• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.1
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• pp.24-32
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• 2018

In this paper, analytical studies were conducted to obtain optimal design factors and analysis parameters of liquid nitrogen cooling exchanger applied in cryogenic refrigerator. The target value of heat transfer rate was more than 1 kW and pressure drop was less than 40 kPa. Design factors of cryogenic heat exchanger included width of channel and configuration of paths. Analytical factors of liquid nitrogen cooling exchanger included temperatures of coolant header surface and inlet liquid nitrogen. The width and number of channels in the design parameters were 0.0050~0.0150 m and 4~8, respectively. The configuration of channel path was 4 ways. Temperatures of coolant header surface and inlet liquid nitrogen in analytical parameters were 74 to 78K and 82 to 86K, respectively. As result, the design factor and analysis parameter satisfying the target values were obtained. The biggest heat transfer rate was 1.36 kW with pressure drop of 32.26 kPa.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.2
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• pp.73-82
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• 2009

The traffic volume of Seoul is extremely high in comparison to other major cities in Korea, and the result has been harmful physical and mental exposure to pollution by Seoulites on a regular basis. The street air pollution is more important than the others, because the air pollution generated by street traffic directly impacts the health of nearby pedestrians. This problem requires urgent attention and resolution. Among the factors creating the air pollution originating from the street, is the configuration of streets, which have emerged as the most significant because it is related to air and pollutant dispersion. Therefore, this study was conducted under the assumption that street form affects the air quality. Study sites were classified by street characteristics, and air quality was analyzed in each class. Then the OSPM (Operational Street Pollution Model) was employed to simulate the relationship between street configuration and air quality of streets within the old city center and new city center in Seoul. After that this study analyzed the correlation between air pollution and the spatial configuration of urban streets (ex. street width, building height, building density, etc.) to determine their contributions to air pollution. The outcome of this study is as follows : First, the result that was derived from the correlation analysis between street configuration and air quality hewed that the air pollution of the street is influenced by the average height of building, width of the roads as well as traffic volume. On the roadside, the concentration level of $NO_2$ is mainly affected by the average height of building and the deviation of building height along the street and CO is affected by street width. The outcome of this study can be used as a basis for more sound urban design policies, and the promotion of desirable street environments for pedestrians.

• Journal of The Korea Institute of Healthcare Architecture
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• v.25 no.1
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• pp.7-16
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• 2019

Purpose: Analysis on the spatial configuration characteristics of dental department in medical center through examining outpatient department of medical center is necessary for the development of architectural planning of the dental healthcare system in Korea. This study has been performed to provide data for the planning of hospital architecture. Methods: Literature review of dental healthcare system and investigation on current status of dental department in medical center have been conducted. The plan and spatial configuration of seven medical centers in Seoul area have been analyzed. Results: The result of this study can be summarized in four points. The first one is that the clinical dental spaces are classified by dental school's dental hospital, dental department in medical center, dental hospital, private dental clinic, and public dental healthcare center in Korea. The second one is that the dental department in medical center is a result from medical law regulation and it is specified and subdivided with dental specialist system. The third one is that the types of the dental department in medical center are divided into independent type or comprehensive type according to the relationship with main outpatient department. The fourth one is that the spatial configuration of dental department in medical center is planned with 5-7 specialized departments and they are allocated in the dental department. Implications: In addition to the spatial configuration of dental department in medical center, it is necessary to analyze the other factors like circulation, relationship with other facilities in medical center to develop the dental healthcare system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.146-170
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• 2017

Joint channel assignment and routing is a well-known problem in multi-radio wireless mesh networks for which optimal configurations is required to optimize the overall throughput and fairness. However, other objectives need to be considered in order to provide a high quality service to network users when it deployed with high traffic dynamic. In this paper, we propose a re-configuration optimization model that optimizes the network throughput in addition to reducing the disruption to the mesh clients' traffic due to the re-configuration process. In this multi-objective optimization model, four objective functions are proposed to be minimized namely maximum link-channel utilization, network average contention, channel re-assignment cost, and re-routing cost. The latter two objectives focus on reducing the re-configuration overhead. This is to reduce the amount of disrupted traffic due to the channel switching and path re-routing resulted from applying the new configuration. In order to adapt to traffic dynamics in the network which might be caused by many factors i.e. users' mobility, a centralized heuristic re-configuration algorithm called State-Aware Joint Routing and Channel Assignment (SA-JRCA) is proposed in this research based on our re-configuration model. The proposed algorithm re-assigns channels to radios and re-configures flows' routes with aim of achieving a tradeoff between maximizing the network throughput and minimizing the re-configuration overhead. The ns-2 simulator is used as simulation tool and various metrics are evaluated. These metrics include channel-link utilization, channel re-assignment cost, re-routing cost, throughput, and delay. Simulation results show the good performance of SA-JRCA in term of packet delivery ratio, aggregated throughput and re-configuration overhead. It also shows higher stability to the traffic variation in comparison with other compared algorithms which suffer from performance degradation when high traffic dynamics is applied.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.105-116
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• 2015

In this study, airside performance of round fin-and-tube heat exchangers are compared with that of the herringbone wave fin-and-tube heat exchangers with an aim to investigate the effect of fin shape on thermal performance. Results show that j factors of the round wave fin are 1.2~22% larger than those of herringbone wave fin. The f factors of the round wave fin are -1.0~29% smaller than those of herringbone wave fin for 1 or 2 row configuration. For 3 row configuration, f factors of the round wave fin are 8.3~23% larger. The reason may be attributed to the reduced recirculation zone in the valley of the fin for round wave fin as compared with that of the herringbone wave fin. For round wave fin, the effect of fin pitch on j and f factor is not significant. In addition, j factors decrease as the number of tube row increases. On the other hand, f factors are independent of the number of tube row. A new correlation was developed based on the present data.

• The Journal of the Korean dental association
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• v.54 no.4
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• pp.252-257
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• 2016

This manuscript aims at discussing the technical and biological aspects of peri-implant disease. The following contents will be discussed. -The difference between peri-implantitis and peri-implant mucositis. -Prevalence of peri-implant disease. -Risk factors for peri-implantitis. -Indications and boundaries of non-surgical and surgical treatment -Treatment flow-chart by Schwarz -Limitations of non-surgical treatment -Methods to decontaminate diseased surfaces -Importance of defect configuration in surgical treatment -Biomechanical factors that influence the progression and decontamination related to peri-implantitis -Maintenance of implants.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.5
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• pp.71-77
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• 2015

Internal ballistics is a phenomenon happened in tens of milliseconds during the gun firing. The configuration variables of the solid propellant are important factors which have influences on the performance of the gun system. In this study, the performance analysis of the 7-perforated propellant has been conducted using the numerical program for the interior ballistics. The effect of the configuration variables on the gun system performance has been analyzed. The propellant design has been conducted for the satisfaction of the performance requirements. As results, the relationship between the configuration variables and the performance has been obtained and the basic design concept of the multi-perforated propellant has been provided.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1177-1183
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• 2012

This study aims to develop a system that maximizes the radiative heat transfer from the heliostat to the receiver by using the configuration factor and a solar tracking device. As the heat transfer from the heliostat to the receiver is delivered by solar radiation, the configuration factor commonly utilized for radiation is applied to control the heliostat. Tracking the sun and calculating its position are possible by using an illuminance sensor (CdS) and Simulink. By applying optimized algorithms programmed using Simulink that maximize the configuration factors among the heliostat, receiver, and sun in real time, the solar absorption efficiency of the receiver can be maximized. Simulations were performed on how to change the angle required to control the elevation and azimuthal angle of the heliostat during the daytime with respect to various distances.

• Journal of Chest Surgery
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• v.54 no.2
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• pp.117-126
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• 2021

Background: Several factors, such as the degree of target vessel stenosis, are known to be associated with radial artery (RA) graft patency in coronary artery bypass grafting (CABG). There is a lack of data regarding the effect of the RA proximal configuration (aortic anastomosis versus T-anastomosis). This study evaluated the effects of the RA proximal configuration on the patency rate and clinical outcomes after CABG. Methods: We conducted a retrospective study, analyzing 328 patients who had undergone CABG with an RA graft. We divided the patients into 2 groups. The primary endpoint was RA patency and the secondary endpoints were overall mortality and major adverse cardiac and cerebrovascular events (MACCE). We performed a propensity score-matched comparison. Results: Aorta-RA anastomosis was performed in 275 patients, whereas the rest of the 53 patients received T-RA anastomosis. The mean age was 67.3±8.7 years in the T-RA anastomosis group and 63.8±9.5 years in the aorta-RA anastomosis group (p=0.02). The mean follow-up duration was 5.13±3.07 years. Target vessel stenosis ≥70% (hazard ratio [HR], 0.42; 95% confidence interval [CI], 0.20-0.91; p=0.03) and T-RA anastomosis configuration (HR, 2.34; 95% CI, 1.01-5.19; p=0.04) were significantly associated with RA occlusion in the multivariable analysis. However, T-RA anastomosis was not associated with higher risks of overall mortality and MACCE following CABG (p=0.30 and p=0.07 in the matched group, respectively). Conclusion: Aorta-RA anastomosis showed a superior patency rate compared to T-RA anastomosis. However, the RA proximal anastomosis configuration was not associated with mortality or MACCE.

• Journal of Korean Neurosurgical Society
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• v.42 no.5
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• pp.371-376
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• 2007

Objective : Balloon kyphoplasty can effectively relieve the symptomatic pain and correct the segmental deformity of osteoporotic vertebral compression fractures. While many articles have reported on the effectiveness of the procedure, there has not been any research on the factors affecting the deformity correction. Here, we evaluated both the relationship between postoperative pain relief and restoration of the vertebral height, and segmental kyphosis, as well as the various factors affecting segmental deformity correction after balloon kyphoplasty. Methods : Between January 2004 and December 2006, 137 patients (158 vertebral levels) underwent balloon kyphoplasty. We analyzed various factors such as the age and sex of the patient, preoperative compression ratio, kyphotic angle of compressed segment, injected PMMA volume, configuration of compression, preoperative bone mineral density (BMD) score, time interval between onset of symptom and the procedure, visual analogue scale (VAS) score for pain rating and surgery-related complications. Results : The mean postoperative VAS score improvement was $4.93{\pm}0.17$. The mean postoperative height restoration rate was $17.8{\pm}1.57%$ and the kyphotic angle reduction was $1.94{\pm}0.38^{\circ}$. However, there were no significant statistical correlations among VAS score improvement, height restoration rate, and kyphotic angle reduction. Among the various factors, the configuration of the compressed vertebral body (p=0.002) was related to the height restoration rate and the direction of the compression (p=0.006) was related with the kyphotic angle reduction. The preoperative compression ratio (p=0.023, p=0.006) and injected PMMA volume (p<0.001, p=0.035) affected both the height restoration and kyphotic angle reduction. Only the preoperative compression ratio was found to be as an independent affecting factor (95% CI : 1.064-5.068). Conclusion : The two major benefits of balloon kyphoplasty are immediate pain relief and local deformity correction, but segmental deformity correction achieved by balloon kyphoplasty does not result in additional pain relief. Among the factors that were shown to affect the segmental deformity correction, configuration of the compressed vertebral body, direction of the most compressed area, and preoperative compression ratio were not modifiable. However, careful preoperative consideration about the modifiable factor, the PMMA volume to inject, may contribute to the dynamic correction of the segmental deformity.