• Education of Primary School Mathematics
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• v.27 no.3
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• pp.281-301
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• 2024

Many students have experienced difficulties due to the discontinuity in instruction between arithmetic and algebra, and in the field of elementary education, algebra is often treated somewhat implicitly. However, algebra must be learned as algebraic thinking in accordance with the developmental stage at the elementary level through the expansion of numerical systems, principles, and thinking. In this study, algebraic thinking-based classes were developed and conducted for 6th graders in elementary school, and the effect on the ability to solve word-problems in fraction division was analyzed. During the 11 instructional sessions, the students generalized the solution by exploring the relationship between the dividend and the divisor, and further explored generalized representations applicable to all cases. The results of the study confirmed that algebraic thinking-based classes have positive effects on their ability to solve fractional division word-problems. In the problem-solving process, algebraic thinking elements such as symbolization, generalization, reasoning, and justification appeared, with students discovering various mathematical ideas and structures, and using them to solve problems Based on the research results, we induced some implications for early algebraic guidance in elementary school mathematics.

• Korean Circulation Journal
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• v.54 no.4
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• pp.203-217
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• 2024

Background and Objective: The effects of radiofrequency catheter ablation (RFCA) for atrial fibrillation (AF) on right ventricular (RV) function are not well known. Methods: Patients who underwent RFCA for AF and underwent pre- and post-procedural echocardiography were enrolled consecutively. Fractional area change (FAC), RV free-wall longitudinal strain (RVFWSL), and RV 4-chamber strain including the ventricular septum (RV4CSL) were measured. Changes in FAC, RVFWSL, and RV4CSL before and after RFCA were compared among paroxysmal AF (PAF), persistent AF (PeAF), and long-standing persistent AF (LSPeAF) groups. Results: A total of 164 participants (74 PAF, 47 PeAF, and 43 LSPeAF; age, 60.8 ± 9.8 years; men, 74.4%) was enrolled. The patients with PeAF and LSPeAF had worse RV4CSL (p<0.001) and RVFWSL (p<0.001) than those with PAF and reference values. Improvements in RVFWSL and RV4CSL after RFCA were significant in the PeAF group compared with the PAF and LSPeAF groups (ΔRV4CSL, 8.4% [5.1, 11.6] in PeAF vs. 1.0% [-1.0, 4.1] in PAF, 1.9% [-0.2, 4.4] in LSPeAF, p<0.001; ΔRVFWSL, 9.0% [6.9, 11.5] in PeAF vs. 0.9% [-1.4, 4.9] in PAF, 1.0% [-1.0, 3.6] in LSPeAF, p<0.001). In patients without recurrence, improvements in RVFWSL and RV4CSL after RFCA were significant in the PeAF group compared to the LSPeAF group. Conclusions: RV systolic function is more impaired in patients with PeAF and LSPeAF than in those with PAF. RV systolic function is more improved after RFCA in patients with PeAF than in those with PAF or LSPeAF.

• The Korean Journal of Financial Management
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• v.24 no.3
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• pp.63-89
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• 2007

This study aims at empirically verifying whether long memory properties exist in returns and volatility of the financial time series and then, empirically observing influential factors of long-memory properties. The presence of long memory properties in the financial time series is examined with the Hurst exponent. The Hurst exponent is measured by DFA(detrended fluctuation analysis). The empirical results are summarized as follows. First, the presence of significant long memory properties is not identified in return time series. But, in volatility time series, as the Hurst exponent has the high value on average, a strong presence of long memory properties is observed. Then, according to the results empirically confirming influential factors of long memory properties, as the Hurst exponent measured with volatility of residual returns filtered by GARCH(1, 1) model reflecting properties of volatility clustering has the level of $H{\approx}0.5$ on average, long memory properties presented in the data before filtering are no longer observed. That is, we positively find out that the observed long memory properties are considerably due to volatility clustering effect.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1149-1155
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• 2003

OFDM/SFH(orthogonal frequency division multiplexing/slow frequency hopping) system is the combination of OFDM communication system with frequency hopping(FH) method and OFDM/DS(orthogonal frequency division multiplexing/direct sequence) system combines the OFDM communication system with direct sequence(DS) method in terms of PN(pseudo noise) sequence. These two systems are also can be used for anti-jamming. In this study we analyze performances of OFDM/SFH system and OFDM/DS system with the equal information rate in partial band jamming and tone jamming channel. We find BER(bit error rate) in the variation of JFR(jamming fractional ratio) and JSR(jamming to signal power ratio) of the partial band jamming. Also, BER is found in the several JSR of the single tone or multi tone jamming. OFDM/DS system shows better performance than OFDM/SFH system in partial band jamming environment. OFDM/DS system has about 2.5 ㏈ SNR(signal to noise power ratio) gains than OFDM/SFH system when JFR=4/16 and JSR=0 ㏈ to meet BER=10$\^$-3/. However, OFDM/SFH system has about 3 ㏈ SNR gains than OFDM/DS system at single tone jamming of JSR=5 ㏈. In multi tone jamming, performance of OFDM/SFH system is considerably degraded than OFDM/DS system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6C
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• pp.656-663
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• 2009

Recently, frequency offset estimation method for orthogonal frequency division multiplexing has been proposed by Ren et al. (REA). The method can estimate an frequency offset independently from training symbol structure. In REA method, however, the detection probability of integer frequency offset is varying according to fractional frequency offset. In this paper, we first analysis REA frequency offset estimation method, and define new detection criteria suitable for the method. Then, we propose efficient integer frequency offset estimation method based on the new detection criteria and maximum likelihood method. The proposed method still has the advantages of REA method, while overcome the drawback. The numerical results demonstrate that the proposed methods outperform the REA method, in terms of integer frequency offset detection probability.

• Food Science of Animal Resources
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• v.30 no.1
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• pp.66-72
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• 2010

Pediococcus pentosaceus SA131 was isolated from jeotgal, is the bacteriocin producer against bovine mastitis pathogens, Streptococcus uberis E290, Enterococcus gallinarum E362, and Staphylococcus epidermidis ATCC 12228. The medium composition for pediocin SA131 production by P. pentosaceus SA131 was optimized using response surface methodology. Component of medium was studied as carbon source (glucose, fructose, lactose, glycerol, sucrose, maltose, and mannitol), nitrogen source (beef extract, yeast extract, peptone, malt extract, and tryptone), mineral and surfactant ($MgSO_4$, $KH_2PO_4$, $(NH_4)_2SO_4$, $MnSO_4$, NaCl, sodium acetate, and Tween 80). Through one factor-at-a-time experiment, glucose, fructose, yeast extract, malt extract, NaCl, $MgSO_4$, and Tween 80 were determined as the good ingredient. The effects of major factors for pediocin SA131 production were investigated by two-level fractional factorial designs (FFD). By a $2^4$ FFD, fructose, yeast extract, and $MnSO_4$ were found to be the important factors for the bacteriocin production. Subsequently, a $2^3$ central composite design (CCD) was adopted to derive a statistical model for optimizing the composition of the fermentation medium. The estimated optimum composition for the production of pediocin SA131 by P. pentosaceus SA131 was as follows; 0.13% fructose, 1% glucose, 1.8% yeast extract, 2.58% $MnSO_4$, 0.2% NaCl, and 0.2% Tween 80. The pediocin production under optimized medium was increased to 1,000 AU/mL, compared to the 400 AU/mL in MRS medium.

• Clinical and Experimental Pediatrics
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• v.61 no.2
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• pp.59-63
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• 2018

Purpose: Cardiomyopathy is becoming the leading cause of death in patients with Duchenne muscular dystrophy because mechanically assisted lung ventilation and assisted coughing have helped resolve respiratory complications. To clarify cardiopulmonary function, we compared cardiac function between the home ventilator-assisted and non-ventilator-assisted groups. Methods: We retrospectively reviewed patients with Duchenne muscular dystrophy from January 2010 to March 2016 at Gangnam Severance Hospital. Demographic characteristics, pulmonary function, and echocardiography data were investigated. Results: Fifty-four patients with Duchenne muscular dystrophy were divided into 2 groups: home ventilator-assisted and non-ventilator-assisted. The patients in the home ventilator group were older ($16.25{\pm}1.85years$) than those in the nonventilator group ($14.73{\pm}1.36years$) (P=0.001). Height, weight, and body surface area did not differ significantly between groups. The home ventilator group had a lower seated functional vital capacity ($1,038{\pm}620.41mL$) than the nonventilator group ($1,455{\pm}603.2mL$). Mean left ventricular ejection fraction and fractional shortening were greater in the home ventilator group, but the data did not show any statistical difference. The early ventricular filling velocity/late ventricular filling velocity ratio ($1.7{\pm}0.44$) was lower in the home ventilator group than in the nonventilator group ($2.02{\pm}0.62$. The mitral valve annular systolic velocity was higher in the home ventilator group (estimated ${\beta}$, 1.06; standard error, 0.48). Patients with Duchenne muscular dystrophy on a ventilator may have better systolic and diastolic cardiac functions. Conclusion: Noninvasive ventilator assistance can help preserve cardiac function. Therefore, early utilization of noninvasive ventilation or oxygen may positively influence cardiac function in patients with Duchenne muscular dystrophy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2C
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• pp.226-233
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• 2009

A novel frequency offset estimation scheme using a periodogram is proposed for orthogonal frequency division multiplexing (OfDM) systems. A conventional scheme proposed by Ren has a problem that the fractional and residual frequency offset estimation steps do not compensate for the difference between the real frequency offset and estimated integer frequency offset in the noise channel. So, the frequency offset estimation performance of Ren's scheme is degraded. In this paper, a frequency offset estimation scheme is proposed, which has a larger estimation range than that of the factional and residual frequency offset estimation steps in Ren's scheme. The proposed scheme can compensate for the difference between the real frequency offset and estimated integer frequency offset, unlike Ren's scheme. From the simulation results, we can observe that the performance of the proposed scheme is better than that of Ren's scheme.

• Korean Journal of Soil Science and Fertilizer
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• v.47 no.4
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• pp.299-305
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• 2014

In this paper, fractional factorial screening design (FFSD) and central composition design (CCD) were used to optimize the medium components for producing chitinase and gelatinase by Lysobacter capsici YS1215. Crab shell powder, nutrient broth and gelatin were proved to have significant effects on chitinase and gelatinase activity by FFSD first. An optimal medium was obtained by using a three factor CCD, which consisted of nutrient broth of $2.0gL^{-1}$, crab shell powder of $2.0gL^{-1}$ and gelatin of $1.0gL^{-1}$, respectively with the highest chitinase activity ($3.34UmL^{-1}$) and gelatinase activity ($14.15UmL^{-1}$). This value was 3.76 and 1.11 fold of the chitinase and gelatinase activity, respectively, compared to the lowest productive medium in the design matrix. In investigating potential of these enzymes partially purified from L. capsici YS1215 for biotechnological use, the crude enzymes was found to be inhibition against pathogenic fungal mycelia: Colletotrichum gleosporioides, Phytophthora capsici, and Rhizoctonia solani. In this study, we demonstrated the optimal medium for producing the chitinolytic and gelatinolytic enzymes by the strain YS1215 and the role of their enzymes that may be useful for further development of a biotechnological use and agricultural use for biological control of phytopathogenic fungi.

• Clinical and Experimental Pediatrics
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• v.54 no.8
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• pp.340-344
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• 2011

Purpose: Brain natriuretic peptide (BNP) has been considered a biochemical marker for myocarditis in Kawasaki disease. We performed this study to determine its quantitative significance. Methods: We attempted to correlate log-transformed BNP concentrations (log-BNP) and clinical, laboratory, and echocardiographic variables in 81 children with Kawasaki disease. Stepwise multiple linear regression analysis was used to determine the variables independently associated with log-BNP concentration. Results: Serum C-reactive protein level (P<0.0001), serum alanine aminotransferase concentration (P =0.0032), white blood cell count (P=0.0030), and left ventricular mass index (P=0.0024) were positively related with log-BNP, and hemoglobin level (P<0.0001), serum albumin level (P<0.0001), $Na^+$ concentrations (P<0.0001), left ventricular fractional shortening (P=0.0080), and peak early diastolic tissue velocity of the left ventricular basal lateral segment (P=0.0045) were negatively related to the log-BNP concentration. Multiple regression analysis showed that serum albumin concentration ($R_2$=0.31, P=0.0098) and left ventricular mass index ($R_2$=0.09, P=0.0004) were significantly associated with the log-BNP concentration. Conclusion: Elevated BNP levels during the acute phase of Kawasaki disease may be attributable to cardiac dysfunction associated with the increase in left ventricular mass, and log-BNP concentration may be a quantitative biochemical marker of myocarditis in Kawasaki disease.