• 대한기계학회논문집B
• /
• 제25권9호
• /
• pp.1209-1218
• /
• 2001

The present paper proposes a new correlation for the flow boiling heat transfer coefficients in the low flow rate condition (Re(sub)LF$\leq$200) within horizontal rectangular channels with small gaps (heights). The gap between the upper and the lower plates of each channel ranges from 0.4 to 2mm while the channel width being fixed to 20mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200kg/㎡s and the channel walls were uniformly heated with the heat flux range of 3-15kW/㎡. The quality range covers from 0.19 to 0.76 and the flow pattern is considered to be annular. The measured heat transfer coefficients increase with the mass flux and the local quality; however the effect of the heat flux appears to be minor. At the low mass flux condition, which is more likely with the smaller gap size, the heat transfer is primarily controlled by the liquid film thickness. The proposed F factor for the heat transfer coefficient in the range of Re(sub)LF$\leq$200 well represents the experimental data within the deviation of $\pm$20%. The Kandlikars flow boiling correlation covers the higher flow-rate range(Re(sub)LF>200) within the deviation of $\pm$20%.

• 대한통합의학회지
• /
• 제8권2호
• /
• pp.97-107
• /
• 2020

Purpose : The purpose of this study is to investigate the effect of squat exercise using a ball on the gap between knees and Q angle of a subject with a genu-varum, and to prove the effect, to provide a clinical basis for developing into a knee correction exercise program. Methods : As a result of posture measurement through GPS, 26 female with genu-varum with a knee length of 5 cm or more were studied. The group was randomly assigned to 13 squat exercise group using ball (experimental group) and 13 general squat exercise groups (control group). The experimental group placed the ball between both knees in a position where the distance between both feet was slightly wider than the shoulder width on a flat support surface, and fixed the ball, and then squat with the start signal. The control group squats without a ball. Each group performed three sets of exercise three times a week for six weeks. Before their exercise, after three and six weeks, EMG, GPS, digital goniometer measurement, the vastus medialis (VM), the vastus lateralis (VL), and the Q-angle were measured in the squat exercise posture. EMG was measured in squat exercise posture. Results : The distance between the knees was reduced. EMG is activated in group A, the group B experimental results showed the high activity of the VL. Q-angle had increased. But the experimental group increased more than the control group. Conclusion : We have confirmed through our experiments that the distance interval between the knees during squat exercises using a ball can be reduced. Furthermore, it would also be helpful to ensure the treatment of genu-varum.

• 대한디지털의료영상학회논문지
• /
• 제17권1호
• /
• pp.33-41
• /
• 2015

This study attempts to examine the clinical usefulness of High b-value DWI (diffusion weighted imaging) for brain tumors with an edema. Subjects were seven patients selected from 65 patients who received an MRI scan for suspected encephalopathy and confirmed diagnosis at our hospital from February to July 2015 (male: 7, average age : 66 years old). As test equipment, 3.0T MR System (ACHIEVA Release, Philips, Best, The Netherlands) and 8Channel SENSE Head Coill were used. DWI checks on the use of the variable TR 5460ms, TE 132ms, Slice Thickness 4mm, gap 1mm, Slice number 29 is, 3D T1WI is TR 8.4ms, TE 3.9ms, matrix size $240{\times}240$, Slice can set 180 piecesIt was. b value of 0, 1,000, 2,000 s/mm2 with DWI acquisition and 3D T1WI enhancement five minutes after the Slice Thickness 3mm, gap 0mm to reconstruct the upper face axis (MPR TRA CE) was. As for the experiment, in b-value 1,000 and 2,000 images, SNR and the lesion at the lesion site and CNR in the normal site opposite to the lesion are measured. WW(window width) and WL(window level) are made equal in MRICro software, and the volume of the lesion is measured from each of b-value and MPR TRA CE image. Using SPSS ver. 1.8.0.0 Mann Whitney-test was analyzed for SNR and CNR, while Kruskal-Wallis test was analyzed for volume.

• 한국광학회지
• /
• 제19권1호
• /
• pp.73-79
• /
• 2008

금속선 도파로 면과 금속 평면이 수직으로 적층된 장거리 표면-플라즈몬 도파로 구조를 제안하였으며, 표면-플라즈몬 모드의 특성을 유전체의 굴절율과 두께 변화에 대하여 이론적으로 분석하고 실험적으로 검증하였다. 위층의 금속선 도파로를 S-곡선과 Y-분기 형태로 변형시킨 이중-금속 도파로를 제작하여, 제안된 이중-금속 도파로 구조의 광 소자 응용 가능성을 살펴보았다. 제안된 이중금속 구조에서는 도파로 코어에 해당하는 두 금속 박막 사이의 유전체 굴절률을 임의로 선택하여도 장거리 표면 플라즈몬 모드가 존재할 수 있으며, 표면-플라즈몬 모드의 전파거리는 두 금속 박막 사이의 유전체 두께를 조절함으로써 증가시킬 수 있다. 또한, 이중-금속 도파로는 표면-플라즈몬을 전달할 뿐만 아니라, 삽입된 코어 유전체에 전압 및 전류를 인가하기에도 매우 적합한 구조로서, 표면-플라즈몬 능동소자 및 비선형 소자 구현에 많은 가능성을 열어줄 것으로 기대된다.

• 대한소아치과학회지
• /
• 제23권2호
• /
• pp.389-400
• /
• 1996

In Class II amalgam restoration in deciduous molar, failure rate and incidence of recurrent caries are high as children become older. In order to preserve deciduous molars till the physiologic exfoliation time, stainless steel crown is a choice of the treatment. As a result of a careless treatment, such as overhanging margin, poor marginal adaptation, poor proximal contour and inadequate mesiodistal width give rise to interfering eruption of the adjacent teeth, recurrent caries and chronic gingival irritation and insufficient arch length respectively. In this study, 252 s.s. crowned teeth extracted due to physiologic exfoliation or periapical lesion. The purpose of this study is to analyze the marginal adaptation of stainless steel crown to the deciduous molar in order to obtain better clinical result. The results were as follows : 1. Between the length of s.s. crown and the marginal gap of crown, positive correlations were shown. 2. Largest amount of marginal gap was shown at buccal side in upper deciduous molars and lower first deciduous molar, lingual side in lower second deciduous molar. But no significant diffrence were found statistically compared to second most largest one. 3. Incidence of exposed restoration and recurrent caries were higher in proximal surface than buccal/lingual surface. And extension of restoration below the margin of s.s. crown gives rise to higher rate of recurrent caries. 4. Defect of contour was found in 34%, frequently found in lower 1st deciduous molar and upper 1st deciduous molar. 5. Marginal polishing defects were found in 23%. 6. Ledge was formed in 10% especially in lower 1st deciduous molar and lower 2nd deciduous molar. 7. 16% of the teeth had wear facet due to traumatic occlusion, 7% of them had occlusal perforation.

• 대한치과보철학회지
• /
• 제38권4호
• /
• pp.510-525
• /
• 2000

The effects of pretreatment of Co-Cr alloy, including two adhesive primers that contain either MDP or MAC-10, and silicoating on the bond The result sobtained as follows; o Strength of 4-META/MMA-TBB resin were investigated using FT-IR, SEM, and EDAX. o In the SEM observation of surface morphologies, the sandblasted specimen exibited a very rough surface, whereas the surfaces of the two groups primed with either MDP or MAC-10 were covered with a layer of primer, and the surface morphology of the silicoated specimen remained almost the same after sandblasting. o Before the thermocycling tests, the group treated with MDP demonstrated the highest mean tensile bond strength and the sandblasted group showed the lowest bond strength. o After 20,000 thermocyling, the mean tensile bond strength of the sandblasted group exhibited a 50% reduction in bond strength, while the others showed a $20\sim30%$ reduction. o Observation of the metal-resin interface revealed that in all groups the resin permeated the rough surface formed by sandblasting thereby producing a mechanical bond between the metal and the resin. It was also found that thermocycling resulted in a gap formation at the metal-resin interface of the specimens, and the sandblasted group exhibited a larger gap width than the other groups. o In fracture mode, all specimens indicated a cohesive fracture within the resin before thermocycling. However, thermocyling produced adhesive failure at the edge of the resin-metal interface in most specimens. The sandblasted group, which exhibited the lowest bond strength after thormocycling, also demonstrated the largest area of adhesive failure.

• 전기전자학회논문지
• /
• 제7권2호
• /
• pp.223-229
• /
• 2003

본 논문에서는 2.4GHz와 5.8GHz 대역의 무선 랜카드에 사용되는 듀얼 역-F형 내부 안테나의 설계 값에 따른 안테나 특성을 분석하였다. 노트북용 WLAN card의 PCB 기판에 인쇄된 형태로 설계하여 안테나의 길이, 단락 스터브의 두께, 피드선과 단락 스터브 사이의 간격, 안테나와 접지면 사이의 간격, 안테나의 두께 및 기판의 두께와 기판의 유전율에 따른 특성 변화를 연구하였다. 설계 값에 따른 특성변화 그래프로부터 설계 값을 튜닝하여 최적의 안테나를 설계하였다. 설계된 안테나는 VSWR이 1.6과 1.14이며, 주파수 대역폭은 170MHz와 500MHz 이며, 최대이득 3.5dBi 의 값을 얻었다.

• Advances in nano research
• /
• 제12권1호
• /
• pp.25-35
• /
• 2022

Within the framework of the density functional theory combined with the method of non-equilibrium Green's functions (DFT + NEGF), the features of electron transport in fullerene nanojunctions, which are «core-shell» nanoobjects made of a combination of fullerenes of different diameters C₂₀, C₈₀, C₁₈₀, placed between gold electrodes (in a nanogap), are studied. Their transmission spectra, the density of state, current-voltage characteristics and differential conductivity are determined. It was shown that in the energy range of -0.45-0.45 eV in the transmission spectrum of the "Au-C₁₈₀-Au" nanojunction appears a HOMO-LUMO gap with a width of 0.9 eV; when small-sized fullerenes C₂₀, C₈₀ are intercalation into the cavity C₁₈₀ the gap disappears, and a series of resonant structures are observed on their spectra. It has been established that distinct Coulomb steps appear on the current-voltage characteristics of the "Au-C₁₈₀-Au" nanojunction, but on the current-voltage characteristics "Au-C₈₀@C₁₈₀-Au", "Au-(C₂₀@C₈₀)@C₁₈₀-Au" these step structures are blurred due to a decrease in Coulomb energy. An increase in the number of Coulomb features on the dI/dV spectra of core-shell fullerene nanojunctions was revealed in comparison with nanojunctions based on fullerene C₆₀, which makes it possible to create high-speed single-electron devices on their basis. Models of single-electron transistors (SET) based on fullerene nanojunctions "Au-C₁₈₀-Au", "Au-C₈₀@C₁₈₀-Au" and "Au-(C₂₀@C₈₀)@C₁₈₀-Au" are considered. Their charge stability diagrams are analyzed and it is shown that SET based on C₈₀@C₁₈₀-, (C₂₀@C₈₀)@C₁₈₀- nanojunctions is output from the Coulomb blockade mode with the lowest drain-to-source voltage.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.596-599
• /
• 2004

The robotic $CO_2$ welding is a manufacturing process to produce high quality joints for metal and it could provide a capability of full automation to enhance productivity. Despite the widespread use in the various manufacturing industries, the full automation of the robotic $CO_2$ welding has not yet been achieved partly because the mathematical model for the process parameters of a given welding task is not fully understood and quantified. Several mathematical models to control welding quality, productivity, microstructure and weld properties in arc welding processes have been studied. However, it is not an easy task to apply them to the various practical situations because the relationship between the process parameters and the bead geometry is non-linear and also they are usually dependent on the specific experimental results. Practically, it is difficult, but important to know how to establish a mathematical model that can predict the result of the actual welding process and how to select the optimum welding condition under a certain constraint. In this research, an attempt has been made to develop an intelligent algorithm to predict the weld geometry (top-bead width, top-bead height, back-bead width and back-bead height) as a function of key process parameters in the robotic $CO_2$welding. To achieve this above objective, Taguchi method was employed using five different process parameters (tip gap, gas flow rate, welding speed, arc current, welding voltage) as a guide for optimization of process parameters.

• Journal of Power Electronics
• /
• 제18권5호
• /
• pp.1336-1346
• /
• 2018

Wide band gap semiconductor devices such as SiC MOSFETs are becoming the preferred devices for high frequency and high power density converters due to their excellent performances. However, the proportion of the switching loss that accounts for the whole inverter loss is growing along with an increase of the switching frequency. In view of the third quadrant working characteristics of a SiC MOSFET, synchronous rectification discontinuous pulse-width modulation is proposed (SRDPWM) to further reduce system losses. The SRDPWM has been analyzed in detail. Based on a frequency domain mathematical model, a quantitative mathematical analysis of the harmonic characteristic is conducted by double Fourier transform. Meanwhile, a switching loss model and a conduction loss model of inverter for SRDPWM have been built. Simulation and experimental results verify the result of the harmonic analysis of the double Fourier analysis and the accuracy of the loss models. The efficiencies of the SRDPWM and the SVPWM are compared. The result indicates that the SRDPWM has fewer losses and a higher efficiency than the SVPWM under high switching frequency and light load conditions as a result of the reduced number of switching transitions. In addition, the SRDPWM is more suitable for SiC MOSFET converters.