Field experiments were conducted from 2012 to 2015 in an arid region of Northwest China to investigate the effects of planting density on plant growth, yield, and water use efficiency(WUE) of maize for seed producti...Field experiments were conducted from 2012 to 2015 in an arid region of Northwest China to investigate the effects of planting density on plant growth, yield, and water use efficiency(WUE) of maize for seed production. Five planting densities of 6.75, 8.25, 9.75, 11.25 and 12.75 plants/m^2 were conducted in 2012, and a planting density of 14.25 plants/m^2 was added from 2013 to 2015. Through comparison with the Aqua Crop yield model, a modified model was developed to estimate the biomass accumulation and yield under different planting densities using adjustment coefficient for normalized biomass water productivity and harvest index. It was found that the modified yield model had a better performance and could generate results with higher determination coefficient and lower error. The results indicated that higher planting density increased the leaf area index and biomass accumulation, but decreased the biomass accumulation per plant. The total yield increased rapidly as planting density increased to 11.25 plants/m^2, but only a slight increase was observed when the density was greater than 11.25 plants/m^2. The WUE also reached the maximum when planting density was 11.25 plants/m^2, which was the recommended planting density of maize for seed production in Northwest China.展开更多
The present paper studies the stabilities of ice blocks in front of an ice cover based on experiments carried out in laboratory by using four types of ice blocks with different dimensions. The forces acting on the ice...The present paper studies the stabilities of ice blocks in front of an ice cover based on experiments carried out in laboratory by using four types of ice blocks with different dimensions. The forces acting on the ice blocks in front of the ice cover are analyzed. The critical criteria for the entrainment of ice blocks in front of the ice cover are established by considering the drag force caused by the flowing water, the collision force, and the hydraulic pressure force. Formula for determining whether or not an ice block will be entrained under the ice cover is derived. All three dimensions of the ice block are considered in the proposed formula. The velocities calculated by using the developed formula are compared with those of calculated by other formulas proposed by other researchers, as well as the measured flow velocities for the entrainment of ice blocks in laboratory. The fitting values obtained by using the derived formula agree well with the experimental results.展开更多
The presence of bridge piers in natural rivers significantly changes the flow and boundary conditions.As a consequence,ice jams can often be initiated in front of bridge piers.With the changes in flow conditions,two t...The presence of bridge piers in natural rivers significantly changes the flow and boundary conditions.As a consequence,ice jams can often be initiated in front of bridge piers.With the changes in flow conditions,two types of ice jam formation may appear:surface accumulation of ice blocks (surface ice blockage) and thickened accumulation of ice blocks (vertical ice blockage).In the present study,the initiation process of ice jam was studied based on experiments.It is found that the critical ice concentration for ice jam blockage depends on the ice block dimension,channel opening and flow conditions.Under surface blockage conditions,a larger ratio of ice cube dimension to channel opening (between piers) can result in a smaller critical ice concentration for ice jam blockage,which has no obvious relation with flow conditions.Under vertical blockage conditions,the critical ice concentration for ice jam blockage increases with flow Froude number and decreases with the ratio of ice dimension to channel opening (between piers).Based on experiments conducted in laboratory,equations for determining critical ice concentration for these two types of ice jam blockage have been developed.展开更多
Experiments are carried out in an "S-shaped" flume in the laboratory under both open flow and ice-jammed conditions to study the impacts of bridge piers in a bend channel on the variation of the water level. The var...Experiments are carried out in an "S-shaped" flume in the laboratory under both open flow and ice-jammed conditions to study the impacts of bridge piers in a bend channel on the variation of the water level. The variations of the water level under the ice jammed condition with bridge piers are compared to those without bridge piers in an 180° bend channel. Results indicate that the bridge piers in the S-shaped channel have obvious impacts on the ice accumulation and the water level. The increment of the water level with the presence of the bridge piers is less than that without the bridge piers in the channel. Different arrangements of the bridge piers result in different increments of the water level. When one bridge pier is installed in the straight section of the channel(between 2 bends) and another one at the bend apex(for a convex bank), the increment of the water level during the equilibrium ice jammed period is between that with a single bridge pier located in the straight section of the bend channel and that with a single bridge pier located at the bend apex. It is also shown that the increment of the water level during the equilibrium ice jammed period increases with the increase of the average thickness of the ice jams.展开更多
Alginates are naturally occurring components of organic matter in natural soil whose effects on nanoparticle (NP) toxicity to plants is not well understood. In the present study, corn plants were grown for one month...Alginates are naturally occurring components of organic matter in natural soil whose effects on nanoparticle (NP) toxicity to plants is not well understood. In the present study, corn plants were grown for one month in soil spiked with 400 mg/kg CeO2 NPs with various alginate concentrations. After one month of growth in the NPs impacted soil, plants were harvested and analyzed for Ce and mineral element concentrations. Chlorophyll concentration and heat shock protein 70, used as biomarkers for oxidative stress, were also evaluated. Results showed that, compared to CeO2 NPs treatment, alginate at 10, 50, and 100 mg/kg increased Ce concentration in roots by approximately 46%, 38%, and 29% and by 115%, 45%, and 56% in shoots, respectively. CeO 2 NPs without alginate increased Mn accumulation in roots by 34% compared to control. CeO2 NPs with low and medium alginate increased Mn by ca. 92% respect to NPs without alginate and by ca. 155% respect to control. CeO2 NPs without/with alginate significantly increased accumulation of Fe and Al in roots. In addition, alginate at 50 mg/kg increased Zn accumulation in roots by 52% compared to control. In shoots, K increased at all NP treatments but the accumulation of other elements was not affected. Alginate enlarged the impact of CeO2 NPs to corn plants by reducing chlorophyll a content and triggering overexpression of heat shock protein 70.展开更多
基金the research grants from the National Natural Science Foundation of China (51379208, 91425302, 51621061)the Government Public Research Funds for Projects of the Ministry of Agriculture (201503125)the Discipline Innovative Engineering Plan (111 Program, B14002)
文摘Field experiments were conducted from 2012 to 2015 in an arid region of Northwest China to investigate the effects of planting density on plant growth, yield, and water use efficiency(WUE) of maize for seed production. Five planting densities of 6.75, 8.25, 9.75, 11.25 and 12.75 plants/m^2 were conducted in 2012, and a planting density of 14.25 plants/m^2 was added from 2013 to 2015. Through comparison with the Aqua Crop yield model, a modified model was developed to estimate the biomass accumulation and yield under different planting densities using adjustment coefficient for normalized biomass water productivity and harvest index. It was found that the modified yield model had a better performance and could generate results with higher determination coefficient and lower error. The results indicated that higher planting density increased the leaf area index and biomass accumulation, but decreased the biomass accumulation per plant. The total yield increased rapidly as planting density increased to 11.25 plants/m^2, but only a slight increase was observed when the density was greater than 11.25 plants/m^2. The WUE also reached the maximum when planting density was 11.25 plants/m^2, which was the recommended planting density of maize for seed production in Northwest China.
基金Project supported by the National Natural Science Foundation of China(Grant No.51379054)
文摘The present paper studies the stabilities of ice blocks in front of an ice cover based on experiments carried out in laboratory by using four types of ice blocks with different dimensions. The forces acting on the ice blocks in front of the ice cover are analyzed. The critical criteria for the entrainment of ice blocks in front of the ice cover are established by considering the drag force caused by the flowing water, the collision force, and the hydraulic pressure force. Formula for determining whether or not an ice block will be entrained under the ice cover is derived. All three dimensions of the ice block are considered in the proposed formula. The velocities calculated by using the developed formula are compared with those of calculated by other formulas proposed by other researchers, as well as the measured flow velocities for the entrainment of ice blocks in laboratory. The fitting values obtained by using the derived formula agree well with the experimental results.
基金the National Natural Science Foundation of China (Grant Nos.51879065,51379054)the Project of Electric Power Construction Corporation of China (Grant No.DJ-ZDZX-2016-02).
文摘The presence of bridge piers in natural rivers significantly changes the flow and boundary conditions.As a consequence,ice jams can often be initiated in front of bridge piers.With the changes in flow conditions,two types of ice jam formation may appear:surface accumulation of ice blocks (surface ice blockage) and thickened accumulation of ice blocks (vertical ice blockage).In the present study,the initiation process of ice jam was studied based on experiments.It is found that the critical ice concentration for ice jam blockage depends on the ice block dimension,channel opening and flow conditions.Under surface blockage conditions,a larger ratio of ice cube dimension to channel opening (between piers) can result in a smaller critical ice concentration for ice jam blockage,which has no obvious relation with flow conditions.Under vertical blockage conditions,the critical ice concentration for ice jam blockage increases with flow Froude number and decreases with the ratio of ice dimension to channel opening (between piers).Based on experiments conducted in laboratory,equations for determining critical ice concentration for these two types of ice jam blockage have been developed.
基金Project supported by the National Natural Science Foundation of China(Grant No.51379054)
文摘Experiments are carried out in an "S-shaped" flume in the laboratory under both open flow and ice-jammed conditions to study the impacts of bridge piers in a bend channel on the variation of the water level. The variations of the water level under the ice jammed condition with bridge piers are compared to those without bridge piers in an 180° bend channel. Results indicate that the bridge piers in the S-shaped channel have obvious impacts on the ice accumulation and the water level. The increment of the water level with the presence of the bridge piers is less than that without the bridge piers in the channel. Different arrangements of the bridge piers result in different increments of the water level. When one bridge pier is installed in the straight section of the channel(between 2 bends) and another one at the bend apex(for a convex bank), the increment of the water level during the equilibrium ice jammed period is between that with a single bridge pier located in the straight section of the bend channel and that with a single bridge pier located at the bend apex. It is also shown that the increment of the water level during the equilibrium ice jammed period increases with the increase of the average thickness of the ice jams.
基金Project supported by the National Science Foundation(NSF)the Environmental Protection Agency under Cooperative Agreement(No.DBI-0830117)+3 种基金the National Institutes of Health(NIH)Grant(No.2R25GM069621-09)the National Institute on Minority Health and Health Disparities(NIMHD)Grant(No.8G12MD007592)the United States Department of Agriculture(USDA)Grant(No.2011-38422-30835)the Research and Engineering Apprenticeship Program(REAP)Grant(No.W11NF-10-2-0076),USA
基金supported by the National Science Foundation (NSF)the Environmental Protection Agency(EPA) under Cooperative Agreement DBI-0830117+1 种基金the USDA grant 2011-38422-30835the NSF Grant CHE-0840525
文摘Alginates are naturally occurring components of organic matter in natural soil whose effects on nanoparticle (NP) toxicity to plants is not well understood. In the present study, corn plants were grown for one month in soil spiked with 400 mg/kg CeO2 NPs with various alginate concentrations. After one month of growth in the NPs impacted soil, plants were harvested and analyzed for Ce and mineral element concentrations. Chlorophyll concentration and heat shock protein 70, used as biomarkers for oxidative stress, were also evaluated. Results showed that, compared to CeO2 NPs treatment, alginate at 10, 50, and 100 mg/kg increased Ce concentration in roots by approximately 46%, 38%, and 29% and by 115%, 45%, and 56% in shoots, respectively. CeO 2 NPs without alginate increased Mn accumulation in roots by 34% compared to control. CeO2 NPs with low and medium alginate increased Mn by ca. 92% respect to NPs without alginate and by ca. 155% respect to control. CeO2 NPs without/with alginate significantly increased accumulation of Fe and Al in roots. In addition, alginate at 50 mg/kg increased Zn accumulation in roots by 52% compared to control. In shoots, K increased at all NP treatments but the accumulation of other elements was not affected. Alginate enlarged the impact of CeO2 NPs to corn plants by reducing chlorophyll a content and triggering overexpression of heat shock protein 70.