In order to carry out tensor analysis in a neighborhood of a reference surface,the principal-direction orthogonal basis accompanying with Lame s coefficients or general curvilinear coordinate systems are widely used.A...In order to carry out tensor analysis in a neighborhood of a reference surface,the principal-direction orthogonal basis accompanying with Lame s coefficients or general curvilinear coordinate systems are widely used.A novel kind of field theory termed as the nonholonomic theory of the Principal-Direction Orthonormal Basis(PDOB)is presented systematically in the present paper,in which the formal Christoffel symbols are related directly to the principal and geodesic curvatures with respect to the principal directions of the surface.Furthermore,a systematic and simple way to determine the curvatures of the surface are presented with some examples.It provides a way to recognize qualitatively the bending property of a surface.展开更多
A hypersurface x: M→S^(n+1) without umbilic point is called a Mbius isoparametric hypersurface if its Mbius form Φ=-ρ^(-2)∑_i(ei(H)+∑_j(h_(ij)-Hδ_(ij))e_j(logρ))θ_i vanishes and its Mbius shape operator S=ρ^(...A hypersurface x: M→S^(n+1) without umbilic point is called a Mbius isoparametric hypersurface if its Mbius form Φ=-ρ^(-2)∑_i(ei(H)+∑_j(h_(ij)-Hδ_(ij))e_j(logρ))θ_i vanishes and its Mbius shape operator S=ρ^(-1)(S-Hid) has constant eigenvalues. Here {e_i} is a local orthonormal basis for I=dx·dx with dual basis {θ_i}, II=∑_(ij)h_(ij)θ_iθ_J is the second fundamental form, H=1/n∑_i h_(ij), ρ~2=n/(n-1)(‖II‖~2-nH^2) and S is the shape operator of x. It is clear that any conformal image of a (Euclidean) isoparametric hypersurface in S^(n+1) is a Mbius isoparametric hypersurface, but the converse is not true. In this paper we classify all Mbius isoparametric hypersurfaces in S^(n+1) with two distinct principal curvatures up to Mbius transformations. By using a theorem of Thorbergsson [1] we also show that the number of distinct principal curvatures of a compact Mbius isoparametric hypersurface embedded in S^(n+1) can take only the values 2, 3, 4, 6.展开更多
An umbilical free oriented hypersurfacex:M→Rnwith non-zero principal curvatures is called a Laguerre isoparametric hypersurface if its Laguerre form C=i Ciωi=iρ1(Ei(logρ)(r ri)Ei(r))ωi vanishes and Lague...An umbilical free oriented hypersurfacex:M→Rnwith non-zero principal curvatures is called a Laguerre isoparametric hypersurface if its Laguerre form C=i Ciωi=iρ1(Ei(logρ)(r ri)Ei(r))ωi vanishes and Laguerre shape operator S=ρ1(S 1 rid)has constant eigenvalues.Hereρ=i(r ri)2,r=r1+r2+···+rn 1n 1is the mean curvature radius andSis the shape operator ofx.{Ei}is a local basis for Laguerre metric g=ρ2III with dual basis{ωi}and III is the third fundamental form ofx.In this paper,we classify all Laguerre isoparametric hypersurfaces in Rn(n〉3)with two distinct non-zero principal curvatures up to Laguerre transformations.展开更多
In this paper, we construct a kind of Weingarten surfaces in E3 and study its geometric properties. We first derive an explicit diffierential relationship between the principal curvatures of them. Then we prove an exi...In this paper, we construct a kind of Weingarten surfaces in E3 and study its geometric properties. We first derive an explicit diffierential relationship between the principal curvatures of them. Then we prove an existence theorem of this kind of surfaces with prescribed principal curvatures. At last, we present two examples involving the rotation surfaces as the special case, and present several figures to the second example.展开更多
In this paper, the authors obtain the Backlund transformation on time-like surfaces with constant mean curvature in R2.1. Using this transformation, families of surfaces with constant mean curvature from known ones ca...In this paper, the authors obtain the Backlund transformation on time-like surfaces with constant mean curvature in R2.1. Using this transformation, families of surfaces with constant mean curvature from known ones can be constructed.展开更多
Let Mn be an n-dimensional complete connected and oriented hypersurface in a hyperbolic space H(n+1)(c) with non-zero constant mean curvature H and two distinct principal curvatures. In this paper, we show that ...Let Mn be an n-dimensional complete connected and oriented hypersurface in a hyperbolic space H(n+1)(c) with non-zero constant mean curvature H and two distinct principal curvatures. In this paper, we show that (1) if the multiplicities of the two distinct principal curvatures are greater than 1,then Mn is isometric to the Riemannian product Sk(r)×H(n-k)(-1/(r2 + ρ2)), where r 〉 0 and 1 〈 k 〈 n - 1;(2)if H2 〉 -c and one of the two distinct principal curvatures is simple, then Mn is isometric to the Riemannian product S(n-1)(r) × H1(-1/(r2 +ρ2)) or S1(r) × H(n-1)(-1/(r2 +ρ2)),r 〉 0, if one of the following conditions is satisfied (i) S≤(n-1)t22+c2t(-2)2 on Mn or (ii)S≥ (n-1)t21+c2t(-2)1 on Mn or(iii)(n-1)t22+c2t(-2)2≤ S≤(n-1)t21+c2t(-2)1 on Mn, where t_1 and t_2 are the positive real roots of (1.5).展开更多
Short time existence and uniqueness for the classical motion are studied by the function of the principal curvatures of a smooth surface and the Evans and Spruck's results are generalized.
A spacelike surface M in 3-dimensional de sitter space S13 or 3-dimensional anti-de Sitter space H13 is called isoparametric, if M has constant principal curvatures. A timelike surface is called isoparametric, if its ...A spacelike surface M in 3-dimensional de sitter space S13 or 3-dimensional anti-de Sitter space H13 is called isoparametric, if M has constant principal curvatures. A timelike surface is called isoparametric, if its minimal polynomial of the shape operator is constant. In this paper, we determine the spacelike isoparametric surfaces and the timelike isoparametric surfaces in S13 and H13.展开更多
In this paper,we study hypersurfaces of H^(2)×H^(2).We first classify the hypersurfaces with constant principal curvatures and constant product angle functions.Then we classify homogeneous hypersurfaces and isopa...In this paper,we study hypersurfaces of H^(2)×H^(2).We first classify the hypersurfaces with constant principal curvatures and constant product angle functions.Then we classify homogeneous hypersurfaces and isoparametric hypersurfaces,respectively.Finally,we classify the hypersurfaces with at most two distinct constant principal curvatures,as well as those with three distinct constant principal curvatures under some additional conditions.展开更多
In this paper, we give a characterization of tori S^1 ( √ nr+2-n/nr)×S^n-1(√ n-2/nr) and S^m ( √n/m ) ×S^n-m (√n-m/n). Our result extends the result due to Li (1996)on the condition that M is ...In this paper, we give a characterization of tori S^1 ( √ nr+2-n/nr)×S^n-1(√ n-2/nr) and S^m ( √n/m ) ×S^n-m (√n-m/n). Our result extends the result due to Li (1996)on the condition that M is an n-dimensional complete hypersurface in Sn+1 with two distinct principal curvatures. Keywords principal curvature, Clifford torus, Gauss equations展开更多
In this paper, we provide simple and explicit formulas for computing Riemannian curvatures, mean curvature vectors, principal curvatures and principal directions for a 2-dimensional Riemannian manifold embedded in IRk...In this paper, we provide simple and explicit formulas for computing Riemannian curvatures, mean curvature vectors, principal curvatures and principal directions for a 2-dimensional Riemannian manifold embedded in IRk with k > 3.展开更多
In this paper, we derive evolution equation of the integral of the Gauss curvature on an evolving hypersurface. As an application, we obtain a monotone quantity on the level surface of the potential function on a 3-di...In this paper, we derive evolution equation of the integral of the Gauss curvature on an evolving hypersurface. As an application, we obtain a monotone quantity on the level surface of the potential function on a 3-dimensional steady gradient Ricci soliton with positive sectional curvature, and prove that such a soliton is rotationally symmetric outside of a compact set under a curvature decaying assumption. Along the way we will also apply our evolution equation to some other cases.展开更多
Given a positive function F on S^n which satisfies a convexity condition, we introduce the r-th anisotropic mean curvature Mr for hypersurfaces in R^n+1 which is a generalization of the usual r-th mean curvature Hr. ...Given a positive function F on S^n which satisfies a convexity condition, we introduce the r-th anisotropic mean curvature Mr for hypersurfaces in R^n+1 which is a generalization of the usual r-th mean curvature Hr. We get integral formulas of Minkowski type for compact hypersurfaces in R^n+1. We give some new characterizations of the Wulff shape by the use of our integral formulas of Minkowski type, in case F=1 which reduces to some well-known results.展开更多
Funk metrics are a kind of important Finsler metrics with constant negative flag curvature. In this paper, it is proved that any isoparametric hypersurface in Funk spaces has at most two distinct principal curvatures....Funk metrics are a kind of important Finsler metrics with constant negative flag curvature. In this paper, it is proved that any isoparametric hypersurface in Funk spaces has at most two distinct principal curvatures. Moreover, a complete classification of isoparametric families in a Funk space is given.展开更多
We consider the Bonnet ruled surfaces which admit only one non-trivial isometry that preserves the principal curvatures. We determine the Bonnet ruled surfaces whose generators and orthogonal trajectories form a speci...We consider the Bonnet ruled surfaces which admit only one non-trivial isometry that preserves the principal curvatures. We determine the Bonnet ruled surfaces whose generators and orthogonal trajectories form a special net called an A-net.展开更多
In this paper, we study isoparametric hypersurfaces in Finsler space forms by investigating focal points, tubes and parallel hypersurfaces of submanifolds. We prove that the focal submanifolds of isoparametric hypersu...In this paper, we study isoparametric hypersurfaces in Finsler space forms by investigating focal points, tubes and parallel hypersurfaces of submanifolds. We prove that the focal submanifolds of isoparametric hypersurfaces are anisotropic-minimal and obtain a general Cartan-type formula in a Finsler space form with vanishing reversible torsion, from which we give some classifications on the number of distinct principal curvatures or their multiplicities.展开更多
基金Project supported by the National Natural Science Foundation of China(11972120,11472082,12032016)。
文摘In order to carry out tensor analysis in a neighborhood of a reference surface,the principal-direction orthogonal basis accompanying with Lame s coefficients or general curvilinear coordinate systems are widely used.A novel kind of field theory termed as the nonholonomic theory of the Principal-Direction Orthonormal Basis(PDOB)is presented systematically in the present paper,in which the formal Christoffel symbols are related directly to the principal and geodesic curvatures with respect to the principal directions of the surface.Furthermore,a systematic and simple way to determine the curvatures of the surface are presented with some examples.It provides a way to recognize qualitatively the bending property of a surface.
基金Partially supported by NSFCPartially supported by TU Berlin, DFG, SRF, SEM+2 种基金Partially supported by Qiushi Award. 973 Project, RFDPthe Jiechu GrantPartially supported by DFG, NSFC and Qiushi Award
文摘A hypersurface x: M→S^(n+1) without umbilic point is called a Mbius isoparametric hypersurface if its Mbius form Φ=-ρ^(-2)∑_i(ei(H)+∑_j(h_(ij)-Hδ_(ij))e_j(logρ))θ_i vanishes and its Mbius shape operator S=ρ^(-1)(S-Hid) has constant eigenvalues. Here {e_i} is a local orthonormal basis for I=dx·dx with dual basis {θ_i}, II=∑_(ij)h_(ij)θ_iθ_J is the second fundamental form, H=1/n∑_i h_(ij), ρ~2=n/(n-1)(‖II‖~2-nH^2) and S is the shape operator of x. It is clear that any conformal image of a (Euclidean) isoparametric hypersurface in S^(n+1) is a Mbius isoparametric hypersurface, but the converse is not true. In this paper we classify all Mbius isoparametric hypersurfaces in S^(n+1) with two distinct principal curvatures up to Mbius transformations. By using a theorem of Thorbergsson [1] we also show that the number of distinct principal curvatures of a compact Mbius isoparametric hypersurface embedded in S^(n+1) can take only the values 2, 3, 4, 6.
基金Supported by National Natural Science Foundation of China(Grant No.10826062)Natural Science Foundation of Fujian Province of China(Grant No.2012J01020)the Fundamental Research Funds for the Central Universities(Grant No.2011121040)
文摘An umbilical free oriented hypersurfacex:M→Rnwith non-zero principal curvatures is called a Laguerre isoparametric hypersurface if its Laguerre form C=i Ciωi=iρ1(Ei(logρ)(r ri)Ei(r))ωi vanishes and Laguerre shape operator S=ρ1(S 1 rid)has constant eigenvalues.Hereρ=i(r ri)2,r=r1+r2+···+rn 1n 1is the mean curvature radius andSis the shape operator ofx.{Ei}is a local basis for Laguerre metric g=ρ2III with dual basis{ωi}and III is the third fundamental form ofx.In this paper,we classify all Laguerre isoparametric hypersurfaces in Rn(n〉3)with two distinct non-zero principal curvatures up to Laguerre transformations.
基金Supported by the SDFDP (Grant No.20050141011)the MATH+X Project Offiered by Dalian University of Technology (Grant No.MXDUT073005)
文摘In this paper, we construct a kind of Weingarten surfaces in E3 and study its geometric properties. We first derive an explicit diffierential relationship between the principal curvatures of them. Then we prove an existence theorem of this kind of surfaces with prescribed principal curvatures. At last, we present two examples involving the rotation surfaces as the special case, and present several figures to the second example.
基金the NNSF(19971084,10101025 and 10231050)of China
文摘In this paper, the authors obtain the Backlund transformation on time-like surfaces with constant mean curvature in R2.1. Using this transformation, families of surfaces with constant mean curvature from known ones can be constructed.
基金supported by NSF of Shaanxi Province (SJ08A31)NSF of Shaanxi Educational Committee (2008JK484+1 种基金2010JK642)Talent Fund of Xi'an University of Architecture and Technology
文摘Let Mn be an n-dimensional complete connected and oriented hypersurface in a hyperbolic space H(n+1)(c) with non-zero constant mean curvature H and two distinct principal curvatures. In this paper, we show that (1) if the multiplicities of the two distinct principal curvatures are greater than 1,then Mn is isometric to the Riemannian product Sk(r)×H(n-k)(-1/(r2 + ρ2)), where r 〉 0 and 1 〈 k 〈 n - 1;(2)if H2 〉 -c and one of the two distinct principal curvatures is simple, then Mn is isometric to the Riemannian product S(n-1)(r) × H1(-1/(r2 +ρ2)) or S1(r) × H(n-1)(-1/(r2 +ρ2)),r 〉 0, if one of the following conditions is satisfied (i) S≤(n-1)t22+c2t(-2)2 on Mn or (ii)S≥ (n-1)t21+c2t(-2)1 on Mn or(iii)(n-1)t22+c2t(-2)2≤ S≤(n-1)t21+c2t(-2)1 on Mn, where t_1 and t_2 are the positive real roots of (1.5).
文摘Short time existence and uniqueness for the classical motion are studied by the function of the principal curvatures of a smooth surface and the Evans and Spruck's results are generalized.
文摘A spacelike surface M in 3-dimensional de sitter space S13 or 3-dimensional anti-de Sitter space H13 is called isoparametric, if M has constant principal curvatures. A timelike surface is called isoparametric, if its minimal polynomial of the shape operator is constant. In this paper, we determine the spacelike isoparametric surfaces and the timelike isoparametric surfaces in S13 and H13.
基金supported by National Natural Science Foundation of China (Grant Nos. 11831005, 12061131014 and 12171437)China Postdoctoral Science Foundation (Grant No. 2022M721871)
文摘In this paper,we study hypersurfaces of H^(2)×H^(2).We first classify the hypersurfaces with constant principal curvatures and constant product angle functions.Then we classify homogeneous hypersurfaces and isoparametric hypersurfaces,respectively.Finally,we classify the hypersurfaces with at most two distinct constant principal curvatures,as well as those with three distinct constant principal curvatures under some additional conditions.
文摘In this paper, we give a characterization of tori S^1 ( √ nr+2-n/nr)×S^n-1(√ n-2/nr) and S^m ( √n/m ) ×S^n-m (√n-m/n). Our result extends the result due to Li (1996)on the condition that M is an n-dimensional complete hypersurface in Sn+1 with two distinct principal curvatures. Keywords principal curvature, Clifford torus, Gauss equations
基金The first author was supported in part by NSF (10241004) of ChinaNational Innovation Fund 1770900+2 种基金 Chinese Academy of Sciencesthe second author was supported in part by NSF grants CCR 9732306KDI-DMS-9873326.
文摘In this paper, we provide simple and explicit formulas for computing Riemannian curvatures, mean curvature vectors, principal curvatures and principal directions for a 2-dimensional Riemannian manifold embedded in IRk with k > 3.
基金Supported by National Natural Science Foundation of China (Grant No. 10926062)Advanced Program for Returned Chinese Overseas Scholars by the Department of Human Resources and Social Security of Zhejiang Province
文摘In this paper, we derive evolution equation of the integral of the Gauss curvature on an evolving hypersurface. As an application, we obtain a monotone quantity on the level surface of the potential function on a 3-dimensional steady gradient Ricci soliton with positive sectional curvature, and prove that such a soliton is rotationally symmetric outside of a compact set under a curvature decaying assumption. Along the way we will also apply our evolution equation to some other cases.
基金Tianyuan Fund for Mathematics of NSFC (Grant No.10526030)Grant No.10531090 of the NSFCDoctoral Program Foundation of the Ministry of Education of China (2006)
文摘Given a positive function F on S^n which satisfies a convexity condition, we introduce the r-th anisotropic mean curvature Mr for hypersurfaces in R^n+1 which is a generalization of the usual r-th mean curvature Hr. We get integral formulas of Minkowski type for compact hypersurfaces in R^n+1. We give some new characterizations of the Wulff shape by the use of our integral formulas of Minkowski type, in case F=1 which reduces to some well-known results.
基金supported by National Natural Science Foundation of China (Grant No. 11471246)Anhui Provincial Natural Science Foundation (Grant No. 1608085MA03)Natural Science Foundation of Higher Education in Anhui Province (Grant No. KJ2014A257)
文摘Funk metrics are a kind of important Finsler metrics with constant negative flag curvature. In this paper, it is proved that any isoparametric hypersurface in Funk spaces has at most two distinct principal curvatures. Moreover, a complete classification of isoparametric families in a Funk space is given.
文摘We consider the Bonnet ruled surfaces which admit only one non-trivial isometry that preserves the principal curvatures. We determine the Bonnet ruled surfaces whose generators and orthogonal trajectories form a special net called an A-net.
基金supported by National Natural Science Foundation of China (Grant Nos. 11971253 and 11471246)AnHui Natural Science Foundation (Grant No. 1608085MA03)。
文摘In this paper, we study isoparametric hypersurfaces in Finsler space forms by investigating focal points, tubes and parallel hypersurfaces of submanifolds. We prove that the focal submanifolds of isoparametric hypersurfaces are anisotropic-minimal and obtain a general Cartan-type formula in a Finsler space form with vanishing reversible torsion, from which we give some classifications on the number of distinct principal curvatures or their multiplicities.