• Journal of the Optical Society of Korea
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• v.11 no.4
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• pp.162-172
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• 2007

Scanning Laser Optical Tweezers(SLOT) is an optical instrument frequently employed on a microscope with laser being delivered through its various ports. In most SLOT systems, a mechanical tilt stage with a mirror on top is used to dynamically move the laser focal point in two-dimensions. The focal point acts as a tweezing spot, trapping nearby microscopic objects. By adding a mechanical translational stage with a lens, SLOT can be expanded to work in three-dimensions. When two mechanical stages operate together, the focal point can address a closed three-dimensional volume that we call a workspace. It would be advantageous to have a large workspace since it means one can trap and work on multiple objects without interruptions, such as translating the microscope stage. However, previous studies have paid less consideration of the volumetric size of the workspace. In this paper, we propose a new method for designing a SLOT such that its workspace is maximized through optimization. The proposed method utilizes a matrix based ray tracing method and genetic algorithm(GA). To demonstrate the performance of the proposed method, experimental results are shown.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.2
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• pp.223-231
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• 2011

The thermal efficiency of energy-to-power conversion becomes uneconomically low when the temperature of heat source drops below $370^{\circ}C$. ORC (Organic Rankine Cycle) has attracted much attention in last few years due to its potential in reducing consumption of fossil fuels and relaxing environmental problems, and its favorable characteristics to exploit low-temperature heat sources. In this work thermodynamic performance of ORC using nine working fluids is comparatively assessed. Special attention is paid to the effect of system parameters such as turbine inlet temperature and pressure on the characteristics of the system such as volumetric flow rate and quality at turbine exit, latent heat, net work as well as thermal efficiency. Results show that in selection of working fluid it is required to consider various criteria of performance characteristics as well as the thermal efficiency. Results also show that the system efficiencies become same irrespective of kind of working fluid when the temperature of heat source decreases to low range.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.83-88
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• 2006

Natural convection flows in a cubical air-filled cavity that has one pair of opposing faces isothermal at different temperatures, $T_h\;and\;T_c$ respectively, the remaining four faces having a linear variation from $T_c\;to\;T_h$ are numerically simulated by a solution code(PowerCFD) using unstructured cell-centered method. An extension to a previously published work, special attention of this work is paid to three-dimensional flow and thermal characteristics in nature convection according to new orientation at Ra= $1{\times}105$. Comparisons of the average Nusselt number at the cold face are made with benchmark solutions and experimental results found in the literature. It is demonstrated that the average Nusselt number on the cold face has a maximum value around the diamond-type inclination angle of $43.2^{\circ}\;at\;Ra=1{\times}105$. We also report the effect of new orientation on the type of flow and temperature structure in a cubical-cavity.

• Architectural research
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• v.16 no.4
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• pp.193-202
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• 2014

This research started from the premise that Jacques Perret, "Savoyard gentleman" of the 17th century - whose only legacy consists of Des fortifications et artifices, a book of fortified town designs - is still an elusive figure in the history of architecture and deserves to be further investigated. In particular, attention needs to be paid to the lack of any attempt by scholars to define his actual professional status and cultural background: was he an architect, an engineer, a professional or an amateur? The intention of this paper is therefore to shed some light on this question by examining selected contents of his book describing five projects of fortified towns. Plates and descriptions are carefully analyzed related to the engineering (defensive structures) and architectural (city layouts, buildings) content. The figure that emerges is that of an articulate personality who does not fit either in the architectural or in the military engineering professional world. In the field of engineering, he simultaneously demonstrated the competence of a professional and the na$\ddot{i}$vety of an immature technician, while in the field of architecture he showed an advanced creativity alongside several technical and theoretical misunderstandings. From the analysis in this study, the assumption is formulated that Jacques Perret was a connoisseur, i.e. an erudite without any direct involvement in real professional activity. This work is intended to provide a hypothesis for further researches that, hopefully, will deepen our understanding of several other aspects of Perret's complex identity and work.

• Culinary science and hospitality research
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• v.10 no.3
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• pp.32-50
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• 2004

The purpose of this study was to examine what caused bakery employees at tourist hotel to leave their job. It's basically meant to lay the foundation for increasing personnel management efficiency and reducing turnover rate, as an attempt to prevent workers from quiting their jobs would be a successful way to take advantage of human resources more efficiently. Both theoretical and experimental approaches were utilized to serve the purpose of this study. First, concerning salaries, their turnover intention was under the influence of whether they were properly paid or gained a sufficient living. Second, as for environmental factors, their turnover intention was affected by performance appraisal and interpersonal trust with colleagues. Third, regarding job-related factors, their turnover intention was impacted by whether their job was clearly defined, how much they were satisfied with their job and whether their posts were suitable. Forth, the change of job was subjected to the influence of the desire for job in another region, job in another company and another kind of job. And there should be a clear distinction between sales and other works, and they should carefully be treated so that they could find their job more satisfactory.

• The Korean Journal of Health Service Management
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• v.9 no.4
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• pp.63-78
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• 2015

Objectives : The aim of this study was to examine how emergency medical technicians(EMT) are affected by job stress, musculoskeletal symptoms(MSSs) and depression. Methods : Data were collected from EMTs at emergency medical institutions and fire stations (n=257). With a questionnaire, the association of job stress and MSSs and depression were examined in this study. Results : When examining job stress by place of work, the level of stress in field situations was significantly higher in EMTs at fire stations than in EMTs at emergency medical institutions. The MSSs of EMTs at emergency medical institutions were significantly higher compared to EMTs at fire stations, For depression, the score was 14.09 out of 60, and MSSs were significantly more common in women. Additionally, the level of job stress for 20-24 and over 35 year olds was significantly higher than that in the other age groups. Job stress had a positive correlation with MSSs and depression of EMTs, and MSSs were associated with depression. Conclusions : To improve the work environment of EMTs, attention should be paid to job stress, MSS, and depression and the presence of positive organizational support should be provided which can prevent negative effects.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.1
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• pp.109-117
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• 2011

Since the thermal performance of cycles for use of low-temperature source is low if a pure working fluid is used, the cycles using ammonia-water binary mixture as a working fluid has attracted much attention over past two decades. Recently, several commercial power plants using Kalina cycles have been built and being operated successfully. In this work thermodynamic performance of Kalina cycles using ammonia-water mixture as a working fluid is investigated for the purpose of extracting maximum power from low-temperature energy source. Special attention is paid to the effect of system parameters such as concentration of ammonia and turbine inlet pressure on the characteristics of the system. Results show that the system performance is influenced sensitively by the ammonia concentration, and the role of the performance of heat exchangers is crucial.

• Journal of the Korean Solar Energy Society
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• v.31 no.1
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• pp.15-22
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• 2011

It is a great interest to convert more energy in the heat source into the power and to improve the efficiency of power generating processes. Since the efficiency of power generating processes becomes poorer as the temperature of the source decreases, to use an ammonia-water mixture instead of water as working fluid is a possible way to improve the efficiency of the system. In this work performance of ammonia-water regenerative Rankine cycle is investigated for the purpose of extracting maximum power from low-temperature waste heat in the form of sensible energy. Special attention is paid to the effect of system parameters such as mass fraction of ammonia and turbine inlet pressure on the characteristics of system. Results show that the power output increases with the mass fraction of ammonia in the mixture, however workable range of the mass fraction becomes narrower as turbine inlet pressure increases and is able to reach 16.5kW per unit mass flow rate of source air at $180^{\circ}C$.

• Journal of the Korean Society of Safety
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• v.18 no.2
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• pp.119-124
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• 2003

Despite rapid technological advance and increased automation facilities, many jobs and activities in our living require manual materials handling(MMH). These include wide variety of activities such as moving things, lifting bags. boxes or cartons, etc. Many studies found that handle could affect on maximum acceptable weight of lifting, but there were few studies f3r the effects of work posture and coupling in lifting tote box. This study performed that ten male college students were required to lift a tote box with and without handle for three postures (bending, straight, right angle posture). From the experiment, following results were obtained. (1) MVC reduced maximum 23% by type of handle. (2) MVC was highest in straight posture, but was lowest in right angle posture. (3) As a result of ANOVA, MVC paid attention to posture and coupling. (p<0.01) (4) To all handle types, biceps brachii activity was increased in right angle posture. but reduced in straight posture. (5) To all posture, biceps brachii activity was most lively in no handle. The results of MVC measurement, subjective rating, EMG analysis, statistic analysis showed that maximum acceptable weight of lifting was influenced by type of handle and straight posture was more comfortable than other postures. Based on these results, it was concluded that acceptable weight of lifting has to differ for work posture and coupling.

• Journal of Family Resource Management and Policy Review
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• v.16 no.2
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• pp.165-186
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• 2012

Studies on time-use have generally concentrated on the amount of time used by each member of a household in Korea. The quality of family relationships could be associated with the amount and types of interactions between family members. This study examined the time that adults spend with their family members on various activities. The purpose of this study is to explore a typology of family time and investigate the characteristics of each type. The data source was the 2009 Time-Use Survey conducted by the Korean National Statistics Office. The people involved in each activity were surveyed for the first time in the 2009 survey in Korea. The data from this study included 10,902 diaries that were filled on weekdays by married adults from ages 20 to 59 years. Data from rural households were excluded. Time use was divided into three categories: family meals, household work and family leisure time. These activities were analyzed using t-test, chi-square analysis and cluster analysis. Family time was classified into four types based on three categories. The four types were named "leisure sharing", "household work sharing", "overall sharing" and "non-sharing". The most common type was non-sharing. The characteristics of each type depended on gender and paid work time. Based on these results, family and labor policies should be developed to increase the work-life balance. Policies that focus on men over 40 years are especially recommended.