• Journal of KIISE
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• v.42 no.2
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• pp.169-176
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• 2015

The atomic write technique is a good solution to solve the problem of the double write buffer. The atomic write technique needs modified I/O subsystems (i.e., file system and I/O schedulers) and a special SSD that guarantees the atomicity of the write request. In this paper, we propose the writing unit aligned block allocation technique (for EXT4 file system) and the merge prevention of requests technique for the CFQ scheduler. We also propose an atomic write-supporting SSD which stores the atomicity information in the spare area of the flash memory page. We evaluate the performance of the proposed atomic write scheme in MariaDB using the tpcc-mysql and SysBench benchmarks. The experimental results show that the proposed atomic write technique shows a performance improvement of 1.4~1.5 times compared to the double write buffer technique.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.22-26
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• 2013

PTCR ceramics of $(Ba_{0.998}Sm_{0.002})TiO_3+0.001MnCO_3+xSiO_2$ (x=1, 2, 3, 4, 5, 6 mol%) were fabricated by solid state method. Disk samples of diameter 5 mm and thickness about 1mm were sintered at $1,290^{\circ}C$ for 2 h in reduced atmosphere of $5%H_2-95%N_2$ followed by re-oxidation at $600^{\circ}C$ for 30 min. in $20%O_2-80%N_2$.and their microstructures and electrical properties were investigated with SEM and Multimeter. The color of sintered samples was strongly dependent on $SiO_2$ content showing that the color of samples with $SiO_2$ of 1~2 mol% was gray but that of samples with $SiO_2$ of 4~6 mol% was changed from gray to blue, which seems to be related with the reduction of samples due to the oxygen vacancies created during the sintering in reduced atmosphere. $SiO_2$ content had a great influence on the microstructure and the electrical properties. With increasing $SiO_2$ content, the grain size of samples increased and the resistivity as well as the resistivity jump ($R_{285}/R_{min}$) decreased, which is considered to be attributed to the resistivity change at grain interior and grain boundary due to the fast mass transfer through $SiO_2$ liquide phase during the sintering. Samples with 2 mol% $SiO_2$ has the resistivity of $202{\Omega}cm$ and the resistivity jump of 3.28. It is expected that $SiO_2$ doped $BaTiO_3$ based PTC ceramics can be used for multilayered PTC thermistor due to the resistance to the sintering in reduced atmosphere.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10a
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• pp.261-266
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• 2006

최근 낸드 플래시 메모리는 임베디드 저장 장치로서 많이 사용되고 있을 뿐만 아니라 플래시 메모리의 저장 용량의 대용량화로 하드 디스크를 대체하는 SSD(solid state disk) 같은 제품이 출시되고 있다. 플래시 메모리는 하드디스크에 비하여 저전력, 빠른 접근성, 물리적 안정성 등의 장점이 있지만 읽기와 쓰기의 연산의 불균형적인 비용과 덮어 쓰기가 안 되고 쓰기 전에 해당 블록을 지워야하는 부가적인 작업을 수행해야 한다. 이와 같은 특징은 플래시 메모리의 쓰기 성능을 저하 시키고 기존의 하드디스크를 대체하는 것을 어렵게 만든다. 이와 같은 플래시 메모리의 단점을 해결하기 위해서 본 논문에서 비휘발성 메모리와 플래시 메모리를 함께 사용하는 방법을 제안한다. 최근 MRAM, FeRAM, PRAM과 같은 차세대 메모리 기술의 발전과 배터리 백업 메모리의 가격 하락으로 인하여 비휘발성 메모리의 상품적 가치가 높아지고 있다. 하지만 아직까지 용량 대비 가격이 비효율적이기 때문에 소용량의 비휘발성 메모리를 활용하여 플래시 메모리의 쓰기 연산에 대한 단점을 보완하는 방법을 제안한다. 본 논문에서는 FTL 에서 비휘발성 메모리를 쓰기 버퍼로 이용한 여러 가지 버퍼 관리 정책을 실험하였고 각 관리 정책에 따른 플래시 메모리의 성능 향상을 측정하였다. 실험을 통하여 최대로 읽기의 횟수는 90% 감소, 쓰기 횟수는 33% 감소, 소거 횟수는 50% 감소 효과를 보였다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.85-91
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• 2019

In this paper, we propose a new logging and recovery scheme that is suited for the high-performance transaction processing system base on flash memory storage. The proposed scheme is designed by considering flash's I/O characteristic of asymmetric costs between page update/read operations. That is, we substitute the costly update operation with writing and real-time usage of snapshot log, which is for the page-level physical redo. From this, we can avoid costly rewriting of a dirty page when it is evicted form a buffering pool. while supporting efficient revery procedure. The proposed scheme would be not lucrative in the case of HDD-based system. However, the proposed scheme offers the performance advance sush as a reduced number of updates and the fast system recovery time, in the case of flash storage such as SSD (solid state drive). Because the proposed scheme can easily be applied to existing systems by saving our snapshot records and ordinary log records together, our scheme can be used for improving the performance of upcoming SSD-based database systems through a tiny modification to existing REDO algorithms.

• Journal of the Korean Ceramic Society
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• v.43 no.6 s.289
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• pp.369-375
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• 2006

[ $(Ba_{0.5}Sr_{0.5})_{0.99}Co_{x}Fe_{1-x}O_{3-{\delta}}$ ] [x=0.8, 0.2](BSCF) powders were synthesized by a Glycine-Nitrate Process (GNP) and the electrochemical performance of the BSCF cathode on a scandia stabilized zirconia, $[(Sc_{2}O_3)_{0.11}(ZrO_2)_{0.89}]-1Al_{2}O_3$ was investigated. In order to prevent unfavorable solid-state reactions between the cathode and zirconia electrolyte, a GDC ($Gd_{0.1}Ce_{0.9}O_{2-{delta}}$) buffer layer was applied on ScSZ. The BSCF (x = 0.8) cathode formed on GDC(Buffer)/ScSZ(Disk) showed poor electrochemical property, because the BSCF cathode layer peeled off after the heat-treatment. On the other hand, there were no delamination or peel off between the BSCF and GDC buffer layer, and the BSCF (x = 0.2) cathode exhibited fairly good electrochemical performances. It was considered that the observed phenomenon was associated with the thermal expansion mismatch between the cathode and buffer layer. The ohmic resistance of the double layer cathode was slightly lower than that of the single layer BSCF cathode due to the incorporation of platinum particle into the BSCF second layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.563-567
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• 2011

The most widely used piezoelectric ceramics are lead oxide based ferroelectrics (PZT). However, the toxicity of lead oxide and its high vapor pressure during processing have led to a demand for alternative lead-free piezoelectric materials. We synthesized Lead-free piezoelectric ceramics of $0.96(K_{0.5}Na_{0.5})NbO_3-0.04SrZrO_3+x$ mol% $ZrO_2$ [KNN-SZ+$xZrO_2$; x= 0~0.10] doped with 0.1 wt% $MnO_2$ by a conventional solid state method. We investigated the piezoelectric properties and microstructures of these disk samples sintered in reduced atmosphere in order to evaluate the possibility of the multilayered piezoelectric ceramics having the base metal such as Ni as a internal electrode. All of these KNN-SZ samples sintered in 3%$H_2-97%N_2$ atmosphere at $1,140^{\circ}C$ exhibit pure perovskite structure irrespective of the content of $ZrO_2$. Meanwhile, the sintering denisty and piezoelectric properties such as $K_p$, $Q_m$ and $d_{33}$ of KNN-SZ samples as a function of $ZrO_2$ content show the maxima ($k_p$=28.07%, $Q_m$= 101.34, $d_{33}$= 156 pC/N) at x= 0.04 and it is likely that there is some morphotropic phase boundary(MPB) in this KNN-SZ+$xZrO_2$ composition system. These results indicate that the ceramic composition is a promising candidate material for applications in lead free multilayer piezoelectric ceramics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2784-2790
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• 2015

The column-oriented database storage is a very advanced model for large-volume data transactions because of its superior I/O performance. Traditional data storages exploit row-oriented storage where the attributes of a record are placed contiguously in hard disk for fast write operations. However, for search-mostly data warehouse systems, column-oriented storage has become a more proper model because of its superior read performance. Recently, solid state drive using flash memory is largely recognized as the preferred storage media for high-speed data analysis systems. In this research, we propose a new transaction recovery scheme for a column-oriented database environment which is based on a flash media file system. We improved traditional shadow paging schemes by reusing old data pages which are supposed to be invalidated in the course of writing a new data page in the flash file system environment. In order to reuse these data pages, we exploit reused shadow list structure in our column-oriented shadow recovery(CoSR) scheme. CoSR scheme minimizes the additional storage overhead for keeping shadow pages and minimizes the I/O performance degradation caused by column data compression of traditional recovery schemes. Based on the results of the performance evaluation, we conclude that CoSR outperforms the traditional schemes by 17%.

• Journal of Internet Computing and Services
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• v.15 no.4
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• pp.125-133
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• 2014

The column-oriented database storage is a very advanced model for large-volume data analysis systems because of its superior I/O performance. Traditional data storages exploit row-oriented storage where the attributes of a record are placed contiguously in hard disk for fast write operations. However, for search-mostly datawarehouse systems, column-oriented storage has become a more proper model because of its superior read performance. Recently, solid state drive using MLC flash memory is largely recognized as the preferred storage media for high-speed data analysis systems. The features of non-volatility, low power consumption, and fast access time for read operations are sufficient grounds to support flash memory as major storage components of modern database servers. However, we need to improve traditional transaction management scheme due to the relatively slow characteristics of column compression and flash operation as compared to RAM memory. In this research, we propose a new scheme called Column-aware Multi-Version Locking (CaMVL) scheme for efficient transaction processing. CaMVL improves transaction performance by using compression lock and multi version reads for efficiently handling slow flash write/erase operation in lock management process. We also propose a simulation model to show the performance of CaMVL. Based on the results of the performance evaluation, we conclude that CaMVL scheme outperforms the traditional scheme.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.94-101
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• 2013

The market for NAND flash-based storage devices has grown significantly as they rapidly replace traditional disk-based storage devices. Heterogeneous NAND flash-based storage devices using both multi-level cell (MLC) and single-level cell (SLC) NAND flash memories are also actively researched since both types of memories complement each other. Heterogeneous NAND flash-based storage devices suffer from the overheads incurred by migration from SLC to MLC and garbage collection of SLC. This paper proposes a new flash translation layer (FTL) for heterogeneous NAND flash-based storage devices to reduce the overheads by utilizing SLC efficiently. The proposed FTL analyzes the access patterns of logical blocks and selects and stores only logical blocks expected to bring performance improvement in SLC. The experimental results show that the total execution time of heterogeneous NAND flash-based storage devices with our proposed FTL scheme is 35% shorter than that with the previously proposed best FTL scheme.

• Korean Chemical Engineering Research
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• v.53 no.4
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• pp.407-411
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• 2015

Dense ceramic membranes have been prepared using the commercial perovsikite $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$, powders synthesized by the solid state reaction method. The as-synthesized powders were compressed into disks with 1.0 mm of thickness and the disk was sintered at $1,100^{\circ}C$ for 2 hr. The oxygen permeation flux of $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ membrane increased with the increasing temperature and oxygen partial pressure. The activation energy for oxygen permeation was increased with the increasing oxygen partial pressure. Oxygen permeation flux at $950^{\circ}C$ were measured at various flow rates of feed and sweep gas. It has been demonstrated that oxygen permeability increased at elevated flow rates of both gases, but the sweep gas is more influential.