• Nuclear Engineering and Technology
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• v.27 no.4
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• pp.503-517
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• 1995

A mechanistic model for forced convective transition boiling has been developed to predict transition boiling heat flux realistically. This model is based on a postulated multi­stage boiling process occurring during the passage time of an elongated vapor blanket specified at a critical heat flux condition. Between the departure from nucleate boiling (DNB) and the departure from film boiling (DFB) points, the boiling heat transfer is established through three boiling stages, namely, the macrolayer evaporation and dryout governed by nucleate boiling in a thin liquid film and the unstable film boiling. The total heat transfer rate during the transition boiling is the sum of the heat transfer rates after the DNB weighted by the time fractions of each stage, which are defined as the ratio of each stage duration to the vapor blanket passage time. The model predictions are compared with some available experimental transition boiling data. From these comparisons, it can be seen that the transition boiling heat fluxes including the maximum heat flux and the minimum film boiling heat flux are nil predicted at low qualities/high pressures near 10 bar.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.295-297
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• 2004

무선 ad-hoc 네트워크란 기반 시설의 도움 없이 노드들 간의 수평적인 통신을 제공하는 임시적인 네트워크이다. 이러한 네트워크 환경에서는 각 노드의 네트워크 창가 밀 이탈이 동적으로 가능하다. 현재 이러한 환경에서 높은 이동성을 지원하는 동시에 라우팅 오버헤드를 최소화하는 연구가 활발히 진행되고 있다. 기존에 제안된 무선 ad-hoc 라우팅 프로토콜들은 부하균형 메커니즘을 지원하지 않으므로 특정 노드에 많은 부하가 발생할 수 있다. 이로 인해 종단 간 지연시간이 길어지며 네트워크의 신뢰성이 낮아질 수 있다. 본 논문에서는 이러한 문제의 해결을 위해 각 노드가 자신의 부하를 측정하고, 경로 요청 시 노드의 부하 정보를 이용해서 부하가 적은 경로를 선택하도록 한다. 또한 데이터 전송 중에 해당 경로의 부하를 확인하여, 보조 경로를 이용하거나 새로운 경로를 검색하여 경로의 혼잡을 해결함으로써 종단 간 지연시간 및 네트워크의 신뢰성을 향상시키는 기법을 제안한다. 본 논문에서 제안하는 기법은 특정 노드에 라우팅 오버헤드가 집중되는 것을 방지하며 이로 인해 종단 간 지연시간을 줄이고 네트워크의 신뢰성 을 향상시킨다.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.193-196
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• 2005

본 논문은 P2P 네트워크 환경에서 VOD 시스템의 새로운 프록시 캐싱 기법을 제안한다. P2P 환경에서 비디오 스트림을 그룹에 포함된 다수의 클라이언트에 저장하고, 이러한 클라이언트의 그룹을 Proxy로 활용하는 P2Proxy 기법을 제안한다. 우선 P2Proxy의 그룹에 포함된 클라이언트들과 서버간의 스트림이 전송되는 과정을 보였으며, 둘째 각 그룹의 생성과정과 서멸 과정에 대해 설명한다. 또한 클라이언트의 캐싱 정보를 공유하기 위한 디렉토리 구조를 기술하고 각 클라이언트의 참여 과정과 이탈과정을 보였다. 또 디렉토리 정보를 이용해 그룹에 참여한 다른 클라이언트의 정보를 계산하는 과정을 보였으며 이를 활용하여 재생과 전송 중에 메시지의 교환을 최소로 하도록 하였다. 제안된 P2Proxy 기법은 기존의 P2VoD 기법에 비하여 서버에 대한 부하의 요구량이 훨씬 작은 결과를 보였다.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.9
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• pp.115-125
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• 1995

부품가공에 있어서 생산성향상을 위하여 버제거를 위한 고도의 기술이 더욱 중요하게 되었다. 특히 CIM 체제에서는 버제거의 자동화를 위하여 가공중에 발생하는 버형성과 파단현상을 정량적으로 예측할 필요성이 더욱 커졌다. 이미 연구된 2차원절삭에서의 버형성 모델을 실제적인 3차원절삭에 적용하기 위하여 기존의 모델을 수정하는 작업이 이루어졌다. 3차원 절삭모델로는 절삭인선에 수직한 면에서의 칩과 공구의 상대운동에 의해서 결정된다고 하는 Rubenstein의 가정이 사용되었다. 본연구에서 다루에되는 롤오버(roll-over) 버는 항상 공구진행방향으로 발생하기 때문에 3차원절삭에서의 버형성을 공구진행방향의 평면내에서의 2차원 절삭의 집합 으로 가정하였다. 공구의 기울림각(inclination angle)이 커질수록 버형성의 크기나 파단면의 크기가 감소하였다. 두종류의 파단이 버형성중에 관찰되었다. 하나는 가공물 끝면에 평행하게 파단면이 발생하였으며 다른 하나는 이에대하여 기울어진 파단이 일어났다. 가공물 끝면에 평행한 경우는 수정된 모델로부터 등가초기공구위치( equivalent initial tool distance)로부터 예측이 가능하며 기울어진 경우는 이결과와 공구의 기울림각으로부터 파단위치를 예측할 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1916-1932
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• 1997

The synchronous stream cipher which require absoulte clock synchronization has the problem of synchronization loss by cycle slip. Synchronization loss makes the state which sender and receiver can't communicate with each other and it may break the receiving system. To lessen the risk, we usually use a continuous resynchronization method which achieve resynchronization at fixed timesteps by inserting synchronization pattern and session key. While we can get resynchronization effectively by continuous resynchroniation, there are some problems. In this paper, we proposed an adaptive resynchronization algorithm for cipher system using HDLC protocol. It is able to solve the problem of the continuous resynchronization. The proposed adaptive algorithm make resynchronization only in the case that the resynchronization is occurred by analyzing the address field of HDLC. It measures the receiving rate of theaddress field in the decision duration. Because it make resynchronization only when the receiving rate is greateer than the threshold value, it is able to solve the problems of continuous resynchronization method. When the proposed adaptive algorithm is applied to the synchronous stream cipher system in packet netork, it has addvance the result in R_e and D_e.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.40 no.4
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• pp.49-57
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• 2022

This study was conducted with the aim of investigating the garden architectural characteristics of Villa d'Este, which occupies a major role in the exploration of the contrasting background, location, and spatial composition characteristics of Italian Renaissance gardens. The survey for the study was divided into a literature survey and a field survey, and the details are as follows. First, in the mid-to-late 16th century, the villa was built under the direction of Cardinal Ippolito d'Este, and afterwards, the ownership of the villa was restored to the Italian government in 1850 due to financial difficulties. The Villa d'Este, which suffered another damage, is now operated with many visitors after going through the restoration process. Second, in the case of location, it has the characteristics of Urbana located in the city center and has valley-type topographical conditions located at the foot of the mountain.Third, in the case of spatial composition, it is orthogonal to the axis, and each part of the garden is developed, influenced by the contrast principles such as the installation of the Cortile del Belvedere and Villa Madama in the early 16th century. The main building is located in the hills so that you can see the garden and the surrounding scenery at a glance. Fourth, among the components, there were stairs, logia, courtyard, and grotto, fountains, cascades, ponds, and vegetation such as laurels, thorn trees.

• Tuberculosis and Respiratory Diseases
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• v.46 no.3
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• pp.350-362
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• 1999

Background: Acute Respiratory failure which is developed after extubation in the weaning process from mechanical ventilation is an important cause of weaning failure. Once it was developed, endotracheal reintubation has been done for respiratory support. Noninvasive Positive Pressure Ventilation (NIPPV) has been used in the management of acute or chronic respiratory failure, as an alternative to endotracheal intubation, using via nasal or facial mask. In this study, we evaluated the usefulness of NIPPV as an alternative method of reintubation in patients who developed acute respiratory failure after extubation. Method: We retrospectively analyzed thirty one patients(eighteen males and thirteen females, mean ages $63\pm13.2$ years) who were developed acute respiratory failure within forty eight hours after extubation, or were extubated unintentionally at medical intensive care unit(MICU) of Asan Medical Center. NIPPV was applied to the patients. Ventilatory mode of NIPPV, level of ventilatory support and inspiratory oxygen concentration were adjusted according to the patient condition and results of blood gas analysis by the attending doctors at MICU. NIPPV was completely weaned when the patients maintained stable clinical condition under 8 $cmH_2O$ of pressure support level. Weaning success was defined as maintenance of stable spontaneous breathing more than forty eight hours after discontinuation of NIPPV. Respiratory rate, heart rate, arterial blood gas analysis, level of pressure support, and level of PEEP were monitored just before extubation, at thirty minutes, six hours, twenty four hours after initiation of NIPPV. They were also measured at just before weaning from NIPPV in success group, and just before reintubation in failure group. Results: NIPPV was successfully applied to thirty-one patients of thirty-two trials and one patient could not tolerated NIPPV longer than thirty minutes. Endotracheal reintubation was successfully obviated in fourteen patients (45%) among them. There was no difference in age, sex, APACHE III score on admission at MICU, duration of intubation, interval from extubation to initiation of NIPPV, baseline heart rate, respiratory rate, arterial blood gas, and $PaO_2/FiO_2$ between the success and the failure group. Heart rate and respiration rate were significantly decreased with increase $SaO_2$ after thirty minutes of NIPPV in both groups(p<0.05). However, in the patients of failure group, heart rate and respiratory rate were increased again with decrease in $SaO_2$ leading to endotracheal reintubation. The success rate of NIPPV treatment was significantly higher in the patients with COPD compared to other diseases(62% vs 39%) (p=0.007). The causes of failure were deterioration of arterial blood gas without aggravation of underlying disease(n=9), aggravation of undelying disease(n=5), mask intolerance(n=2), and retained airway secretion(n=l). Conclusion: NIPPV would be a useful therapeutic alternative which can avoid reintubation in patient who developed acute respiratory failure after extubation.

• Journal of the Korean Society for information Management
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• v.29 no.4
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• pp.7-23
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• 2012

This paper explores how interface environments have an influence on novice users' performance in social virtual worlds (SVWs), which are emerging user-centric three-dimensional cyberspaces. Despite their early popularity, SVWs have experienced that numerous new users leave the cyberspaces soon before they become long-term users. One possible reason is that unfamiliar interfaces of SVWs can be a barrier to novice users' adaptation of the technology. To understand a role of interfaces in the users' assimilation of SVWs, we examine an impact of three interface factors (presence, affordance, and feedback) on performance which is regarded as a yardstick for users' adaptation of SVWs. Forty participants were recruited and went through one-hour experimental sessions with seven tasks in Second Life; they were also asked to answer a questionnaire. Findings indicate that while affordance and feedback are significant factors influencing novice users' performance, presence has no impact on their performance.

• Science of Emotion and Sensibility
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• v.20 no.2
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• pp.11-22
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• 2017

For the elderly whose path-finding capability and distance perception abilities have been weakened, the study intends to provide UI design of a wrist type walking aid device which allows the elderly to receive both visual and haptic information that induces the elderly' occasional attention by utilizing currently available haptic technology. The study asked 30 the elderly older than 65 years old, target consumers of the technology, to wear a smart watch and find a path by following the directions provided by four different UI versions of Wizard of Oz. Then, the study has conducted post-experience interview. Quantitative analyses was performed their preference level, number of misguided participants and the number of deviations incurred. Based on the data collected, the study has applied grounded theory, a qualitative research methodology, in order to grasp new understanding about the research, and has consequently reached some significant implications for further research on wrist type walking aid device for the elderly, who show self-contradictory demands.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1499-1505
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• 2010

In general, magnetic abrasive polishing can be used to effectively produce a mirror-like surface; however, industrial applications of this process involve some unsolved problems. For example, the polishing efficiency is low, and the used abrasives have to be treated. In this study, which is aimed at solving these problems, a novel medium of silicone gel, consisting of ferromagnetic particles and abrasives, is developed, and the effect of this medium is assessed on the basis of Taguchi's experimental method. The workpiece is a tungsten carbide steel and the surface roughness after magnetic abrasive polishing using the silicone gel is evaluated.