We investigate the impact of the modified gravity(MOG)field and the quintessence scalar field on horizon evolution,black hole(BH)shadow and the weak gravitational lensing around a static spherically symmetric BH.We fi...We investigate the impact of the modified gravity(MOG)field and the quintessence scalar field on horizon evolution,black hole(BH)shadow and the weak gravitational lensing around a static spherically symmetric BH.We first begin to write the BH metric associated with the MOG parameter and quintessence scalar field.We then determine the BH shadow and obtain numerical solutions for the photon sphere and shadow radius.We show that the MOG(α)and the quintessence(c)parameters have a significant impact on the BH shadow and photon sphere.Based on the analysis,we further show that the combined effects of the MOG parameter and quintessence field can increase the values of BH shadow and photon sphere radii.We also obtain constraints on the BH parameters by applying the observational data of Sgr A^(★)and M87^(★).Finally,we consider the weak deflection angle of BH within the context of the Gauss-Bonnet theorem(GBT)and show that the combined effects of the MOG and quintessence parameters do make the value of the deflection angle increase,and find this remarkable property is in good agreement with the physical meaning of both parameters that can maintain the strong gravitational field in the surrounding environment of a BH.展开更多
Gravity models given by higher-order scalar curvature corrections are believed to bear important consequences. Einstein-Bel-Robinson (EBR) gravity with quartic curvature modification motivated Sajadi et al. to explore...Gravity models given by higher-order scalar curvature corrections are believed to bear important consequences. Einstein-Bel-Robinson (EBR) gravity with quartic curvature modification motivated Sajadi et al. to explore static spherically symmetric black hole solutions using perturbative methods. In this study, inspired by their work, we investigate AdS black hole shadows in EBR gravity and demonstrate how the gravity parameter alters the energy emission rate. Finally, we address the same problem in the presence of plasma, because the black holes are thought to be surrounded by a medium that changes the geodesic of photons.展开更多
This paper presents an adaptive method of objects and shadows detection in video streams. Models of background are firstly set up and adaptively updated in Hue Saturation Intensity (HSI) color space to detect motion r...This paper presents an adaptive method of objects and shadows detection in video streams. Models of background are firstly set up and adaptively updated in Hue Saturation Intensity (HSI) color space to detect motion regions. Then, detection errors are dealt with by motion continuity and velocity consistency. Finally, cast shadows are removed by the generic properties of luminance, chrominance and gradient density. Experimental results and their evaluation are presented to verify the effectiveness of this new method.展开更多
A theoretical analysis of the refracted shadows produced by steady and time-decaying liquid vortices under uniform illumination from above is given in this article. An expression for the induced shadow intensity is de...A theoretical analysis of the refracted shadows produced by steady and time-decaying liquid vortices under uniform illumination from above is given in this article. An expression for the induced shadow intensity is derived and found to be a function of the vortex＇s free surface profile, i.e., function of the static pressure distribution. The patterns for different focusing depth are given and compared with previous visualization results from the literature. The phenomenon is examined and illustrated as a bench mark case by using both steady and time-decaying algebraic vortex models. However, this study can be extended to check the feasibility of recovering the main flow properties by analyzing the luminous image intensity of the refracted patterns. The present analysis is valid only when the swirl velocity is order of magnitude higher than the meridional flow components and the vorticity is concentrated within the core region and of intense conditions.展开更多
Using China’s county-level panel data of 2007-2016,this paper verifies the existence of agglomeration shadows from an infrastructure development perspective.With high-speed railway(HSR)launch as a quasi-natural exper...Using China’s county-level panel data of 2007-2016,this paper verifies the existence of agglomeration shadows from an infrastructure development perspective.With high-speed railway(HSR)launch as a quasi-natural experiment,we find that the launch of HSR lines was followed by a decrease in GDP per capita of counties along the route by 2.6 percentage points.This conclusion remains valid after a series of robustness tests and the treatment of potential endogeneity problem.Mechanism analysis suggests that such effect is the most significant for counties within a distance of 97 to 195 km to the nearest central city,which is a manifestation of the“agglomeration shadows.”We also uncover that HSR would spur economic growth for counties with favorable endowments.However,HSR also has a significant negative impact on permanent population in counties.When change in permanent population is taken into account,HSR’s negative impact on the countywide economy becomes smaller.Shrinking permanent population in counties after HSR launch is a manifestation of such agglomeration shadows.HSR has facilitated the free flow of population.These findings point to the possibility that HSR may have induced regional economic equilibrium amid agglomeration.展开更多
In this study,we investigate the shadow and photon sphere of the black bole in clouds of strings and quintessence with static and infalling spherical accretions.We obtain the geodesics of the photons near a black hole...In this study,we investigate the shadow and photon sphere of the black bole in clouds of strings and quintessence with static and infalling spherical accretions.We obtain the geodesics of the photons near a black hole with different impact parameters b to investigate how the string cloud model and quintessence influence the specific intensity by altering the geodesic and the average radial position of photons.In addition,the range of the string cloud parameter a is constrained to ensure that a shadow can be observed.Moreover,the light sources in the accretion follow a normal distribution with an attenuation factorγ,and we adopt a model of the photon emissivity j(v_(e))to obtain the specific intensities.Furthermore,the shadow with static spherical accretion is plotted,which demonstrates that the apparent shape of the shadow is a perfect circle,and the value ofγinfluences the brightness of the photon sphere.Subsequently,we investigate the profile and specific intensity of the shadows with static and infalling spherical accretions,respectively.The interior of the shadows with an infalling spherical accretion will be darker than that with the static spherical accretion,and the specific intensity with both static and infalling spherical accretions gradually converges.展开更多
基金supported by the National Natural Science Foundation of China under Grant No. 11675143the National Key Research and Development Program of China under Grant No. 2020YFC2201503the support from Research Grant F-FA-2021-432 of the Ministry of Higher Education, Science and Innovations of the Republic of Uzbekistan。
文摘We investigate the impact of the modified gravity(MOG)field and the quintessence scalar field on horizon evolution,black hole(BH)shadow and the weak gravitational lensing around a static spherically symmetric BH.We first begin to write the BH metric associated with the MOG parameter and quintessence scalar field.We then determine the BH shadow and obtain numerical solutions for the photon sphere and shadow radius.We show that the MOG(α)and the quintessence(c)parameters have a significant impact on the BH shadow and photon sphere.Based on the analysis,we further show that the combined effects of the MOG parameter and quintessence field can increase the values of BH shadow and photon sphere radii.We also obtain constraints on the BH parameters by applying the observational data of Sgr A^(★)and M87^(★).Finally,we consider the weak deflection angle of BH within the context of the Gauss-Bonnet theorem(GBT)and show that the combined effects of the MOG and quintessence parameters do make the value of the deflection angle increase,and find this remarkable property is in good agreement with the physical meaning of both parameters that can maintain the strong gravitational field in the surrounding environment of a BH.
基金Supported by the Internal Project(2023/2211)of Excellent Research of the Faculty of Science of Hradec Kralove University。
文摘Gravity models given by higher-order scalar curvature corrections are believed to bear important consequences. Einstein-Bel-Robinson (EBR) gravity with quartic curvature modification motivated Sajadi et al. to explore static spherically symmetric black hole solutions using perturbative methods. In this study, inspired by their work, we investigate AdS black hole shadows in EBR gravity and demonstrate how the gravity parameter alters the energy emission rate. Finally, we address the same problem in the presence of plasma, because the black holes are thought to be surrounded by a medium that changes the geodesic of photons.
基金the National Natural Science Foundation of China (60472072)the Specialized Research Foundation for the Doctoral Program of Higher Education (20040699034)+1 种基金the Aeronautical Science Foundation of China (04I50370)the Natural Science Foundation of Shaan’xi Province (2004K05-G23).
文摘This paper presents an adaptive method of objects and shadows detection in video streams. Models of background are firstly set up and adaptively updated in Hue Saturation Intensity (HSI) color space to detect motion regions. Then, detection errors are dealt with by motion continuity and velocity consistency. Finally, cast shadows are removed by the generic properties of luminance, chrominance and gradient density. Experimental results and their evaluation are presented to verify the effectiveness of this new method.
文摘A theoretical analysis of the refracted shadows produced by steady and time-decaying liquid vortices under uniform illumination from above is given in this article. An expression for the induced shadow intensity is derived and found to be a function of the vortex＇s free surface profile, i.e., function of the static pressure distribution. The patterns for different focusing depth are given and compared with previous visualization results from the literature. The phenomenon is examined and illustrated as a bench mark case by using both steady and time-decaying algebraic vortex models. However, this study can be extended to check the feasibility of recovering the main flow properties by analyzing the luminous image intensity of the refracted patterns. The present analysis is valid only when the swirl velocity is order of magnitude higher than the meridional flow components and the vorticity is concentrated within the core region and of intense conditions.
文摘Using China’s county-level panel data of 2007-2016,this paper verifies the existence of agglomeration shadows from an infrastructure development perspective.With high-speed railway(HSR)launch as a quasi-natural experiment,we find that the launch of HSR lines was followed by a decrease in GDP per capita of counties along the route by 2.6 percentage points.This conclusion remains valid after a series of robustness tests and the treatment of potential endogeneity problem.Mechanism analysis suggests that such effect is the most significant for counties within a distance of 97 to 195 km to the nearest central city,which is a manifestation of the“agglomeration shadows.”We also uncover that HSR would spur economic growth for counties with favorable endowments.However,HSR also has a significant negative impact on permanent population in counties.When change in permanent population is taken into account,HSR’s negative impact on the countywide economy becomes smaller.Shrinking permanent population in counties after HSR launch is a manifestation of such agglomeration shadows.HSR has facilitated the free flow of population.These findings point to the possibility that HSR may have induced regional economic equilibrium amid agglomeration.
基金Supported by the National Natural Science Foundation of China(11947408,12047573)。
文摘In this study,we investigate the shadow and photon sphere of the black bole in clouds of strings and quintessence with static and infalling spherical accretions.We obtain the geodesics of the photons near a black hole with different impact parameters b to investigate how the string cloud model and quintessence influence the specific intensity by altering the geodesic and the average radial position of photons.In addition,the range of the string cloud parameter a is constrained to ensure that a shadow can be observed.Moreover,the light sources in the accretion follow a normal distribution with an attenuation factorγ,and we adopt a model of the photon emissivity j(v_(e))to obtain the specific intensities.Furthermore,the shadow with static spherical accretion is plotted,which demonstrates that the apparent shape of the shadow is a perfect circle,and the value ofγinfluences the brightness of the photon sphere.Subsequently,we investigate the profile and specific intensity of the shadows with static and infalling spherical accretions,respectively.The interior of the shadows with an infalling spherical accretion will be darker than that with the static spherical accretion,and the specific intensity with both static and infalling spherical accretions gradually converges.
