• E2M - 전기 전자와 첨단 소재
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• 제10권3호
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• pp.274-283
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• 1997

These days, according to surprising development of communication enterprises, every soft of devices is getting smaller and cheaper. Among these Devices, microwave dielectric ceramics are studied and progressed briskly as the materials of dielectric resonator. Dielectric properties of BaO-S $M_{2}$ $O_{3}$-Ti $O_{2}$, one of the BaO Lnsub 2/ $O_{3}$-Ti $O_{2}$ (Ln=La, Sm, Nd, Pr…) system, synthesized by solid-reaction and coprecipitation method were investigated. Disk-type samples were sintered at 1250-1400.deg. C for 2hrs. As a result, single phase was not synthesized in both method. First created the second phase of S $M_{2}$ $Ti_{2}$ $O_{7}$, and then the last phase of $Ba_{3.75}$S $m_{9.5}$ $Ti_{18}$ $O_{54}$, Ti $O_{2}$, and $Ba_{2}$ $Ti_{9}$ $O_{20}$. When the sample was sintered at 1280.deg. C (in solid reaction method) and at 1310.deg. C (in coprecipitation method), it obtained highest dielectric constant (72.96 and 71.70, respectively) and high Q value. Above that temperature, dielectric constant and Q value decreased because of lattice defect according to oxygen vacancies........

• 구강회복응용과학지
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• 제21권1호
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• pp.69-81
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• 2005

The objective of this study was to evaluate the toothbrush abrasion characteristics of class V restorations. Thirty extracted human premolars, which were collected from oral surgery clinics were used. We mounted five teeth in a metal ring mold of 50 mm in diameter and 15 mm in height using chemically cured acrylic resin. Class V cavities were prepared in lingual cervical root surfaces and restored using one of following restorative materials : Dentin Conditioner/Fuji II LC (Group FL), All Bond II/Z-250 (Group ZT), One-up Bond F/Palfigue Estelite (Group PE), F2000 Primer/Adhesive (Group FT), and Prime & Bond 2.1/Dyract AP (Group DR). They were stored under distilled water at $37^{\circ}C$ for seven days. The toothbrush abrasion test was conducted using a wear testing machine of pin-on disk type under a load of 1.5 N for 100,000 cycles. We have examined the bonded interfaces, the changes of surface roughness and color of abraded surfaces. From this experiment, the following results were obtained. 1. The change of surface roughness showed high degree: RMGIC>compomer>composite resin (p<0.05). 2. Because of the protrusion and missing of filler particles, SEM observation of abraded surfaces of RMGIC and compomers revealed the increase of surface roughness due to the selective removal of matrix resin. 3. The color change by toothbrush abrasion was affected in large part by the change of $L^*$ and $b^*$ of resin composites (p<0.05). 4. The color change by toothbrush abrasion was so small to detect by human eyes. 5. SEM observation of abraded surfaces revealed the interface bonding was the best in the FT group.

• 대한기계학회논문집A
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• 제21권5호
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• pp.791-799
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• 1997

The wear characteristics and wear mechanisms of plasma sprayed Al/sub 2/ O/sub 3/-40%TiO/sub 2/ and Cr/sub 2/O/sub 3/ deposited on casting aluminum alloy(AC4C) were investigated. Specimens were processed for various coating thicknesses. Ball on disk type wear tester was used for wear test. The scratch test on plasma sprayed coating surface showed that critical load to break the coating layer was greater than 40 N. The critical load increase with the increase of coating thickness of specimens. The friction coefficient of Cr/sub 2/O/sub 3/ coating layer was less than that of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer. The wear resistance of Cr/sub 2/O/sub 3/ coating layer was greater than that of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer. Microscopic observation of worn surfaces was made by SEM. SEM observation showed that the main mechanism of wear for Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer was abrasive wear under 50 N. For the case of Al/sub 2/O/sub 3/-40%TiO/sub 2/ coating layer, as the surface cracks perpendicular to sliding direction propagated, the wear debris was generated in wear track. However, the main mechanism of wear for Cr/sub 2/O/sub 3/ coating layer was brittle fracture under 150 N.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권4호
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• pp.291-302
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• 2013

NAND flash memory (NFM) based storage devices, e.g. Solid State Drive (SSD), are rapidly replacing conventional storage devices, e.g. Hard Disk Drive (HDD). As NAND flash memory technology advances, its specification has evolved to support denser cells and larger pages and blocks. However, efforts to fully understand their impacts on design objectives such as performance, power, and cost for various applications are often neglected. Our research shows this recent trend can adversely affect the design objectives depending on the characteristics of applications. Past works mostly focused on improving the specific design objectives of NFM based systems via various architectural solutions when the specification of NFM is given. Several other works attempted to model and characterize NFM but did not access the system-level impacts of individual parameters. To the best of our knowledge, this paper is the first work that considers the specification of NFM as the design parameters of NAND flash storage devices (NFSDs) and analyzes the characteristics of various synthesized and real traces and their interaction with design parameters. Our research shows that optimizing design parameters depends heavily on the characteristics of applications. The main contribution of this research is to understand the effects of low-level specifications of NFM, e.g. cell type, page size, and block size, on system-level metrics such as performance, cost, and power consumption in various applications with different characteristics, e.g. request length, update ratios, read-and-modify ratios. Experimental results show that the optimized page and block size can achieve up to 15 times better performance than the conventional NFM configuration in various applications. The results can be used to optimize the system-level objectives of a system with specific applications, e.g. embedded systems with NFM chips, or predict the future direction of NFM.

• 대한조선학회논문집
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• 제50권3호
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• pp.145-152
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• 2013

Recently, with oil price jumping and environmental issues, Green ship is paid deep attention to by ship owner, operator, builder, class and government. Fuel efficiency and reduction of $CO_2$ emissions are expected to have a strong influence on the design and operation of merchant ships. Many ship owners and operators are seeking the more economic method by the best operating route and the application of reliable and effective energy saving devices. With the Energy Efficiency Design Index (EEDI) in 2013 attention will more than ever be focused at achieving maximum fuel economy in the hydrodynamic design of hull forms, their appendages and propellers. IMO requirements for $CO_2$ emission for ships will now be implemented for vessels ordered from 1st January 2013. So far, a lot of new idea and patents have been proposed, tested, claimed and applied for various kinds of ship type. This paper shows numerical and experimental work related to a study on a energy saving devices particularly for fuller ship such as merchant vessel of Tanker and Bulker. From the bare hull wake measurements, typical upper/lower asymmetry of hull wake at the propeller disk was found. The pre-swirl duct have been designed and reviewed to recover the loss of propeller running in that condition. The general function of the pre-swirl duct was set to work against this asymmetry of wake and generate pre-swirled flow into the propeller against the propeller rotating direction.

• 천문학회보
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• 제35권1호
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• pp.33.2-33.2
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• 2010

We have investigated a relationship among the solar proton events (SPEs), coronal mass ejections (CMEs) and solar flares during the solar cycle 23 (1997-2006). Using 63 SPE dataset, we found that SPE rise time, duration time, and decrease times depend on CME speed and SPE peak intensity depends on the CME earthward direction parameter as well as CME speed and x-ray flare intensity. While inspecting the relation between SPE peak intensity and the CME earthward direction parameter, we found that there are two groups: first group consists of large 6 SPEs (> 10,000 pfu at >10 MeV proton channel of GOES satellite) and shows a very good correlation (cc=0.65) between SPE peak intensity and CME earthward direction parameter. The second group has a relatively weak SPE peak intensity and shows poor correlation between SPE peak intensity and the CME earthward direction parameter (cc=0.01). By investigating characteristics of 6 SPEs in the first group, we found that there are special common conditions of the extremely large proton events (group 1); (1) all the SPEs are associated with very fast halo CME (>1400km/s), (2) they are almost located at disk region, (3) they also accompany large flare (>M7), (4) all they are preceded by another wide CMEs, and (5) they all show helmet streamer nearby the main CME. In this presentation, we will give details of the energy spectra of the 6 SPE events from the ERNE/HED aboard the Solar and Heliospheric Observatory (SOHO), and onset time comparison among the SPE, flare, type II burst, and CME.

• 한국세라믹학회지
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• 제46권4호
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• pp.419-424
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• 2009

Congruent or stoichiometric $LiNbO_3$ fiber single crystals were grown by the $\mu$-PD method, and the grown fiber crystals have the several (2 or 3) ridges with a diameter of $1.35{\sim}1.5\;mm$ and a length of $40{\sim}100\;mm$. In this $\mu$-PD process, different growth rates ($10{\sim}60\;mm/h$) were applied. Pt wire or $LiNbO_3$ crystal was used as a seed. The properties of grown $LiNbO_3$ fiber single crystals having a-axis or c-axis according to seeds were effected by the grown conditions(Pt tube diameter, pulling speed, after heater etc.). Disk-type $LiNbO_3$ samples were poled in condition of DC 5 V/cm at 1050, 1075 or $1100^{\circ}C$. XRD, SEM, conoscope image through the polarized microscope, $T_C$ measuring apparatus, optical transmittance measuring instrument are used to identify the properties of $LiNbO_3$.

• 한국전자파학회논문지
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• 제18권8호
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• pp.913-921
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• 2007

본 논문에서는 새로운 구조의 방향 탐지용 소형 안테나를 제안하였다. 제안한 안테나는 800 MHz 이상의 고주파 대역에서도 안테나의 복사 패턴이 일그러지지 않도록 끝이 구부러진 스커트 모양의 디스크가 연결되었으며, 200 MHz 이하의 저주파 대역에서 증폭기와의 임피던스 매칭이 가능하도록 다단 구조의 매칭 스터브가 삽입되었다. $20{\sim}700 MHz$에서 제안된 안테나는 60cm 다이폴 안테나에 비해 크기가 1/2로 축소되었음에도 불구하고 유사한 성능을 가진다. 또한, 다이폴 안테나와 달리 $700{\sim}1,300 MHz$에서 복사 패턴이 크게 일그러지지 않고 주 빔 방향으로 널이 발생하지 않으며 넓은 빔 폭을 가진다.

• 한국항행학회논문지
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• 제18권1호
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• pp.50-55
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• 2014

최근 다양한 유형의 증거 분석에서 디지털 증거 분석 기법의 도입이 가속화되고 있으며 중요도가 증가하고 있다. 하지만 개인용 디스크 용량이 커지면서 저장하는 파일의 용량의 수가 증가하면서 전체 데이터를 모두 분석하는 것은 시간과 노력이 많이 소요된다. 대부분의 디지털 증거는 항상 시간정보를 저장하고 있으며, 시간 정보는 디지털 증거 분석에서 가장 중요한 요소 중 하나이다. 하지만 시간 유형이 다양하여 단순히 저장된 시간을 기준으로 사건을 분석하면 잘못된 분석결과를 도출할 가능성이 크다. 따라서 본 논문에서는 다양한 디지털 증거의 시간 유형에 대하여 고찰하고, 하나의 시간 축을 기준으로 디지털 증거 분석을 수행할 수 있는 타임라인 분석 기법에 대하여 설명한다.

• 대한의생명과학회지
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• 제13권4호
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• pp.293-304
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• 2007

The emergence of extended spectrum $\beta$-lactamase (ESBL) producing bacteria is worldwide concern. Until recently, the most frequently identified strains in the Republic of Korea were E. coli and Klebsiella spp. The incidence of resistance to extended spectrum $\beta$-lactam antibiotics is increasing in Wonju city, Korea. Total 57 strains of ESBL producing E. coli and Klebsiella species were isolated from Wonju Christian Hospital during a 9 month-period from April to December, 2003. To determine the prevalence and genotypes of the ESBL producing clinical isolates, antibiotic susceptibility and ESBL activity test by VITEK system and double disk synergy (DDS) test, and PCR based genotyping were performed. Fourteen (82%) isolates of 17 ESBL producing E. coli were found to have $bla_{TEM}$ gene and 5 (29%) isolates were found to have $bla_{CTX-M}$ gene by polymerase chain reaction (PCR). Thirty (75%) isolates of 40 ESBL producing Klebsiella species with $bla_{TEM}$ gene, 38 (95%) isolates with $bla_{SHV}$ gene, and 7 (20%) isolates with $bla_{CTX-M}$ type gene were also identified. Enterobacterial repetitive intergenic consensus (ERIC) PCR and similarity index by dendrogram for genetical similarity to band pattern of each clinical isolates were examined. ESBL producing E. coli were grouped into 6 clusters up to 84% of similarity index and Klebsiella species were grouped into 12 clusters up to 76% of similarity index. In conclusion, ESBL producing clinical isolates were characterized with the results from antimicrobial resistance pattern and genetical similarity using ERiC PCR.