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Search Results: 1 - 10 of 461779 matches for " A. Caminha "
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Minimal Lie group homomorphisms
A. Caminha
Mathematics , 2009,
Abstract: Let $G_1$ and $G_2$ be Lie groups furnished with bi-invariant metrics and $f:G_1\rightarrow G_2$ be a Lie group homomorphism which is also a minimal isometric immersion. If $G_1$ is compact and connected, we prove that either $G_1$ is isometric to a flat torus or $f$ is unstable as a harmonic map. We also apply this result to the case in which $f$ is the inclusion of a compact, connected Lie subgroup of a Lie group, as well as to construct several examples of unstable harmonic maps into the orthogonal group.
The geometry of closed conformal vector fields on Riemannian spaces
A. Caminha
Mathematics , 2009,
Abstract: In this paper we examine different aspects of the geometry of closed conformal vector fields on Riemannian manifolds. We begin by getting obstructions to the existence of closed conformal and nonparallel vector fields on complete manifolds with nonpositive Ricci curvature, thus generalizing a theorem of T. K. Pan. Then we explain why it is so difficult to find examples, other than trivial ones, of spaces having at least two closed, conformal and homothetic vector fields. We then focus on isometric immersions, firstly generalizing a theorem of J. Simons on cones with parallel mean curvature to spaces furnished with a closed, Ricci null conformal vector field; then we prove general Bernstein-type theorems for certain complete, not necessarily cmc, hypersurfaces of Riemannian manifolds furnished with closed conformal vector fields. In particular, we obtain a generalization of theorems J. Jellett and A. Barros and P. Sousa for complete cmc radial graphs over finitely punctured geodesic spheres of Riemannian space forms.
Stability of Spacelike Hypersurfaces in Foliated Spacetimes
A. Barros,A. Brasil,A. Caminha
Mathematics , 2006,
Abstract: We show that a given $x:M^n\to \bar{M}^{n+1}=I\times_{\phi}F^{n}$ closed spacelike hypersurface with constant mean curvature $H$ and warping function $\phi$ satisfying \phi ''\geq \ma\{H\phi'',0\}$ is either minimal or a spacelike slice $\{t_{o}\}\times F$ for some $t_{o}\in I$.
Complete Foliations of Space Forms by Hypersurfaces
A. Caminha,P. Sousa,F. Camargo
Mathematics , 2009,
Abstract: We study foliations of space forms by complete hypersurfaces, under some mild conditions on its higher order mean curvatures. In particular, in Euclidean space we obtain a Bernstein-type theorem for graphs whose mean and scalar curvature do not change sign but may otherwise be nonconstant. We also establish the nonexistence of foliations of the standard sphere whose leaves are complete and have constant scalar curvature, thus extending a theorem of Barbosa, Kenmotsu and Oshikiri. For the more general case of {\em r-}minimal foliations of the Euclidean space, possibly with a singular set, we are able to invoke a theorem of Ferus to give conditions under which the nonsigular leaves are foliated by hyperplanes.
Lavagem nasal como método de avalia??o das cavidades nasais
Caminha, Guilherme P.;Cain, William S.;Jalowayski, Alfredo A.;
Revista Brasileira de Otorrinolaringologia , 2001, DOI: 10.1590/S0034-72992001000600016
Abstract: the evaluation of the nasal cavities of subjects with nasal pathologies and those exposed to environmental contaminants is very important. nasal mucosal histology is similar to that in the lower airways. therefore, an inflammatory response seen in the nasal passages may be a warning signal of inflammation in the lower airways. biomarkers in the nasal cavities can be easily detected in many ways. however, it is necessary to have a method of quantifying this effects that is safe and simple to perform. nasal lavage fulfills these criteria and should be considered when studying this area.
Lavagem nasal como método de avalia o das cavidades nasais
Caminha Guilherme P.,Cain William S.,Jalowayski Alfredo A.
Revista Brasileira de Otorrinolaringologia , 2001,
Abstract: A avalia o das cavidades nasais é extremamente importante nos indivíduos portadores de patologias nasais e nos que est o expostos a substancias potencialmente nocivas presentes no meio ambiente. Como a histologia da mucosa nasal é similar à das vias respiratórias inferiores, uma resposta inflamatória vista no nariz pode ser um sinal de alerta de inflama o na via aérea inferior. A presen a de biomarcadores nas cavidades nasais pode ser facilmente detectada através de inúmeras técnicas. Entretanto, é necessário dispormos de um método para avalia o das altera es encontradas nesta regi o que seja simples e seguro. A lavagem nasal preenche estes critérios e deve ser considerada sempre que se deseje estudar esta regi o.
On the Geometry of Conformally Stationary Lorentz Spaces
F. Camargo,A. Caminha,H. de Lima,M. Velasquez
Mathematics , 2010,
Abstract: In this paper we study several aspects of the geometry of conformally stationary Lorentz manifolds, and particularly of GRW spaces, due to the presence of a closed conformal vector field. More precisely, we begin by extending to these spaces a result of J. Simons on the minimality of cones in Euclidean space, and apply it to the construction of complete, noncompact maximal submanifolds of both de Sitter and anti-de Sitter spaces. Then we state and prove very general Bernstein-type theorems for spacelike hypersurfaces in conformally stationary Lorentz manifolds, one of which not assuming the hypersurface to be of constant mean curvature. Finally, we study the strong $r$-stability of spacelike hypersurfaces of constant $r$-th mean curvature in a conformally stationary Lorentz manifold of constant sectional curvature, extending previous results in the current literature.
On the $r-$stability of spacelike hypersurfaces
F. Camargo,A. Caminha,H. de Lima,M. Silva
Mathematics , 2009, DOI: 10.1016/j.geomphys.2010.05.004
Abstract: In this paper we study the strong stability of spacelike hypersurfaces with constant $r$-th mean curvature in Generalized Robertson-Walker spacetimes of constant sectional curvature. In particular, we treat the case in which the ambient spacetime is the de Sitter space.
On the stability of minimal cones in warped products
K. S. Bezerra,A. Caminha,B. P. Lima
Mathematics , 2014,
Abstract: In a seminal paper published in $1968$, J. Simons proved that, for $n\leq 5$, the Euclidean (minimal) cone $CM$, built on a closed, oriented, minimal and non totally geodesic hypersurface $M^n$ of $\mathbb S^{n+1}$ is unstable. In this paper, we extend Simons' analysis to {\em warped} (minimal) cones built over a closed, oriented, minimal hypersurface of a leaf of suitable warped product spaces. Then, we apply our general results to the particular case of the warped product model of the Euclidean sphere, and establish the unstability of $CM$, whenever $2\leq n\leq 14$ and $M^n$ is a closed, oriented, minimal and non totally geodesic hypersurface of $\mathbb S^{n+1}$.
$r$-Stable Hypersurfaces in Conformally Stationary Spacetimes
F. Camargo,A. Caminha,H. de Lima,M. Velásquez
Mathematics , 2010,
Abstract: In this paper we study the r-stability of closed spacelike hypersurfaces with constant $r$-th mean curvature in conformally stationary spacetimes of constant sectional curvature. In this setting, we obtain a characterization of $r-$stability through the analysis of the first eigenvalue of an operator naturally attached to the $r$-th mean curvature. As an application, we treat the case in which the spacetime is the de Sitter space.
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