Showing papers by "Lei Wang published in 2003"
01 Jan 2003
TL;DR: In this paper, an experimental system was designed and constructed to investigate the oscillating flow characteristics of a regenerator under low temperatures, and it was found that the value of the cycle-averaged pressure drop of the oscillated flow in the regenerator was 5~6 times higher than that of a steady flow at the same Reynolds number based on the cross-sectional mean velocity.
Abstract: An experimental system was designed and constructed to investigate the oscillating flow characteristics of a regenerator under low temperatures. Experimental data on the pressure drops of a regenerator subject to oscillating flow under low-temperature conditions have been obtained. It is found that the value of the cycle-averaged pressure drop of the oscillating flow in the regenerator under liquid nitrogen temperatures is 5~6 times higher than that of a steady flow at the same Reynolds number based on the cross-sectional mean velocity. A correlation equation for the friction factor at liquid nitrogen temperatures has been obtained, and a comparison is made with that obtained at ambient temperatures. Because the test conditions are very close to the operating conditions of practical high frequency cryocoolers, the experimental data should be useful for the prediction of performance and design of cryogenic regenerators.
5 citations
TL;DR: In this article, the femtosecond pump-probe spectroscopy has been used to study ultrafast relaxation dynamics in low-temperature-grown AlGaAs/GaAs multiple quantum wells (MQW's).
Abstract: Femtosecond pump-probe spectroscopy has been used to study ultrafast relaxation dynamics in low-temperature-grown AlGaAs/GaAs multiple quantum wells (MQW's). It was found that the carrier lifetime of as-grown MQW's was much longer than those that had been subjected to 30 s rapid thermal annealing. The carrier lifetimes of samples annealed to three different temperatures (600, 700, and 800 degreesC) were measured and that annealed to 700 degreesC was found to be shorter than that of the other two. We also observed the quantum beats of heavy-hole and light-hole exciton in as-grown AlGaAs/GaAs MQW's at low temperature, but not in the annealed samples. The beat frequency was 3.7 THz, corresponding to the energy difference between heavy- and light-hole excitons in the as-grown AlGaAs/GaAs MQW's. As the temperature rose, the beats disappeared. We gave two possible reasons to explain this phenomenon. We tuned the central frequency of femtosecond Ti:sapphire laser through the resonant frequencies of heavy holes and light holes, while the phase of the quantum beats did not change.
4 citations