• Wind and Structures
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• v.21 no.5
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• pp.523-536
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• 2015

To study the vibration frequency of super high-rise buildings in the process of vortex induced vibration (VIV), wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity ($V_r$), as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When $V_r$ is less than 8, the drift magnitude of the frequency is typically positive. When $V_r$ is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When $V_r$ is larger than12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Furthermore, the vibration frequency does not lock in the vortex shedding frequency completely, and it can even be significantly modified by the vortex shedding frequency when the reduced wind velocity is close to 10.5.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1320-1332
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• 1996

In the present study, we consider modified 5-node equivalent solid element which has smallest degree of freedom among 2-dimensional solid elements accounting bending deformation as well as extensional and shear deformations, We shall investigate static and dynamic characteristics of this element, which is very effective in thin beam, thick beam, large displacement problems, beam of variable thickness, and asymmetrically stepped beam, etc., as well as relatively simple problems of beam. The degree of freedom of this element is 10, which is smaller than 18 of 9-node element, 16 of 8-node elemtns, 12 of modified 6-node element and Q6 element. Therefore, this element is expected to broaden the effective range of application of the solid elements in the bending problems further.

• Journal of Environmental Science International
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• v.19 no.5
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• pp.577-584
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• 2010

The generation of $TiO_2$ nanoparticles by a thermal decomposition of titanium tetraisopropoxide (TTIP) was carried out experimentally using a tubular electric furnace at various synthesis temperatures (700, 900, 1100 and $1300^{\circ}C$) and precursor heating temperatures (80, 95 and $110^{\circ}C$). Effects of degree of crystallinity, surface area and anatase mass fraction of those $TiO_2$ nanoparticles on photocatalytic properties such as decomposition of methylene blue was investigated. Results show that the primary particle diameter obtained from thermal decomposition of TTIP was considerably smaller than the commercial photocatalyst (Degussa, P25). Also, those specific surface areas were more than 134.4 $m^2$/g. Resultant $TiO_2$ nanoparticles showed improved photocatalytic activity compared with Deggusa P25. This is contributed to the higher degree of crystallinity, surface area and anatase mass fraction of $TiO_2$ nanoparticles compared with P25.

• Polymer(Korea)
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• v.28 no.4
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• pp.352-359
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• 2004

Membrane technology was used for the optical resolution of the various racemic compounds such as tryptophan, tyrosine and phenylalanine, using enantioselective membranes prepared from sodium alginate (SA) and glutaraldehyde as a membrane material and crosslinking agent, respectively, The chemical structure of the membranes was characterized with FT-IR spectrophotometry and 3D molecular structure modeling study was done to figure out the optical resolution mechanism through the membrane. Effects of degree of crosslinking, feed concentration, operating pressure and different kinds of feed solution on the membrane performances were studied. As results, it was found that with increasing degree of crosslinking and membrane thickness, and decrease in the concentration of the feed solution and smaller size of solutes, the enantinselectivity of the membrane was improved. When the sodium alginate membranes with 80% of swelling index and 79${\mu}{\textrm}{m}$ of thickness were used, 77% of enantiomeric excess was obtained.

• Bulletin of the Korean Chemical Society
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• v.4 no.4
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• pp.162-169
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• 1983

The swelling and stress-elongation experiments have been performed for two kinds of gels of tactic poly (2-hydroxyethyl methacrylate) (P-HEMA) with varying crosslinker concentrations. The gels of isotactic and syndiotactic P-HEMA were swollen in aqueous salt solutions upon varying molal concentrations. The solute used were NaCl, $MgCl_2$, $Na_2SO_4$, $MgSO_4$ and urea. The water content at equilibrium swelling and the salt partition coefficient were determined, and stress-elongation curves of the gels were obtained. From these results, the effective number of chain (${\nu}_e$) and the Flory-Huggins interaction parameter (${\chi}_1$) were also obtained. The swelling experiment was also performed under varying solvents, and the degree of swelling was determined. The solubility parameter of P-HEMA was obtained as 13.4 (cal/mole)$^{l/2}$ using the correlation between the degree of swelling and the solubility parameter (${\delta}_1$) of solvents. The mechanical properties of syndiotactic P-HEMA is stronger than that of isotactic P-HEMA, and the water content of both gels become smaller when the crosslinking increases. Isotactic P-HEMA contains more water content than syndiotactic P-HEMA does.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.99-105
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• 2021

In this study, the thermal stratification in solar seasonal thermal storage tanks was numerically simulated. The effects of the aspect ratio (AR) and inlet velocity on the thermal stratification in the diffuser type heat storage tank were investigated. The temperature distributions inside the tank were similar with velocity fields. Jet flows from opposite diffusers encountered each other at the tank center region. Thereafter, the downward flows occurred, and this flows strongly affected the thermal stratification. When AR was smaller than 2, these downward flows influenced a further distance and enhanced mixing inside the tank. Thermal stratification was evaluated by thermocline thickness and degree of stratification, and AR of 3 had the highest degree of stratification. The inlet velocity effect was expressed with the ratio (Re/Ri) of Reynolds and Richardson numbers. The second-order approximation was found for the relationship between the thermocline thickness and log Re/Ri.

• Journal of ILASS-Korea
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• v.26 no.4
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• pp.189-196
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• 2021

Spray drift of agricultural nozzles has become a big issue because it causes low precision targeting and environmental pollution. In order to reduce the spray drift, study spray characteristics of agricultural nozzles is virtually important. In this study, shadowgraph and Mie-scattering visualization techniques were used to study the macroscopic spray and atomization characteristics of an agricultural nozzle. PDPA was used to measure the atomization characteristics of spray. The injection pressure is set to 1 bar, 3 bar and 5 bar, which covers the working range of the nozzle. For the PDPA experiment, 75 points were measured in an area of 160 mm × 120 mm at 10 mm intervals directly below the nozzle to grasp the overall atomization characteristics of the spray. It was found that the spray width and sheet width showed a linear correlation. As the injection pressure increased, the sheet expansion in the 0-degree direction and the sheet swing in the 90-degree direction jointly promoted the breakup of the sheet. In addition, the area close to the central axis had a large droplet velocity, and since a large droplet velocity promoted atomization of spray, the area close to the central axis had a smaller spray droplet diameter than the left and right regions.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.6
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• pp.51-63
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• 2023

To improve the problem that the settlement curve of the consolidation theory of Terzaghi does not match well with the actual settlement curve, we included a secondary compression settlement and analyzed it by varying the beginning point and then obtained the following results. The current methods of calculating the compression index from the  log𝜎 curve and the coefficient of consolidation from the time-dependent settlement curve for each consolidation pressure proved that the final settlement amount will be consistent after a long time, but the actual settlement amount will always be smaller than the predicted settlement amount during the settlement progress stage. The consolidation factors estimated by the curve fitting with the condition that the secondary compression begins in the second half of the primary compression showed similar values to the consolidation factors estimated by the curve fitting for the primary compression only, and the settlement curves were in better agreement throughout the compression. It showed different values, showing low validity. It can be inferred that secondary compression acts from the point when a significant portion of the excess pore water pressure is dissipated, and the loading stress begins to have more influence on the skeletal structure of the soil. Analysis results show that secondary compression begins at the range of 91 % to 98 % on the average degree of primary consolidation.

• Journal of Nutrition and Health
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• v.29 no.6
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• pp.651-660
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• 1996

The purpose of this study was to examine and analyze the degrees and the influence factors of job satisfaction of dietitians working in hospitals in relation to performance of duty in their works and to provide effective management of hospital dietitians for high quality health and food service in hospital. The questionaire was prepared with reference to the previous studies on job satisfaction of dietitians working in hospitals throughout the nation. 201 dietitians in the country were surveyed. The period of research was from January 20 to February 28, 1995. The results are as follows. 1) In regard to the degree of job satisfaction of hospital dietitians, they showed the highest degree of job satisfaction in the relationships with fellow dietitians followed by worth and self-confidence, aptitude and interests, relationships with cooks, job stability, degree of recognition of the dietitians competence, supervision of the superiors, degree of application of professional knowledge, work load, wage level, degree of recognition of the importance of duty, cooperative relationships with load, wage level, degree of recognition of the importance of duty, cooperative relationships with doctors, degree of performance of clinical work, the number of dietitians, the prromotion system, and welfare system in that order. On the other hand, they showed the highest dissatisfaction with food service facilities. 2) The influence factors on job satisfaction are as follows. (1) Wage factor : Shorter weekday working hours and higher bonuses make greaster job satisfaction (R2=0.3115). (2) Working condition factor : Larger number of monthly holidays(R2=0.5142), shorter weekday working hours(R2=0.1077), longer previous food service experience and computer utilization (R2=0.1432) make greater job satisfaction. (3) Welfare factor : Welfare system (R2=0.4132) and promotion system (R2=0.1624) have to do with computer utilization. Job stability has to do with marital status and computer utilization (R2=0.1165). consequently, those married dietitians who use computers show higher job satisfaction. (4) Human relationship factor : Smaller mumber of patients receiving food makes greater job satisfaction (R2=0.1334). (5) Superivision factor : Shorter weekday working hours and larger number of monthly holidays make greater job satisfaction (R2=0.1709). (6) Achievement factor : Marriage, larger number of dietitians(R2=9.2293), age, larger number of monthly holiday, higher monthly wages and computer utiliazation (R2=0.1088) make greater job satisfaction. (7) Speciality factor : Marriage, longer current hospital tenure, higher position and working in seoul(R2=0.1142) make higher job satisfaction. (8) Job inclination factor : working in general hospitals rather than in oriental hispitals, working in seoul(R2=0.1776) and better bonuses(R2=0.1078)make greater job satisfaction. As a result, the following is suggested for the job satisfaction of hospital dietitions on the basis of this study : hospital dietitians can achieve miximum job satisfaction through smooth relationships with coworkers, and the responsible managers should improve welfare and working conditions for the job satisfaction of hospital dietitians.

• The Korean Journal of Community Living Science
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• v.19 no.1
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• pp.157-169
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• 2008

On the general trends of weight control for slimness, this study surveyed and compared eating attitude influenced by eating disorder, eating habits, and nutrition knowledge by obesity index in middle school girls. The purpose of this study was to investigate the eating disorders and eating habits, and analyzed these data by degree of obesity. This will provide basic information of nutrition education for adolescents who need to have proper body shape and dieting habits. This survey was conducted to one of girls' middle school in Incheon and all the data was analysed by SAS(Statistical Analysis System) program. The average height, weight and PIBW were 158.7cm, 48.2kg, and 93.9% in students. However, 50.8% of students were underweight or severely underweight. Most of female students perceived that they were normal or overweight even though they had underweight or normal. There was a significant difference in experience and intention of weight control by degree of obesity. In the overweight group, EAT-26 score tendency was high, especially preoccupation with losing weight(factor 1). It shows that obesity index had meaningful correlation with EAT-26 score and factor1. In dietary habit, overweight group showed more irregular meals tendency, and overeat frequently. On the other hand, this group had lower frequency and of smaller amount snacks. The intake frequency of meals and snacks showed in the affirmative way regardless of degree of obesity. The average score for nutrition knowledge about calorie and weight control was low. Correct answer rates were increased in higher overweight group. In conclusion, teenage girls who concerned too much about their slim body image need to be educated about accuracy concept of the body image. Also, practical and systematic nutrition education should be done for the correct nutrition knowledge and its application ability of individuals.