A remark on harmonic maps into the unit sphere

2013 ◽  
Vol 1 ◽  
pp. 149-157 ◽  
Author(s):  
Junichi Aramaki
Keyword(s):  
2019 ◽  
Vol 0 (0) ◽  
Author(s):  
David Kalaj

Abstract Given two annuli {\mathbb{A}(r,R)} and {\mathbb{A}(r_{\ast},R_{\ast})} , in {\mathbf{R}^{3}} equipped with the Euclidean metric and the weighted metric {\lvert y\rvert^{-2}} , respectively, we minimize the Dirichlet integral, i.e., the functional \mathscr{F}[f]=\int_{\mathbb{A}(r,R)}\frac{\lVert Df\rVert^{2}}{\lvert f\rvert% ^{2}}, where f is a homeomorphism between {\mathbb{A}(r,R)} and {\mathbb{A}(r_{\ast},R_{\ast})} , which belongs to the Sobolev class {\mathscr{W}^{1,2}} . The minimizer is a certain generalized radial mapping, i.e., a mapping of the form {f(\lvert x\rvert\eta)=\rho(\lvert x\rvert)T(\eta)} , where T is a conformal mapping of the unit sphere onto itself and {\rho(t)={R_{\ast}}\bigl{(}\frac{r_{\ast}}{R_{\ast}}\bigr{)}^{{\frac{R(r-t)}{(% R-r)t}}}} . It should be noticed that, in this case, no Nitsche phenomenon occurs.


Filomat ◽  
2019 ◽  
Vol 33 (16) ◽  
pp. 5167-5180
Author(s):  
Selcen Perktaş ◽  
Adara Blaga ◽  
Feyza Erdoğan ◽  
Bilal Acet

In the present paper, we study bi-f-harmonic maps which generalize not only f-harmonic maps, but also biharmonic maps. We derive bi-f-harmonic equations for curves in the Euclidean space, unit sphere, hyperbolic space, and for hypersurfaces of Riemannian manifolds.


2020 ◽  
Vol 7 (1) ◽  
pp. 129-140
Author(s):  
Robert Ream

AbstractIn this paper we study an analog of minimal surfaces called Weyl-minimal surfaces in conformal manifolds with a Weyl connection (M4, c, D). We show that there is an Eells-Salamon type correspondence between nonvertical 𝒥-holomorphic curves in the weightless twistor space and branched Weyl-minimal surfaces. When (M, c, J) is conformally almost-Hermitian, there is a canonical Weyl connection. We show that for the canonical Weyl connection, branched Weyl-minimal surfaces satisfy the adjunction inequality\chi \left( {{T_f}\sum } \right) + \chi \left( {{N_f}\sum } \right) \le \pm {c_1}\left( {f*{T^{\left( {1,0} \right)}}M} \right).The ±J-holomorphic curves are automatically Weyl-minimal and satisfy the corresponding equality. These results generalize results of Eells-Salamon and Webster for minimal surfaces in Kähler 4-manifolds as well as their extension to almost-Kähler 4-manifolds by Chen-Tian, Ville, and Ma.


2021 ◽  
Vol 51 (3) ◽  
Author(s):  
Václav Voráček ◽  
Mirko Navara

AbstractWe show that there is no non-constant assignment of zeros and ones to points of a unit sphere in $$\mathbb{R}^3$$ R 3 such that for every three pairwisely orthogonal vectors, an odd number of them is assigned 1. This is a new strengthening of the Bell–Kochen–Specker theorem, which proves the non-existence of hidden variables in quantum theories.


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