• 생명과학회지
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• 제8권5호
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• pp.582-588
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• 1998

징거미 새우의 정소는 한 쌍의 관으로 되어 있고, 정소의 중앙 후반부에서 기원된 수정관은 제 5보각의 기부에 위치한 생식공까지 연결되어 있다. 수정관은 기부, 나선부, 말단부, 사정관으로 구분되었다. 수정관은 simple columnar ephithelium, high columnar ephithelium, 종주근과 환상근으로 이루어져 있다. AG는 수정관의 말단부에서 사정관에 걸쳐 위치하고 있다. AG의 형태는 불규칙한 세포 덩어리로 되어져 있고, hematoxyline에 약하게 염색되는 염색질과 둥글고 커다란 핵을 가진다. 핵질과 세포질은 염기성 핵막을 경계로 쉽게 구분되나, 세포질과 세포질사이의 경계는 그 구별이 어렵다. 암컷의 복판에 부착된 정포는 호산성기질, 호염기성기질 그리고 호염기성기질에 싸여있는 한 쌍의 정자덩어리로 구성되어 있다. 성숙정자는 압정형태이고, 두부는 가운데 부분이 약간 오목한 원반형이고, 미부는 두부 중앙부 하단의 약간 볼록한 부분에서 연장된 하나의 spike를 이루고 있다. 정자의 크기는 두부의 직경이 약 8 $\mu$m, 미부의 길이가 약 10 $\mu$m였다.

• 한국방사선학회논문지
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• 제14권7호
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• pp.981-989
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• 2020

본 연구는 Pitch의 변화에 따른 CT 감약계수(CT Number)와 잡음(Noise)의 변화를 정량적으로 측정하고자 자체 제작한 맞춤형 팬텀(Customized Phantom)을 사용하였다. 팬텀을 이용한 영상의 획득을 위해 팬텀 내부는 멸균증류수로 가득 채웠다. 유리관 내부에는 생리식염수와 조영제의 비율을 각각 생리식염수 100%, 400:1, 200:1, 100:1, 50:1로 희석한 용액을 담은 후 영상화하였고, 이때 용액의 희석비율별로 pitch를 0, 0.35, 0.7, 1.05, 1.4의 단계로 나누어 각각 영상화하였다. 희석비율별로 모든 ROI에서 측정한 CT number와 noise 값의 평균이 pitch의 변화에 따라 유의한 차이를 보이는지 검증하고자 일원 배치 분산분석(One-way ANOVA Analysis)과 사후검정을 시행하였다. 실험 결과 각 희석비율별 pitch의 변화에 대한 CT number의 변화는 통계적으로 유의한 차이가 없었지만, noise 값은 pitch의 증가에 따라 증가하는 경향을 보였으며, 통계적으로도 유의한 차이를 보이는 것으로 나타났다. 나선형 영상획득 방식은 pitch에 따라 noise가 유의한 수준으로 달라질 수 있다. 따라서 나선형 영상획득 방식을 적용한 CT 영상의 화질평가 항목과 기준을 설정할 필요가 있을 것이다.

• 설비공학논문집
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• 제7권2호
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• pp.298-309
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• 1995

Low-fin tubes are widely used to enhance condensation heat transfer. In this study, condensation heat transfer experiment was conducted on the low-fin tube using R-11. Three different fin densities-787 fpm (fins per meter), 1102 fpm. 1378 fpm-were tested. The results show that low-fin tube enhances the condensation heat transfer considerablely. The enhancement increases as the fin density increases. It was also found that the fin shape and height have a significant effect on the condensation heat transfer coefficient. Slender or high fins showed a higher condensing heat transfer coefficient compared with fat, low fins. For the tube with 1378 fpm, however, excessive fin height decreased the condensing heat transfer coefficient. The reason may be attributed to the increasing condensate retention angle as the fin density increases. The experimental data are compared with existing prediction models. Results show that Webb's surface tension model predicted the data best (within ${\pm}20%$), which confirms that surface tension plays the major role in low-fin tube condensation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.45-50
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• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of a 0.2 % aqueous solution of sodium carbomethyl cellulose (CMC) at a inner cylinder rotational speed of $0{\sim}600$ rpm. The transitional flow has been examined by the measurement of pressure losses, to reveal the relation of the Reynolds numbers with the skin-friction coefficients, in the laminar and transitional flow regimes. The occurrence of transition has been checked by the gradient change of pressure losses and skin-friction coefficient with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• 대한기계학회논문집
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• 제18권5호
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• pp.1264-1274
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• 1994

Heat transfer performance of integral-fin tube which is used in recipro turbo refrigerator or high compact heat exchangers is studied. Eight tubes with trapezoidal shaped integral-fins having fin densities from 748 to 1654 fpm and 10, 30 internal grooves are tested. A plain tube having the same(inner and outer) diameter as the fin tubes is also tested for comparison. Pool boiling heat transfer of R-11 is investigated experimentally and theoretically on single tube arrangement. The refrigerant evaporates at saturation state of 1 bar on the outside tube surface and heat is supplied by not water which circulates inside of the tube. From the result of eight fin tubes and one plain tube tested, a tube having 1299 fpm-30 grooves shows the best performance. A maximum overall heat transfer coefficient of this tube is about 4000 $W/m^{2}K$ at 2.8m/s of water velocity. The maximum heat transfer enhancement (i.e., the ratio of overall heat transfer coefficients of finned to plain tubes)is about 2.1.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2095-2100
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• 2003

This Experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin-friction coefficients have been measured for fully developed flow of bentonite-water solution(5%) when the inner cylinder rotates at the speed $0{\sim}400rpm$. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number $R_o$ With respect to the skin friction coefficients. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regime, the skin friction coefficient is increased by the inner cylinder rotation. The critical (bulk flow) Reynolds number $Re_c$ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.631-636
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• 2000

The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• 대한기계학회논문집
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• 제18권5호
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• pp.1275-1287
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• 1994

Heat transfer performance improvement by fin and grooves is studied for condensation of R-11 on integral-fin tubes. Eight tubes with trapezoidal shaped integral-fins having fin densities from 748 to 1654 fpm and 10, 30 grooves are tested. A plain tube having the same diameter as the finned tubes is also tested for comparison. R-11 condenses at saturation state of $32^{\circ}C$ on the outside tube surface cooled by inside water flow. All of test data ate taken at steady state. Beatty and Katz's, Rudy's and Webb's theoretical models are used to predict the R-11 condensation coefficient of tubes having 748, 1024 and 1299 fpm. The predicted value by Betty and Katz's model is within 10% of experimental values in this study at fpm<1024 and Rudy's model predicted the experimental data at fpm>1024 within 15%. The tube having fin density of 1299 fpm and 30 grooves has the best overall heat transfer performance. This tube shows the overall heat transfer coefficient of 11500 $W/m^{2}K$,/TEX> at coolant velocity of 3.0m/s.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.1113-1118
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• 2006

A numerical investigation of single phase heat and flow characteristics in circular tubes with a single set of spiral micro fins was performed with varying geometrical parameters like fin height, spiral angle, and number of fins. The properties of $40^{\circ}C$ water was used as a working fluid to simulate a condenser and the RNG $k-{\epsilon}$ turbulence model was adopted. Calculation results were obtained in fully developed turbulent flow with constant surface heat flux boundary condition. Relative terms were introduced to investigate the substitution effect of conventional smooth tubes. The dimensionless terms were the heat transfer enhancement factor, the pressure drop penalty factor, and the efficiency index. Additionally, a numerical optimization was carried out to maximize thermal performance with the concept of the robust design. A statistical analysis showed that fin height interacts with number of fins and spiral angle.

• 드라이브 ㆍ 컨트롤
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• 제19권4호
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• pp.29-35
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• 2022

In this paper, we developed a workload index for monitoring the durability test using operation information of an excavator. First, the acceleration and cylinder pressure were selected as load factors by analyzing operation data. Through load correlation analysis according to each load factor, Root Mean Square (RMS) and Work Load Range (WLR) were respectively derived as a load feature representing mechanical load. In addition, the workload index was used to quantify load features. For applying the workload index to monitoring, a real-time monitoring system consisting of sensors and embedded controller was installed on the excavator and the system was integrated with a remote monitoring environment using a wireless network. Results of load monitoring and analysis verified that the developed workload index was effective from the viewpoint of the relative comparison of the workload.