We construct a branched Helfrich immersion satisfying Dirichlet boundary conditions. The number of branch points is finite. We proceed by a variational argument and hence examine the Helfrich energy for oriented varifolds. The main contribution of this paper is a lower semicontinuity result with respect to oriented varifold convergence for the Helfrich energy and a minimising sequence. For arbitrary sequences this is false by a counterexample of Große-Brauckmann.Keywords. Dirichlet boundary conditions, Helfrich immersion, Existence MSC. 35J35, 35J40, 58J32, 49Q20, 49Q10 * The author thanks Prof. Reiner Schätzle for discussing the Helfrich energy and providing insight into geometric measure theory.

In this paper, existence for Willmore surfaces of revolution is shown, which satisfy non-symmetric Dirichlet boundary conditions, if the infimum of the Willmore energy in the admissible class is strictly below {4\pi}. Under a more restrictive but still explicit geometric smallness condition we obtain a quite interesting additional geometric information: The profile curve of this solution can be parameterised as a graph over the x-axis. By working below the energy threshold of {4\pi} and reformulating the problem in the Poincaré half plane, compactness of a minimising sequence is guaranteed, of which the limit is indeed smooth. The last step consists of two main ingredients: We analyse the Euler–Lagrange equation by an order reduction argument by Langer and Singer and modify, when necessary, our solution with the help of suitable parts of catenoids and circles.

We minimise the Canham–Helfrich energy in the class of closed immersions with prescribed genus, surface area, and enclosed volume. Compactness is achieved in the class of oriented varifolds. The main result is a lower-semicontinuity estimate for the minimising sequence, which is in general false under varifold convergence by a counter example by Große-Brauckmann. The main argument involved is showing partial regularity of the limit. It entails comparing the Helfrich energy of the minimising sequence locally to that of a biharmonic graph. This idea is by Simon, but it cannot be directly applied, since the area and enclosed volume of the graph may differ. By an idea of Schygulla we adjust these quantities by using a two parameter diffeomorphism of $${{\mathbb {R}}}^3$$ R 3 .

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In this article, we consider positivity issues for the clamped plate equation with high tension $$\gamma >0$$ γ > 0 . This equation is given by $$\Delta ^2u - \gamma \Delta u=f$$ Δ 2 u - γ Δ u = f under clamped boundary conditions. Here, we show that given a positive f, i.e. upwards pushing, we find a $$\gamma _0>0$$ γ 0 > 0 such that for all $$\gamma \ge \gamma _0$$ γ ≥ γ 0 the bending u is indeed positive. This $$\gamma _0$$ γ 0 only depends on the domain and the ratio of the $$L^1$$ L 1 and $$L^\infty $$ L ∞ norm of f. In contrast to a recent result by Cassani and Tarsia, our approach is valid in all dimensions.