Let G be a finite group of order n. The strong power graph of G is the undirected graph whose vertex set is G and two distinct vertices x and y are adjacent if x^n1 = y^n2 for some positive integers n1,n2 < n. In t...Let G be a finite group of order n. The strong power graph of G is the undirected graph whose vertex set is G and two distinct vertices x and y are adjacent if x^n1 = y^n2 for some positive integers n1,n2 < n. In this paper, we give the characteristic polynomials of the distance and adjacency matrix of the strong power graph of G, and compute its distance and adjacency spectrum.展开更多
.The intersection power graph of a finite group G is a simple graph whose vertex set is G,in which two distinct vertices and y are adjacent if and only if either one of a and y is the identity element,or(a)n(y)is non-....The intersection power graph of a finite group G is a simple graph whose vertex set is G,in which two distinct vertices and y are adjacent if and only if either one of a and y is the identity element,or(a)n(y)is non-trivial.A number of important graph classes,including cographs,chordal graphs,split graphs,and threshold graphs,can be defined either structurally or in terms of forbidden induced subgraphs.In this paper,we characterize the finite groups whose intersection power graphs are cographs,split graphs,and threshold graphs.We also classify the finite nilpotent groups whose intersection power graphs are chordal.展开更多
The bidirectional reflectance distribution function(BRDF)of the land surface contains information relating to its physical structure and composition.Accurate BRDF modeling for heterogeneous pixels is important for glo...The bidirectional reflectance distribution function(BRDF)of the land surface contains information relating to its physical structure and composition.Accurate BRDF modeling for heterogeneous pixels is important for global ecosystem monitoring and radiation balance studies.However,the original kerneldriven models,which many operational BRDF/Albedo algorithms have adopted,do not explicitly consider the heterogeneity within heterogeneous pixels,which may result in large fitting residuals.In this paper,we attempted to improve the fitting ability of the kernel-driven models over heterogeneous pixels by changing the inversion approach and proposed a dynamic weighted least squares(DWLS)inversion approach.The performance of DWLS and the traditional ordinary least squares(OLS)inversion approach were compared using simulated data.We also evaluated its ability to reconstruct multiangle satellite observations and provide accurate BRDF using unmanned aerial vehicle observations.The results show that the developed DWLS approach improves the accuracy of modeled BRDF of heterogeneous pixels.The DWLS approach applied to satellite observations shows better performance than the OLS method in study regions and exhibits smaller mean fitting residuals both in the red and near-infrared bands.The DWLS approach also shows higher BRDF modeling accuracy than the OLS approach with unmanned aerial vehicle observations.These results indicate that the DWLS inversion approach can be a better choice when kernel-driven models are used for heterogeneous pixels.展开更多
基金Supported by the National Natural Science Foundation of China(Grant No.11801441)the Scientific Research Program Funded by Shaanxi Provincial Education Department(Program No.18JK0623)the Natural Science Foundation of Shaanxi Province(Grant No.2019JQ-056)
文摘Let G be a finite group of order n. The strong power graph of G is the undirected graph whose vertex set is G and two distinct vertices x and y are adjacent if x^n1 = y^n2 for some positive integers n1,n2 < n. In this paper, we give the characteristic polynomials of the distance and adjacency matrix of the strong power graph of G, and compute its distance and adjacency spectrum.
基金supported by the National Natural Science Foundation of China(Grant Nos.11801441,61976244)the Natural Science Basic Research Program of Shaanxi(Program No.2020JQ-761)the Shaanxi Fundamental Science Research Project for Mathematics and Physics(Grant No.22JSQ024).
文摘.The intersection power graph of a finite group G is a simple graph whose vertex set is G,in which two distinct vertices and y are adjacent if and only if either one of a and y is the identity element,or(a)n(y)is non-trivial.A number of important graph classes,including cographs,chordal graphs,split graphs,and threshold graphs,can be defined either structurally or in terms of forbidden induced subgraphs.In this paper,we characterize the finite groups whose intersection power graphs are cographs,split graphs,and threshold graphs.We also classify the finite nilpotent groups whose intersection power graphs are chordal.
基金supported by the National Natural Science Foundation of China(Nos.42090013,42192580,and 42271356).
文摘The bidirectional reflectance distribution function(BRDF)of the land surface contains information relating to its physical structure and composition.Accurate BRDF modeling for heterogeneous pixels is important for global ecosystem monitoring and radiation balance studies.However,the original kerneldriven models,which many operational BRDF/Albedo algorithms have adopted,do not explicitly consider the heterogeneity within heterogeneous pixels,which may result in large fitting residuals.In this paper,we attempted to improve the fitting ability of the kernel-driven models over heterogeneous pixels by changing the inversion approach and proposed a dynamic weighted least squares(DWLS)inversion approach.The performance of DWLS and the traditional ordinary least squares(OLS)inversion approach were compared using simulated data.We also evaluated its ability to reconstruct multiangle satellite observations and provide accurate BRDF using unmanned aerial vehicle observations.The results show that the developed DWLS approach improves the accuracy of modeled BRDF of heterogeneous pixels.The DWLS approach applied to satellite observations shows better performance than the OLS method in study regions and exhibits smaller mean fitting residuals both in the red and near-infrared bands.The DWLS approach also shows higher BRDF modeling accuracy than the OLS approach with unmanned aerial vehicle observations.These results indicate that the DWLS inversion approach can be a better choice when kernel-driven models are used for heterogeneous pixels.
