and BC2 F2 with another japonica rice variety Zhonghua 11 were used as mapping populations. Linkage analyses demonstrated that two genes controlling grain weight, designated as GW3 and GW6, were mapped to chromosome 3 and chromosome 6, respectively. Fine mapping delimited GW3 to a 122 kb physical distance between two sequence tagged site markers (WGWt6 and WGW19) containing 16 open reading frames annotated by The Institute for Genomic Research (http://www.tigr.org). GW6 was further mapped between two simple sequence repeat markers (RM7179 and RM3187). These results are useful for both marker assisted selection of grain weight, and for further cloning of GW genes, which will contribute to the dissection of the molecular mechanism underlying grain weight in rice.
基金National Key Research and Development Program of China(2016YFC0503700)
文摘The spatio-temporal characteristics of net primary productivity(NPP) since implementation of the Grain to Green Program(GTGP) are important for understanding ecological restoration of the Loess Plateau in China. Here, we conduct spatio-temporal analysis of NPP using MODIS datasets(500 m, 8-day intervals) and VPM(Vegetation Photosynthesis Model) from 2000–2015. We found that NPP on the Loess Plateau increased significantly from 2000 to 2015(p0.05). Significant increases in NPP were observed in core areas of the GTGP, including northern Shaanxi and Lüliang Mountain in Shanxi. NPP in alluvial plains decreased due to urban expansion into cropland. Significant increases in NPP from 2006–2010 were located north of the area of change in 2000–2005. NPP increased across three vegetation types and four slope gradients. In hilly-gully regions prone to soil erosion, such as central and southeastern parts of the Loess Plateau, obvious vegetation restoration was detected.
文摘The response of grain yield, biomass yield and harvest index of maize to the application of commercial organic ameliorants was inconsistent and poor. Hence it was hypothesized that the supply of N and P to maize plants was inadequate during vegetative growth, resulting in low concentrations of the two nutrients in maize biomass. The effects of nine ameliorants on the N and P concentrations of maize plants at ninth leaf (V9) and silking (R1) stages of maize were studied over three years at Bothaville (8% clay), Ottosdal (12% clay) and Potchefstroom (34% clay). All ameliorants were applied as prescribed by manufacturers. The N and P concentrations in maize biomass of the ameliorants at V9 and R1 were lower, comparable or higher, showing that the inconsistent and poor response of yield parameters can not be ascribed to inadequate uptake of N and P. A matter of concern that justifies thorough investigation, is the prescribed use of Crop care and Growmor with partial and of Montys and Promis with no NPK fertilization, an unsustainable practice over the long term. Characterization of the active ingredient(s) of the ameliorants is deemed also of importance for better insight.
文摘Oat (Avena sativa L.) and wheat (Triticum aestivum L.) vary in the structure of their inflores-cences and also in how pollination proceeds within the inflorescence. In both species the grain position in the spikelet determines grain weight potential. Primary grains in oat and proximal grains in wheat weigh more than secondary and distal grains. This variation in grain weight can potentially result from differences in post-pollination cell division in the grain. In this study pollination duration and dynamics were analyzed from head samples collected at two-day intervals, starting from the pollination of the most advanced floret. The number of grain cells was determined for individual grains throughout the inflorescence, starting from the pollination event. When mature, grain position in the spikelet and spike was noted and grain weight assessed. Pollination advance in oat proceeded from the uppermost primary floret towards the basal spikelets in ten to eleven days. Within the spikelet, the primary floret was pollinated on average one day earlier than the secondary floret. In wheat, pollination duration was four to five days, starting from the proximal florets in the mid-section of the inflorescence progressing towards the apical and basal spikelets. Proximal florets were pollinated one to two days earlier than distal florets. Maximum cell number in primary grains exceeded that of secondary grains in two oat cultivars. Similarly, primary grains were heavier than secondary grains. Cell number and single grain weight were correlated in terms of grain position in the spikelet (primary – secondary) and cultivar. Oat cultivar Belinda had a higher single grain weight than Fiia, which was also expressed as larger grain cell number. In wheat, proximal grains had higher maximum cell numbers and were also heavier than distal grains. This grain weight gradient was apparent throughout the inflorescence. Consequently, grain cell number is one of the possible regulators of grain-filling capacity in both cereal crops.
文摘The influence of ageing time on microstructure and mechanical properties of low-cost beta (LCB) titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstructure and fatigue crack initiation and growth was also studied. Increasing ageing time tended to increase the volume fraction of the secondary α-precipitates, β-grain size and partial spheroidization of primary α-phase. The maximum tensile strength (1565 MPa) and fatigue limit (750 MPa) were obtained for the samples aged at 500 °C for 0.5 h, while the minimum ones of 1515 MPa and 625 MPa, respectively, were reported for the samples aged at 500 °C for 4 h. The samples aged at 500 °C for 4 h showed a transgranular fracture mode. However, the samples aged at 500 °C for 0.5 h revealed a mixture fracture mode of transgranular and intergranular. The formed cracks on the outer surface of the fatigue samples were found to propagate through the β-grains connecting the primary α-particles existing at the β-grain boundaries.
基金Financial supports from Innovate UK(grant number 11019)National Natural Science Foundation of China(grant number 51571133,51731007 and 52071189)。
文摘AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic AlSi alloys,but the morphological correlation between AlP and primary Si is still confusing.In the present work,the morphologies of AlP crystals were studied comprehensively by experimental observation and theorical prediction.It is found that AlP collected from an Al-0.03 P melt could be divided into two categories:spinel twin crystals and non-twin crystals.During the nucleation process,these two kinds of AlP crystals triggered morphologically templated nucleation of primary Si phase,resulting in the formation of hexagonal primary Si twin and octahedral non-twin crystals,respectively.As such,the percentage of primary Si twin crystals in the experimental Al-18 Si alloy was also increased obviously after the morphologically templated nucleation via Al P.The morphologically templated nucleation also eliminated the dendritic growth of primary Si phase and the formation of hopper structures inside primary Si,forcing primary Si to maintain to be faceted solid crystals through layer-by-layer growing mechanism.The insight into morphologically templated nucleation offers a new view in understanding the mechanism of heterogeneous nucleation of primary Si phase on AlP nuclei.
基金financially supported by the Science and Technology Program of Guangzhou,China(No.2015B090926013)Postdoctoral Science Foundation of China(No.2015M581348)+1 种基金Postdoctoral Science Foundation of Northeastern University(No.20150302)the Doctoral Foundation of Chinese Ministry of Education(No.20130042130001)
文摘The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.
基金This work was supported by the National Natural Science Foundation of China (30370866)the National 863 Program of China.
文摘Studies were conducted with rice varieties developed in recent years in Liaoning Province of China as test materials. Results showed that the varieties tested could be divided into three types: (1) the high-yielding (HYV), (2) the mediumyielding (MYV), and (3) the low-yielding (LYV). The panicle population was in the order of HYV〈 MYV 〈 LYV, while the grain number per panicle and seed-setting rate were just opposite. There was no significant difference in the 1 000-grain weight. Biomass was higher in HYV than in MYV and LYV, while the harvest index was higher in HYV and MYV than in LYV. Yield was inversely correlated with panicle population, but positively correlated with the grain number per panicle, seed-setting rate, the number of primary and secondary branch grains, seed density and harvest index. Yield was most closely linked with the grain number per panicle which was determined chiefly by the number of secondary branch grains and to a lesser degree by seed density and the number of primary branch grains. The seed-setting rate of the secondary branches was positively correlated with that of the whole panicle and yield. The peak value of primary branches for HYV, MYV and LYV was 12-14, 10-13 and 8-12, respectively. LYV had fewer secondary branch grains, while MYV and HYV had more. Such grains distributed mainly in the middle and lower parts of panicle axis for LYV and in the middle and upper parts for MYV and HYV.