14,451 research outputs found
Topological phase transition based on the attractive Hubbard model
We theoretically investigate the effect of an attractive on-site interaction
on the two-band magnetic Dirac fermion model based on a square lattice system.
When the attractive fermion interaction is taken into account by the mean-field
approximation, a phase diagram is obtained. It is found that a quantum phase
transition from a band insulator state to quantum anomalous Hall state occurs
with increased attractive interaction. For an existing quantum anomalous Hall
state, the attractive interaction enlarges its nontrivial band gap and makes
the topological edge states more localized, which protects the transport of
linear-dispersive edge states against finite-size and further disorder effects.Comment: 5 pages, 4 figure
Behavior of Externally Fiber-Reinforced Polymer Reinforced Shrinkage-Compensating Concrete Beams
The major cause of cracking in bridge decks, concrete pavements, as well as slabs on grade, is restrained shrinkage of the concrete. The resulting steel corrosion problem causes tremendous increase of maintenance and replacement cost. Shrinkage-compensating concrete (SHCC) and fiber-reinforced polymer (FRP) are explored to develop a hybrid slab system as one possible method of delaying the cracking and eliminating corrosion. To achieve the objective, a hybrid FRP reinforced SHCC structural system was developmed, and short-term and long-term behavior of this hybrid FRP-SHCC beams were investigated in this dissertation.
In the first-stage development, a series of “coffee can” tests were carried out to measure and compare the expansion of SHCC from two candidate materials which were ettringite-system SHCC and lime-system SHCC. The selected SHCC candidate mix was then optimized to get the maximum expansion as well as a reasonable concrete strength. The optimized SHCC mix was used to make FRP-SHCC beams. The expansion of the concrete was measured through strain gauges on the FRP composite sheets during curing. Both glass FRP (GFRP) composite sheets and carbon FRP (CFRP) composite sheets were used for comparison. A series of third-point loading experiments were conducted to study the behavior of the proposed hybrid FRP-SHCC beams. In the second-stage development, long term prestress loss and static structural test of the proposed beams are investigated. Test results were evaluated based on maximum expansion strain, cracking load, crack width, load-deflection and ultimate load.The results indicate that the proposed system is promising in terms of its ability to develop a residual pre-stressing effect. Tests also show that the pre-stressing effect from the expansion of SHCC increases as the axial stiffness of the FRP reinforcement increases. A lime-system SHCC structural system shows higher prestress strain and less prestress loss than an ettringite-system SHCC system over the long term
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