1. Given that the circumradius of $\triangle A B C$ is $R$, and
$$
2 R\left(\sin ^{2} A-\sin ^{2} C\right)=(\sqrt{2} a-b) \sin B,
$$

where $a$ and $b$ are the sides opposite to $\angle A$ and $\angle B$ respectively. Then the size of $\angle C$ is