• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.207-212
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• 2001

In this paper, a method to be able to decide the possible maximum gain of P, PI control for the retarded processes under stable condition is proposed. At first, adjustable parameter set causing stability limit are obtained based on the frequency domain condition which makes the roots of transfer function locate on the $j\omega$ axis. And the cut-in frequency $\omega{_p}$ to bring the parameter set to P control from PI control is derived by an equation with 2 parameters L and $T_m$ given, then $\omega{_p}$ is used to compute the maximum gain with stable condition. For the calculation, the controlled process of first order system with time delay element is introduced and all parameters are presumed to be time invariant.

• Journal of Korean society of Dental Hygiene
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• v.1 no.1
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• pp.19-37
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• 2001

The purpose of this study was to develop effective oral health education programs for mentally retarded children and promote their oral health, by offering oral health education for 45 mentally retarded children between age 6 to 20, tracking the change of their knowledge depending on the frequency of education, and examining the educational effect before and after oral health education. The children with mental retardation attended a special school for idiots in Gweonseon-gu, Suwon, Kyonggi Province, being able to take training(IQ 25-49). The education program was designed to be suitable for their cognitive power after consultation with a special school teacher. A teacher provided the same education seven times, once a week, and an interview was held with each of them to assess their correct answer rate. The findings of this study were as below: 1. The repeated oral health education served to have the children with mental retardation acquire better knowledge about harmful food for the teeth, what had to be done after eating cookies or candies between meals, the right time for toothbrushing, the concept of dental caries, and how to cope with dental caries(p<0.01). But after that education was offered four times, the frequency of that education made no difference. 2. The repeated oral health education increased, their knowledge on the role of the teeth and the right choice of toothbrush(p<0.01), yet there was no significant difference in their knowledge about oral health behavior, because they had already been familiar with that. 3. As a result of investigating the change of their oral health know-ledge before and after oral health education according to the type of handicap, the type of handicap made no significant difference to the change of their oral health knowledge. 4. The oral health education for the children with menial retardation had a significantly different effect on their knowledge about harmful food for the teeth, what had to be done after eating between meals, the right time for toothbrushing, the role of the teeth. the right choice and use of toothbrush, how to do toothbrushing, and fluorine(p<0.01).

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.7
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• pp.569-574
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• 2014

In order to investigate low frequency swishing noise of wind turbines, acoustic source model using a singularity in circular motion is introduced to derive analytic solution of Lowson acoustic analogy in time domain. Results in time and frequency domains computed by the solution show apparent modulation of amplitude and frequency. The solution indicates that time histories of acoustic pressure at receiver points varied significantly according to receiver's directional location, even when the retarded time distributions are similar. However, the corresponding time-averaged spectra of sound pressure at the receiver locations where the retarded time distributions are almost same are not significantly different. It can be inferred from these results that the time-averaged sound pressure spectra which cannot take into account the detailed difference in the time-variation of wind turbine noise may not represent the sound quality of wind turbines due to its swishing. Finally, as an introduction of procedure to quantify low frequency swishing noise level, relative variation of overall sound pressure level is obtained using tonal low frequency noise model.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.5
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• pp.1086-1090
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• 2001

In this paper, a method deciding the permissible gains of the P and PT controllers for a retarded process under stable condition is proposed. For analysis, the controlled process is assumed to be first-order system with time delay. At first, the adjustable parameter sets causing stability limit are obtained based on the frequency domain condition which makes the roots of the characteristic equation locate on the imaginary axis. And the cut-in frequency ${\omega}_p$ to bring the parameter set to P control from PI control is derived is derived in terms of L and $T_m$ then ${\omega}_p$ is used to compute the maximum gain with stable condition. The results indicate that the permissible controller gains can be described by a unique if parameters L and $T_m$ are know.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1191-1195
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• 2007

Many approximate models for interaction between a flexible structure and an infinite external acoustic medium have been developed for a long time. Among them, Doubly Asymptotic Approximations (DAAs) are very well known approximations. But, it has shortcomings in intermediate frequency range and can't fully describe the acoustic medium. So, this paper presents the modified approximation by applying the retarded and advanced potentials to Kirchhoff's formula. It describes the external acoustic medium more in detail and shows a good result in early time transient responses when it was applied to a spherical shell. Through a spherical shell interacting with external acoustic medium, the transient responses for the proposed model is compared to Huang's exact solution and DAA2.

• Archives of Pharmacal Research
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• v.18 no.5
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• pp.314-319
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• 1995

Antacid granules were prepared by agglomeration and powder method in high speed agitation type granulator. The copmositions of the test antacids were sodium bicarbonate nad magnesium carbonate nad a coating material was powder of polyvinylacetal diethyl-aminocacetate (AEA) and an additive material was talc powder. The dissolution characteristics of base from the antacid granules were investigated to evaluate neutralization capacity of hydrochloric profile of base and neutralization behavior, the following results were obtained : The prepared granules showed a pH-dependent dissolution pattern of a base. The dissolution profile of a base was varied with addition of talc powder as well as coating amount of AEA. The relationship between the ratio of dissolution retarded time for 20% and 10% AEA. The relationship between the ratio of dissolution retarded time for 20% AEA coated granules $\theta_{20}/\theta_{10}$ and the diameter reduction of the granules was explained by the rate process of neutralization of hydrochloric acid.

• YAKHAK HOEJI
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• v.28 no.4
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• pp.223-229
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• 1984

Microcapsules of indomethacin were prepared by the complex coacervation technique using gelatin-gum arabic as the wall-forming material. The effects of varying drug-to-matrix ratios and formalization time, and hydroxy propyl cellulose (HPC) added on the release of drug from microcapsules were studied. As the amount of wall-forming material increased, the drug content in the microcapsules decreased and the release of drug from microcapsules was retarded. The drug content was lower in the HPC added microcapsules than that in the microcapsules was retarded. The drug content was lower in the HPC added microcapsules than that in the microcapsules without HPC and the microcapsules with 1:4 drug-to-matrix ratio showed the slowest release. The release rate of the drug from microcapsules with 1:2 drug-to-matrix was delayed according to the increase of formalization time and the microcapsules formalized for 24hr showed ratio the most retardation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.95-98
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• 2003

This paper presents the results of field experiment to apply the difference of setting tine method using super retarding agent for reducing hydration heat of mass concrete of foundation. According to the results, as the properties of fresh concrete, base concrete satisfies aimed slump and air content, and there is no difference of slump and air content with mixture of super retarding agent. The mixing ratio of super retarding agent is determined for setting time to be retarded by 12 hours in comparison with base concrete, but because the temperature of the air and concrete is low, the difference of setting time is retarded to 24 hours. In man concrete of foundation to which the difference of setting time method is applied, crack by hydration heat is not seen because the lower concrete of super retarding agent generates heat after generation of hydration heat of the upper concrete.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10b
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• pp.1930-1933
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• 1991

In this paper, the robustness of self turning controller on the continuous time-delay system is investigated. The polynomial identification method using continuous time exponentially weighted least square algorithm is used for estimating the time.-delay system parameters. The pole-zero and pole placement method are adopted for the control algorithm. On considering the control weighting factor and reliability filter the effect of unmodeled dynamics of the plant are examined by the simulation.

• Journal of the Korean Ceramic Society
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• v.33 no.3
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• pp.307-312
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• 1996

In following addition of 0.3, -0.6, 0.8, 1.0 and 5 weight percent MgSiF66H2O studies have been made of the setting and hardening characteristics of ordinary portland cement. MgSiF66H2O retarded the setting time of ordinary portland cement and extended the induction pariod of the hydration. In ordinary portland cement the setting characteristics were drastically altered especially at high MgSiF66H2O contents. Evidence was also obtained by the formation of a KSiF6 which was very fine particle. The results wee as follows. 1. Slump was slightly decreased when MgSiF66H2O added. 2. Setting time was retarded depending on the amount of retarding agent 2 to 8 hours 3. Compressive strength was almost same or some increased in comparision with opc. 4. When MgSiF66H2O was added to cement paste K2SiF6 were formed It was fine-sized distributed uniformly in cement grain and caused retardation of cement setting.