Inverse spectral problems for integro-differential operators address the challenge of reconstructing the underlying operator – often comprising both differential and integral components – from its ...

Quasi-normal modes, namely the complex frequencies encoding the linear response of resonators under tiny perturbations, have acquired major importance in recent years in different settings of physics, ...

Let T = H + iK be hyponormal and 𝜑 be a strictly monotone increasing continuous function on σ(H). We define $\tilde{\varphi}(T)$ by $\tilde{\varphi}(T)=\varphi (H)+iK$. In this paper, we show that if ...