• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.1
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• pp.43-54
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• 1997

This paper presents an approximate analytical solution to a two-region one-dimensional model for the charging process of stratified thermal storage tanks with variable inlet temperature in the presence of momentum-induced mixing. Based on the superposition principle, an arbitrary-varying inlet temperature is decomposed into inherent discontinuous steps and continuous intervals approximated as a finite number of piecewise linear functions. This approximation allows the temperature of the upper perfectly-mixed layer to be expressed in terms of constant, linear and exponential functions with respect to time. Applying the Laplace transform technique to the model equation for the lower thermocline layer subject to each of three representative interfacial conditions yields compact-form solutions, a linear combination of which constitutes the final temperature profile. A systematic method for deriving solutions to the plug-flow problem having polynomial-type boundary conditions is also established. The effect of adiabatic exit boundary on solution behaviors proves to be negligible under the actual working conditions, which justifies the assumption of semi-infinite domain introduced in the solution procedure. Finally, the approximate solution is validated by comparing it with an exact solution obtained for a specific variation of inlet temperature. Excellent agreements between them suffice to show the necessity and utility of this work.

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1521-1525
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• 2009

Thermosensitive block copolymers of ethylene oxide and N-isopropylacrylamide (NIPAM) were synthesized. A five armed star shape oligo(ethylene oxide) initiator with a cyclotriphosphazene core was prepared and used for the atom transfer radical polymerization (ATRP) of NIPAM. The lower critical solution temperatures (LCSTs) of the copolymers were 36 to 46 ${^{\circ}C}$, higher than that of PNIPAM (32 ${^{\circ}C}$), depending on their molecular weights. The copolymers were soluble in water below the LCSTs but formed micelles above the LCSTs. The thermosensitive micellization behaviors of the polymers were investigated by fluorescence spectroscopy. With increasing the temperature of an aqueous solution of P2 and pyrene above the LCST, the peak of 333 nm red-shifted to appear around 339 nm and its intensity increased significantly, indicating the micelle formation. The transfer of pyrene into the micelles was also confirmed by a confocal laser scanning microscope. The fluorescence image obtained from P2 in an aqueous pyrene solution exhibited a green emission resulting from the pyrene transferred into the micelles. Salt effects on the solubility of the copolymers in an aqueous solution were investigated. The LCST of P2 decreased sharply as the concentration of sodium chloride increased, while decreased slowly with potassium chloride.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.184-192
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• 1998

This paper deals with an extended analytical solution for the mixture solidification problem, in which temperature is inherently coupled with the solute transport due to the presence of volume contraction induced flow. A new exact solution to the energy equation accounting for the convection effect in the melt is successfully derived, which allows the present analysis to cover a high initial superheating. Difference in properties between the solid and liquid phases is rigorously incorporated into the model equations in the solid fraction weighted form. Taking advantage of linearized correction factors, a systematic and easy-to-implement algorithm for determining the solidus and liquidus positions is introduced, which proves not only to converge stably but also to be very efficient. For a specific case, the present results show excellent agreements with the existing solution. The effect of convection in the melt becomes appreciable with increasing the initial superheating. It is revealed that variable properties in the mushy region significantly affect the solidification behaviors. The present study is also capable of resolving the interaction between microsegregation and macrosegregation.

• The Journal of Korean Academic Society of Nursing Education
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• v.13 no.2
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• pp.257-265
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• 2007

Purpose: This study was done to investigate sexual problem behaviors of high school students in one province, North Cholla. Method: The participants in this research were 951 high school students, grades 1, 2 and 3, chosen at random in big cities, small towns and rural areas of North Cholla Province. Result: The routes for sexual knowledge acquisition were through a peer group or an older member(35.8%), internet(29.8%), classes and the teacher at school(18.8%), multimedia(8.4%) and parents (7.2%). The percentages for domains of sexual problem behaviors were masturbation 36.7%, sexual impulse 35.6%, voyeurism 12.6%, sexual violence 9.6%, transvestism 4.1%, prostitution 3.5%, exhibitionism 3.1%, and pregnancy of a female student 0.6%. Sexual problem behaviors experienced by 30% or more of the students were reported as the experience of the desire to embrace, the desire to kiss, the desire to touch a friend's body of the opposite sex, masturbation and the desire to sleep with a friend of the opposite sex. The biggest sexual problem behaviors for the students were sexual impulses toward friends of the opposite sex and masturbation. These experience rates were higher for boys than for girls(p<.05), higher vocationally than academicly(p<.05), and higher in the largest cities than smaller cities and rural area(p<.05). Conclusion: These findings suggest that systematic programs that focus on a problem solution method should be developed for sexual problem behavior prevention.

• Korean Journal of Community Nutrition
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• v.18 no.6
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• pp.555-564
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• 2013

The purpose of this study was to compare and analyze the assessment of salty taste and high-salt dietary behaviors of Korean university students and their Chinese counterparts. The researchers developed a taste assessment computer program focusing on preference for salty taste, and it was applied to 300 university students, including 100 Korean students, and 100 Chinese students in Daegu of South Korea, and 100 Chinese students in Shenyang of China (144 males and 156 females). The results of the taste assessment of Chinese and Korean university students are as follows. Among males, Koreans (36.0%), Chinese students in Korea (36.2%), and Chinese (40.4%) scored highest in the "a bit salty" followed by "normal." Among females, Koreans (36.0%), Chinese students in Korea (49.1%), and Chinese (28.3%) scored highest in the "normal". In terms of salt concentration in solution, among the male subjects, most Koreans favored the salt concentration of 0.31%, which is considered to be a "normal" concentration; most Chinese students in Korea favored 0.63%, which is considered to be "a bit salty", and most Chinese favored the concentration of 1.25%, which is considered to be "salty". As for the female subjects, Koreans, Chinese students studying abroad, and Chinese favored 0.31%, the "normal" level of concentration. Korean students scored higher than Chinese students in Korea and Chinese students both in males and females (p < 0.001, p < 0.01), in terms of high-salt dietary behaviors favored salty taste. This study suggests that Chinese university students need nutrition education in terms of modifying eating behaviors to reduce dietary salt intake.

• Korean Institute of Interior Design Journal
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• v.20 no.5
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• pp.23-33
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• 2011

Starting with 21st Century, the role of the design has been widened and designers began to regard the psychological and behavioral factors as main design considerations. These factors are the core elements especially in designing interactive space. This research proposed the user-centered design methodology for interactive space. It developed Programming Process for Supporting Interactive Behaviors. To compose the process, this research analyzed the influential factors on the interactivity and the results were applied on the process. This newly proposed Programming Process contains four basic stages which are 'Opportunity Identification Cell', 'Intersubject Cell', 'Interaction & Interface Cell', and 'Programming Solution Cell'. More detailed tasks are also specified for each stage. This research asserts that the design process for Interactive space should differ from the past design processes in the fact that it puts much more attention on systemizing the psychological and behavioral elements than before. Therefore the design process for Interactive space should be reinforced with the data related to these psychological and behavioral understandings. The Programming Process of this paper is an attempt to enlarge the roles of these data in designing interactive space, and thus it is an attempt to accommodate the contemporary user-centered design paradigm.

• Advances in nano research
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• v.16 no.3
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• pp.313-324
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• 2024

The main aims of this study are to develop a new nonlocal quasi-3D theory for the free vibration behaviors of the functionally graded sandwich nanobeams. The sandwich beams consist of a ceramic core and two functionally graded material layers resting on elastic foundations. The two layers, linear spring stiffness and shear layer, are used to model the effects of the elastic foundations. The size-effect is considered using nonlocal elasticity theory. The governing equations of the motion of the functionally graded sandwich nanobeams are obtained via Hamilton's principle in combination with nonlocal elasticity theory. Then the Navier's solution technique is used to solve the governing equations of the motion to achieve the nonlocal free vibration behaviors of the nanobeams. A deep parametric study is also provided to demonstrate the effects of some parameters, such as length-to-height ratio, power-law index, nonlocal parameter, and two parameters of the elastic foundation, on the free vibration behaviors of the functionally graded sandwich nanobeams.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.695-702
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• 2002

Nonlinear dynamics of striped diffusion flames, by the diffusional-thermal instability with Lewis numbers sufficiently less than unity, is numerically investigated by examining various two-dimensional flame-structure solutions. The Lewis numbers for fuel and oxidizer are assumed to be identical and an overall single-step Arrhenius-type chemical reaction rate is employed in the model. Particular attention is focused on identifying the flame-stripe solution branches corresponding to each distinct stripe pattern and hysteresis encountered during the transition. At a Damkohler number slightly greater than the extinction Damkohler number, eight-stripe solution first emerges from one dimensional solution. The eight-stripe solution survives Damkohler numbers much smaller than the extinction Damkohler number until the transition to four-stripe solution occurs at the first forward transition Damkohler number. At the second forward transition Damkohler number, somewhat smaller than the first transition Damkohler number, the transition to two-stripe solution occurs. However, anu further transition from two-stripe solution to one-stripe solution is not always possible even if one-stripe solution can be independently accessed for particular initial conditions. The Damkohler number ranges for two-stripe and one-stripe solutions are found to be virtually identical because each stripe is an independent structure if distance between stripes is sufficiently large. By increasing the Damkohler number, the backward transition can be observed. In comparison with the forward transition Damkohler numbers, the corresponding backward transition Damkohler numbers are always much greater, thereby indicating significant hysteresis between the stripe patterns of strained diffusion flames.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.17 no.1
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• pp.18-28
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• 1991

Spectral behaviors of cationic dye, crystal violet(CV), in aqueous solution and with varying concentrations of Triton X-100(TX-100), sodium dodecylsulfate (SDS) and cetyl trimethyl amonium bromide(CTAB) were studied. The characteristic changes of the absorption spectra observed in the dye-SDS interacting systems with the SDS concentration are analyzed. The behaviors of both a- and J-bands of the each componet dye suggest that the following four sequential steps are occurring : the formation of dye-SDS complex, the stacking of the dye molecules arising from the association of the dye-SDS complex, breaking of the dye stacking due to the formation of micelles, redistribution of the dye molecules in the surface of micelles at high SDS concentration.

• Journal of the Korea Safety Management & Science
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• v.15 no.3
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• pp.19-28
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• 2013

While the reduction of industrial accidents has been stagnant, many researchers have been studying and focusing on safety behaviors including safety perception, attitude and safety culture as a new solution as well as a turning-point of this issue. However, we do not pay attention to those studies and researches in Korean construction. Therefore, this study is to introduce preceding researches and case studies in other countries and suggest a new direction to Korean construction. This study found out the current situation and problems in Korean construction studies after tracing the safety perception, attitude and safety culture in Korea and reviewing the background and trend of overseas studies and researches with regard to safety behaviors. Fundamental researches and systematic studies must be conducted in Korean construction with the reference and research data of this study.