This letter presents a 0.5 V low-voltage op-amp in a standard 0.18 μm CMOS process for switched-capacitor circuits. Unlike other two-stage 0.5 V op-amp architectures, this op-amp consists of CMOS inverters that utilize floating voltage sources and forward body bias for obtaining high-speed operation. And two improved common-mode rejection circuits are well combined to achieve low power and chip area reduction. Simulation results indicate that the op-amp has an open-loop gain of 62 dB, and a high unity gain bandwidth of 56 MHz. The power consumption is only 350 μW.
Utilization of fiber reinforced polymer(FRP) material has been increased to solve construction material problems such as corrosion, etc. However, there are still many problems in using a linear-shaped FRP material for a tunnel structure with curved section. In this study, the loading tests were performed on the curved FRP-concrete composite material to evaluate its behavior as tunnel support. These tests were based on the result from preliminary numerical analysis on FRPconcrete composite material. Also, additional numerical analysis considering interface characteristics between FRP and cement-concrete was conducted to compare the result of loading test on FRP-concrete composite material. From the results of the loading test and numerical analysis, the analysis method suggested from this study is reasonable to evaluate the mechanical behavior of FRP-concrete composite material.
An experimental study on the resistance of concrete containing air-cooled slag (AS) and water-cooled slag (WS) against freeze–thaw cycles was conducted. For comparison, the durability of ASTM Type I ordinary Portland cement (OPC) concrete exposed to the same freeze–thaw environment was examined. To evaluate the durability of concrete exposed to the freeze–thaw environment, an experiment was conducted according to ASTM C 666 procedure A. Furthermore, the relative dynamic modulus of elasticity, surface electrical resistivity, and compressive strength of concrete specimens were measured after exposing them to freeze–thaw cycles for a predetermined period, and the results were compared with those of OPC concrete. The relationship between the freeze and thaw resistances of concrete and the air-void system (spacing factor and specific surface area) was identified. Furthermore, the microstructure of concrete exposed to freeze–thaw cycles was observed using scanning electron microscopy to identify the interfacial transition zone, cracks, and micropores. Experimental results showed that the resistance of blended cement concrete containing WS and AS against freeze–thaw cycles was significantly higher than that of OPC concrete. The concrete in which 10% of OPC was replaced by AS exhibited a similar durability as that of the concrete in which 40% of OPC was replaced only by WS. Therefore, it is expected that blended cement concrete containing WS and AS based on an appropriate mix proportion design will exhibit excellent durability in regions experiencing freezing temperatures.
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