فهرست نشریات علمی دسترسی آزاد ایران

In this article, firstly we investigate some properties of the boundary curvature of the numerical range. In the next, we define $M(T)$ as the smallest constant such that $dist(\lambda,\sigma(T))\leq M(T) R_\lambda (T),$ for all $\lambda \in \partial W(T)$, where $R_\lambda (T)$, the radius curvature at the point $\lambda$, is defined. Also, we investigate for non-convexoid $T$, $M(T)=\sup\frac{dist(\lambda,\sigma(T))}{R_{\lambda}(T)}$, where the supremum on the right-hand side is taken along all points $\lambda\in \partial W(T)$ with finite non-zero curvature. Finally, the value of $M(T)$ will be calculated for the self-inverse operators.