• Journal of Electrical Engineering and Technology
• /
• v.13 no.4
• /
• pp.1474-1482
• /
• 2018

As an essential means of generator voltage regulation, excitation control plays an important role in controlling the stability of the power system. Therefore, the reasonable design of an excitation controller can help improve the system stability. In order to raise the robustness of the generator exciting system under outside interference and parametric perturbation and eliminate chattering in the sliding mode control, this paper presents a generator excitation control based on the quasi-sliding mode pseudo-variable structure control. A mathematical model of the synchronous generator is established by selecting its power, speed and voltage deviation as state variables. Then, according to the existing conditions of the quasi-sliding mode, a quasi-sliding mode pseudo-variable structure controller is designed, and the parameters of the controller are obtained with the method of pole configuration. Simulations show that compared with the existing methods, the proposed method is not only useful for accurate voltage regulation, but also beneficial to improving the robustness of the system at a time when perturbance happens in the system.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.7
• /
• pp.333-338
• /
• 2006

This paper proposes an improved do-noising method using multi-thresholding function based on translation-invariant (W) wavelet proposed by Donoho et al. for underwater radiated noise measurement. The traditional wavelet thresholding de-noising method causes Pseudo-Gibbs phenomena near singularities due to discrete wavelet transform. In order to suppress Pseudo-Gibbs Phenomena, a do-noising method combining multi-thresholding function with the translation-invariant wavelet transform is proposed in this paper. The multi-thresholding function is a modified soft-thresholding to each node according to the discriminated threshold so as to reject かon external noise and white gaussian noise. It is verified by numerical simulation. And the experimental results are confirmed through sea-trial using multi-single sensors.

• Journal of Korean Society of Environmental Engineers
• /
• v.33 no.11
• /
• pp.804-811
• /
• 2011

The aim of this study is to evaluate the applicability of adsorption models for understanding adsorption properties of adsorbents. For this study, the adsorption charateristics of $NO_3^-$ by commercial anion exchange resin, PA-308, were investigated in bach process. The adsorption kinetic data for $NO_3^-$ by anion exchange resin showed two stage process comprising a fast initial adsorption process and a slower second adsorption process. Both the pseudo-first-order kinetic model and the pseudo-second-order kinetic model could not be used to predict the adsorption kinetics of $NO_3^-$ onto anion exchange resin for the entire sorption period. Only the fast initial portion ($t{\leq}20min$) of adsorption kinetics was found to follow pseudo-first-order kinetic model and controlled mainly by external diffusion that is very fast and high, whereas, the slower second portion (t > 20 min) of adsorption kinetics seems to be controlled by a second-order chemical reaction and by intraparticle diffusion.

• Journal of the Korea Society of Computer and Information
• /
• v.18 no.10
• /
• pp.173-182
• /
• 2013

Typographical mistakes made in the writing process of drafts of electronic documents are more common than any other type of errors. The majority of these errors caused by mistyping are regarded as consequently still typo-errors, but a considerable number of them are developed into the grammatical errors and the semantic errors. Pseudo semantic errors among these errors due to typographical errors have more noticeable peculiarities than pure semantic errors between senses of surrounding context words within a sentence. These semantic errors can be detected and corrected by simple algorithm based on the co-occurrence frequency because of their prominent contextual discrepancy. I propose a method for detection and correction based on the co-occurrence frequency in order to detect semantic errors due to typo-errors. The co-occurrence frequency in proposed method is counted for only words with immediate dependency relation, and the cosine similarity measure is used in order to detect pseudo semantic errors. From the presented experimental results, the proposed method is expected to help improve the detecting rate of overall proofreading system by about 2~3%.

• Journal of the Korean Magnetics Society
• /
• v.12 no.6
• /
• pp.212-217
• /
• 2002

The pseudo spin valve with a structure of Tl/CoFe(t $\AA$)/Cu(30 $\AA$)/NiFe(50 $\AA$)/Ta, showing giant magnetoresistance properties by utilizing coercivity difference between only two soft ferromagnetic layers were produced by d.c UHV magnetron sputtering system. In pseudo spin valve Ta/CoFe/Cu/NiFe/Ta, the magnetic and magnetoresistance properties with change of CoFe thickness were investigated. When the thickness of CoFe was 60 $\AA$, a typical MR curve of pseudo spin valve structure was obtained, showing MR ratio of 3.8 cio and the coercivity difference of 27.4 Oe with a sharp change of hard layer switching. When the CoFe thickness was varied from 20 to 100 $\AA$, coercivity difference between two layers was increased to 40 $\AA$. and decreased to 100 $\AA$ gradually. It is thought the change in coercivity of hard layer was due to the crystallinity and magnetostriction of thin CoFe layer. In order to improve the MR property in CoFe/Cu/NiFe trier layer structure, CoFe layer with change of 2-20 $\AA$ thick was inserted between Cu and NiFe. When the thickness of CoFe was 10 $\AA$, MR ratio was 6.7％, showing excellent MR property. This indicates 50 ％ higher than that of CoFe/Cu/NiFe pseudo spin valve.

• Korean Journal of Ecology and Environment
• /
• v.39 no.4 s.118
• /
• pp.450-461
• /
• 2006

In this study, sorption kinetics of lead (Pb) and cadmium (Cd) onto coastal sediments were investigated at pH 5.5 using laboratory batch adsorbers. Four different models: one-site mass transfer model (OSMTM), pseudo-first-order kinetic model (PFOKM) ,pseudo-second-order kinetic model (PSOKM) and two compartment first-order kinetic model (TCFOKM) were used to analyze the sorption kinetics. As expected from the number of model parameters involved, the three-parameter TCFOKM was better than the two-parameter OSMTM, PFOKM and PSOKM in describing sorption kinetics of Pb and Cd onto sediments. Most sorption of Pb and Cd was rapidly completed within the first three hours, followed by slow sorption in the subsequent period of sorption. All models predicted that the sorbed amount at the apparent sorption ($q_{e,s}$) equilibria increased as the CEC and surface area of the sediments increased, regardless of initial spiking concentration ($C_0$) and heavy metal and the sediment type. The sorption rate constant ($k_s,\;hr^{-1}$) in OSMTM also increased as the CEC and BET surface area increased. The rate constant of pseudo-first-order sorption ($k_{p1,s},\;hr^{-1}$) in PFOKM were not correlated with sediment characteristics. The results of PSOKM analysis showed that the rate constant of pseudo-second-order sorption ($k_{p2,s},\;g\;mmol^{-1}\;hr^{-1}$) and the initial sorption rate ($v_{o,s},\;mg\;g^{-1}\;hr^{-1}$) were not correlated with sediment characteristics. The fast sorption fraction ($f_{1,s}$) in TCFOKM increased as CEC and BET surface increased regardless of initial aqueous phase concentrations. The sorption rate constant of fast fraction ($k_{1,s}=10^{0.1}-10^{1.0}\;hr^{-1}$) was much greater than that of slow sorption fraction ($k_{2,s}=10^{-2}-10^{-4}\;hr^{-1}$) respectively.

• Communications of the Korean Mathematical Society
• /
• v.20 no.1
• /
• pp.1-14
• /
• 2005

The aim of this paper is to study order-congruences on a S-poset A and to characterize the order-congruences by the concepts of pseudooreders on A and quasi-chains module a congruence p. Some homomorphism theorems of S-posets are given which is similar to the one of ordered semigroups. Finally, It is shown that there exists the non-trivial order-congruence on a S-poset by an example.

• Journal of Environmental Science International
• /
• v.14 no.9
• /
• pp.881-888
• /
• 2005

The biosorption of dye, Rhodamine B(Rh-B), onto waste activated sludge was investigated. The biosorption capacity and contact time were shown as a simulation of dye adsorption equilibrium and kinetics models. We observed that biosorption of Rh-B occurred rapidly less than 4 hr. These experimental data could be better fitted by a pseudo-second-order rate equation than a pseudo-first-order rate equation. The equilibrium dependence between biosorption capacity and initial concentration of Rh-B was estimated and it was found that the equilibrium data of biosorption were fitted by four kinds of model such as Langmuir, Freundlich, Redlich-Peterson, and Koble-Corrigan model. The average percentage errors, $\varepsilon(\%)$, observed between experimental and predicted values by above each model were $21.19\%,\;9.97\%,\;10.10\%\;and\;11.76\%$, respectively, indicating that Freundlich and Redlich-Peterson model could be fitted more accrately than other models.

• Advances in environmental research
• /
• v.1 no.2
• /
• pp.143-151
• /
• 2012

Nitrate removal from aqueous solution was investigated using $ZnCl_2$ and phosphoric acid activated carbon developed from pomegranate peel with particle size 0.4 mm. Potassium nitrate solution was used in batch adsorption experiments for nitrate removal from water. The effects of activated carbon dosage, time of contact, and pH were studied. The equilibrium time was fond to be 45 min. Two theoretical adsorption isotherms namely Langmuir and Freundlich were used to describe the experimental results. The Langmuir fit the isotherm with the theoretical adsorption capacity ($q_t$) was fond 78.125 mg g-1. Adsorption kinetics data were modeled using the pseudo-first, pseudo-second order, and intraparticle diffusion models. The results indicate that the second-order model best describes adsorption kinetic data. Results show activated carbon produced from pomegranate is effective for removal of nitrate from aqueous solution.

• Bulletin of the Korean Chemical Society
• /
• v.26 no.7
• /
• pp.1037-1043
• /
• 2005

Kinetic study on the cleavage of N-methylphthalamic acid (NMPA) in mixed acidic aqueous-acetonitrile solvent reveals the formation of both phthalic anhydride (PAn) (through O-cyclization) and N-methylphthalimide (NMPT) (through N-cyclization). The formation of NMPT varies from $\sim$20% to $\sim$3% with the increase in the content of acetonitrile from 2 to 70% v/v. Pseudo first-order rate constants for the formation of PAn are more than 4-fold larger than those for the formation of NMPT at 2% v/v $CH_3CN$ in mixed aqueous solvents. Pseudo first-order rate constants for alkaline hydrolysis of NMPT reveal a nonlinear decrease with increase in the content of $CH_3CN$ in mixed aqueous solvents.