Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foa...Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foam to absorb sound at a given frequency,and then fabricate it through sintering,it is expected to have optimized metal foams for the best sound absorption.Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient.In this study,the Lu model was used to optimize the morphological parameters of aluminum metal foam for the best sound absorption coefficient.For this purpose,the Lu model was numerically solved using written codes in MATLAB software.After validating the proposed codes with benchmark data,the genetic algorithm(GA)was applied to optimize the affecting morphological parameters on the sound absorption coefficient.The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz.The optimized parameters ranged from 50%to 95%for porosity,0.1 mm to 4.5 mm for pore size,and 0.07 mm to 0.6 mm for pore opening size.The result of this study was applied to fabricate the desired aluminum metal foams for the best sound absorption.The novel approach applied in this study,is expected to be successfully applied in for best sound absorption in desired frequencies.展开更多
During the SARS-CoV-2(COIVD-19)outbreak,China repeatedly stressed that the response to the pandemic required action at all levels of government,including the issuance of Pandemic Bonds to help the country return to wo...During the SARS-CoV-2(COIVD-19)outbreak,China repeatedly stressed that the response to the pandemic required action at all levels of government,including the issuance of Pandemic Bonds to help the country return to work and production.However,studies on the effectiveness of Pandemic Bonds during that period are rare.Starting with China’s national financial bond market data after COVID-19 in 2020,this paper focuses on the correlation between the Credit Spreads of the relevant bonds and the corresponding bond market rate of return,based on the Copula model.The empirical analysis is also carried out for multiple dimensional groupings such as enterprises,industries,provinces,and bond maturities.The results show that there is a significant positive correlation between the Credit Spreads of Pandemic Bonds and market returns.In addition,the market correlation is higher for Pandemic Bonds issued in Hubei Province,which is at the center of the 2020 pandemic,and the shorter the maturity of the Pandemic Bond issued,the stronger the relationship with market returns.Finally,this paper provides recommendations for financial regulators and policy makers to consider in their decisions on how to build a more resilient financial system under heavy economic,fiscal,and social pressures.展开更多
In this paper, we design a one-dimensional （1D） parity-time-symmetric periodic ring optical waveguide network （PTSPROWN） and investigate its extraordinary optical characteristics. It is found that quite different ...In this paper, we design a one-dimensional （1D） parity-time-symmetric periodic ring optical waveguide network （PTSPROWN） and investigate its extraordinary optical characteristics. It is found that quite different from traditional vacuum/dielectric optical waveguide networks, 1D PTSPROWN cannot produce a photouic ordinary propagation mode, but can generate simultaneously two kinds of photonic nonpropagation modes： attenuation propagation mode and gain propagation mode. It creates neither passband nor stopband and possesses no photonic band structure. This makes 1D PTSPROWN possess richer spontaneous PT-symmetric breaking points and causes interesting extremum spontaneous PT-symmetric breaking points to appear, where electromagnetic waves can create ultrastrong extraordinary transmission, reflection, and localization, and the maximum can arrive at 6.6556 × 10^12 and is more than 7 orders of magnitude larger than the results reported previously. 1D PTSPROWN may possess potential in designing high-efficiency optical energy saver devices, optical amplifiers, optical switches with ultrahigh monochromaticity, and so on.展开更多
基金paper was the output of a research project(Registration No.9597/22)which was financially supported by Shahid Beheshti University of Medical Sciences.
文摘Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foam to absorb sound at a given frequency,and then fabricate it through sintering,it is expected to have optimized metal foams for the best sound absorption.Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient.In this study,the Lu model was used to optimize the morphological parameters of aluminum metal foam for the best sound absorption coefficient.For this purpose,the Lu model was numerically solved using written codes in MATLAB software.After validating the proposed codes with benchmark data,the genetic algorithm(GA)was applied to optimize the affecting morphological parameters on the sound absorption coefficient.The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz.The optimized parameters ranged from 50%to 95%for porosity,0.1 mm to 4.5 mm for pore size,and 0.07 mm to 0.6 mm for pore opening size.The result of this study was applied to fabricate the desired aluminum metal foams for the best sound absorption.The novel approach applied in this study,is expected to be successfully applied in for best sound absorption in desired frequencies.
基金supported by the National Natural Science Foundation of China(No.72042004)the Research Project of Shanghai Science and Technology 26 Commission(No.20dz2260300)the Fundamental Research Funds for the Central 27 Universities.
文摘During the SARS-CoV-2(COIVD-19)outbreak,China repeatedly stressed that the response to the pandemic required action at all levels of government,including the issuance of Pandemic Bonds to help the country return to work and production.However,studies on the effectiveness of Pandemic Bonds during that period are rare.Starting with China’s national financial bond market data after COVID-19 in 2020,this paper focuses on the correlation between the Credit Spreads of the relevant bonds and the corresponding bond market rate of return,based on the Copula model.The empirical analysis is also carried out for multiple dimensional groupings such as enterprises,industries,provinces,and bond maturities.The results show that there is a significant positive correlation between the Credit Spreads of Pandemic Bonds and market returns.In addition,the market correlation is higher for Pandemic Bonds issued in Hubei Province,which is at the center of the 2020 pandemic,and the shorter the maturity of the Pandemic Bond issued,the stronger the relationship with market returns.Finally,this paper provides recommendations for financial regulators and policy makers to consider in their decisions on how to build a more resilient financial system under heavy economic,fiscal,and social pressures.
基金National Natural Science Foundation of China(NSFC)(11674107,11775083,61475049,61771205,61774062)Natural Science Foundation of Guangdong Province(2015A030313374)Scientific Research Foundation of Graduate School of South China Normal University(2015lkxm27,2017lkxm091)
文摘In this paper, we design a one-dimensional （1D） parity-time-symmetric periodic ring optical waveguide network （PTSPROWN） and investigate its extraordinary optical characteristics. It is found that quite different from traditional vacuum/dielectric optical waveguide networks, 1D PTSPROWN cannot produce a photouic ordinary propagation mode, but can generate simultaneously two kinds of photonic nonpropagation modes： attenuation propagation mode and gain propagation mode. It creates neither passband nor stopband and possesses no photonic band structure. This makes 1D PTSPROWN possess richer spontaneous PT-symmetric breaking points and causes interesting extremum spontaneous PT-symmetric breaking points to appear, where electromagnetic waves can create ultrastrong extraordinary transmission, reflection, and localization, and the maximum can arrive at 6.6556 × 10^12 and is more than 7 orders of magnitude larger than the results reported previously. 1D PTSPROWN may possess potential in designing high-efficiency optical energy saver devices, optical amplifiers, optical switches with ultrahigh monochromaticity, and so on.
