• Journal of Korean society of Dental Hygiene
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• v.2 no.1
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• pp.115-129
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• 2002

The purpose of this study was to examine the actual dental hygiene status of workers in cement industry in an effort to serve as a basis for enhancing their dental hygiene. The subjects in this study were 420 laborers from the cities of Curi, Donghae and Samcheok who handled cement. As a result of conducting a survey, the following findings were given : l. The workers investigated found their working environment satisfactory, getting a mean score of 323. They also expressed a high job satisfaction with a mean score of 333. 2. They didn't have a big interest in oral health. By age group, those who were aged between 36 and 40, or who cared less about health management, showed a higher interest in oral health. Besides, the laborers who kept smoking for a longer period, or who drunk more, expressed greater interest. 3. The toothbrushing method was considered most important for periodontal health, by 45.0% of the workers, and the next most crucial one was regular dental examination, followed by refraining from smoking and staying away from sweet food in the order named. 4. Concerning daily mean toothbrushing frequency, 455% brushed their teeth three times a day on the average. More than half them didn't pay enough attention to toothbrushing. 5. Regarding scaling, the large number of the workers, 42.4%, had no experience to get their teeth scaled, 37.6%, the greatest percentage, didn't have their teeth scaled because it seemed to make their teeth painful or cold. 6. As fororal health education experience, 67.6%, the great number of them, had no experience to receive dental health education. The above-mentioned findings suggest that the cement-related workers generally neglected dental health management. They should be encouraged to correct their wrong oral health knowledge or habit to make their oral cavity more healthy. To make it happen, it's required to provide oral health education and promote organized dental health projects.

• Journal of the Korean Society of Costume
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• v.65 no.6
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• pp.79-98
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• 2015

This article studied women's headdresses that appeared in the paintings of Joseon Dynasty. This examined the shapes of women's headdresses painted in genre paintings, record paintings and nectar ritual paintings from Joseon Dynasty and compared them to literatures and relics in order to analyze their types and characteristics. Headdress can be categorized into three types: (1) square cloth worn on the top of the head; (2) a kind of small cap; (3) Cloth that completely covers the head. The first type of headdress resembles the shape of Garima. In the early period of Joseon Dynasty, it was worn not only by Gisaeng, but also by both upper and lower class women. The second type of headdress includes a cap made by connecting several cloths, round cap, and cone-shaped cap. These two types are worn on top of the head. However, sometimes these were worn between the head and the chignon to fix the chignon. Also, these were used as hair accessories for decorative purposes. In particular, old women wore these headdresses and braided their white hair around them to fix the chignon. This way, the headdress not only kept the head warm, but also hid the old women's scanty hair. Headdress was usually made of black fabric and it was a simple hair accessory that replaced the wig. The third type of headdress was widely worn among lower class women. The cloth completely covered the head so that the hair would not fall when working. It also provided protection from cold and hot weather. According to paintings, there were many ways of wearing the cloth around the head.

• Tunnel and Underground Space
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• v.2 no.1
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• pp.116-122
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• 1992

A comprehensive, nonsteady state, computer simulation program for the environmental conditions in advancing tunnels (the HEADSIM simulation program) is constructed and successfully validated with heat balance amongst all heat sources, and with mass conservation amongst various airflows including the leakage air from ducts, under timedependent variations of inlet air conditions. which include sudden, diurnal and seasonal changes. Heat conduction in the wall strata and face strata is simulated with most complicated boundary conditions using the finite difference method, and the climatic conditions in roadway sections which contain air ducts, booster fan, spray cooler, compressed air pipes, cold water pipes, return water pipes, machinery and broken rock are simulated taking into account the variations of face operation and the heat storage mechanism in the strata. The limitations of simulation time steps and roadway section lengths are defined according to the stability criteria satisfying the principles of thermodynamics. Variations of heat transfer coefficients, which are newly set, and those of wetness factors are taken into account according to the variations of other parameters and the stepwise advance of the face. Newly-derived formulae are used for computing the air duct leakage and the pressure inside of the duct. A new concept of an 'imaginary duct' is introduced to simulate the climatic conditions in tunnels during holiday periods, which directly affect conditions on subsequent working days under the consideration of natural convection. A subsidiary program (the WALLSIM simulation program) is made to compute the dimensionless tunnel surface temperatures and to compare the results with those from analytical approaches, and to demonstrate the stability, convergence and accuracy of the strata heat conduction simulation, adopting the finite difference method. The WALLSIM also has wide applications, including those for the computation of age coefficients.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.111-117
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• 2003

In the design of the split type free displacer Stilting cryocooler the motion of the displacer is very important to decide the cooling capacity, which depends upon the working gas pressure, the swept volume in the compression space and the expansion space, operating frequency, the phase shift between piston and displacer, etc. In this study, Stirling cryocooler actuated by the electric farce of the dual linear motor is designed and manufactured. Cool down characteristics of the cold end with laser displacement sensor in the expander of the Stilting cryocooler is evaluated. The charging pressure was 15kg$_{f}$/$\textrm{cm}^2$ and operating frequency was 50Hz. Input power and the lowest temperature were about 32W and 67K, respectively. And, displacement of the piston is measured by LVDTs (Linear Variable Differential Transformers), displacement of thedisplacer is measured by laser optic method, and phase shift between piston and displacer is discussed. As the peak-to-peak pressure of the compressor was increased, peak-to-peak displacement of the displacer was increased. The peak-to-peak displacement of the displacer increases in the range of 0 - 64.5Hz(resonant frequency of the displacer), but decreases steeply when the operating frequency is bigger than the resonant frequency. Finally when the phase shift between displacements of the Piston and displacer is 45。, operating frequency is optimum and is decided by resonant frequency of the expander, mass and cross section area of the displacer and constant by friction and flow resistance.e.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.20-24
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• 2020

The purpose of this analytic study is to design and examine an efficient hydrogen liquefaction cycle by using a pre-cooler. The liquefaction cycle is primarily comprised of a pre-cooler and a refrigerator. The fed hydrogen gas is cooled down from ambient temperature (300 K) to the pre-cooling coolant temperature (either 77 K or 120 K approximately) through the pre-cooler. There are two pre-cooling methods: a single pre-coolant pre-cooler and a cascade pre-cooler which uses two levels of pre-coolants. After heat exchanging with the pre-cooler, the hydrogen gas is further cooled and finally liquefied through the refrigerator. The working fluids of the potential pre-cooling cycle are selected as liquid nitrogen and liquefied natural gas. A commercial software Aspen HYSYS is utilized to perform the numerical simulation of the proposed liquefaction cycle. Efficiency is compared with respect to the various conditions of the heat exchanging part of the pre-cooler. The analysis results show that the cascade method is more efficient, and the heat exchanging part of the pre-coolers should have specific UA ratios to maximize both spatial and energy efficiencies. This paper presents the quantitative performance of the pre-cooler in the hydrogen liquefaction cycle in detail, which shall be useful for designing an energy-efficient liquefaction system.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.335-342
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• 2000

The microhardness of rhenium sheets was determined as a function of indentation load and temperature. The temperature dependence of the microhardness between room temperatures and $1000 ^{\circ}C$was studied using a hot microhardness tester equipped with a Vickers indenter. The load dependence of the microhardness was investigated using oth a Vickers and a Knoop indenter. The indentation size effect (ISE) was well explained using the normalized Meyers law. The hardness of the annealed rhenium sheet approached that of the as-rolled sheets at large indentation loads because of work-hardening under the indenter during indentation. The hardness at zero load(obtained from extrapolation of the load dependence of the hardness) suggested that the hardness is controlled by two different mech-anisms having different thermal activation. At low temperature the activation energy for the mechanism controlling the hardness was approximately 0.02 eV , Whereas at higher temperatures that was approximately 0.15eV. The tranisi-tion temperature between the two different controlling mechanisms was about $250^{\circ}C$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.2
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• pp.681-687
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• 2013

This study examined whether the combination of the indoor temperature on the learning environment and the colors of the learning materials affect the learning performance. To do this, the condition of indoor temperature was divided into three conditions: the neutral condition which is the appropriate temperature condition of the learning activities ($22.5{\sim}24^{\circ}C$), the high-temperature condition (> $24^{\circ}C$), and the low-temperature condition (< $22.5^{\circ}C$). In addition, colors of red, blue, black, and green were used as the warm, cold, and neutral colors, and the verbal-working memory task was used as the learning task. As a result, it was not significant differences in the response time of the learning task, whereas, in the accuracy rate of the learning task, the performance was more accurate in red- and black-color conditions. These results could be interpreted as the saliency and color-temperature of the red color, and the familiarity and specificity of the black color.

• Smart Structures and Systems
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• v.13 no.3
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• pp.353-374
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• 2014

Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.4
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• pp.175-185
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• 2018

This research investigates the internal flow and heat transfer in a plate heat exchanger with chevron shape by utilizing the computational fluid dynamics (CFD) software. The basic unit of the plate heat exchanger is generally composed of a hot channel, an intermediate chevron plate, and a cold channel. Several studies have reported experimental and numerical simulation of heat transfer and pressure drop. This study focused on the detailed numerical simulation of flow and heat transfer in the complicated chevron shape channel. The long chevron plate was designed to include 16 chevron patterns. For proper mesh resolution, the number of cells was determined after the grid sensitivity test. The working fluid is water, and its properties are defined as a function of temperature. The Reynolds number ranges from 900 to 9,000 in the simulation. A realizable $k-{\varepsilon}$ model and non-equilibrium wall function are properly considered for the turbulent flow. The friction factors and heat transfer coefficient are validated by comparing them with existing empirical correlations, and other patterned flow phenomena are also investigated.

• Strategy21
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• s.38
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• pp.193-220
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• 2015

Leaving the legacies of the Cold War and other difficulties behind them, South Korea and China are building up their successful strategic cooperative partnership, moving forward toward through the development of new economic exchanges and diplomatic cooperation between the two countries, and this process is expected to gain momentum during 2015. 2015 is the third year since President Park of South Korea and President Xi of China came into office, and also the first year they have begun to implement the many declarations and promises which they have made within the context of the strategic cooperative partnership. The two nations share a common cultural heritage, and their governments should take this opportunity to leverage their partnership to enhance their economies and to improve their people's quality of life, especially for the younger generation. At a summit held in July 2014, the two leaders agreed to launch a working-level group on maritime boundary delimitation. The first meeting took place on January 29, 2015, and addressed issues of Exclusive Economic Zones (EEZs) and continental shelves in the Yellow Sea, which has an area of about 380,000 ㎢. It is greatly to be hoped that the 2015 maritime boundary delimitation meeting between South Korea and China will not impair the future of bilateral relations, but rather will improve their prospects. South Korea and China must take the opportunity to secure a definitive delimitation of their maritime boundary; their strategic cooperative partnership is in good order and China is currently taking a somewhat more flexible stance on the ECS and the SCS, so an agreement on boundaries will serve as a useful model for regional maritime cooperation.