• Journal of Ocean Engineering and Technology
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• v.36 no.5
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• pp.340-352
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• 2022

This article presents a modeling method for the uncorrelated measurement error of the ultra-short baseline (USBL) acoustic positioning system for aiding navigation of underwater vehicles. The Mahalanobis distance (MD) and principal component analysis are applied to decorrelate the errors of USBL measurements, which are correlated in the x- and y-directions and vary according to the relative direction and distance between a reference station and the underwater vehicles. The proposed method can decouple the radial-direction error and angular direction error from each USBL measurement, where the former and latter are independent and dependent, respectively, of the distance between the reference station and the vehicle. With the decorrelation of the USBL errors along the trajectory of the vehicles in every time step, the proposed method can reduce the threshold of the outlier decision level. To demonstrate the effectiveness of the proposed method, simulation studies were performed with motion data obtained from a field experiment involving an autonomous underwater vehicle and USBL signals generated numerically by matching the specifications of a specific USBL with the data of a global positioning system. The simulations indicated that the navigation system is more robust in rejecting outliers of the USBL measurements than conventional ones. In addition, it was shown that the erroneous estimation of the navigation system after a long USBL blackout can converge to the true states using the MD of the USBL measurements. The navigation systems using the uncorrelated error model of the USBL, therefore, can effectively eliminate USBL outliers without loss of uncontaminated signals.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.4
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• pp.259-273
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• 2009

Most of large-scale distributed file systems decouple a metadata operation from read and write operations for a file. In the distributed file systems, a certain server named a metadata server (MDS) maintains metadata information in file system such as access information for a file, the position of a file in the repository, the namespace of the file system, and so on. But, the existing systems used restrictive metadata management schemes, because most of the distributed file systems designed to focus on the distributed management and the input/output performance of data rather than the metadata. Therefore, in the existing systems, the metadata throughput and expandability of the metadata server are limited. In this paper, we propose a new non-shared metadata management scheme in order to provide the high metadata throughput and scalability for a cluster of MDSs. First, we derive a dictionary partitioning scheme as a new metadata distribution technique. Then, we present a load balancing technique based on the distribution technique. It is shown through various experiments that our scheme outperforms existing metadata management schemes in terms of scalability and load balancing.

• The Journal of Korean Medical History
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• v.36 no.1
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• pp.1-9
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• 2023

To be an adjunct professor(gyeomgyosu) literally means to act as an instructor while also holding a different position. Adjunct professors were initially introduced under Confucianism. Gradually, technical offices also appointed adjunct professors using Confucian-educated bureaucrats for the purpose of educating lower-level technical officials and cadets. This paper examines the history of the civil service system related to adjunct professors through the Code of Laws, and examines those who have been appointed to the public office described in various documents. This paper argues that changes in the medical office's adjunct professor system reflect changes in the national medical talent training policy. The main basis of specific recognizing medical personnel is to decouple the appointment of Confucian scholars from that of full-time doctors. The replacement of the role of medical educators from Confucian scholars to full-time doctors was largely accomplished during the reign of King Jungjong(中宗) and was completed during the period of King Injo(仁祖). The time when Euiyakdongcham was created and the Office of Euiyakdongcham was established coincided with the period when the adjunct professor was disrupted in the medical office. However, this change in the adjunct professor system of medical authorities is in contrast to interpretation, which is a representative technical field. In the case of interpretation, Moonshin's sayeogwon position as adjunct professor was maintained even in the late Joseon Dynasty, and apart from this, there was a hanhagmunsin in Seungmunwon. Interpreter families had institutional arrangements that prevented them from making interpretation their own monopoly. Therefore, families of medical bureaucrats had more room for institutional growth than those of bureaucratic interpreters. Of course, these institutional devices did not prevent the growth of interpreting bureaucratic families in the late Joseon Dynasty. However, the situation in which medicine was accepted only as a kind of knowledge, not as an object of full-time work for sadaebue, would have been an opportunity to rise for those in technical jobs who were full-time medicine. As medicine became more differentiated and developed in the late Joseon Dynasty, medical knowledge and the knowledge about the medical profession became more important. The politicians could not avoid the use of a philosophically oriented system in which a confucian-educated bureaucrat equipped with only Confucian knowledge might replace a full-time doctor. Thus, the contradiction between the reality and the ideal of ignoring or denying reality was reproduced like other Confucian-centered societies. These contradictions have implications for us living in the modern age. Establishing the relationship between philosophy (or belief) and technology should not end with the superiority of one side or the other.