Big and small elements in Chevalley groups

Let $\widetilde G$ be a reductive algebraic group which is defined and split over a field $K$. Here we consider the Zariski open subset $\mathfrak B$ of the group $\widetilde G$ which consists of elements such that their conjugacy classes intersect the Big Bruhat Cell. In particular, we give a description of the set $\mathfrak B(K)$ in the case $\widetilde G=\mathrm{GL}_n,\mathrm{SL}_n$. Bibl. 16 titles.