• The Transactions of the Korea Information Processing Society
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• v.7 no.12
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• pp.3866-3873
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• 2000

In this paper, we investigates the long-term memory and the Correct answer rate of the foreign exchange data (Yen/Dollar) that is one of economic time series, There are many cases where two kinds of fractal dimensions exist in time series generated from dynamical systems such as AR models that are typical models having a short terrr memory, The sample interval separating from these two dimensions are denoted by kcrossover. Let the fractal dimension be $D_1$ in K < $k^{crossover}$,and $D_2$ in K > $k^{crossover}$ from the statistics mode. In usual, Statistic models have dimensions D1 and D2 such that $D_1$ < $D_2$ and $D_2\cong2$ But it showed a result contrary to this in the real time series such as NIKKEL The exchange data that is one of real time series have relation of $D_1$ > $D_2$ When the interval between data increases, the correlation between data increases, which is quite a peculiar phenomenon, We predict exchange data by neural networks, We confirm that $\beta$ obrained from prediction errors and D calculated from time series data precisely satisfy the relationship $\beta$ = 2-2D which is provided from a non-linear model having fractal dimension, And We identified that the difference of fractal dimension appeaed in the Correct answer rate.

• Architectural research
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• v.11 no.2
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• pp.19-26
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• 2009

The effect of rebirthing technique on the genetic algorithm (GA)-based size optimization is investigated. The GA mimics the principles of nature and it can gradually improve structural design through biological operations such as fitness, selection, crossover and mutation. However, premature optimum has been often detected in the generic GA with continuous design variable. Since then, the so-called rebirthing technique has been proposed to avoid this problem. However, the performance of the rebirthing technique has not been reported. Therefore, the size optimizations of spatial structures are tackled to investigate the performance of the rebirthing technique on the generic GA. From numerical results, it is well proved that the rebirthing technique is very effective to produce the optimum values regardless of the values of parameters used in the GA operations.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.180-182
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• 2007

PEMFC의 상용화 진입에 있어서 걸림돌 중의 하나가 열화(degradation)에 의한 성능감소이다. PEMFC 고분자 막의 열화가 PEMFC 성능 감소에 많은 영향을 미친다. 고분자 막의 성능 감소 원인은 여러가지가 있지만 무가습/OCV조건에서 성능 감소가 잘 된다. 그 이유에 대해서는 OCV/무가습 조건에서 과산화수소나 라디칼이 많이 형성될 수 있다는 것과, OCV조건에서 사용되지 못하는 수소와 산소의 gas-crossover 가 많기 때문이라는 것 그리고 무가습 조건에서 수소와 산소의 분압이 높아 gas-crossover 가 유리하고 악의 건조에 따른 물리적인 영향 등등이 거론되고 있다. 본 연구에서는 같은 조건에서 Cell 운전온도가 막열화에 미치는 영향을 실험하였다. OCV 여려 조건 에서 단위전지 실험을 한 후 I-V, 수소 투과도, 임피던스, FER(fluoride emission rate)등을 측정해 그 결과를 검토 분석하였다. OCV/Anode 무가습 조건이 알려진 대로 막열화 가속조건 이었음을 확인하였고, 실험 결과 Cell 운전온도가 $10^{\circ}C$증가 할 때마다 FER(fluroide emission rate)이 즉 막 열화속도가 약 2배정도 증가함을 보였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.948-953
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• 2002

The electronic expansion valve (EEV) may be used to control the refrigerant flow rate for the multi-type heat pump. Stepping motor driven EEV may precisely control the refrigerant flow rate to meet each internal load requirement. To control the EEV, PI algorithm may be used. But the hysteresis of EEV deteriorates the performance of superheat control. To reduce the performance degradation, the PI algorithm along with the dither signal may be used. The dither signal, with about 10 times higher frequency than the system crossover frequency and about 10 times larger magnitude than the deadband of hysteresis, was selected for the superheat control of EEV. Experimental results showed the improvement of EEV control by adding the dither signal to the PI algorithm.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.11-19
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• 2010

The performance of the crossover system of a centrifugal compressor stage consisting of static components of $180^{\circ}$ U-bend, return channel vanes and exit ducting with a $90^{\circ}$ bend is investigated. This study is confined to the assessment of performance of the crossover system by varying the shape of the return channel vanes. For this purpose two different types of Return Channel Vanes (RCV1 and RCV2) were experimentally investigated. The performance of the crossover system is discussed in terms of total pressure loss coefficient, static pressure recovery coefficient and vane surface pressure distribution. The experimentation was carried out on a test setup in which static swirl vanes were used to simulate the flow at the exit of an actual centrifugal compressor impeller with a design flow coefficient of 0.053. The swirl vanes are connected to a mechanism with which the flow angle at the inlet of U-bend could be altered. The measurements were taken at five different operating conditions varying from 70% to 120% of design flow rate. On an overall assessment RCV1 is found to give better performance in comparison to RCV2 for different U-bend inlet flow angles. The performance of RCV2 was verified using numerical studies with the help of a CFD Code. Three dimensional sector models were used for simulating the flow through the crossover system. The turbulence was predicted with standard k-$\varepsilon$, 2-equation model. The iso-Mach contour plots on different planes and development of secondary flows were visualized through this study.

• YAKHAK HOEJI
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• v.39 no.4
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• pp.401-410
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• 1995

Pharmacolinetic profiles of omeprazole enteric coated granules including Ramezole$^\circledR$, Losec$^\circledR$, omeprazole-Na and omeprazole-resin salt were studied using the crossover design in rats and rabbits. The absorption variance of the preparations at the altered pH condition of the gastrointestinal tract was also studied. After oral administration of four omeprazole enteric coated pellets (10mg/kg) with and without concomitant administration NaHCO$_{3}$ (5 mg/ml, 60 mM) in the rats, the differences of absorplion rate and extent were evaluated. In the NaHCO$_{3}$, administration group, the T$_{max}$ appeared to be 2~10 times shorter than water administration group, and the $C_{max}$ also increased to about 4 times, and the AUC increased to about 2.5 times. Pharmacokinetic parameters of four omeprazole enteric coated pellets in rats showed no statistical significance (ANOVA, P>0.05) in both groups. In the crossover study, the second dosed drug showed 4~5 times increased bioavailability than first dosed drug, which shows the strong carry-over effect of acid secretion of the first dosed drug. The differences of the pharmacokinetic parameters of the two test formulations (Losec$^\circledR$ and omeprazole-resin) showed no statistical significance.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.119-125
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• 2008

The FAS(Fluoroalkylsilane)/Nafion inorganic-organic composite electrolyte membrane was successfully fabricated through sol-gel method. The FAS having hydrophobic functional group and silanol ligands is impregnated in $Nafion^{(R)}$ membrane to reduce methanol crossover. The prepared FAS/Nafion inorganic-organic composite electrolyte membrane consist of the hydrophobic FAS-derived silicate nano-particles and $Nafion^{(R)}$ matrix showed decrease of methanol crossover and reduction of humidity dependence without large sacrifice of proton conductivity. The microstructural analysis of the composite membranes was performed using FESEM and FTIR. And the effect of the incorporation of the hydrophobic FAS-derived silicate nano-particles into $Nafion^{(R)}$ membrane was investigated via solvent uptake, membrane expansion rate, humidity dependency of proton conductivity and contact angle measurement.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.3
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• pp.292-298
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• 2011

This study examines the effects of the ambient temperature (AT), methanol feeding temperature (MFT), methanol concentration (MC) and methanol flow rate (MFR) on the performance and cell temperature (CT) of a 5-stacked direct methanol fuel cell (DMFC). The AT, MFT, MC, and MFR are varied from $-10^{\circ}C$ to $+40^{\circ}C$, $50^{\circ}C$ to $90^{\circ}C$, 0.5M to 3.0M and 11.7 mL $min^{-1}$ to 46.8 mL $min^{-1}$, respectively. The performance of the DMFC under various operating conditions is analyzed from the I-V polarization curve, and the methanol crossover is estimated by gas chromatography (GC). The performance of the DMFC improves significantly with increasing AT. The open circuit voltage (OCV) decreases with increasing MC due to the enhanced likelihood of methanol crossover. The cell performance is improved significantly when the MFR is increased from 11.7 mL $min^{-1}$ to 28.08 mL $min^{-1}$. The change in cell performance is marginal with further increases in MFR. The CT increases significantly with increasing AT. The effect of the MFT and MFR is moderate, and the effect of MC is marginal on the CT of the DMFC.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.12C
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• pp.1215-1227
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• 2002

This paper presents a genetic algorithmic approach to shortest path (SP) routing problem. Variable-length chromosomes (strings) and their genes (parameters) have been used for encoding the problem. The crossover operation that exchanges partial chromosomes (partial-routes) at positionally independent crossing sites and the mutation operation maintain the genetic diversity of the population. The proposed algorithm can cure all the infeasible chromosomes with a simple repair function. Crossover and mutation together provide a search capability that results in improved quality of solution and enhanced rate of convergence. Computer simulations show that the proposed algorithm exhibits a much better quality of solution (route optimality) and a much higher rate of convergence than other algorithms. The results are relatively independent of problem types (network sizes and topologies) for almost all source-destination pairs.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.749-754
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• 2014

In this paper, we suggest tree-structure-aware GP (Genetic Programming) operators that heed tree distributions in structure space and their possible structural difficulties. The main idea of the proposed GP operators is to place the generated offspring of crossover and/or mutation in a specified region of tree structure space insofar as possible by biasing the tree structures of the altered subtrees, taking into account the observation that most solutions are found in that region. To demonstrate the effectiveness of the proposed approach, experiments on the binomial-3 regression, multiplexor and even parity problems are performed. The results show that the results using the proposed tree-structure-aware operators are superior to the results of standard GP for all three test problems in both success rate and number of evaluations.