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arXiv 0708.3480math.DG
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四维欧几里得空间中的曲面理论

On the Theory of Surfaces in the Four-dimensional Euclidean Space

Georgi Ganchev, Velichka Milousheva

摘要:

对于四维欧几里得空间中的二维曲面,在曲面的切空间中引入Weingarten型不变线性映射,生成两个不变量k和kappa.条件k = kappa = 0表征由平坦点组成的曲面。极小曲面的特征在于等式kappa^2=k。具有平坦法联络的曲面类的特征在于条件kappa = 0。对于一般类型的曲面,我们在每一点上得到一个几何确定的正交标架场,并导出Frenet型导数公式。我们将这一理论应用于旋转曲面类,证明了这类曲面具有平坦的法向联络,并用常数不变量描述了旋转曲面。

英文摘要:

For a two-dimensional surface in the four-dimensional Euclidean space we introduce an invariant linear map of Weingarten type in the tangent space of the surface, which generates two invariants k and kappa. The condition k = kappa = 0 characterizes the surfaces consisting of flat points. The minimal surfaces are characterized by the equality kappa^2=k. The class of the surfaces with flat normal connection is characterized by the condition kappa = 0. For the surfaces of general type we obtain a geometrically determined orthonormal frame field at each point and derive Frenet-type derivative formulas. We apply our theory to the class of the rotational surfaces, which prove to be surfaces with flat normal connection, and describe the rotational surfaces with constant invariants.

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