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If $u_n\rightharpoonup u$ in $L^2(0,T;L^2(\Omega))$. Can we find a subsequence such that $u_{n_k}(t)\rightharpoonup u(t)$ almost everywhere on $[0,T]$?

I'm not sure if this question is trivial or not, and how to even start! Any hints would be great!


IEdit 1: I would add that $\Omega$ is a bounded open subset of $\mathbb{R}^n$.


Edit 2: I want to apologize for the confusion caused by the symbol "$\rightharpoonup$", which means weak convergence. I used it under the assumption that it is standard.

Thank you for the counter-example and the answer. Bill Johnson mentioned in the comments that the sequence $\{t\mapsto \sin(nt)\}$ converges weakly in $L^2(0,T;L^2(0,1))$, but no subsequence has the sought after property.

Which urges the question: what is a non-trivial sufficient condition so that the question has a positive answer?

If $u_n\rightharpoonup u$ in $L^2(0,T;L^2(\Omega))$. Can we find a subsequence such that $u_{n_k}(t)\rightharpoonup u(t)$ almost everywhere on $[0,T]$?

I'm not sure if this question is trivial or not, and how to even start! Any hints would be great!


I would add that $\Omega$ is a bounded open subset of $\mathbb{R}^n$.

If $u_n\rightharpoonup u$ in $L^2(0,T;L^2(\Omega))$. Can we find a subsequence such that $u_{n_k}(t)\rightharpoonup u(t)$ almost everywhere on $[0,T]$?

I'm not sure if this question is trivial or not, and how to even start! Any hints would be great!


Edit 1: I would add that $\Omega$ is a bounded open subset of $\mathbb{R}^n$.


Edit 2: I want to apologize for the confusion caused by the symbol "$\rightharpoonup$", which means weak convergence. I used it under the assumption that it is standard.

Thank you for the counter-example and the answer. Bill Johnson mentioned in the comments that the sequence $\{t\mapsto \sin(nt)\}$ converges weakly in $L^2(0,T;L^2(0,1))$, but no subsequence has the sought after property.

Which urges the question: what is a non-trivial sufficient condition so that the question has a positive answer?

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If $u_n\rightharpoonup u$ in $L^2(0,T;L^2)$ then there is a subsequence such that $w_n$u_n(t)\rightharpoonup wu(t)$ almost everywhere?

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If $u_n\rightharpoonup u$ in $L^2(0,T;L^2)$ then there is a subsequence such that $w_n(t)\rightharpoonup w(t)$ almost everywhere?

If $u_n\rightharpoonup u$ in $L^2(0,T;L^2(\Omega))$. Can we find a subsequence such that $u_{n_k}(t)\rightharpoonup u(t)$ almost everywhere on $[0,T]$?

I'm not sure if this question is trivial or not, and how to even start! Any hints would be great!


I would add that $\Omega$ is a bounded open subset of $\mathbb{R}^n$.