Broadband sound absorption at low frequency is notoriously difficult because the thickness of the absorber should be proportional to the working wavelength. Here we report an acoustic metasurface absorber following t...Broadband sound absorption at low frequency is notoriously difficult because the thickness of the absorber should be proportional to the working wavelength. Here we report an acoustic metasurface absorber following the recent theorydeveloped for electromagnetics. We first show that there is an intrinsic analogy between the impedance description of sound and electromagnetic metasurfaces. Subsequently, we demonstrated that the classic Salisbury and Jaumann ab-sorbers can be realized for acoustic applications with the aid of micro-perforated plates. Finally, the concept of coherent perfect absorption is introduced to achieve ultrathin and ultra-broadband sound absorbers. We anticipate that the ap-proach proposed here can provide helpful guidance for the design of future acoustic and electromagnetic devices.展开更多
The acute toxic effect of the pesticide cypermethrin to Daphnia magna HB was examined. D. magna HB was exposed to cypermethrin at concentrations of 0, 1, 3, 5, 7, and 9 mg/L for 24 h. Data showed that the 24 h-LC 5...The acute toxic effect of the pesticide cypermethrin to Daphnia magna HB was examined. D. magna HB was exposed to cypermethrin at concentrations of 0, 1, 3, 5, 7, and 9 mg/L for 24 h. Data showed that the 24 h-LC 50 of cypermthrin on D. magna HB was 4.81 mg/L. In contrast, the 24 h-LC 50 of K 2Cr 2O 7(the national standard toxicant) to Daphnia magna was 0.38 mg/L in the current study. Results indicated that the Daphnia magna was very sensitive to pesticides. In addition, the effects of the culture condition(such as hardness, temperature and DO etc.) on Daphnia magna HB was also studied.展开更多
基金We acknowledge the financial support by 973 Program of China under con-tract No. 2013CBA01700 and the National Natural Science Foundation of China under contract No. 61622509 and 61575203.
文摘Broadband sound absorption at low frequency is notoriously difficult because the thickness of the absorber should be proportional to the working wavelength. Here we report an acoustic metasurface absorber following the recent theorydeveloped for electromagnetics. We first show that there is an intrinsic analogy between the impedance description of sound and electromagnetic metasurfaces. Subsequently, we demonstrated that the classic Salisbury and Jaumann ab-sorbers can be realized for acoustic applications with the aid of micro-perforated plates. Finally, the concept of coherent perfect absorption is introduced to achieve ultrathin and ultra-broadband sound absorbers. We anticipate that the ap-proach proposed here can provide helpful guidance for the design of future acoustic and electromagnetic devices.
文摘The acute toxic effect of the pesticide cypermethrin to Daphnia magna HB was examined. D. magna HB was exposed to cypermethrin at concentrations of 0, 1, 3, 5, 7, and 9 mg/L for 24 h. Data showed that the 24 h-LC 50 of cypermthrin on D. magna HB was 4.81 mg/L. In contrast, the 24 h-LC 50 of K 2Cr 2O 7(the national standard toxicant) to Daphnia magna was 0.38 mg/L in the current study. Results indicated that the Daphnia magna was very sensitive to pesticides. In addition, the effects of the culture condition(such as hardness, temperature and DO etc.) on Daphnia magna HB was also studied.
