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Lower semicontinuity of some functionals under PDE constraints: An \mathcal{A}-quasiconvex pair
Authors:A V Demyanov
Institution:(1) St. Petersburg State University, St.Petersburg, Russia
Abstract:The problem of establishing necessary and sufficient conditions for l.s.c. under PDE constraints is studied for a special class of functionals:

$$(u,v,\chi ) \mapsto \int_\Omega  {\left\{ {\chi (x) \cdot F^ +  (x,u(x),v(x)) + (1 - \chi (x)) \cdot F^ -  (x,u(x),v(x)) + (1 - \chi (x))} \right\}} dx,$$
with respect to the convergence un → u in measure, vn ⇀ v in Lp(Ω;ℝd) 
$$\mathcal{A}v_n  \to 0$$
in W−1,p(Ω), and χn ⇀ χ in Lp(Ω), where χn ∈ Z:= {χ ∈ L(Ω): 0 ≤ χ(x) ≤ 1 for a.e. x}. Here 
$$\mathcal{A}v = \sum\nolimits_{i = 1}^N {A^{(i)} \tfrac{{\partial v}}{{\partial x_i }}} $$
is a constant-rank partial differential operator. The main result is that if the characteristic cone of 
$$\mathcal{A}$$
has the full dimension, then the l.s.c. is equivalent to the fact that the F± are both 
$$\mathcal{A}$$
-quasiconvex and

$$F^ +  (x,u, \cdot ) - F^ -  (x,u, \cdot ) \equiv C(x,u)$$
for a.e. x ∈ Ω and for all u ∈ ℝd. As a corollary, we obtain several results for the functional

$$(u,v,\chi ) \mapsto \int_\Omega  {\chi (x) \cdot f(x,u(x),v(x))dx} $$
with respect to the same convergence. We show that this functional is l.s.c. iff

$$f(x,u,v) \equiv g(x,u).$$
Bibliography: 14 titles. Published in Zapiski Nauchnykh Seminarov POMI, Vol. 318, 2004, pp. 100–119.
Keywords:
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