scholarly journals Sharp one-sided curvature estimates for fully nonlinear curvature flows and applications to ancient solutions

2020 ◽  
Vol 2020 (765) ◽  
pp. 1-33
Author(s):  
Mat Langford ◽  
Stephen Lynch
Keyword(s):  
Principal Curvature ◽  
Sharp Estimate ◽  
Fully Nonlinear ◽  
Sharp Estimates ◽  
Ancient Solutions ◽  
Curvature Estimates ◽  
Recent Idea

AbstractWe prove several sharp one-sided pinching estimates for immersed and embedded hypersurfaces evolving by various fully nonlinear, one-homogeneous curvature flows by the method of Stampacchia iteration. These include sharp estimates for the largest principal curvature and the inscribed curvature (“cylindrical estimates”) for flows by concave speeds and a sharp estimate for the exscribed curvature for flows by convex speeds. Making use of a recent idea of Huisken and Sinestrari, we then obtain corresponding estimates for ancient solutions. In particular, this leads to various characterisations of the shrinking sphere amongst ancient solutions of these flows.

scholarly journals Optimal Curvature Estimates for Homogeneous Ricci Flows

2017 ◽  
Vol 2019 (14) ◽  
pp. 4431-4468 ◽  
Author(s):  
Christoph Böhm ◽  
Ramiro Lafuente ◽  
Miles Simon
Keyword(s):  
Homogeneous Space ◽  
Homogeneous Spaces ◽  
Convergence Result ◽  
Einstein Metric ◽  
Type I ◽  
Extinction Time ◽  
Ricci Flows ◽  
Gap Theorem ◽  
Ancient Solutions ◽  
Curvature Estimates

AbstractWe prove uniform curvature estimates for homogeneous Ricci flows: For a solution defined on $[0,t]$ the norm of the curvature tensor at time $t$ is bounded by the maximum of $C(n)/t$ and $C(n)({\mathrm{scal}}(g(t)) - {\mathrm{scal}}(g(0)) )$. This is used to show that solutions with finite extinction time are Type I, immortal solutions are Type III and ancient solutions are Type I, with constants depending only on the dimension $n$. A further consequence is that a non-collapsed homogeneous ancient solution on a compact homogeneous space emerges from a unique Einstein metric on that space. The above curvature estimates follow from a gap theorem for Ricci-flatness on homogeneous spaces. This theorem is proved by contradiction, using a local $W^{2,p}$ convergence result which holds without symmetry assumptions.

scholarly journals Power convexity of a class of Hessian equations in the ball

2015 ◽  
Vol 3 (3) ◽  
pp. 134
Author(s):  
Yunhua Ye
Keyword(s):  
Lower Bound ◽  
Gaussian Curvature ◽  
Principal Curvature ◽  
Power Functions ◽  
Strictly Convex ◽  
Hessian Equations ◽  
Curvature Estimates ◽  
Admissible Solutions ◽  
Special Case

<p>Power convexities of a class of Hessian equations are considered in this paper. It is proved that some power functions of the smooth admissible solutions to the Hessian equations are strictly convex in the ball. For a special case of the equation, a lower bound principal curvature and Gaussian curvature estimates are given.</p>

scholarly journals Sharp estimates of approximation of classes of differentiable functions by entire functions

2021 ◽  
pp. 3
Author(s):  
V.F. Babenko ◽  
A.Yu. Gromov
Keyword(s):  
Exponential Type ◽  
Best Approximation ◽  
Entire Functions ◽  
Sharp Estimate ◽  
Sharp Estimates ◽  
The Best Approximation ◽  
Differentiable Functions ◽  
Functions Of Exponential Type

In the paper, we find the sharp estimate of the best approximation, by entire functions of exponential type not greater than $\sigma$, for functions $f(x)$ from the class $W^r H^{\omega}$ such that $\lim\limits_{x \rightarrow -\infty} f(x) = \lim\limits_{x \rightarrow \infty} f(x) = 0$,$$A_{\sigma}(W^r H^{\omega}_0)_C = \frac{1}{\sigma^{r+1}} \int\limits_0^{\pi} \Phi_{\pi, r}(t)\omega'(t/\sigma)dt$$for $\sigma > 0$, $r = 1, 2, 3, \ldots$ and concave modulus of continuity.Also, we calculate the supremum$$\sup\limits_{\substack{f\in L^{(r)}\\f \ne const}} \frac{\sigma^r A_{\sigma}(f)_L}{\omega (f^{(r)}, \pi/\sigma)_L} = \frac{K_L}{2}$$

scholarly journals Type II ancient compact solutions to the Yamabe flow

2018 ◽  
Vol 2018 (738) ◽  
pp. 1-71 ◽  
Author(s):  
Panagiota Daskalopoulos ◽  
Manuel del Pino ◽  
Natasa Sesum
Keyword(s):  
Curvature Operator ◽  
Type Ii ◽  
Toda System ◽  
Yamabe Flow ◽  
Sharp Estimates ◽  
Ancient Solutions ◽  
Rotationally Symmetric ◽  
New Type ◽  
Error Terms ◽  
The Right

AbstractWe construct new type II ancient compact solutions to the Yamabe flow. Our solutions are rotationally symmetric and converge, as{t\to{-}\infty}, to a tower of two spheres. Their curvature operator changes sign. We allow two time-dependent parameters in our ansatz. We use perturbation theory, via fixed point arguments, based on sharp estimates on ancient solutions of the approximated linear equation and careful estimation of the error terms which allow us to make the right choice of parameters. Our technique may be viewed as a parabolic analogue of gluing two exact solutions to the rescaled equation, that is the spheres, with narrow cylindrical necks to obtain a new ancient solution to the Yamabe flow. The result generalizes to the gluing ofkspheres for any{k\geq 2}, in such a way the configuration of radii of the spheres glued is driven as{t\to{-}\infty}by aFirst order Toda system.

Farfield extension of fully nonlinear nearfield ship waves

1999 ◽  
Author(s):  
Chi Yang ◽  
Rainald Lohner ◽  
Francis Noblesse
Keyword(s):  
Fully Nonlinear ◽  
Ship Waves
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