• Journal of Welding and Joining
• /
• 제24권4호
• /
• pp.32-38
• /
• 2006

The objective of present research works is to investigate the effects of process parameters, including the power of laser, cutting speed, material thickness, and the edge angle, on the melted area in the sharp edge of the cut material fur the case of cutting of a low carbon steel sheet using high-power CW Nd:YAG laser. In order to investigate the influence of edge angle and size of loop on the melted area in the sharp edge, angular cutting tests and loop cutting tests have been carried out. From the results of angular cutting tests, the relationship between the edge angle and the melted area has been obtained. The results of the experiments have been shown that the melted area is rapidly reduced from $120^{\circ}$ of the edge angle and the melted area is nearly zero at $150^{\circ}$ of the edge angle. Through the results of loop cutting experiments, the relationship between the cutting angle on the melted area in the edge according to the size of loop have been obtained. In addition, it has been shown that a proper size of loop is nearly 3 mm as the corner angle is greater than $90^{\circ}$ and 5 mm as the comer angle is less than $90^{\circ}$. The results of above experiments will be reflected on the knowledge base to generate optimal cutting path of the laser.

• 대한치과교정학회지
• /
• 제12권1호
• /
• pp.21-26
• /
• 1982

This study was undertaken to document relations between facial skeletal pattern and dental occlusion. The data in .this study were collected from pretreatment cephalometric radiographs and study models of patients' records present in the files of Orthodontic Department, Seoul National University Hospital. Patients were selected on the basis of a mandibular plane-sella nasion angle equal to or greater than $38^{\circ}$ (high SN-MP angle) or equal to or less than $26^{\circ}$ (low SN-MP angle). Patients in the mixed dentition and with missing permanent teeth were excluded for ease of assessing tooth size / arch circumference relationships and then 30 high SN-MP and 11 low SN-MP patients were selected among them. The mean age of these two groups of patients was high SN-MP, $12.8{\pm}1.23$ years and low SN-MP, $13.0{\pm}1.48$ years. The following conclusions were obtained. 1. In the maxilla and mandible the mean tooth size of high SN-MP patients was nearlly identical to the low SN-MP patients. 2. The mean maxillary arch circumference was increased in low SN-MP group compared with high SN-MP group and a smilar, but smaller, mean increase was present in mandible. 3. The difference between the mean maxillary circumference required and the mean maillary circumference present ranged from -4.8mm in the high SN-MP group to -1.3mm in the low SN-MP group. A small range of means occurred in the mandible (high SN-MP: -4.0mm to low SN-MP: -1.8mm). 4. In the maxilla and mandible the mean arch length was nearly identical in the high and low SN-MP groups. 5. The mean incisor inclination was increased as the SN-MP angle decreased in the maxilla and mandible. 6. The men distance of the maxillary first molar from anterior border of the pterygomaxillary fissure was nearly similar between high and low groups. 7. The mean mandibular intermolar width was increased from high SN-MP to low SN-MP patients.

• 한국운동역학회지
• /
• 제20권4호
• /
• pp.381-386
• /
• 2010

This study examined the changes in the walking pattern during level walking under low illumination conditions. Fourteen male subjects ($22.1{\pm}2.21$ years, $174{\pm}3.74\;cm$, $68.86{\pm}10.81\;kg$) with normal vision and no disabilities were enrolled in this study. All experiments were performed on a level walkway with three conditions: normal walking (preferred & low speed) and walking with low illumination. 3D motion capturing system was used for acquisition and analysis of the walking motion data with a sampling frequency of 120Hz. The walking speed, normalized jerk(NJ) at the center of mass(COM), wrist and heel, knee and elbow joint angle, ratio of the knee joint angle to elbow joint angle and the toe clearance on stance phase were used to compare the differences in walking pattern between the two illumination conditions, The results showed that the walking speed and joint angles decreased in low illumination, whereas the NJ and toe minimum clearance increased. In low illumination, most variables were similar to effects of low speed walking, but toe clearance was different from the effects of low speed. These results can be used as primary data for examining the changes in the level walking pattern of young adults under low illumination. Further study will be needed to compare these results in young adults with those in the elderly.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1998년도 추계학술대회 논문집
• /
• pp.61-64
• /
• 1998

We have investigated the effects of ultraviolet (UV) light irradiation condition and imidization temperature for the generation of pretilt angle in nematic liquid crystal (NLC) on the two kinds of the polyimide (PI) surfaces. High pretilt angle of NLC is generated with oblique p-polarized UV light irradiation of 30$^{\circ}$ on PI surface for 20 min. Also, the high pretilt angle of NLC is generated with oblique p-polarized UV light irradiation of 10-30$^{\circ}$ on PI surface at 20min. The pretilt angle of NLC decreases with increasing the imidization temperature on all rubbed PI surfaces ; the pretilt angle of NLC with oblique p-polarized UV light irradiation of 30$^{\circ}$on PI surface decreases with increasing the imidization temperature. The high pretilt angle of NLC is observed due to high photo-depolymerization reaction by low surface energy at low imidization temperature. We suggest that the pretilt angle of NLC is strongly attributed to the photo-depolymerization reaction with the UV light irradiation condition and imidization temperature.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.414-419
• /
• 2011

Missile am fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 60 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure distribution, etc. are analyzed according to the angle of attack. The results at a low angle of attack are compared with other results before a stall condition. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution on the airfoil surface, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2005년도 추계학술발표회 및 workshop
• /
• pp.178-178
• /
• 2005

• 대한인간공학회지
• /
• 제5권2호
• /
• pp.37-44
• /
• 1986

This study investigates display station physical adjustments preferred by a sample of visual display terminal operators. Participants in the study were selected to assure representation of extremely short and extremely tall persons, as well as persons of midrange physical stature. Individual operators were led through a step-by-step sequence to determine their preferred initial settings of seat height, keyboard height and slope angle, and CRT height and tilt angle. Each operator then performed a brief text input tase, after which final preferred adjustments were measured. Intermeasure correlation strongly suggest that "flat" (low slope angle) keyboards are in appropriate for short operators who select low seat heights. In addition, the keyboard angle adjustments preferred by most operators substantially exceed a current German ergonomic display station requirement.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
• /
• pp.142-148
• /
• 1998

Recently for the impressive gains of performance and efficiency over vaneless diffuser with apparently little or no loss in flow range, the use of LSVD(Low Solidity Vaned Diffuser) is well recommended. The experiments on the effect of the vane turning angle variation(positive, negative, zero) with other design parameters fixed on the performance and flow range were carried out. Diffuser with zero turning angle has the best characteristics in terms of performance and efficiency and The FFT results show the different frequency characteristics due to the vane turning angle in low flow range.

• 설비공학논문집
• /
• 제13권7호
• /
• pp.588-594
• /
• 2001

The purpose of this study is to investigate the thermal and hydrodynamic characteristics of the channel in corrugated plate type heat exchangers numerically. Numerical work has been conducted using the Reynolds Stress Model(RSM) by utilizing the commercial finite-volume code, FLUENT. Based on this model, the dependence of heat transfer and friction factor on geometrical parameters have been investigated. It is found that larger corrugation angle give higher values of heat transfer coefficients and friction factors. As the reynolds number increases, the heat transfer coefficient also increases. It is also observed that the heat transfer coefficient reaches maximum while the friction factor stays relatively low at same corrugation angle. Through the analysis, it is found that the optimum corrugation angle for the heat exchanger performance exists. It is noted that the flow repulsions at the contact point of the two fluid streams make the low mixing more active for larger corrugation angle and high reynolds number.

• 한국전기전자재료학회논문지
• /
• 제17권5호
• /
• pp.526-529
• /
• 2004

The nematic liquid crysta](NLC) aligning capabilities using a-C:H thin film deposited at the three kinds of rf bias condition were investigated. A high pretilt angle of NLC on low substrate rf bias applied a-C:H thin films was observed and the low pretilt angle of the NLC on high substrate rf bias applied a-C:H thin films was observed. Consequently, the high NLC pretilt angle and the good aligning capabilities of LC alignment by the IB alignment method on the a-C:H thin film deposited at 1 W rf bias condition can be achieved. It is considered that pretilt angle of the NLC may be attributed to substrate rf bias condition and IB energy time. Therefore, LC alignment is affected by topographical structure forming strong IB energy.