• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.35S no.10
• /
• pp.135-143
• /
• 1998

Several equalizers are applied to the DVD-ROM(Digital Versatile Disc-Read Only Memory) system. Because imperfect writing process may cause nonlinear distortion in the reply signal, neural equalizers which have strong nonlinear mapping capability are applied to the system to compensate the nonlinear distortion. Experimental results to verify that the combination of decision-feedback type equalizers and modulation code is formidable are also given. The experimental results shwo that the SNR gain of the neural equalizers over the conventional equalizers becomes much as the nonlinearity in the channel increases. Furthermore, the decision-feedback type equalizers outperform the equalizers which have no decision-feedback in eliminating ISI(Intersymbol Interference) of random data sequence but there is no performance gain of the decision-feedback type equalizers over the equalizers without decision-feedback when these are applied to compensate the ISI of modulation-encoded data sequence.

• Journal of KIISE:Databases
• /
• v.31 no.4
• /
• pp.409-421
• /
• 2004

A database sharing system (DSS) couples a number of computing nodes for high performance transaction processing, and each node in DSS shares database at the disk level. In case of node failures in DSS, database recovery algorithms are required to recover the database in a consistent state. A database recovery process in DSS takes rather longer time compared with single database systems, since it should include merging of discrete log records in several nodes and perform REDO tasks using the merged lo9 records. In this paper, we propose a two version caching (2VC) algorithm that improves the cache fusion algorithm introduced in Oracle 9i Real Application Cluster (ORAC). The 2VC algorithm can achieve faster database recovery by eliminating the use of merged log records in case of single node failure. Furthermore, it can improve the performance of normal transaction processing by reducing the amount of unnecessary disk force overhead that occurs in ORAC.

• Journal of KIISE:Databases
• /
• v.34 no.2
• /
• pp.133-140
• /
• 2007

Flash memory has penetrated our life in various forms. For example, flash memory is important storage component of ubiquitous computing or mobile products such as cell phone, MP3 player, PDA, and portable storage kits. Behind of the wide acceptance as memory is many advantages of flash memory: for instances, low power consumption, nonvolatile, stability and portability. In addition to mentioned strengths, the recent development of gigabyte range capacity flash memory makes a careful prediction that the flash memory might replace some of storage area dominated by hard disks. In order to have overwriting function, one block must be erased before overwriting is performed. This difference results in the cost of reading, writing and erasing in flash memory[1][5][6]. Since this difference has not been considered in traditional buffer replacement technologies adopted in system software such as OS and DBMS, a new buffer replacement strategy becomes necessary. In this paper, a new buffer replacement strategy, reflecting difference I/O cost and applicable to flash memory, suggest and compares with other buffer replacement strategies using workloads as Zipfian distribution and real data.

• 보존과학연구
• /
• s.33
• /
• pp.5-17
• /
• 2012

An Ola leaf manuscript, which consists of words carved on an Ola leaf and is filled up with a mixture of herbal oils made from Vateria acuminata Hyne and charcoal, is one of the native writing media in Sri Lanka. According to historical records, Ola leaf manuscripts had been used from the 1st to the 18th century A.D. From the recent findings that Ola leaf manuscripts have been preserved well for the past 400 years and are in good state of preservation, it is supposed that herbal oils preserve Ola leaves against environmental and biological factors such as fungi and insects. To evaluate the anti-biological susceptibility of the herbal oils, the molds isolated from wooden printing blocks in Janggyeong Panjeon of Haeinsa Temple in South Korea and bacteria and fungi isolated from Ola leaves were cultured. After spreading the microorganisms suspension on an agar plate, a disk paper containing a certain volume of herbal oil was placed on the agar plate. It was found in the experiment that herbal oil exhibits a clear zone, which is optically clear and inhibits the growth of microorganisms, against some molds and bacteria. The study results indicate that the herbal oil from the plant Vateria acuminata Hyne has the anti-bacterial and anti-fungal properties.

• Journal of KIISE:Databases
• /
• v.28 no.3
• /
• pp.494-511
• /
• 2001

In the environment that database management systems manage disk spaces for storing databases directly, this paper proposes a correct and efficient scheme of performing pending actions for the removal of database files. As for performing pending actions, upon performing recovery, the recovery process must identify unperformed pending actions of not-yet-terminated transactions and then perform those actions completely. Making the recovery process identify those actions through the analysis of log records in the log file is the basic idea of this paper. This scheme, as an extension of the execution of transactions, fuzzy checkpoint, and recovery of ARIES, uses the following methods: First, to identify not-yet-terminated transactions during recovery, transactions perform pending actions after writing 'pa_start'log records that signify both the commit of transactions and the start of executing pending actions, and then write 'eng'log records. Second, to restore pending-actions-lists of not-yet-terminated transactions during recovery, each transaction records its pending-actions-list in 'pa_start'log record and the checkpoint process records pending-actions-lists of transactions that are decided to be committed in 'end_chkpt'log record. Third, to identify the next pending action to perform during recovery, whenever a page is updated during the execution of pending actions, transactions record the information that identifies the next pending action to perform in the log record that has the redo information against the page.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.30 no.3
• /
• pp.23-33
• /
• 2012

We studied simultaneously the electronically written data affected in the use of thermal transfer discs and the recoding strategy between recoding drives for the stable long term preservation of optical discs which are commonly used in an electronic data storage device. The most important thing in the archiving preservation might be a choice of a device, however the use of thermal transfer recording discs is not good for long term data preservation because the thermal effect on the recoding data is critical which means that the data are recorded not under best condition but under bad condition. We inspect the strategies of recoding data from 12 brands of optical discs and drives of 7 brands and it turns out the recoding strategy is needed first for the long term preservation of electronic recording data. Thus, without affecting data quality and deformation of optical discs, the choice of optimal disc and drive in recoding data will be a solution for the long term preservation of recoding data.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2005.11a
• /
• pp.531-534
• /
• 2005

한국천문연구원에서는 한국우주전파관측망(Korean VLBI Network: KVN)을 위한 전파영상합성기(상관기) 개발을 진행하고 있다. 전파관측 VLBI 시스템 중 상관기(Correlater) 시스템의 한 구성요소로서 데이터 입력 부분에 각 관측 사이트의 데이터를 사전 처리하는 Station Unit(SU)이 있다. VLBI 시스템에서, 디지털화된 데이터의 다중채널은 테이프 또는 하드디스크에 다중트랙 형태로 인코딩된다. 이 SU의 주요기능은 다중트랙으로부터 인코딩된 데이터를 디코딩하고, 마치 기록되지 않은 것과 같이 채널기반의 샘플 스트림으로 이 데이터를 복원하는 것이다. 이 기능을 원활하게 수행하기 위해서, SU는 논리적으로 재생기 시스템과 함께 시스템이 통합될 필요가 있다. 본 논문에서는 전파 천문 VLBI 시스템 중 SU의 기능과 구조에 대해 고찰하고자 한다.

• Journal of Institute of Control, Robotics and Systems
• /
• v.8 no.8
• /
• pp.682-690
• /
• 2002

This paper presents an output feedback controller design method for uncertain linear systems with sinusoidal disturbance of uncertain frequencies. The controller needs to compensate for the performance deterioration due to the uncertain frequencies of sinusoidal disturbance. To this end, we introduce a virtual system including the dynamics corresponding to the uncertain frequencies and design a controller which minimizes the output difference between the virtual system and the closed-loop system. In other words, the controller is designed so that the closed-loop system approximates the virtual system. The feedback controller is achieved by solving an LMI optimization problem involving a robust $H_{\infty}$ constraint. The advantages of the proposed design method are examined by comparing it with a design method that only minimizes the $H_{\infty}$ norm of the transfer function between the sinusoidal disturbance and the output. The proposed design method is applied to the track-following system of rewritable optical disk drives and is evaluated through an experiment.

• Journal of the Korean Institute of Telematics and Electronics T
• /
• v.36T no.2
• /
• pp.32-41
• /
• 1999

The design method that the structure of double actuators of read-only or read-writable DVD optical pick-up of high density can be compact into the structure of one actuator, is proposed. The designed actuator has the structure of the shaft sliding type in which the moving part can be rotated about the shaft accord to a used optical disc and an objective lens can be switched, and is suspended with magnetic spring. In this actuator, Coulomb's friction is used as damping force and the moving part is designed by finite element method so that the second natural vibration mode can not occur within the servo band. The mock-up of the actuator designed in this paper is made, and its dynamic characteristics is measured and estimated.

• Proceedings of the Korean Information Science Society Conference
• /
• 2006.06a
• /
• pp.151-153
• /
• 2006

본 논문은 NAND 플래시 메모리를 기반으로 한 임베디드 시스템에서 빠른 부팅을 지원하는 파일 시스템을 제안한다. 플래시 메모리는 비휘발성이며 기존의 하드디스크와 같은 자기 매체에 비해서 크기가 작고 전력소모도 적으며 내구성이 높은 장점을 지니고 있다. 그러나 제자리 덮어쓰기가 불가능하고 지움 연산단위가 쓰기 연산 단위보다 크다. 또한 지움 연산 획수가 제한되는 단점이 있다. 이러한 특성 때문에 기존의 파일 시스템들은 갱신 연산 발생 시, 갱신된 데이터를 다른 위치에 기록한다. 따라서 마운팅 시, 최신의 데이터를 얻기 위해 전체 플래시 메모리 공간을 읽어야만 한다. 이러한 파일 시스템의 마운팅 과정은 전체 시스템의 부팅 시간을 지연시킨다. 본 논문은 임베디드 시스템에서 빠른 부팅을 제공할 수 있는 NAND 플래시 메모리 파일 시스템의 구조를 제안한다. 제안된 시스템은 플래시 메모리 이미지 정보와 메타 데이터 블록만을 읽어 파일 시스템을 구축한다. 메타 데이터가 데이터 위치를 포함하기 때문에 마운팅 시, 전체 플래시 메모리 영역을 읽을 필요가 없으며 파일 데이터 위치 저장을 위한 별도의 자료 구조를 RAM 상에 유지할 필요가 없다. 실험 결과, YAFFS에 비해 $76%{\sim}85%$ 마운팅 시간은 감소시켰다. 또한 YAFFS에 비해 $64%{\sim}75%$ RAM 사용량을 감소시켰다.