In this paper,we investigate the optical properties of a non-rotating charged black hole(BH)in the Einstein-Maxwell-scalar(EMS)theory,together with a plasma medium.We first consider the photon sphere and shadow radius...In this paper,we investigate the optical properties of a non-rotating charged black hole(BH)in the Einstein-Maxwell-scalar(EMS)theory,together with a plasma medium.We first consider the photon sphere and shadow radius under the impact of the plasma medium existing in the environment surrounding the BH in the EMS theory.We show that the radius of the photon sphere and the BH shadow decrease under the influence of the parameterβ.We further study gravitational weak lensing in detail by adapting general methods and derive the light ray's deflection angle around the BH together with the plasma environment.It is found that for uniform plasma,the deflection angle increases with the rise of the plasma parameter,whereas it decreases with the increase of the plasma parameter for non-uniform plasma.Besides,we also study the magnification of image brightness.展开更多
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
Strong low-frequency energy beneath a hydrocarbon reservoir is called a seismic low-frequency shadow and can be used as a hydrocarbon indicator （Tarter et al., 1979） bu the physical mechanism of the observed low-fre...Strong low-frequency energy beneath a hydrocarbon reservoir is called a seismic low-frequency shadow and can be used as a hydrocarbon indicator （Tarter et al., 1979） bu the physical mechanism of the observed low-frequency shadow is still unclear. To stud） the mechanism, we performed seismic numerical simulation of geological models with a hydrocarbon-bearing zone using the 2-D diffusive-viscous wave equation which car effectively model the characteristics of velocity dispersion and transform the seismic dat~ centered in a target layer slice within a time window to the time-frequency domain by usinl time-frequency signal analysis and sort the frequency gathers to common frequency cubes. Then, we observe the characteristics of the seismic low-frequency shadow in the common frequency cubes. The numerical simulations reveal that the main mechanism of seismic lowfrequency shadows is attributed to high attenuation of the medium to high seismic frequency components caused by absorption in the hydrocarbon-filled reservoir. Results from a practical example of seismic low-frequency shadows show that it is possible to identify the reservoir by the low-frequency shadow with high S/N seismic data.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
Automatic pavement crack detection is a critical task for maintaining the pavement stability and driving safety.The task is challenging because the shadows on the pavement may have similar intensity with the crack,whi...Automatic pavement crack detection is a critical task for maintaining the pavement stability and driving safety.The task is challenging because the shadows on the pavement may have similar intensity with the crack,which interfere with the crack detection performance.Till to the present,there still lacks efficient algorithm models and training datasets to deal with the interference brought by the shadows.To fill in the gap,we made several contributions as follows.First,we proposed a new pavement shadow and crack dataset,which contains a variety of shadow and pavement pixel size combinations.It also covers all common cracks(linear cracks and network cracks),placing higher demands on crack detection methods.Second,we designed a two-step shadow-removal-oriented crack detection approach:SROCD,which improves the performance of the algorithm by first removing the shadow and then detecting it.In addition to shadows,the method can cope with other noise disturbances.Third,we explored the mechanism of how shadows affect crack detection.Based on this mechanism,we propose a data augmentation method based on the difference in brightness values,which can adapt to brightness changes caused by seasonal and weather changes.Finally,we introduced a residual feature augmentation algorithm to detect small cracks that can predict sudden disasters,and the algorithm improves the performance of the model overall.We compare our method with the state-of-the-art methods on existing pavement crack datasets and the shadow-crack dataset,and the experimental results demonstrate the superiority of our method.展开更多
Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. Th...Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases： slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.展开更多
In case of complex textures,existing static shadow detection and removal algorithms are prone to false detection of the pixels.To solve this problem,a static shadow detection and removal algorithm based on support vec...In case of complex textures,existing static shadow detection and removal algorithms are prone to false detection of the pixels.To solve this problem,a static shadow detection and removal algorithm based on support vector machine(SVM)and region sub-block matching is proposed.Firstly,the original image is segmented into several superpixels,and these superpixels are clustered using mean-shift clustering algorithm in the superpixel sets.Secondly,these features such as color,texture,brightness,intensity and similarity of each area are extracted.These features are used as input of SVM to obtain shadow binary images through training in non-operational state.Thirdly,soft matting is used to smooth the boundary of shadow binary graph.Finally,after finding the best matching sub-block for shadow sub-block in the illumination region based on regional covariance feature and spatial distance,the shadow weighted average factor is introduced to partially correct the sub-block,and the light recovery operator is used to partially light the sub-block.The experimental results show the number of false detection of the pixels is reduced.In addition,it can remove shadows effectively for the image with rich textures and uneven shadows and make a natural transition at the boundary between shadow and light.展开更多
We give a brief review on the formation and the calculation of black hole shadows.Firstly,we introduce the concept of a black hole shadow and the current works on a variety of black hole shadows.Secondly,we present th...We give a brief review on the formation and the calculation of black hole shadows.Firstly,we introduce the concept of a black hole shadow and the current works on a variety of black hole shadows.Secondly,we present the main methods of calculating photon sphere radius and shadow radius,and then explain how the photon sphere affects the boundary of black hole shadows.We review the analytical calculation for black hole shadows which have analytic expressions for shadow boundary due to the integrable photon motion system.And we introduce the fundamental photon orbits which can explain the patterns of black hole shadow shape.Finally,we review the numerical calculation of black hole shadows with the backward ray-tracing method and introduce some chaotic black hole shadows with self-similar fractal structures.Since the gravitational waves from the merger of binary black holes have been detected,we introduce a couple of shadows of binary black holes,which all have eyebrowlike shadows around the main shadows with the fractal structures.We discuss the invariant phase space structures of the photon motion system in black hole space-time,and explain the formation of black hole shadow is dominated by the invariant manifolds of certain Lyapunov orbits near the fixed points.展开更多
In this paper,we study the shadows and observational appearance of the Ayón-Beato-García(ABG)black hole,which is surrounded by a thin disk accretion.For a four-dimensional ABG black hole,as the charge q incr...In this paper,we study the shadows and observational appearance of the Ayón-Beato-García(ABG)black hole,which is surrounded by a thin disk accretion.For a four-dimensional ABG black hole,as the charge q increases,the event horizon r+,radius rp and impact parameter bp of the photon sphere decrease,while the maximum value of effective potential Veff increases.However,as the termγassociated with nonlinear electrodynamics increases,the related physical quantities r+,rp and bp increase,but the maximum value of Veff decreases.When the light ray reaches the vicinity of the ABG black hole,one can observe the trajectories of the light rays appearing as three types,i.e.,direct emission,lens ring and photon ring.Furthermore,the shadows and the observational appearance of the ABG black hole are studied.The results show that the charge q and the termγhave a great influence on the shape and intensity of the black hole shadow.When the relevant state parameters change or the emission model changes,it can be argued that it is the direct emission that plays a decisive role in the total observed intensity of the ABG black hole,while the contribution of the lens ring to the total observed intensity is small and the photon ring makes almost no contribution.展开更多
In general,topographic shadow may reduce performance of forest mapping over mountainous regions in remotely sensed images.In this paper,information in shadow was synthesized by using two filling techniques,namely,roif...In general,topographic shadow may reduce performance of forest mapping over mountainous regions in remotely sensed images.In this paper,information in shadow was synthesized by using two filling techniques,namely,roifill and imfill,in order to improve the accuracy of forest mapping over mountainous regions.These two methods were applied to Landsat Enhanced Thematic Mapper (ETM +) multispectral image from Dong Yang County,Zhejiang Province,China.The performance of these methods was compared with two conventional techniques,including cosine correction and multisource classification.The results showed that by applying filling approaches,average overall accuracy of classification was improved by 14 percent.However,through conventional methods this value increased only by 9 percent.The results also revealed that estimated forest area on the basis of shadow-corrected images by 'roifill' technique was much closer to the survey data compared to traditional algorithms.Apart from this finding,our finding indicated that topographic shadow was an accentuated problem in medium resolution images such as Landsat ETM+ over mountainous regions.展开更多
The main reservoirs in different fields in the YP oil region of the eastern Pearl River Estuary Basin are all fault-locked reservoirs.A large amount of seismic data in this area has fault-influenced distortion imaging...The main reservoirs in different fields in the YP oil region of the eastern Pearl River Estuary Basin are all fault-locked reservoirs.A large amount of seismic data in this area has fault-influenced distortion imaging zones,which poses a challenge to the tectonic evaluation of the area.Traditional solutions to fault shadows generally use reacquisition of multi-directional seismic data or targeted processing for fault imaging,which involves the acquisition of high cost and long processing cycle.In this paper,we propose to quantitatively depict the shadow zone range of faults using 3D stratigraphic dip attributes,and then combine it with the lateral distribution of marine stratigraphy features in the YP oil region,we introduced a support vector regression algorithm to calculate a high-precision nonlinear tectonic trend surface in the area.Under the constraint of this trend surface,we completed the prediction of distortion area structure of the fault shadow zone.The theoretical model test calculations and the production application of an oil field in the YP oil region show that the method has a great potential for application.展开更多
Fince the release of Nang Nak in 1999,Thai movies involving the supernatural have left a mark on world cinema with strong ethnic flavors and Buddhist undertones.Their appeal is grounded in the prevalence of Buddhism i...Fince the release of Nang Nak in 1999,Thai movies involving the supernatural have left a mark on world cinema with strong ethnic flavors and Buddhist undertones.Their appeal is grounded in the prevalence of Buddhism in the Southeast Asian country,where more than 90 percent of the population practice Theravada Buddhism.Ghosts also constitute a key element of Thai culture.Gods and ghosts,the two seemingly irreconcilable beings。展开更多
We explored two f(R,T)gravity models and derived black hole solutions within these models.We focus on investigating how the f(R,T)model influences the thermodynamic characteristics of black holes by studying their the...We explored two f(R,T)gravity models and derived black hole solutions within these models.We focus on investigating how the f(R,T)model influences the thermodynamic characteristics of black holes by studying their thermodynamic topology and thermodynamic geometry.We consid-ered five specific values of the thermodynamic parameter w,which signify five different classes of black hole solutions in general relativity(GR).We observed significant changes in the local topological properties of these black holes compared to GR,depending on the model parameters.Notably,we identified an additional topological class W=O for some values of w that is absent in the GR framework.We also studied the ther-modynamic geometry of the black hole using the Geometrothermodynam-ics(GTD)formalism.Our analysis demonstrates that the singular point,where the GTD scalar curvature diverges,corresponds exactly to the point where the heat capacity changes sign.Additionally,we constrained the model parameters of both models considered by utilizing black hole shadow data from the Sgr A*black hole,measured by the Event Horizon Telescope(EHT).展开更多
We investigated the shadows and optical appearances of a new type of regular black holes(BHs)with a Minkowski core under various spherical accretion scenarios.These BHs are constructed by modifying the Newtonian poten...We investigated the shadows and optical appearances of a new type of regular black holes(BHs)with a Minkowski core under various spherical accretion scenarios.These BHs are constructed by modifying the Newtonian potential based on the minimum observable length in the Generalized Uncertainty Principle(GUP).They correspond one-to-one with traditional regular BHs featuring a de-Sitter(dS)core(such as Bardeen/Hayward BHs),characterized by a quantum gravity effect parameter(α_(0))and spacetime deformation factor(n).We found that the characteristic parameters give rise to some novel observable features.For these new BHs,both the shadow and photon sphere radii decrease with the increase in α_(0),while the observed specific intensity increases.Conversely,as n increases,the shadow and photon sphere radii increase,while the observed specific intensity decreases.Under different spherical accretion scenarios,the shadows and photon sphere radii remain identical;however,the observed specific intensity is greater under static spherical accretion than under infalling spherical accretion.Additionally,we found that these regular BHs with different cores exhibit variations in shadows and optical appearances,particularly under static spherical accretion.Compared with Bardeen BH,the new BHs exhibit a lower observed specific intensity,a dimmer photon ring,and smaller shadow and photon sphere radii.Larger values of α_(0) lead to more significant differences,and a similar trend was also observed when comparing with Hayward BH.Under infalling spherical accretion,the regular BHs with different cores exhibit only slight differences in observed specific intensity,which become more evident when α_(0) is relatively large.This suggests that the unique spacetime features of these regular BHs with different cores can be distinguished through astronomical observation.展开更多
By incorporating first-order QED effects,we explored the shadows of Kerr-Newman black holes with a magnetic charge through the numerical backward ray-tracing method.Our investigation encompassed both the direct influe...By incorporating first-order QED effects,we explored the shadows of Kerr-Newman black holes with a magnetic charge through the numerical backward ray-tracing method.Our investigation encompassed both the direct influence of the electromagnetic field on light rays and the distortion of the background spacetime metric due to QED corrections.We found that the area of the shadow increases with the QED effect,mainly owing to the fact that the photons travel more slowly in the effective medium,making them more susceptible to being trapped by the black hole.展开更多
We investigate the optical properties of the spacetime surrounding a Sen black hole,focusing on the black hole shadow,weak gravitational lensing,and time delay effects.Our analysis reveals that the effective charge of...We investigate the optical properties of the spacetime surrounding a Sen black hole,focusing on the black hole shadow,weak gravitational lensing,and time delay effects.Our analysis reveals that the effective charge of the Sen black hole significantly influences these phenomena.Specifically,an increase in the effective charge leads to a decrease in the radius of the photon sphere and a corresponding decrease in the size of the black hole shadow.Additionally,the bending angle of light rays diminishes as the effective charge increases.Our study provides observational bounds on the effective charge based on these optical characteristics.We also examine the magnification of source brightness using the lens equation and analyze the time delay of light in the presence of a surrounding plasma medium.Our findings offer new insights into the impact of effective charge and plasma on the observational signatures of Sen black holes.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
In this study,we investigated the optical properties of charged black holes within the Einstein-Maxwellscalar(EMS)theory.We evaluated the shadow cast by these black holes and obtained analytical solutions for both the...In this study,we investigated the optical properties of charged black holes within the Einstein-Maxwellscalar(EMS)theory.We evaluated the shadow cast by these black holes and obtained analytical solutions for both the radius of the photon sphere and that of the shadow.We observed that black hole parametersγandβboth influence the shadow of black holes.We also found that the photon sphere and shadow radius increase as a consequence of the presence of the parameterγ.Interestingly,the shadow radius decreases first and then remains unchanged owing to the impact of the parameterβ.Finally,we analyzed the weak gravitational lensing and total magnification of lensed images around black holes.We found that the charge of the black holes and the parameterβboth have a significant impact,reducing the deflection angle.Similarly,the same behavior for the total magnification was observed,also as a result of the effect of the charge of the black holes and the parameterβ.展开更多
Accompanied by music,a humorous story unfolds as a turtle and a crane engage in playful antics,brought to life through the clever interplay of light and curtain in a Chinese shadow puppetry performance.The audience ap...Accompanied by music,a humorous story unfolds as a turtle and a crane engage in playful antics,brought to life through the clever interplay of light and curtain in a Chinese shadow puppetry performance.The audience appears very much entertained,with bursts of laughter echoing throughout the shenanigans unfolding on stage.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.2020YFC2201503。
文摘In this paper,we investigate the optical properties of a non-rotating charged black hole(BH)in the Einstein-Maxwell-scalar(EMS)theory,together with a plasma medium.We first consider the photon sphere and shadow radius under the impact of the plasma medium existing in the environment surrounding the BH in the EMS theory.We show that the radius of the photon sphere and the BH shadow decrease under the influence of the parameterβ.We further study gravitational weak lensing in detail by adapting general methods and derive the light ray's deflection angle around the BH together with the plasma environment.It is found that for uniform plasma,the deflection angle increases with the rise of the plasma parameter,whereas it decreases with the increase of the plasma parameter for non-uniform plasma.Besides,we also study the magnification of image brightness.
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 National Hi-tech Research and Development Program of China (863 Program) (Grant No. 2006AA0AA 02 - 2).
文摘Strong low-frequency energy beneath a hydrocarbon reservoir is called a seismic low-frequency shadow and can be used as a hydrocarbon indicator （Tarter et al., 1979） bu the physical mechanism of the observed low-frequency shadow is still unclear. To stud） the mechanism, we performed seismic numerical simulation of geological models with a hydrocarbon-bearing zone using the 2-D diffusive-viscous wave equation which car effectively model the characteristics of velocity dispersion and transform the seismic dat~ centered in a target layer slice within a time window to the time-frequency domain by usinl time-frequency signal analysis and sort the frequency gathers to common frequency cubes. Then, we observe the characteristics of the seismic low-frequency shadow in the common frequency cubes. The numerical simulations reveal that the main mechanism of seismic lowfrequency shadows is attributed to high attenuation of the medium to high seismic frequency components caused by absorption in the hydrocarbon-filled reservoir. Results from a practical example of seismic low-frequency shadows show that it is possible to identify the reservoir by the low-frequency shadow with high S/N seismic data.
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 in part by the 14th Five-Year Project of Ministry of Science and Technology of China(2021YFD2000304)Fundamental Research Funds for the Central Universities(531118010509)Natural Science Foundation of Hunan Province,China(2021JJ40114)。
文摘Automatic pavement crack detection is a critical task for maintaining the pavement stability and driving safety.The task is challenging because the shadows on the pavement may have similar intensity with the crack,which interfere with the crack detection performance.Till to the present,there still lacks efficient algorithm models and training datasets to deal with the interference brought by the shadows.To fill in the gap,we made several contributions as follows.First,we proposed a new pavement shadow and crack dataset,which contains a variety of shadow and pavement pixel size combinations.It also covers all common cracks(linear cracks and network cracks),placing higher demands on crack detection methods.Second,we designed a two-step shadow-removal-oriented crack detection approach:SROCD,which improves the performance of the algorithm by first removing the shadow and then detecting it.In addition to shadows,the method can cope with other noise disturbances.Third,we explored the mechanism of how shadows affect crack detection.Based on this mechanism,we propose a data augmentation method based on the difference in brightness values,which can adapt to brightness changes caused by seasonal and weather changes.Finally,we introduced a residual feature augmentation algorithm to detect small cracks that can predict sudden disasters,and the algorithm improves the performance of the model overall.We compare our method with the state-of-the-art methods on existing pavement crack datasets and the shadow-crack dataset,and the experimental results demonstrate the superiority of our method.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51323006 and 51425502)the Tribology Science Fund of State Key Laboratory of Tribology(Grant No.SKLTKF17B18)
文摘Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases： slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.
基金University and College Scientific Research Fund of Gansu Province(No.2017A-026)Foundation of A hundred Youth Talents Training Program of Lanzhou Jiaotong University。
文摘In case of complex textures,existing static shadow detection and removal algorithms are prone to false detection of the pixels.To solve this problem,a static shadow detection and removal algorithm based on support vector machine(SVM)and region sub-block matching is proposed.Firstly,the original image is segmented into several superpixels,and these superpixels are clustered using mean-shift clustering algorithm in the superpixel sets.Secondly,these features such as color,texture,brightness,intensity and similarity of each area are extracted.These features are used as input of SVM to obtain shadow binary images through training in non-operational state.Thirdly,soft matting is used to smooth the boundary of shadow binary graph.Finally,after finding the best matching sub-block for shadow sub-block in the illumination region based on regional covariance feature and spatial distance,the shadow weighted average factor is introduced to partially correct the sub-block,and the light recovery operator is used to partially light the sub-block.The experimental results show the number of false detection of the pixels is reduced.In addition,it can remove shadows effectively for the image with rich textures and uneven shadows and make a natural transition at the boundary between shadow and light.
基金supported by the National Natural Science Foundation of China under Grant No.12105151,1187026,11875025 and 12035005the Shandong Provincial Natural Science Foundation of China under Grant No.ZR2020QA080
文摘We give a brief review on the formation and the calculation of black hole shadows.Firstly,we introduce the concept of a black hole shadow and the current works on a variety of black hole shadows.Secondly,we present the main methods of calculating photon sphere radius and shadow radius,and then explain how the photon sphere affects the boundary of black hole shadows.We review the analytical calculation for black hole shadows which have analytic expressions for shadow boundary due to the integrable photon motion system.And we introduce the fundamental photon orbits which can explain the patterns of black hole shadow shape.Finally,we review the numerical calculation of black hole shadows with the backward ray-tracing method and introduce some chaotic black hole shadows with self-similar fractal structures.Since the gravitational waves from the merger of binary black holes have been detected,we introduce a couple of shadows of binary black holes,which all have eyebrowlike shadows around the main shadows with the fractal structures.We discuss the invariant phase space structures of the photon motion system in black hole space-time,and explain the formation of black hole shadow is dominated by the invariant manifolds of certain Lyapunov orbits near the fixed points.
基金the National Natural Science Foundation of China(Grant Nos.11875095 and 11903025)the starting fund of China West Normal University(Grant No.18Q062)+2 种基金the Sichuan Youth Science and Technology Innovation Research Team(21CXTD0038)the Chongqing Science and Technology Bureau(cstc2022ycjh-bgzxm0161)the Natural Science Foundation of SiChuan Province(2022NSFSC1833).
文摘In this paper,we study the shadows and observational appearance of the Ayón-Beato-García(ABG)black hole,which is surrounded by a thin disk accretion.For a four-dimensional ABG black hole,as the charge q increases,the event horizon r+,radius rp and impact parameter bp of the photon sphere decrease,while the maximum value of effective potential Veff increases.However,as the termγassociated with nonlinear electrodynamics increases,the related physical quantities r+,rp and bp increase,but the maximum value of Veff decreases.When the light ray reaches the vicinity of the ABG black hole,one can observe the trajectories of the light rays appearing as three types,i.e.,direct emission,lens ring and photon ring.Furthermore,the shadows and the observational appearance of the ABG black hole are studied.The results show that the charge q and the termγhave a great influence on the shape and intensity of the black hole shadow.When the relevant state parameters change or the emission model changes,it can be argued that it is the direct emission that plays a decisive role in the total observed intensity of the ABG black hole,while the contribution of the lens ring to the total observed intensity is small and the photon ring makes almost no contribution.
基金supported by the funding from National Natural Science Foundation of China(Grant No 30671212)partially by NASA projects NNX08AH50G and G05GD49G at Michigan State University
文摘In general,topographic shadow may reduce performance of forest mapping over mountainous regions in remotely sensed images.In this paper,information in shadow was synthesized by using two filling techniques,namely,roifill and imfill,in order to improve the accuracy of forest mapping over mountainous regions.These two methods were applied to Landsat Enhanced Thematic Mapper (ETM +) multispectral image from Dong Yang County,Zhejiang Province,China.The performance of these methods was compared with two conventional techniques,including cosine correction and multisource classification.The results showed that by applying filling approaches,average overall accuracy of classification was improved by 14 percent.However,through conventional methods this value increased only by 9 percent.The results also revealed that estimated forest area on the basis of shadow-corrected images by 'roifill' technique was much closer to the survey data compared to traditional algorithms.Apart from this finding,our finding indicated that topographic shadow was an accentuated problem in medium resolution images such as Landsat ETM+ over mountainous regions.
基金This study was financially supported by the National Natural Science Foundation of China(Grant No.42104131,41774142)Open Fund(PLC20211101)of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Chengdu University of Technology).
文摘The main reservoirs in different fields in the YP oil region of the eastern Pearl River Estuary Basin are all fault-locked reservoirs.A large amount of seismic data in this area has fault-influenced distortion imaging zones,which poses a challenge to the tectonic evaluation of the area.Traditional solutions to fault shadows generally use reacquisition of multi-directional seismic data or targeted processing for fault imaging,which involves the acquisition of high cost and long processing cycle.In this paper,we propose to quantitatively depict the shadow zone range of faults using 3D stratigraphic dip attributes,and then combine it with the lateral distribution of marine stratigraphy features in the YP oil region,we introduced a support vector regression algorithm to calculate a high-precision nonlinear tectonic trend surface in the area.Under the constraint of this trend surface,we completed the prediction of distortion area structure of the fault shadow zone.The theoretical model test calculations and the production application of an oil field in the YP oil region show that the method has a great potential for application.
文摘Fince the release of Nang Nak in 1999,Thai movies involving the supernatural have left a mark on world cinema with strong ethnic flavors and Buddhist undertones.Their appeal is grounded in the prevalence of Buddhism in the Southeast Asian country,where more than 90 percent of the population practice Theravada Buddhism.Ghosts also constitute a key element of Thai culture.Gods and ghosts,the two seemingly irreconcilable beings。
基金B.H.would like to thank DST-INSPIRE,Ministry of Science and Technology fellowship program,Govt.of India for awarding the DST/INSPIRE Fellowship(IF220255)for financial support.
文摘We explored two f(R,T)gravity models and derived black hole solutions within these models.We focus on investigating how the f(R,T)model influences the thermodynamic characteristics of black holes by studying their thermodynamic topology and thermodynamic geometry.We consid-ered five specific values of the thermodynamic parameter w,which signify five different classes of black hole solutions in general relativity(GR).We observed significant changes in the local topological properties of these black holes compared to GR,depending on the model parameters.Notably,we identified an additional topological class W=O for some values of w that is absent in the GR framework.We also studied the ther-modynamic geometry of the black hole using the Geometrothermodynam-ics(GTD)formalism.Our analysis demonstrates that the singular point,where the GTD scalar curvature diverges,corresponds exactly to the point where the heat capacity changes sign.Additionally,we constrained the model parameters of both models considered by utilizing black hole shadow data from the Sgr A*black hole,measured by the Event Horizon Telescope(EHT).
基金Supported by Sichuan Science and Technology Program(2023NSFSC1352)the starting fund of China West Normal University(20E069,20A013,22kA005)。
文摘We investigated the shadows and optical appearances of a new type of regular black holes(BHs)with a Minkowski core under various spherical accretion scenarios.These BHs are constructed by modifying the Newtonian potential based on the minimum observable length in the Generalized Uncertainty Principle(GUP).They correspond one-to-one with traditional regular BHs featuring a de-Sitter(dS)core(such as Bardeen/Hayward BHs),characterized by a quantum gravity effect parameter(α_(0))and spacetime deformation factor(n).We found that the characteristic parameters give rise to some novel observable features.For these new BHs,both the shadow and photon sphere radii decrease with the increase in α_(0),while the observed specific intensity increases.Conversely,as n increases,the shadow and photon sphere radii increase,while the observed specific intensity decreases.Under different spherical accretion scenarios,the shadows and photon sphere radii remain identical;however,the observed specific intensity is greater under static spherical accretion than under infalling spherical accretion.Additionally,we found that these regular BHs with different cores exhibit variations in shadows and optical appearances,particularly under static spherical accretion.Compared with Bardeen BH,the new BHs exhibit a lower observed specific intensity,a dimmer photon ring,and smaller shadow and photon sphere radii.Larger values of α_(0) lead to more significant differences,and a similar trend was also observed when comparing with Hayward BH.Under infalling spherical accretion,the regular BHs with different cores exhibit only slight differences in observed specific intensity,which become more evident when α_(0) is relatively large.This suggests that the unique spacetime features of these regular BHs with different cores can be distinguished through astronomical observation.
基金supported by the National Nature Science Foundation of China(12275004)。
文摘By incorporating first-order QED effects,we explored the shadows of Kerr-Newman black holes with a magnetic charge through the numerical backward ray-tracing method.Our investigation encompassed both the direct influence of the electromagnetic field on light rays and the distortion of the background spacetime metric due to QED corrections.We found that the area of the shadow increases with the QED effect,mainly owing to the fact that the photons travel more slowly in the effective medium,making them more susceptible to being trapped by the black hole.
基金partly supported by Research(FZ-20200929344,F-FA-2021-510)of the Uzbekistan Ministry for Innovative DevelopmentSERB-DST for project(CRG/2021/005771)。
文摘We investigate the optical properties of the spacetime surrounding a Sen black hole,focusing on the black hole shadow,weak gravitational lensing,and time delay effects.Our analysis reveals that the effective charge of the Sen black hole significantly influences these phenomena.Specifically,an increase in the effective charge leads to a decrease in the radius of the photon sphere and a corresponding decrease in the size of the black hole shadow.Additionally,the bending angle of light rays diminishes as the effective charge increases.Our study provides observational bounds on the effective charge based on these optical characteristics.We also examine the magnification of source brightness using the lens equation and analyze the time delay of light in the presence of a surrounding plasma medium.Our findings offer new insights into the impact of effective charge and plasma on the observational signatures of Sen black holes.
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Supported by the National Natural Science Foundation of China(11675143)the National Key Research and Development Program of China(2020YFC2201503)the support from Research Grant F-FA-2021-432 of the Ministry of Higher Education,Science and Innovations of the Republic of Uzbekistan。
文摘In this study,we investigated the optical properties of charged black holes within the Einstein-Maxwellscalar(EMS)theory.We evaluated the shadow cast by these black holes and obtained analytical solutions for both the radius of the photon sphere and that of the shadow.We observed that black hole parametersγandβboth influence the shadow of black holes.We also found that the photon sphere and shadow radius increase as a consequence of the presence of the parameterγ.Interestingly,the shadow radius decreases first and then remains unchanged owing to the impact of the parameterβ.Finally,we analyzed the weak gravitational lensing and total magnification of lensed images around black holes.We found that the charge of the black holes and the parameterβboth have a significant impact,reducing the deflection angle.Similarly,the same behavior for the total magnification was observed,also as a result of the effect of the charge of the black holes and the parameterβ.
文摘Accompanied by music,a humorous story unfolds as a turtle and a crane engage in playful antics,brought to life through the clever interplay of light and curtain in a Chinese shadow puppetry performance.The audience appears very much entertained,with bursts of laughter echoing throughout the shenanigans unfolding on stage.
