• Computers and Concrete
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• 제26권5호
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• pp.451-465
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• 2020

This paper presents experimental and numerical investigations on mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC) with four types of steel fibers; micro steel (MS), crimped (C), round crimped (RC) and hooked-end (H), in two fiber contents of 1% and 2% (by volume) and two lengths of 13 and 30 mm. Compression, direct tension, and four-point bending tests were carried out on four types of specimens (prism, cube, dog-bone and cylinder), to study tensile and flexural strength, fracture energy and modulus of elasticity. Results were compared with UHPC specimens without fibers, as well as with available equations for the modulus of elasticity. Specimens with MS fibers had the best performance for all mechanical properties. Among macro fibers, RC had better overall performance than H and C fibers. Increased fibers improved all mechanical properties of UHPFRC, except for modulus of elasticity, which saw a negligible effect (mostly less than 10%). Moreover, nonlinear finite element simulations successfully captured flexural response of UHPFRC prisms. Finally, nonlinear regression models provided reasonably well predictions of flexural load-deflection behavior of tested specimens (coefficient of correlation, R² over 0.90).

• 한국표면공학회지
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• 제28권6호
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• pp.386-392
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• 1995

The RF planar magnetron sputtering technique was used to fabricate uniform ZnO/$SiO_2$/Si thin films at high growth rate. A detailed crystallographic character of these thin films has been carried oct using XRD, XRC, and SEM. These thin films have the configuration of c-axis orientation perpendicular to $SiO_2$/ Si substrate. The dependence of the thickness of ZnO/$SiO_2$/Si films on applied RF power parameters was also investigated. The crystallinity of films was improved as the substrate temperature was high, RF input power increased, and Ar/$O_2$ ratio decreased. Also, most of ZnO films fabricated on $SiO_2$/Si were suitable for SAW filter since a standard deviation of XRC (002) peak was less than $6^{\circ}$. The presence of the $SiO_2$ layer has a beneficial effect on the crystalline quality of the grown ZnO films.

• 재활간호학회지
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• 제13권1호
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• pp.53-61
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• 2010

Purpose: The purpose of this study was to investigate the relationships of social networks to health status among the urban low income elderly. Method: Using a sample of 598 elderly aged 65 years and higher, social networks, health status were measured by the Social Networks Scale (LSNS), Perceived Health Status, GDSSF-K, K-ADL respectively. The t-test, ANOVA and Tukey-test and Pearson's correlation analyses were performed using SPSS 18.0. Results: 41% of subjects didn't contact with relatives at least once a month. 56% of subjects saw or heard less than monthly from relative with whom they have the most contact. 47% didn't have relatives who one can rely on private matters. Social networks among the low income elderly significantly differed by marital status, health insurance type, economic status, regular exercise, living with family. Social networks were significantly correlated with perceived health status (r=.201), cognitive function (r=-.154) and depressive symptoms (r=-.301). Conclusion: Poor social networks were found in urban low income elderly. Poorer social networks were related to worse health status and more depressive symptoms. Interventions targeting at increasing social networks are urgently needed for low income elderly.

• 한국환경보건학회지
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• 제19권4호
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• pp.38-43
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• 1993

The characteristics of food wastewater treatment in an anaerobic packed bed reactor (APBR) with polyurethane as a packing material and sludge bed reactor (ASBR) was studied. The reactor of 9cm-ID, 150cm-height was fed in a continuous mode from bottom of reactor. For the purpose of constant temperature of reactor, water jacket was installed. The used packing materials was polyurethane sponge foam. Methane which was produced by decomposed organics collected at the top of the reactor for using as a fuel. The substrates used were synthetic, mixed and food wastewater. For the acclimatization of microorganisms, mixed wastewater was used. The major analyses were gas production, COD, pH and volatile acids. Based upon the completed works, the results are as follows: When food wastewater was fed the quantity of produced gas was less than that of synthetic wastewater, but food process saw higher methane content than synthetic process. As well as COD removal efficiency of food process reached at about 85%. In aspect of effluent volatile acid, food process showed low concentration of below 500 mg/l, therefore anaerobic reaction stabled. Conclusively food wastewater used can be digested by anaerobic treatment, especially anaerobic packed bed reactor showed 82% of COD removal, 75% of methane content, 10 l of gas production, and anaerobic sludge bed reactor did 79% of COD removal, 75% of methane content, 81 of gas production at 4 kgCOD/m$^3$day, 36$\circ$C.

• 한국레이저가공학회지
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• 제11권2호
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• pp.8-14
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• 2008

Sintered specimen which used for a blade of diamond tool was manufactured in order to verify $CO_2$ laser weldability depend on sintered temperature. Five kind of specimen were prepared and the range of temperature is from $600^{\circ}C$ to $1000^{\circ}C$ at intervals of $100^{\circ}C$. As a result of the sintered density test, the porosity rate appeared in the range of $2.1%{\sim}21.4%$. After welding, the most segments had exceeds the minimum fracture stress (600MPa, The Standard Safety of Europe) at the welding strength test except on the sintered at $600^{\circ}C$. In case of the sintered at $700^{\circ}C$, even satisfied the safety allowable stress but cannot get the good quality for bead appearance because of humping defect. In the conclusion, we could know that it showed not only relatively soundness bead but also enough welding strength when the sintered blade of diamond tool is included less than 4% of porosity rate.

• 한국산학기술학회논문지
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• 제3권4호
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• pp.233-239
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• 2002

21세기에 가장 시급하게 확보되어야 하는 기술은 BT(Biotechonolgy)와 NT(Nano technology)를 접목시키는 기술이다. 특히, 이들을 종합한 MEMS 에 관한 연구는 가장 광범위한 분야에서 활발하게 이루어지고 있어 그 기술적 가치가 점차 중요시되고 있다. 본 연구는 Simulation을 통하여 Bio-MEMS 기술에서 사용되는 미세Pump 내에서의 유체흐름을 Fluent 프로그램을 사용하여 알아보고자 하였다. 즉, 미세Pump 내로 유체가 흐를 경우, 유체의 압력변화나 온도변화 및 Model에 따른 유동의 흐름을 관찰하여 미세Pump 내에서의 최적의 외부조건과 최적의 Pump Model을 알아보고자 실험하였다. 유동의 흐름을 조사해 본 결과 Chamber의 유무에 따라 압력과 온도의 변화를 관찰할 수 있었다. Chamber가 있는 경우 압력의 변화가 적었고 온도의 변화 또한 적었다. 따라서 Chamber가 있는 Pump가 유체의 흐름에 영향을 적게 줌을 알 수 있었으며 이는 Chamber가 있는 Pump를 설계하는 것이 필요하다고 할 수 있다.

• Restorative Dentistry and Endodontics
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• 제18권1호
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• pp.205-213
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• 1993

The purpose of the study was to evaluate the degree of the marginal leakage of esthetic restorative materials on root caries restoration. 120 cavities were prepared to $90^{\circ}$ butt joint on all margins on the crown and root portion, and divided into 4 groups. The four groups of cavity were filled with Amalgam(Dongmuyung Dental Alloy Co., Ltd, KOREA), Silux$^{(R)}$(3M Co., USA)-Scotch Bond 2$^{(R)}$(3M Co., USA), Silux$^{(R)}$-All Bond$^{(R)}$(BISCO USA), and GC Fuji II$^{(R)}$(G-C Co., JAPAN) respectively. The apical margin of the preparation was finished to leave a flash of restorative material. The coronal margin of the preparation was finished not to leave a flash of restorative material. All specimens were sectioned longitudinally with Isomet Low speed saw(Buether Ltd, USA). The degree of dye penetration was evaluated as the parameter of marginal leakage under the stereoscope. The results were as follows. 1. At the enamel and dentin/cementum margins, the margin were finished to leave a flash of material showed less marginal leakage than that were finished not to leave a flash of material (P<0.001). 2. The enamel margins showed less marginal leakage than the dentin/cementum margins(P<0.001). 3. There was no significant difference in the degree of the marginal leakage between Silux$^{(R)}$-Scotch Bond 2$^{(R)}$ group and Silux$^{(R)}$-All Bond$^{(R)}$ group.

• Applied Biological Chemistry
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• 제27권1호
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• pp.21-28
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• 1984

호주산(産) 밀 6종류(種類)에 대(對)한 제분특성(製粉特性)을 $B{\ddot{u}}hler$ test mill로 조사(調査)하고 우리나라 재래종(在來種) 수원 219호와 비교(比較)하였다. 또한 이들로부터 얻어진 밀가루(patent flour)에 대한 반죽형성능력 및 전분(澱粉)호화성질을 Farinograph, Mixograph, Amylograph, 침강시험(沈降試驗) 및 Pelshenke 시험(試驗)등을 통하여 조사(調査)하였다. 호주산(産) 밀의 제분율(製粉率)은 $59{\sim}66%$ 범위(範圍)에 속하였다. 제분율(製粉率)은 천립중(千粒重)과 밀접(密接)한 관계(關係)를 나타내었으며 liter 중(重)과는 유의적 상관관계(相關關係)를 나타내지 않았다. 이들 밀로부터 얻어진 밀가루의 단백질 함량(含量)은 밀의 종류(種類)에 따라 14.47%에서부터 6.59%로 크게 상이(相異)하였으며 반죽의 물성(物性)도 밀의 종류(種類)에 따라 큰 차이(差異)를 보였다. Australian Prime Hard와 Australian Hard는 강력한 gluten 형성능력을 가진 반면 Australian Standard White와 Australian Soft Wheat는 매우 약(弱)한 gluten 형성능력(形成能力)을 보였다. 한편 Australian Standard White와 Western Australian Wheat는 대단히 높은 호화점도를 가지는 반면 South Australian Wheat는 이례적으로 낮은 호화점도를 보였다.

• 한국균학회지
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• 제41권2호
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• pp.85-90
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• 2013

본 연구에서는 표고톱밥 지면재배에서 참나무 톱밥 조직의 분해와 배지의 갈변 특성을 내외부 형태적으로 조사하였다. 표고균 접종 50일후에는 갈변이 시작되었다. 접종 110일 후 표고균사는 참나무 톱밥 목부조직내 도관, 목섬유, 유세포의 내외부에서 세포벽을 분해하고, 톱밥 표면에 밀집한 균사는 세포외벽을 부정형으로 분해하였다. 그동안에 흰색인 배지 표면 균사는 대부분 깨끗한 갈색으로 변하였고, 이 갈변층 두께는 약 0.34 mm로 표고균사가 치밀하였고, 그 아래에는 흰색의 활력있는 균사층이 있었다. 반면에 검정색 층은 두께가 약 1.17 mm로 미끈거리는 표면에는 세균과 잡균 균사 및 포자들이 점유하고, 그 아래에는 활력이 쇠퇴한 균사층이 존재하였다. 갈변표면의 경도는 약 $0.73kgf/cm^2$로 검정색 표면의 경도 약 $0.91kgf/cm^2$보다 물렀으나 탄력이 있었다. 표고 자실체는 표고균사 접종 150일 후에 밝은 갈색의 배지 표면에서는 발생하였으나, 검정색 표면층에서는 발생하지 않았다.

• 한국멀티미디어학회논문지
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• 제15권2호
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• pp.226-233
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• 2012

최근에 발생한 3.4 DDoS 사이버 테러에서 볼 수 있듯이 사이버테러의 유형은 점점 복합화, 지능화, 대형화 되어가고 있고 사이버 위협 대상도 국가 전체로 확대되고 있다. 미래 사이버 테러를 대비하기 위해 기존에 시도되지 않았던 새로운 공격기법에 대해 미리 예상하고 구현하여 아직 드러나지 않은 시스템의 취약점을 공격자보다 앞서 인식할 필요가 있다. 본 논문에서는 윈도우 시스템에서 레지스트리 변조를 통해 사이버공격을 하는 것처럼 보이게 하는 새로운 사이버테러 공격 기법에 대해 연구한다. 제안하는 새로운 공격기법은 시스템의 레지스트리 default ttl값을 패킷의 송수신 시 필요한 값보다 작은 값으로 변조하여, 이동 중인 패킷이 중간에 폐기되도록 함으로써 에이전트(Agent)의 네트워크 연결을 제한한다.