预应力混凝土空心管桩在冬期施工中应用

通过工程实例,介绍冬期工程施工中应用"预应力混凝土空心管桩",不仅是可行,而且是最佳,可以获得技术与经济双丰收。

Stomatal response of Pinus sylvestriformis to elevated CO2 concentrations during the four years of exposure

Four-year-old Pinus sylvestriformis were exposed for four growing seasons in open top chambers to ambient CO2 concentration (approx. 350 μmol·mol-1) and high CO2 concentrations (500 and 700 μmol·mol-1) at Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences at Antu Town, Jilin Province, China (42oN, 128oE). Stomatal response to elevated CO2 concentrations was examined by stomatal conductance (gs), ratio of intercellular to ambient CO2 concentration (ci/ca) and stomatal number. Reciprocal transfer experiments of stomatal conductance showed that stomatal conductance in high-[CO2]-grown plants increased in comparison with ambient-[CO2]-grown plants when measured at their respective growth CO2 concentration and at the same measurement CO2 concentration (except a reduction in 700 μmol·mol-1 CO2 grown plants compared with plants on unchambered field when measured at growth CO2 concentration and 350 μmol·mol-1CO2). High-[CO2]-grown plants exhibited lower ci/ca ratios than ambient-[CO2]-grown plants when measured at their respective growth CO2 concentration. However, ci/ca ratios increased for plants grown in high CO2 concentrations compared with control plants when measured at the same CO2 concentration. There was no significant difference in stomatal number per unit long needle between elevated and ambient CO2. However, elevated CO2 concentrations reduced the total stomatal number of whole needle by the decline of stomatal line and changed the allocation pattern of stomata between upper and lower surface of needle.

Geochemical Characteristics of Heavy Metals in Riparian Sediment Pore Water of Songhua River, Northeast China

This study reports the geochemical characteristics of zinc (Zn), copper (Cu), lead (Pb), nickel (Ni), mercury (Hg), iron (Fe), and manganese (Mn) in the riparian sediment pore water of the Songhua River, Northeast China. In total, 36 pore water samples and 18 surface water samples from three typical sections were collected and analyzed in June 2009. Cluster analysis of heavy metals was performed to analyze the pollution sources of the metals. Results showed that Hg concentrations in the pore water were greater than those in the surface water, indicating a potential ability of Hg release from riparian sediment system to river water. However, concentrations of Fe and Mn in the surface water were greater than those in the pore water, demonstrating that the microenvironments of riparian and riverbed sediment systems were quite different. Variations of Zn, Cu, Pb and Ni between the surface and the pore water were different in each section. Most metals had similar horizontal and profile distribution characteristics in the three sections except for Zn and Ni. Hg, Fe and Mn concentrations in the pore water increased gradually with the increase in horizontal distance from water body, in contrast to this, Cu decreased, and Pb presented a fluctuating trend. With the increase in depth, Pb and Fe, Cu and Mn showed the same trends, and Hg showed a variable trend. The above distribution characteristics could mainly be attributed to the properties and the interactions of metals, pH and oxidation-reduction conditions, and the complex pollution sources and hydrologic regime in history. The probable sources of metals include the historical and ongoing discharge of industrial wastewater, mining activities, sewage irrigation for agricultural production, and atmospheric deposition from coal-fired plants.

The study on neuroprotective mechanism of water extract of Fomitopsis Pinicola on mesencephala dopaminergic neurons induced by MPP+

Objective: To observe the neuroprotective mechanism of water extract of Fomito^p^is Pinicola on MPP+ induced apoptosis of mesencephala dopaminergic cells in vitro. Methods: The antioxidant activity of fungi was determined by FRAP method. The anti-inflammatory activity of the fungi was detected by LPS-induced NO release method. Mesencephalic dopaminergic neurons were labeled by TH staining to observe the survival of THir neurons. Results: In the anti-oxidant activity assay, the Trolox equivalent anti-oxidant capacity (TEAC) of water extract of Fomitopsis Pinicola was determined to be ( 165.80±7.13 )μmol Trolox/g extract. Water extracts o f Fomitopsis Pinicola treatment(100, 5 0 ,2 5 , 12.5^g/ml) decreased NO formation significantly. MPP+ induced significant chromatin condensation in the nuclei of mesencephala dopaminergic neurons with nuclear lysis, the mitochondrial membrane potential decreased remarkably, and ROS production increased significantly. Compared with the MPP+ control group, the morphological changes of cell nuclei after apoptosis was reversed by water extract of Fomitopsis Pinicola. Water extract of Fomitopsis Pinicola treatment (50,25,12.5^g/ml) dramatically increased relative mitochondrial membrane potential compared with MPP+ control respectively. Compared with the MPP+ control, water extract of Fomitopsis Pinicola treatment (50, 25^g/ml) significantly decreased relative ROS formation respectively. Conclusions: Water extract of Fomitopsis Pinicola showed significant neuroprotective effect on mesencephala dopaminergic cells induced by MPP+. The water extract of Fomitopsis Pinicola showed antioxidant and anti-inflammatory activities. The mechanism of neuroprotective effect of water extract of Fomitopsis Pinicola may be related to inhibitory on mitochondrial oxidative stress.

Forced Convective Heat Transfer in a Plate Channel Filled with Solid Particles

A numerical study of fluid flow and convective heat transfer in a plate channel filled with solid (metallic)particles is presented in this paper.The study uses the thermal equilibrium model and a newly developed numerical model which does not assume idealized local thermal equilibrium between the solid particles and the fluid.The numerical simulation results are compared with the experimental data in reference[2].The paper investigates the effects of the assumption of local thermal equilibrium versus non-thermal equilibrium,the thermal conductivity of the solid particles and the particle diameter on convective heat transfer.For the conditions studied,the convective heat transfer and the temperature field assuming local thermal equilibrium are much different from that for the non-thermal equilibrium assumption when the difference between the solid and fluid thermal conductivities is large. The relative values of the thermal conductivities of the solid particles and the fluid also have a profound effect on the temperature distribution in the channel.The pressure drop decreases as the particle diameter increases and the convective heat transfer coefficient may decrease or increase as the particle diameter increases depending on the values of ε,λs,λf,λd,αv, ρu.

The Asymptotic Behavior and the Quasineutral Limit for the Bipolar Euler-Poisson System with Boundary Efects and a Vacuum

In this paper, a one-dimensional bipolar Euler-Poisson system （a hydrodynamic model） from semiconductors or plasmas with boundary effects is considered. This system takes the form of Euler-Poisson with an electric field and frictional damping added to the momentum equations. The large-time behavior of uniformly bounded weak solutions to the initial-boundary value problem for the one-dimensional bipolar Euler-Poisson system is firstly presented. Next, two particle densities and the corresponding current momenta are verified to satisfy the porous medium equation and the classical Darcy＇s law time asymp- totically. Finally, as a by-product, the quasineutral limit of the weak solutions to the initial-boundary value problem is investigated in the sense that the bounded L∞ entropy solution to the one-dimensional bipolar Euler-Poisson system converges to that of the cor- responding one-dimensional compressible Euler equations with damping exponentially fast as t → ＋∞. As far as we know, this is the first result about the asymptotic behavior and the quasineutral limit for the one-dimensional bipolar Euler-Poisson system with boundary effects and a vacuum.

Poisson-Fokker-Planck model for biomolecules translocation through nanopore driven by electroosmotic flow

A non-continuous electroosmotic flow model(PFP model)is built based on Poisson equation,Fokker-Planck equation and Navier-Stokse equation,and used to predict the DNA molecule translocation through nanopore.PFP model discards the continuum assumption of ion translocation and considers ions as discrete particles.In addition,this model includes the contributions of Coulomb electrostatic potential between ions,Brownian motion of ions and viscous friction to ion transportation.No ionic diffusion coefficient and other phenomenological parameters are needed in the PFP model.It is worth noting that the PFP model can describe non-equilibrium electroosmotic transportation of ions in a channel of a size comparable with the mean free path of ion.A modified clustering method is proposed for the numerical solution of PFP model,and ion current translocation through nanopore with a radius of 1 nm is simulated using the modified clustering method.The external electric field,wall charge density of nanopore,surface charge density of DNA,as well as ion average number density,influence the electroosmotic velocity profile of electrolyte solution,the velocity of DNA translocation through nanopore and ion current blockade.Results show that the ion average number density of electrolyte and surface charge density of nanopore have a significant effect on the translocation velocity of DNA and the ion current blockade.The translocation velocity of DNA is proportional to the surface charge density of nanopore,and is inversely proportional to ion average number density of electrolyte solution.Thus,the translocation velocity of DNAs can be controlled to improve the accuracy of sequencing by adjusting the external electric field,ion average number density of electrolyte and surface charge density of nanopore.Ion current decreases when the ion average number density is larger than the critical value and increases when the ion average number density is lower than the critical value.Our numerical simulation shows that the translocation velocity of DNA given by the PFP model agrees with the experimental,results better than that given by PNP model or PB model.