Lead-free halide double perovskites have recently attracted significant attention due to their exceptional stability and favorable band gaps,making them promising candidates for solar cell applications.However,the rel...Lead-free halide double perovskites have recently attracted significant attention due to their exceptional stability and favorable band gaps,making them promising candidates for solar cell applications.However,the relationship between their structural characteristics and intrinsic band gap remains under-explored.This study presents a method to investigate the structure-band gap correlation in a typical halide double perovskite,MA_(2)Pt_(6)(MA^(+)=CH_(3)NH_(3)^(+)),using high pressure techniques.The band gap of MA_(2)PtI_(6)is effectively reduced at two different rates of 0.063 eV/GPa and 0.079 eV/GPa before and after 1.2 GPa,and progressively closes as pressure further increases.These optical changes are closely related to the pressure induced structural evolution of MA_(2)PtI_(6).Moreover,a phase transition from trigonal(R-3m)to monoclinic(P2/m)occurs at 1.2 GPa and completes by 2.0 GPa,driven by pressure-induced distortion of the[PtI_(6)]^(2-)octahedra,which is responsible for the variation of the band gap.These promising findings pave the way for potential applications in the structural and band gap tuning of halide double perovskites.展开更多
Until late in this century,most Ameri-cans spent time with people of all generations.Now baby boomers may not have muchcontact with old people until they re relativelyold themselves.That s because we group people by a...Until late in this century,most Ameri-cans spent time with people of all generations.Now baby boomers may not have muchcontact with old people until they re relativelyold themselves.That s because we group people by age.We put our three-year-olds together in day-care centers,our 13-year-olds in schools展开更多
In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation be...In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition （ESQPT） in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.展开更多
A new model of periodic structure is proposed and analyzed.This structure is composed of an inner fluid-conveying pipe with periodic material arrangement carrying periodic arrays of outer cantilever pipes.The generali...A new model of periodic structure is proposed and analyzed.This structure is composed of an inner fluid-conveying pipe with periodic material arrangement carrying periodic arrays of outer cantilever pipes.The generalized differential quadrature rule(GDQR)method combined with the Bloch theorem is used to calculate the vibration band gaps of the structure.Results are verified by the forced vibration responses obtained using the GDQR method.Results indicate that the first two band gaps of the fluid-conveying pipe with periodic material arrangement can get close to each other and move to low frequency regions by changing the length of cantilever pipes.For high fluid velocity values in which the first band gap starts from zero frequency,since the second band is very close to the first band,this periodic structure can be used for vibration reduction over a wide band gap starting from zero frequency.Based on these results,it can be concluded that instead of increasing the total size of the periodic structure,these periodic arrays of cantilever pipes can be implemented to create a wide ultra-low-frequency band gap.Finally,verification of the GDQR method shows that it can be used as a precise numerical method for vibration analysis of the structures such as fluid-conveying pipes and moving belts.展开更多
Advances in precision treatment promise to greatly improve the extent to which therapies for mental disorders are better matched to patient characteristics.At the same,we need to ensure that more readily disseminable ...Advances in precision treatment promise to greatly improve the extent to which therapies for mental disorders are better matched to patient characteristics.At the same,we need to ensure that more readily disseminable and available nonprecison treatments are further developed as well.These treatments refer to standardized interven-tions that do not have to be individualized and are more readily available.Impetus for this call stems from the treatment gap,namely,the huge difference in the proportion of individuals who are in need of mental health services and who actually receive any form of treatment.The prevalence rates for mental disorders worldwide are high and in low-,middle-,and high-income countries and the vast majority of individuals in need of services receive none.To address the need,we need interventions that can reach large numbers of individuals and espe-cially target those individuals least likely to receive services.Standardized treatments that can be widely applied may be in a better position at present to reach people in need who otherwise receive no care.展开更多
China’s rapidly aging society has made providing security for the elderly a government priority The Ministry of Labor and Social Security has announced an"ambi- tious"goal to provide all of the coun- try’s...China’s rapidly aging society has made providing security for the elderly a government priority The Ministry of Labor and Social Security has announced an"ambi- tious"goal to provide all of the coun- try’s senior citizens with a pension by 2020."This goal is achievable,"stressed Yuan Xinli,Deputy Director of the China National Committee on Aging(CNCA),an agency dedicated to promoting the well- being of the elderly,"but it must be pointed out that such a widespread safety net can only guarantee the minimum living standard of senior citizens."展开更多
Anyone who follows China affairs will know that the country has embarked on a path toward building a harmonious society. To help clarify the concept of a harmonious society, the Central Committee of the Communist Part...Anyone who follows China affairs will know that the country has embarked on a path toward building a harmonious society. To help clarify the concept of a harmonious society, the Central Committee of the Communist Party of China (CPC) has issued the Resolutions on Major Issues Regarding the Building of a Harmonious Socialist Society after a plenary session in October, as a guide to the process. Below we have two commentaries by Ji Li, a commentator with Study Times and Professor Gu Yumin from the Marxism Sch...展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12474414)the Natural Science Foundation of Henan(Grant No.242300421157)the ADXRD measurement was performed at the 4W2 beamline,the Beijing Synchrotron Radiation Facility(BSRF).
文摘Lead-free halide double perovskites have recently attracted significant attention due to their exceptional stability and favorable band gaps,making them promising candidates for solar cell applications.However,the relationship between their structural characteristics and intrinsic band gap remains under-explored.This study presents a method to investigate the structure-band gap correlation in a typical halide double perovskite,MA_(2)Pt_(6)(MA^(+)=CH_(3)NH_(3)^(+)),using high pressure techniques.The band gap of MA_(2)PtI_(6)is effectively reduced at two different rates of 0.063 eV/GPa and 0.079 eV/GPa before and after 1.2 GPa,and progressively closes as pressure further increases.These optical changes are closely related to the pressure induced structural evolution of MA_(2)PtI_(6).Moreover,a phase transition from trigonal(R-3m)to monoclinic(P2/m)occurs at 1.2 GPa and completes by 2.0 GPa,driven by pressure-induced distortion of the[PtI_(6)]^(2-)octahedra,which is responsible for the variation of the band gap.These promising findings pave the way for potential applications in the structural and band gap tuning of halide double perovskites.
文摘Until late in this century,most Ameri-cans spent time with people of all generations.Now baby boomers may not have muchcontact with old people until they re relativelyold themselves.That s because we group people by age.We put our three-year-olds together in day-care centers,our 13-year-olds in schools
基金Supported by the National Natural Science Foundation of China under Grant Nos 11204012 and 91321103
文摘In our previous work [Phys. Rev. A 85 （2012） 044102], we studied the Berry phase of the ground state and exited states in the Lipkin model. In this work, using the Hellmann-Feynman theorem, we derive the relation between the energy gap and the Berry phase closed to the excited state quantum phase transition （ESQPT） in the Lipkin model. It is found that the energy gap is approximately linearly dependent on the Berry phase being closed to the ESQPT for large N. As a result, the critical behavior of the energy gap is similar to that of the Berry phase. In addition, we also perform a semiclassical qualitative analysis about the critical behavior of the energy gap.
文摘A new model of periodic structure is proposed and analyzed.This structure is composed of an inner fluid-conveying pipe with periodic material arrangement carrying periodic arrays of outer cantilever pipes.The generalized differential quadrature rule(GDQR)method combined with the Bloch theorem is used to calculate the vibration band gaps of the structure.Results are verified by the forced vibration responses obtained using the GDQR method.Results indicate that the first two band gaps of the fluid-conveying pipe with periodic material arrangement can get close to each other and move to low frequency regions by changing the length of cantilever pipes.For high fluid velocity values in which the first band gap starts from zero frequency,since the second band is very close to the first band,this periodic structure can be used for vibration reduction over a wide band gap starting from zero frequency.Based on these results,it can be concluded that instead of increasing the total size of the periodic structure,these periodic arrays of cantilever pipes can be implemented to create a wide ultra-low-frequency band gap.Finally,verification of the GDQR method shows that it can be used as a precise numerical method for vibration analysis of the structures such as fluid-conveying pipes and moving belts.
文摘Advances in precision treatment promise to greatly improve the extent to which therapies for mental disorders are better matched to patient characteristics.At the same,we need to ensure that more readily disseminable and available nonprecison treatments are further developed as well.These treatments refer to standardized interven-tions that do not have to be individualized and are more readily available.Impetus for this call stems from the treatment gap,namely,the huge difference in the proportion of individuals who are in need of mental health services and who actually receive any form of treatment.The prevalence rates for mental disorders worldwide are high and in low-,middle-,and high-income countries and the vast majority of individuals in need of services receive none.To address the need,we need interventions that can reach large numbers of individuals and espe-cially target those individuals least likely to receive services.Standardized treatments that can be widely applied may be in a better position at present to reach people in need who otherwise receive no care.
文摘China’s rapidly aging society has made providing security for the elderly a government priority The Ministry of Labor and Social Security has announced an"ambi- tious"goal to provide all of the coun- try’s senior citizens with a pension by 2020."This goal is achievable,"stressed Yuan Xinli,Deputy Director of the China National Committee on Aging(CNCA),an agency dedicated to promoting the well- being of the elderly,"but it must be pointed out that such a widespread safety net can only guarantee the minimum living standard of senior citizens."
文摘Anyone who follows China affairs will know that the country has embarked on a path toward building a harmonious society. To help clarify the concept of a harmonious society, the Central Committee of the Communist Party of China (CPC) has issued the Resolutions on Major Issues Regarding the Building of a Harmonious Socialist Society after a plenary session in October, as a guide to the process. Below we have two commentaries by Ji Li, a commentator with Study Times and Professor Gu Yumin from the Marxism Sch...
