최만수 교수

The unbalanced nature of distribution systems due to single-phase laterals and loads gives difficulty in the fault location. This paper proposes a new fault location algorithm developed by the direct three-phase circuit analysis for unbalanced distribution systems, which has not been investigated due to high complexity. The proposed algorithm overcomes the limit of the conventional algorithm, which requires the balanced system. It is applicable to any power system, but especially useful for the

In this paper, an effective fault location algorithm and intelligent fault diagnosis scheme are proposed. The proposed scheme first identifies fault locations using an iterative estimation of load and fault current at each line section. Then an actual location is identified, applying the current pattern matching rules. If necessary, comparison of the interrupted load with the actual load follows and generates the final diagnosis decision. Effect of load uncertainty and fault resistance has been

We investigate the effects of spin-polarized leads on the Kondo physics of a quantum dot using the numerical renormalization group method. Our study demonstrates in an unambiguous way that the Kondo effect is not necessarily suppressed by the lead polarization: While the Kondo effect is quenched for the asymmetric Anderson model, it survives even for finite polarizations in the regime where charge fluctuations are negligible. We propose the linear tunneling magnetoresistance as an experimental s

We study a double quantum dot, each dot of which is tunnel coupled to superconducting leads. In the Coulomb blockade regime, a spin-dependent Josephson coupling between two superconductors is induced, as well as an antiferromagnetic Heisenberg exchange coupling between the spins on the double dot that can be tuned by the superconducting phase difference. We show that the correlated spin states---singlet or triplets---on the double dot can be probed via the Josephson current in a dc-superconducti

Current KEPCO's distribution automation system (DAS) provides a very effective restoration solution for the single fault case but cannot handle multiple faults. This paper proposes a two-step restoration scheme-sequential and simultaneous restoration-for multiple fault cases. Efficiency has been achieved by introduction of restoration performance index (RPI) and load-balancing algorithm. Test results to show effectiveness of the proposed scheme are presented, and field experience of DAS in Korea

We study the Kondo effect in a single-electron transistor device realized in a single-wall carbon nanotube (NT). The $K\text{\ensuremath{-}}{K}^{\ensuremath{'}}$ double orbital degeneracy of a NT, which originates from the peculiar two-dimensional band structure of graphene, plays the role of a pseudospin. Screening of this pseudospin, together with the real spin, can result in an SU(4) Kondo effect at low temperatures. In order to have such an exotic Kondo effect it is crucial that this orbital

We report nonequilibrium transport measurements of gate-tunable Andreev bound states in a carbon nanotube quantum dot coupled to two superconducting leads. In particular, we observe clear features of two types of Kondo ridges, which can be understood in terms of the interplay between the Kondo effect and superconductivity. In the first type (type I), the coupling is strong and the Kondo effect is dominant. Levels of the Andreev bound states display anticrossing in the middle of the ridge. On the

As a communication technology plays an integral part in a power system, security issues become major concerns. This paper deals with the security problems in the distribution automation system (DAS) which has an inherent vulnerability to cyber attacks due to its high dependency on the communication and geographically widely spread terminal devices. We analyze the types of cyber threats in many applications of the distribution system and formulate security goals. Then we propose an efficient secu

We analyze charge tunneling statistics and current noise in a superconducting single-electron transistor in a regime where the Josephson-quasiparticle cycle is the dominant mechanism of transport. Due to the interplay between Coulomb blockade and Josephson coherence, the probability distribution for tunneling events strongly deviates from a Poissonian and displays a pronounced even-odd asymmetry in the number of transmitted charges. The interplay between charging and coherence is reflected also

We study intrinsic noise of current in a superconducting single-electron transistor, taking into account both coherence effects and Coulomb interaction near a Cooper pair resonance. Because of this interplay, the statistics of tunneling events deviates from the Poisson distribution and, more important, it shows even-odd asymmetry in the transmitted charge. The zero-frequency noise is suppressed significantly when the quasiparticle tunneling rates are comparable to the coherent oscillation freque

This paper is devoted to an analysis of the experiment by Nakamura {\it et al.} (Nature {\bf 398}, 786 (1999)) on the quantum state control in Josephson junctions devices. By considering the relevant processes involved in the detection of the charge state of the box and a realistic description of the gate pulse we are able to analyze some aspects of the experiment (like the amplitude of the measurement current) in a quantitative way.

We investigate the quantum phase transitions in two capacitively coupled chains of ultrasmall Josephson junctions, where the particle-hole symmetry is broken by the gate voltage applied to each superconducting island. Near the maximal-frustration line, cotunneling of the particles along the two chains is shown to play a major role in the transport and to drive a quantum phase transition out of the charge-density-wave insulator, as the Josephson-coupling energy is increased. We also argue briefly

We examine the Jarzynski equality for a quenching process across the critical point of second-order phase transitions, where absolute irreversibility and the effect of finite-sampling of the initial equilibrium distribution arise in a single setup with equal significance. We consider the Ising model as a prototypical example for spontaneous symmetry breaking and take into account the finite sampling issue by introducing a tolerance parameter. The initially ordered spins become disordered by quen

Abstract The quantum coherent behaviors of superconducting devices at macroscopic scales and recent technical advances in fine tunability have brought the conventional cavity quantum electrodynamics (QED) to superconducting circuits. With an ultra‐strong cavity photon–artificial atom coupling and the inherent nonlinearity of the Josephson junctions, the so‐called circuit QED offers new opportunities to explore new realms of physics that have remained a challenge for conventional cavity QED. Circ