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Mechanisms of Vascular Calcification: The Pivotal Role of Pyruvate Dehydrogenase Kinase 4
임재찬,이인규 대한내분비학회 2016 Endocrinology and metabolism Vol.31 No.1
Vascular calcification, abnormal mineralization of the vessel wall, is frequently associated with aging, atherosclerosis, diabetes mellitus, and chronic kidney disease. Vascular calcification is a key risk factor for many adverse clinical outcomes, including ischemic cardiac events and subsequent cardiovascular mortality. Vascular calcification was long considered to be a passive degenerative process, but it is now recognized as an active and highly regulated process similar to bone formation. However, despite numerous studies on the pathogenesis of vascular calcification, the mechanisms driving this process remain poorly understood. Pyruvate dehydrogenase kinases (PDKs) play an important role in the regulation of cellular metabolism and mitochondrial function. Recent studies show that PDK4 is an attractive therapeutic target for the treatment of various metabolic diseases. In this review, we summarize our current knowledge regarding the mechanisms of vascular calcification and describe the role of PDK4 in the osteogenic differentiation of vascular smooth muscle cells and development of vascular calcification. Further studies aimed at understanding the molecular mechanisms of vascular calcification will be critical for the development of novel therapeutic strategies.
Performance Degradation Due to Particle Impoverishment in Particle Filtering
임재찬 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.6
Particle filtering (PF) has shown its outperforming results compared to that of classicalKalman filtering (KF), particularly for highly nonlinear problems. However, PF may not be universallysuperior to the extended KF (EKF) although the case (i.e. an example that the EKF outperforms PF) isseldom reported in the literature. Particularly, PF approaches show degraded performance for problemswhere the state noise is very small or zero. This is because particles become identical within a fewiterations, which is so called particle impoverishment (PI) phenomenon; consequently, no matter howmany particles are employed, we do not have particle diversity regardless of if the impoverishedparticle is close to the true state value or not. In this paper, we investigate this PI phenomenon, andshow an example problem where a classical KF approach outperforms PF approaches in terms of meansquared error (MSE) criterion. Furthermore, we compare the processing speed of the EKF and PFapproaches, and show the better speed performance of classical EKF approaches. Therefore, PFapproaches may not be always better option than the classical EKF for nonlinear problems. Specifically, we show the outperforming result of unscented Kalman filter compared to that of PFapproaches (which are shown in Fig. 7(c) for processing speed performance, and Fig. 6 for MSEperformance in the paper).
임재찬 한국통신학회 2016 Journal of communications and networks Vol.18 No.1
In this paper, we propose a number of blind equalizationapproaches for time-varying andmulti-path channels. The approachesemploy cost reference particle filter (CRPF) as the symbolestimator, and additionally employ either least mean squaresalgorithm, recursive least squares algorithm, or H1 filter (HF)as a channel estimator such that they are jointly employed for thestrategy of “Rao-Blackwellization,” or equally called “mixture filtering.”The novel feature of the proposed approaches is that theblind equalization is performed based on direct channel estimationwith unknown noise statistics of the received signals and channelstate system while the channel is not directly estimated in the conventionalmethod, and the noise information if known in similarKalman mixture filtering approach. Simulation results show thatthe proposed approaches estimate the transmitted symbols andtime-varying channel very effectively, and outperform the previouslyproposed approach which requires the noise information inits application.