The Antarctic runnel can be highly variable in space and time; however, this environment has provided aninteresting habitat for terrestrial algal colonization. The runnel of Reeve Hill, Casey Station (66°16.855′...The Antarctic runnel can be highly variable in space and time; however, this environment has provided aninteresting habitat for terrestrial algal colonization. The runnel of Reeve Hill, Casey Station (66°16.855′S, 110°31.045′E), Antarctica, which occurs intermittently only during the brief austral summer showed high colonization by microalgaedominated mainly by Cyanobacteria mats and diatoms. 9 freshwater microalgae species which includesOscillatoria frac-ta, Oscillatoriasp., Navicula muticopsis, Pinnularia borealis, Nitzschiasp., Prasiola crispa, Chlorococcumsp., Syene-chococcus aeruginosusandSyenechococcus maiorwere recorded during the study. The algal community in the runnel to beobserved closely resembles that in the larger running water ecosystems in the continent. However, intrusion of seawater,direct exposure to sunlight and influence of sea current in the lower part changes the species community. The lower run-nel showed total dominance consists mainly of the marine planktonic Bacillariophycea. Other species detected includes Flagilaria kerguelensis, Flagilaria linearis, Eucampia antarctica, Thalassiosira tumida,Pseudonitzschia lineola, Pseud-onitzschia turgiduloides, Achnanthes brevipesand Odontella litigiosa. Lower algal species diversity observed in this studysuggests that the number of species obtained is related to the area of environment from which the samples were derived.The local assemblages simply contain species that is favored by the environmental conditions.展开更多
The effect of deficiency in tunnel crown thickness on the Yellow River Crossing Tunnel with post-tensioned concrete inner lining was investigated by the elasto-plastic finite element method. Changes in the deformation...The effect of deficiency in tunnel crown thickness on the Yellow River Crossing Tunnel with post-tensioned concrete inner lining was investigated by the elasto-plastic finite element method. Changes in the deformations and circumferential stresses of the post-tensioned concrete inner lining with the gradual decrease of the tunnel crown thickness were compared, and the potential bearing risk of insufficient tunnel crown thickness for the Yellow River Crossing Tunnel was revealed. Based on the finite element calculation results of circumferential stresses under different defective cases, the corresponding reinforcement schemes were proposed. The calculation results show that the inner lining can still maintain a satisfactory stress state when the tunnel crown thickness is equal to or greater than 0. 28 m. When the tunnel crown thickness decreases below 0.28 m, the external surface of the crown and internal surface of the crown＇s adjacent areas may be under tension. The tension stresses will incrementally increase and ultimately exceed the tensile strength of the inner lining concrete as the tunnel crown thickness further decreases gradually. Then, the Yellow River Crossing Tunnel cannot operate normally, and severe cracking, leaking or even failure may occur. When the tunnel crown thickness is equal to or greater than 0.28 m, the reinforcement suggestions are that the void spaces between the inner lining and the outer lining should be back-filled with concrete. When the tunnel crown thickness is less than 0. 28 m, the inner lining should be reinforced by steel plates after concrete back-filling.展开更多
文摘The Antarctic runnel can be highly variable in space and time; however, this environment has provided aninteresting habitat for terrestrial algal colonization. The runnel of Reeve Hill, Casey Station (66°16.855′S, 110°31.045′E), Antarctica, which occurs intermittently only during the brief austral summer showed high colonization by microalgaedominated mainly by Cyanobacteria mats and diatoms. 9 freshwater microalgae species which includesOscillatoria frac-ta, Oscillatoriasp., Navicula muticopsis, Pinnularia borealis, Nitzschiasp., Prasiola crispa, Chlorococcumsp., Syene-chococcus aeruginosusandSyenechococcus maiorwere recorded during the study. The algal community in the runnel to beobserved closely resembles that in the larger running water ecosystems in the continent. However, intrusion of seawater,direct exposure to sunlight and influence of sea current in the lower part changes the species community. The lower run-nel showed total dominance consists mainly of the marine planktonic Bacillariophycea. Other species detected includes Flagilaria kerguelensis, Flagilaria linearis, Eucampia antarctica, Thalassiosira tumida,Pseudonitzschia lineola, Pseud-onitzschia turgiduloides, Achnanthes brevipesand Odontella litigiosa. Lower algal species diversity observed in this studysuggests that the number of species obtained is related to the area of environment from which the samples were derived.The local assemblages simply contain species that is favored by the environmental conditions.
基金The Natural Science Foundation of Hubei Province(No.2017CFB667)the National Natural Science Foundation of China(No.51079107)
文摘The effect of deficiency in tunnel crown thickness on the Yellow River Crossing Tunnel with post-tensioned concrete inner lining was investigated by the elasto-plastic finite element method. Changes in the deformations and circumferential stresses of the post-tensioned concrete inner lining with the gradual decrease of the tunnel crown thickness were compared, and the potential bearing risk of insufficient tunnel crown thickness for the Yellow River Crossing Tunnel was revealed. Based on the finite element calculation results of circumferential stresses under different defective cases, the corresponding reinforcement schemes were proposed. The calculation results show that the inner lining can still maintain a satisfactory stress state when the tunnel crown thickness is equal to or greater than 0. 28 m. When the tunnel crown thickness decreases below 0.28 m, the external surface of the crown and internal surface of the crown＇s adjacent areas may be under tension. The tension stresses will incrementally increase and ultimately exceed the tensile strength of the inner lining concrete as the tunnel crown thickness further decreases gradually. Then, the Yellow River Crossing Tunnel cannot operate normally, and severe cracking, leaking or even failure may occur. When the tunnel crown thickness is equal to or greater than 0.28 m, the reinforcement suggestions are that the void spaces between the inner lining and the outer lining should be back-filled with concrete. When the tunnel crown thickness is less than 0. 28 m, the inner lining should be reinforced by steel plates after concrete back-filling.
