Ultrasound has been widely used in clinics. Cellular responses to low-intensity ultrasound are parameter-dependent. Proper parameter setting is vital to its exact use. To get guidelines for parameter setting, lowinten...Ultrasound has been widely used in clinics. Cellular responses to low-intensity ultrasound are parameter-dependent. Proper parameter setting is vital to its exact use. To get guidelines for parameter setting, lowintensity ultrasound stimulation on the proliferation and reproductivity of Hep G2 and 3T3 cells in vitro was examined with a 1.06 MHz-generator by changing the parameters(including intensity, pulse repetition frequency and duty cycle)in a wide range. Cell viability and reproductivity at different time after sonication were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)and colony formation assay to indicate timerelated proliferation. The results illustrate that ultrasound irradiation at 0.4—0.8 W/cm^2 and high pulse repetition frequency(100 Hz)can facilitate cell proliferation, while above 0.8 W/cm^2 would resist it. The extent of resistance closely correlated with duty cycle and pulse repetition frequency. Resistance effect at low pulse repetition frequency(1 Hz)is greater than that at high pulse repetition frequency(100 Hz)and not time-related. The influence of high pulse repetition frequency is time-accumulated, indicating cellular process involved. These findings would provide valuable guidelines for the application of low-intensity ultrasound in stem cell transformation and tissue engineering.展开更多
A 5-level PFC （power factor correction） topology with fault-diagnostic and fault-tolerant capability is proposed and compared to known structures. It is derived from a 3-level non differential double-boost PFC inclu...A 5-level PFC （power factor correction） topology with fault-diagnostic and fault-tolerant capability is proposed and compared to known structures. It is derived from a 3-level non differential double-boost PFC including fly-cap cells. The series-connection of the two low-voltage switching-cells is decoupled by a single flying capacitor that provides a direct fault-tolerant capability and a post-failure operation increasing the availability of converter. The monitoring of the voltages across flying capacitors allows a rapid detection and localization either for open circuit failure or short-circuits failure. A PWM （pulse width modulation） phase-disposition type reconfiguration is also used and presented in order to optimize both normal operation and post-fault continuation. The design and the most important features are highlighted thanks to a digital control frame and a mock-up rated to： AC voltage network 115 V-load 400 V-nominal power 4 kW-switching frequency 62 kHz.展开更多
基金Supported by the Natural Science Foundation of Tianjin(No.12JCYBJC18300)
文摘Ultrasound has been widely used in clinics. Cellular responses to low-intensity ultrasound are parameter-dependent. Proper parameter setting is vital to its exact use. To get guidelines for parameter setting, lowintensity ultrasound stimulation on the proliferation and reproductivity of Hep G2 and 3T3 cells in vitro was examined with a 1.06 MHz-generator by changing the parameters(including intensity, pulse repetition frequency and duty cycle)in a wide range. Cell viability and reproductivity at different time after sonication were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)and colony formation assay to indicate timerelated proliferation. The results illustrate that ultrasound irradiation at 0.4—0.8 W/cm^2 and high pulse repetition frequency(100 Hz)can facilitate cell proliferation, while above 0.8 W/cm^2 would resist it. The extent of resistance closely correlated with duty cycle and pulse repetition frequency. Resistance effect at low pulse repetition frequency(1 Hz)is greater than that at high pulse repetition frequency(100 Hz)and not time-related. The influence of high pulse repetition frequency is time-accumulated, indicating cellular process involved. These findings would provide valuable guidelines for the application of low-intensity ultrasound in stem cell transformation and tissue engineering.
文摘A 5-level PFC （power factor correction） topology with fault-diagnostic and fault-tolerant capability is proposed and compared to known structures. It is derived from a 3-level non differential double-boost PFC including fly-cap cells. The series-connection of the two low-voltage switching-cells is decoupled by a single flying capacitor that provides a direct fault-tolerant capability and a post-failure operation increasing the availability of converter. The monitoring of the voltages across flying capacitors allows a rapid detection and localization either for open circuit failure or short-circuits failure. A PWM （pulse width modulation） phase-disposition type reconfiguration is also used and presented in order to optimize both normal operation and post-fault continuation. The design and the most important features are highlighted thanks to a digital control frame and a mock-up rated to： AC voltage network 115 V-load 400 V-nominal power 4 kW-switching frequency 62 kHz.
