A novel hollow star-shaped chiral metamaterial(SCM)is proposed by incorporating chiral structural properties into the standard hollow star-shaped metamaterial,exhibiting a wide band gap over 1500 Hz.To broaden the ban...A novel hollow star-shaped chiral metamaterial(SCM)is proposed by incorporating chiral structural properties into the standard hollow star-shaped metamaterial,exhibiting a wide band gap over 1500 Hz.To broaden the band gap,solid single-phase and two-phase SCMs are designed and simulated,which produce two ultra-wide band gaps(approximately 5116 Hz and 6027 Hz,respectively).The main reason for the formation of the ultra-wide band gap is that the rotational vibration of the concave star of two novel SCMs drains the energy of an elastic wave.The impacts of the concave angle of a single-phase SCM and the resonator radius of a two-phase SCM on the band gaps are studied.Decreasing the concave angle leads to an increase in the width of the widest band gap,and the width of the widest band gap increases as the resonator radius of the two-phase SCM increases.Additionally,the study on elastic wave propagation characteristics involves analyzing frequency dispersion surfaces,wave propagation directions,group velocities,and phase velocities.Ultimately,the analysis focuses on the transmission properties of finite periodic structures.The solid single-phase SCM achieves a maximum vibration attenuation over 800,while the width of the band gap is smaller than that of the two-phase SCM.Both metamaterials exhibit high vibration attenuation capabilities,which can be used in wideband vibration reduction to satisfy the requirement of ultra-wide frequencies.展开更多
This research looks at any relevance between Altman’s Z-score and the stock market performance of airline companies in the United States(US).Nearly a thousand pieces of data on various aspects of operation and financ...This research looks at any relevance between Altman’s Z-score and the stock market performance of airline companies in the United States(US).Nearly a thousand pieces of data on various aspects of operation and financial status from 81 airline companies in the US are available.Additionally,stock return is used as an indicator of firm stock performance in this paper.In order to satisfy the purpose of determining the relationship between Z-score and stock performance as well as what may be inferred from high stock returns with regard to Z-score,two different regression processes are carried out.The first regression tests the relationship between Z-score and stock return,while the second regression examines whether there is a difference in Z-scores between well-performing airline companies and poorly performing ones using dummy variables.The results reveal that there is a significant positive correlation between the Z-scores of US airline companies and their stock performance;besides,high stock returns potentially imply relatively high Z-scores and vice versa.Therefore,one of the crucial steps that US airline companies must make is to strengthen their balance sheets in order to draw investors to make investments in their businesses.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12372019,12072222,12132010,12021002,and 11991032)the Open Projects of State Key Laboratory for Strength and Structural Integrity of China(No.ASSIKFJJ202303002)+1 种基金the State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures of China(No.SKLTESKF1901)the Aeronautical Science Foundation of China(No.ASFC-201915048001)。
文摘A novel hollow star-shaped chiral metamaterial(SCM)is proposed by incorporating chiral structural properties into the standard hollow star-shaped metamaterial,exhibiting a wide band gap over 1500 Hz.To broaden the band gap,solid single-phase and two-phase SCMs are designed and simulated,which produce two ultra-wide band gaps(approximately 5116 Hz and 6027 Hz,respectively).The main reason for the formation of the ultra-wide band gap is that the rotational vibration of the concave star of two novel SCMs drains the energy of an elastic wave.The impacts of the concave angle of a single-phase SCM and the resonator radius of a two-phase SCM on the band gaps are studied.Decreasing the concave angle leads to an increase in the width of the widest band gap,and the width of the widest band gap increases as the resonator radius of the two-phase SCM increases.Additionally,the study on elastic wave propagation characteristics involves analyzing frequency dispersion surfaces,wave propagation directions,group velocities,and phase velocities.Ultimately,the analysis focuses on the transmission properties of finite periodic structures.The solid single-phase SCM achieves a maximum vibration attenuation over 800,while the width of the band gap is smaller than that of the two-phase SCM.Both metamaterials exhibit high vibration attenuation capabilities,which can be used in wideband vibration reduction to satisfy the requirement of ultra-wide frequencies.
文摘This research looks at any relevance between Altman’s Z-score and the stock market performance of airline companies in the United States(US).Nearly a thousand pieces of data on various aspects of operation and financial status from 81 airline companies in the US are available.Additionally,stock return is used as an indicator of firm stock performance in this paper.In order to satisfy the purpose of determining the relationship between Z-score and stock performance as well as what may be inferred from high stock returns with regard to Z-score,two different regression processes are carried out.The first regression tests the relationship between Z-score and stock return,while the second regression examines whether there is a difference in Z-scores between well-performing airline companies and poorly performing ones using dummy variables.The results reveal that there is a significant positive correlation between the Z-scores of US airline companies and their stock performance;besides,high stock returns potentially imply relatively high Z-scores and vice versa.Therefore,one of the crucial steps that US airline companies must make is to strengthen their balance sheets in order to draw investors to make investments in their businesses.
