The Imaging Science Subsystem(ISS)mounted on the Cassini spacecraft has taken a lot of images,which provides an important source of high-precision astrometry of some planets and satellites.However,some of these images...The Imaging Science Subsystem(ISS)mounted on the Cassini spacecraft has taken a lot of images,which provides an important source of high-precision astrometry of some planets and satellites.However,some of these images are degraded by trailed stars.Previously,these degraded images cannot be used for astrometry.In this paper,a new method is proposed to detect and compute the centers of these trailed stars automatically.The method is then performed on the astrometry of ISS images with trailed stars.Finally,we provided 658 astrometric positions between 2004 and 2017 of several satellites that include Enceladus,Dione,Tethys,Mimas and Rhea.Compared with the JPL ephemeris SAT427,the mean residuals of these measurements are 0.11 km and 0.26 km in R.A.and decl.,respectively.Their standard deviations are 1.08 km and 1.37 km,respectively.The results show that the proposed method performs astrometric measurements of Cassini ISS images with trailed stars effectively.展开更多
Political instability has increased drastically in Pakistan during the last few decades.This may intensify the fear of investors and eventually affect investment decisions.Therefore,the stock market’s reaction to pol...Political instability has increased drastically in Pakistan during the last few decades.This may intensify the fear of investors and eventually affect investment decisions.Therefore,the stock market’s reaction to political stability must be explored and appropriate policy measures should be prescribed.This paper examines the effect of political stability on stock market returns and volatility using time series data from Pakistan for the period from January 02,2004,to May 31,2018.The study uses the Generalized Autoregressive Conditional Heteroskedastic(GARCH)and Exponential Generalized Autoregressive Conditional Heteroskedastic(EGARCH)models to achieve the main objectives.The findings of the GARCH and EGARCH models confirm that political stability has a positive and significant influence on both stock market returns and volatility in Pakistan.In addition,the EGARCH findings indicate that negative shock(political instability)creates more volatility in the stock market than positive shock(political stability).The results of this study reveal that financial market investors are affected more by political instability.In conclusion,this study suggests that political stability is an essential factor affecting financial market volatility,and it leads to stable financial markets.It also emphasizes that political instability needs to be resolved to achieve stable financial markets.展开更多
基金partly supported by the Joint Research Fund in Astronomy under cooperative agreement between the National Natural Science Foundation of China and Chinese Academy of Sciences(No.U2031104)the National Natural Science Foundation of China(No.62071201)the Natural Science Foundation of Guangdong Province(No.2023A1515011340)。
文摘The Imaging Science Subsystem(ISS)mounted on the Cassini spacecraft has taken a lot of images,which provides an important source of high-precision astrometry of some planets and satellites.However,some of these images are degraded by trailed stars.Previously,these degraded images cannot be used for astrometry.In this paper,a new method is proposed to detect and compute the centers of these trailed stars automatically.The method is then performed on the astrometry of ISS images with trailed stars.Finally,we provided 658 astrometric positions between 2004 and 2017 of several satellites that include Enceladus,Dione,Tethys,Mimas and Rhea.Compared with the JPL ephemeris SAT427,the mean residuals of these measurements are 0.11 km and 0.26 km in R.A.and decl.,respectively.Their standard deviations are 1.08 km and 1.37 km,respectively.The results show that the proposed method performs astrometric measurements of Cassini ISS images with trailed stars effectively.
文摘Political instability has increased drastically in Pakistan during the last few decades.This may intensify the fear of investors and eventually affect investment decisions.Therefore,the stock market’s reaction to political stability must be explored and appropriate policy measures should be prescribed.This paper examines the effect of political stability on stock market returns and volatility using time series data from Pakistan for the period from January 02,2004,to May 31,2018.The study uses the Generalized Autoregressive Conditional Heteroskedastic(GARCH)and Exponential Generalized Autoregressive Conditional Heteroskedastic(EGARCH)models to achieve the main objectives.The findings of the GARCH and EGARCH models confirm that political stability has a positive and significant influence on both stock market returns and volatility in Pakistan.In addition,the EGARCH findings indicate that negative shock(political instability)creates more volatility in the stock market than positive shock(political stability).The results of this study reveal that financial market investors are affected more by political instability.In conclusion,this study suggests that political stability is an essential factor affecting financial market volatility,and it leads to stable financial markets.It also emphasizes that political instability needs to be resolved to achieve stable financial markets.
