• Journal of the korean academy of Pediatric Dentistry
• /
• v.25 no.2
• /
• pp.368-382
• /
• 1998

The purpose of this study is to evaluate and compare the results of argon laser for 5 seconds, argon laser for 10 seconds, and visible light for 40 seconds photo-polymerization in compressive strength, microhardness, curing depth, temperature rising during polymerization, and polymerization shrinkage. Hybrid type composite resin(Z-100) and compomer(Dyract) were used to be compared. The compressive strength was measured by an Instron(1mm/min cross head speed) in 60 specimens and the microhardness of the surface was expressed by Vickers Hardness Number(VHN) in 30 specimens. The curing depth was evaluated comparing the different values of upper and lower VHN according to irradiation time and thickness for the light source polymerization in 60 specimens. The temperature rising during photopolymerization was observed by the temperature change with thermocouple sensitizer beneath 40 specimens at the argon laser for 10 seconds and visible light 40 seconds irradiation. The polymerization shinkage was evaluated by calculating the decrease of % volume by using a dilatometer in 30 specimens. The results were as follows ; 1. In the case of compressive strength, the argon laser polymerization groups were higher than visible light group in Z-100 (p<0.05). In Dyract, the argon laser 5 seconds group did not show a significant difference with the visible light 40 seconds group. The argon laser 10 seconds group showed the markedly low value when compared with other groups (p<0.05) 2. In microhardness, Z-100 was better than Dyract when comparing by VHNs (p<0.05); however, there was not a significant difference between two materials in the visible light 40 seconds group and the argon laser 10 seconds group. 3. In the study of curing depth, Z-100 showed the consistent polymerization in argon laser irradiation because there was no difference in the VHN decrease according to the thickness change. Over the thickness control, the results did not show a significant difference between visible light and argon laser group in Z-100; however, in the case of Dyract, the visible light 40 seconds group was better than the argon laser groups(p<0.05). 4. There was a significant difference between the two materials in temperature rising during polymerization (p<0.05), but not a significant difference between irradiation times, 5. There was not a significant difference between the two materials in polymerization shrink age. The argon laser 5 seconds group was smaller than the other groups (p<0.05). It could be concluded that Z-100 polymerization was recommended to use the argon laser for reduction of the irradiation time while Dyract was recommended to use the visible light polymerization.

• Journal of Korea Multimedia Society
• /
• v.23 no.3
• /
• pp.460-467
• /
• 2020

The medical service, accompanied by various disease and disease of modern people, must collect various information about patients through various tests, and demand continued to increase. As a result, interest in waiting time for medical services is rising, and various studies are underway to reduce waiting time. However, medical procedure is complex and diverse in the procedure of the services need to be conducted for each procedure. In this study, we are going to propose ways to improve the waiting time of the test procedures that are basically experienced by outpatients through the simulation experimental method. Based on the actual measurement data, the Arena Simulation program was used to implement the hospital's ophthalmic examination model and alternative model. Through this analysis, the waiting time of the examination procedure, the size of the queue, and density of the waiting room were analyzed.

• 정보저장시스템학회:학술대회논문집
• /
• 2005.10a
• /
• pp.139-144
• /
• 2005

Because of the photorefractive recording dynamics, each newly recorded hologram partially erases all previously stored image. Thus achieving the desired diffraction efficiency profile for the entire sequence after all images have been recorded requires exposure time schedule. The often cited classical exposure-schedule model predicts a rising-exponential build-up and an exponential decay in An with an exposure time. However because we cannot directly measure the An, it's difficult to establish the relation of both. In this paper, we deduce the relation of diffraction efficiency and exposure time from experiment data and suggest an algorithm to make time schedule profile in angle/fractal multiplexing of holographic data storage. After that, we present simulated result with equal hologram diffraction efficiency for a sequence of 250 holograms recorded by angle/fractal multiplexing.

• Polymer(Korea)
• /
• v.25 no.4
• /
• pp.528-535
• /
• 2001

Polyurethane specimens were mainly composed of polyol, MDI, silicone surfactant, and water. The effects of ethylene glycol on the cell size, forming magnification, cream time, gel time, take free time, final free rising height, and reactive temperature were investigated. The cyclopentane was used for PU foam as a physical blowing agent. The components were hand-mixed at about 5000 rpm within 4 seconds at room temperature. The mixtures with various ethylene glycol contents were foamed in the wood mold. When the index of isocyanate was fixed, as the amount of ethylene glycol increased, cell size and thermal conductivity were decreased by about 5.1% and 14%, respectively.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.5
• /
• pp.85-91
• /
• 1997

Air grinding time in grinding process has a great effect on its efficiency due to low feedrate. This paper presents a reduction methos of air grinding time in cylindrical plunge grinding operation. Tje reduction of air grinding time is accomplished by finding the distance between contact point and rising point of ultra- sonic signal of the grinding wheel to workpiece. It uses a variation of sound signal generated by the flow of coolant when the grinding wheel approaches to workpiece. The ultrasonic sensor with 23 kHz center fre- quency and 8 kHz bandwidth is used to find the nearest approaching point(NAP). Monitoring and control system of the grinding conditions is implemented with CNC controller to control feedrate override and ultrasonic sensor to find NAP. The experimental result shows that the ultrasonic signal is a good measure- ment to find NAP. But it needs the considerations for the effect of the relationship between flowrate of coolant and diameter of workpiece.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.35 no.5
• /
• pp.329-338
• /
• 2017

This study attempts to classify 1008 alley markets in Seoul through cluster analysis using Dynamic Time Warping, one of the methods used to analyze the similarity of time series, and evaluate the possibility of opening new stores. The sequence of the gross sales of an alley market and that of gross sales per store stand for the potential of growth and profitability of the market, respectively and are used as variables for cluster analysis. Five clusters are obtained for the gross sales and four clusters for the gross sales per store. These two types of clusters are again classified as rising and falling trends, respectively, and the combination of these trends produces four categories. These categories are used to evaluate the possibility of opening new stores in alley markets. The results show that the southeast which is relatively wealthy inferior to other regions in opening new stores. Alley markets in the northeast and the southwest are better than other regions such that opening a new store is justified. In the northwest, there are many markets with trend of gross sales and that of gross sales per store moving in opposite directions, and new store openings in these markets should be postponed.

• Journal of Power System Engineering
• /
• v.11 no.3
• /
• pp.66-72
• /
• 2007

This study proposed new method to decide the reference model necessary for design PID controller. In generally, control design problems using the reference model have the following two factors. One factor is that numerical model of the controlled system can be obtained extremely, and the other is that specification for the closed-loop dynamic performance is pure moderate. Therefore, the control design procedure is essentially based on the partial reference model matching which offers a reasonable method to simplify the design and the controller configuration under the controlled system uncertainty. ITAE(Integral of time-multiplied absolute error) performance index and Kitamori method etc. which were used a reference model method had a limit to settling time and rising time of reference model that it arrived to steady state response according to the controlled system. On this study, if it only knew peak time of overshoot and settling time by measurement signal of the controlled system, it can be made the reference model easily. We proposed new method to improve performance index of the reference model superior to existing reference model index and illustrate the numerical simulation results to show the effectiveness of proposed control method design.

• Journal of the Korean Society of Visualization
• /
• v.6 no.1
• /
• pp.41-46
• /
• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble stream in a rectangular water tank is studied. The time-resolved PIV technique is adopted for the quantitative visualization and analysis. 488 nm Ar-ion CW laser is used for illumination and orange fluorescent ($\lambda_{ex}=540nm,\;\lambda_{em}=560nm$) particle images are acquired by a PCO 10bit high-speed CCD camera (1280$\times$1024). To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is 3 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by time-resolved POD analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortex structures moving along with large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy.

• Geomechanics and Engineering
• /
• v.37 no.2
• /
• pp.179-187
• /
• 2024

In this paper, a unified time-dependent constitutive model of Darcy flow and non-Darcy flow is proposed. The influencing factors of flow velocity are discussed, which demonstrates that permeability coefficient is the most significant factor. Based on this, the dynamic evolution characteristics of water inrush during tunneling through fault fracture zone is analyzed under the constant permeability coefficient condition (CPCC). It indicates that the curves of flow velocity and hydrostatic pressure can be divided into typical three stages: approximate high-velocity zone inside the fault fracture zone, velocity-rising zone near the tunnel excavation face and attenuation-low velocity zone in the tunnel. Furthermore, given the variation of permeability coefficient of the fault fracture zone with depth and time, the dynamic evolution of water flow in the fault fracture zone under the variable permeability coefficient condition (VPCC) is also studied. The results show that the time-related factor (α) affects the dynamic evolution distribution of flow velocity with time, the depth-related factor (A) is the key factor to the dynamic evolution of hydrostatic pressure.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.49 no.3
• /
• pp.177-185
• /
• 2000

In this study, the characteristics of various electricity and high resistivity ash collection were measured at superimposed nanosecond pulse energization. The pulse was generated through the hydrogen thyratron. Superimposed pulse was nanosecond duration pulse that had fast pulse rising time 100[ns], short pulse width 500∼850[ns] and pulse fall time 400∼750[ns]. The results of this study are summarized as followings; Frist, compared with the DC ESP(electrostatic precipitator), superimposed pulse ESP could induce higher peak voltage, and had the about 30[%] reduction of ESP collection area and 50∼80[%] reduction of power consumption. showing the same efficiency. Second, enhancement factor H had 1.9∼3.6 with the increase of migration velocity.