• Journal of applied mathematics & informatics
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• 제26권1_2호
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• pp.395-400
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• 2008

Although the properties of flatness and condition (E) for Sacts over a monoid S are incomparable, Liu([10]) showed that necessary and sufficient condition for a monoid S over which all left S-acts that satisfy condition (E) are flat is the regularity of S. But the problem of describing a monoid over which all cyclic flat left S-acts satisfy condition (E) is still open. Thus the purpose of this paper is to characterize monoids over which all cyclic flat right S-acts satisfy condition (E).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.414-417
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• 2001

Recently, developments of device using characteristics of ceramics as a new technical material is in progress. While doing so, Ultrasonic motor which is a part of research & development of piezo-actuator by piezo-effects is being used in the various applications. So, we fabricated a flat-type $L_{1}-B_{8}$ mode Ultrasonic motor and measured the operation characteristics of its. The size of USM is 80*20*1.5[$mm^{3}$](length*width*thickness) and is constructed with stator by piezo-ceramics and stainless elastic body and rotator by bearings. As results of experiments, the fastest speed of revolution(v), the maximum torque(T) and the efficiency( $\eta$ ) were 37.5[cm/sec], 5.0[ $mN{\cdot}m$ ] and 1.17[%] respectively when 27.9[kHz], 150[gf], 50[V] were applied. So, we think this $flat-type_{1}-B_{8}$ mode Ultrasonic motor is able to be used for applications in forwarding device of a paper or electric card and so on.

• 해양환경안전학회지
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• 제22권6호
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• pp.723-730
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• 2016

현재 국내바지락 양식 산업은 연안선 변화, 양식 환경악화로 생산량이 감소하는 반면, 수입량 급증으로 인한 어려움에 직면해 있다. 현 실태를 극복하고 지속적인 양식을 위해 서식환경을 종합적으로 이해하는 것이 중요하며, 바지락의 서식환경은 양식장의 생산력과 밀접한 관련이 있다. 본 연구에서는 2015년 6월부터 2016년 5월까지 근소만에 위치한 파도와 법산 갯벌어장에 대하여 생존(입도, 해수유동), 성장(Chlorophyll a, DIN, DIP, 노출시간), 환경(수온, DO, 퇴적물 COD, IL)을 이용하여 서식환경 특성을 구명하였다. 조사결과 파도(최대값; 모래함량 48.76 %, 해수 유속 10.59 cm/s, Chlorophyll a 12.70 ug/L, 노출시간 3시간, DO 18.65 mg/L)는 법산(최대값; 모래함량 37.40 %, 해수 유속 6.02 cm/s, Chlorophyll a 6.41 ug/L, 노출시간 7시간, DO 14.81 mg/L)보다 높은 유속과 모래함량, 풍부한 DO와 영양염으로 바지락 서식에 유리한 조건을 가지고 있었으며, 실제로도 더 높은 서식밀도를 나타내었다. 본 연구는 파도와 법산 바지락 서식지 환경을 파악하여 근소만 갯벌어장의 최적 관리 방안 및 잠재적 적지선정을 위한 기초자료로 활용될 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.485-487
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• 1994

A novel control scheme for a Switched Reluctance Motor(SRM) drive is described. The control scheme which is to increase torque, to decrease torque ripples and easy to commutate is suggested. The conditions for high torque drive which includes flat-topped phase current and voltage control arc analyzed and adopted in this control scheme. Flat-topped current is achived via dc-link voltage control. The suggested control system was tested to verify this suggestion.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1595-1600
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• 2004

When a shock wave arrives at a duct, an impulsive wave is discharged from the duct exit and causes serious noise and vibration problems. In the current study, the characteristics of the impulsive wave discharged from a partial closed duct exit is numerically investigated using a CFD method. The Yee-Roe- Davis's total variation diminishing(TVD) scheme is used to solve the axisymmetric, unsteady, compressible Euler equations. With several partial closed duct exits, the Mach number of the incident shock wave $M_s$ and the distance L/D between the duct exit and a flat plate are varied in the range of $M_s$ = 1.01 ${\sim}$ 1.50 and L/D = 1.0 ${\sim}$ 4.0, respectively. The results obtained show that the magnitude of the impulsive wave impinging upon the flat plate strongly depends upon $M_s$, L/D and the partial closure of duct exit. The impulsive wave on the flat plate can be considerably alleviated by the partial closure of duct exit and, thus, the present method can be a passive control for the impulsive wave.

• 한국연초학회지
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• 제20권2호
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• pp.139-143
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• 1998

The occurrence and physico-chemical properties of flat leaves found in 1997 curing trial related to the prevention of occurrence of flat leaves at bulk curing of flue-cured tobacco were investigated and compared with those of normal leaves. Cured leaves of NC82 were separated into 4 classes of none, slight, fair and severe symptoms of flat leaf by the percentage of flattened parts to whole leaf area. The flat leaves were mostly found among the leaves of lower stalk position, and it was estimated that growth rate of lower leaves also influenced on the occurrence of flat leaves. In chromatic aberration of cured leaf, flat leaves showed remarkably lower b and L values than in those of normals but there was no difference in a value. On the other hand, in chemical analyses of flat leaf samples, nicotine, total sugar, ether extract and total nitrogen contents were decreased with the degree of flat symptoms. In physical properties, filling capacity of cured leaves was decreased with the degree of flat symptoms comparing with those of normal leaves, while shatter index was showed a reverse tendency, and then within the same leaf, flat parts were decreased in total sugar, ether extract and filling capacity compared with those of normal ones, but remarkably increased in shatter index, and there was no difference in nicotine and total nitrogen contents.

• Animal cells and systems
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• 제13권3호
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• pp.315-321
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• 2009

The growth and estimated production of Acanthogobius flavimanus (1.9${\sim}$24.7 cm TL) were investigated in an eelgrass bed and unvegetated tidal flat of Dongdae Bay, Korea from March 2006 to February 2007. Growth in fish total length was expressed by the von Bertalanffy's growth equation as: $L_t=43.238(1-e^{-03138(t+02507)})$. Estimated densities, biomass, daily and annual production, and P/B ratio were higher at eelgrass bed than those of at unvegetated tidal flat. Monthly variation in daily production was large; the peak numbers occurred in November 2006 ($0.0014g/m^2$/day) at eelgrass bed, whereas was $0.002g/m^2$/day in July 2006 at unvegetated tidal flat. The eelgrass bed has been supported to maintain capacity of higher production of A. flavimanus than those of in unvegetated tidal flat.

• 상하수도학회지
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• 제21권2호
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• pp.195-201
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• 2007

A submerged flat-sheet membrane separation system integrated with PAC (powdered activated carbon) was used in this research in order to investigate the effects of PAC on the efficiencies of operation and treatment and to evaluate the performance of the system. The experiments were carried out under operating conditions of a filtration rate of 0.38 m/d, water temperature of $20-28^{\circ}C$, and PAC dose of 0 g/L (Run-A) and 20 g/L (Run-B). The influent concentrations of TOC (total organic carbon), $NH_4{^+}-N$ (ammonia nitrogen) and $UV_{254}$ (UV absorbance at 254 nm) were 2.48 mg/L, 1.4 mg/L and 2.53 1/m, respectively. TOC removal of 43.2 and 73.6%, ammonia nitrogen removal of 4.9 and 15.9%, and $UV_{254}$ removal of 20.6 and 31.6% were obtained for Run-A and Run-B, respectively. During an experimental period of 33 days, no change was found in TMP (Run-B), but the TMP in Run-A increased by 5 kPa after 29 days. This research showed that the filtrate quality and the performance efficiency were enhanced when PAC was introduced into the filtration system.

• 대한기계학회논문집
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• 제16권8호
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• pp.1566-1574
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• 1992

본 연구에서는 원형수직 충돌분류에 의한 가열평판의 전열특성을 해석하기 위 하여 최근 표면온도 측정에 많이 사용되고 있는 liquid crystal을 이용하였다. 즉 liquid crystal의 감온특성과 영상처리 기법을 이용하여 레이놀즈수 및 노즐과 충돌판 사이의 거리(L/D) 변화에 따른 전열면의 온도장 변화를 측정하였다.

• 대한기계학회논문집B
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• 제37권3호
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• pp.285-292
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• 2013

본 연구의 목적은 평판의 선단에 설치된 트리핑 와이어에 의한 경계층 박리가 층류에서 난류로의 천이에 미치는 영향과 그 결과로 발생하는 물질전달에 미치는 영향을 규명하는 것이다. 나프탈렌승화법을 사용하여 평판에서의 국소물질전달계수를 측정하였으며, 유동 경계층의 효과를 평가하기 위해 발달된 유동과 발달하는 유동의 조건에서 트리핑 와이어가 설치된 평판에서의 국소물질전달계수를 설치되지 않은 평판에서의 값과 비교하였다. 발달하는 유동에서 국소물질전달계수가 변화하는 경향은 트리핑 와이어가 설치된 평판과 설치되지 않은 평판이 비슷하지만 발달된 유동에서는 상당히 다르게 나타났다. 평균 Sherwood 수는 경계층 박리로 인하여 트리핑와이어가 설치된 평판이 설치되지 않은 평판에 비해서 훨씬 높았다.