Seung Han Yoo

An alternative proof for the existence of Radner equilibria

This paper explores ‘competitive equilibrium under uncertainty’ by Radner (1968). We provide a simple proof for the existence of a Walrasian equilibrium and characterize the maximal number of markets in the extended Arrow–Debreu economy.

Strategic analysis of influence peddling

This paper analyzes “influence peddling” in a model that portrays interactions involving human capital transfer and collusion-building, in which each government official regulates multiple firms simultaneously. We show that there exists a collusion maximizing equilibrium between a sequence of “qualified” regulators and a firm such that the qualified bureaucrat manipulates regulation rates for two firms by regulating the colluding firm leniently for the maximized sum of their payoffs, but regulating the non-colluding firm stringently for the signaling in order to “compensate” for the lenient regulatory stance taken toward the colluding firm.

Diagnosis of Zygomaticus Muscle Paralysis Using Needle Electromyography With Ultrasonography

A 22-year-old woman visited our clinic with a history of radiofrequency volumetric reduction for bilateral masseter muscles at a local medical clinic. Six days after the radiofrequency procedure, she noticed a facial asymmetry during smiling. Physical examination revealed immobility of the mouth drawing upward and laterally on the left. Routine nerve conduction studies and needle electromyography (EMG) in facial muscles did not suggest electrodiagnostic abnormalities. We assumed that the cause of facial asymmetry could be due to an injury of zygomaticus muscles, however, since defining the muscles through surface anatomy was difficult and it was not possible to identify the muscles with conventional electromyographic methods. Sono-guided needle EMG for zygomaticus muscle revealed spontaneous activities at rest and small amplitude motor unit potentials with reduced recruitment patterns on volition. Sono-guided needle EMG may be an optimal approach in focal facial nerve branch injury for the specific localization of the injury lesion.