• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.6
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• pp.288-295
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• 2001

Predischarges in nonuniform electric field stressed by lightning impulse voltagesin SF(sub)6-$N_2$mixtures are initiated by streamer coronas. Due to field ehnancement at a protrusion point of electrodes new ionization processes occur and a precursor, which leads to a first leader, is created. The leader proceeds step by step to the opposite electrode and the final jump bridges the test gap. It was found that the predischarge is propagated with a leader mechanism of stepwise expansion from the predischarge current waveforms measured by a shunt. The predischarge current is closely related to the amplitude and polarity of applied voltages, the gas pressure and the gap geometry. The time intervals between step leaders for the positive and negative polarities were inversely proportional to V.P$^2$. When the gas pressure increases in the positive polarity, statistical time lag to statistical time lag to streamer corona inception increase slightly, but the formative time lag to flashover is significantly decreased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.1
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• pp.85-93
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• 2000

In this paper, the predischarge propagation processes of SF\ulcorner gas stressed by impulse voltages under nonuniform electric field perturbed by a needle protrusion are described. The statistical and formative time-lags and the time interval between leader pulses were investigated on the basis of the predischarge current measured in the gas pressure range of 0.1~0.5 MPa. The predischarge current is closely related to the waveform, amplitude and polarity of applied votages, the gas pressure and the gap geometry. Both the positive and negative predischarge processes in nonuniform electric field develop in a regime of stepwise leader propagation leading to electrical breakdown. The mean of the time interval between leader pulses gives about a factor of 10 higher for the negative than for the positive leader current puls-es. According as the gas pressure increases, the statistical time-lag was almost unchangeable, but the formative time-lag was gradually decreased.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.577-582
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• 2007

The plasma display panel is an image expression display using gas discharge plasma. However, gas discharge characteristics vary with temperature as gas discharge is sensitive to temperature. The discharge time lag extends a lot in low temperature and it is known as the cause which hinders high speed addressing which is essential for the size enlargement of the panel. Accordingly this research aims at identifying the temperature-dependent discharge characteristic. The lower temperature becomes, the longer addressing discharge time lag becomes. Particularly the statistical time lag extends much in low temperature. The increasing of electric field shortens discharge time lag in low temperature. Also, when priming particles are sufficiently supplied, stable discharge can be performed regardless of the influence of temperature.

• The Korean Journal of Applied Statistics
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• v.16 no.1
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• pp.87-100
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• 2003

Most of statistical data are generated by a set of dynamic, stochastic, and simultaneous relations. An important question is how to specify statistical models so that they are consistent with the dynamic feature of those data. A general hypothesis is that the lagged effect of a change in an explanatory variable is not felt all at once at a single point in time, but The impact is distributed over a number of future points in time. In other words, current control variables are determined by a function that can be reduced to a distributed lag function of past observations. It is possible to explain the relationship between variables in different points of time and to estimate the long-run impacts of a change in a variable on another if time lag series of explanatory variables are incorporated in the model specification. In this study, distributed lag structure is applied to the domestic stock market model to capture the dynamic response of the market by exogenous shocks. The Domestic market is found more responsive to the changes in foreign market factors both in the short and the long run.

• Communications for Statistical Applications and Methods
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• v.17 no.3
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• pp.377-390
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• 2010

In the case of time-series analysis, it is often more convenient to rely on the frequency domain than the time domain. Spectral density is the core of the frequency-domain analysis that describes autocorrelation structures in a time-series process. Possible ways to estimate spectral density are to compute a periodogram or to average the periodogram over some frequencies with (un)equal weights. This can be an attractive tool to measure the similarity between time-series processes. We employ the metrics based on a smoothed periodogram proposed by Park and Kim (2008) for the classification of different classes of time-series processes. We consider several lag windows with unequal weights instead of a modified Daniel's window used in Park and Kim (2008). We evaluate the performance under various simulation scenarios. Simulation results reveal that the metrics used in this study split the time series into the preassigned clusters better than do the raw-periodogram based ones proposed by Caiado et al. 2006. Our metrics are applied to an economic time-series dataset.

• The Korean Journal of Applied Statistics
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• v.25 no.3
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• pp.377-387
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• 2012

Job competition among generations has become an important social issue that has yet to be studied from an academic viewpoint. This study performs statistical tests to investigate the interrelation of employment among generations using seasonally adjusted monthly time series data. Employment by generations is not found to be strongly interrelated, even if the employment of 30-year-olds appears to affect those of 40-yearolds in some tests.

• The Korean Journal of Applied Statistics
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• v.26 no.3
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• pp.401-411
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• 2013

This study investigates the controversial chickens-eggs dilemma and empirically performs statistical tests to examine if there exists a causality between them. Granger and Hsiao tests are applied to both level and stationary variables to identify the lead-lag relationships. Each of these test is found to have the robust result where the causality runs from eggs to chickens; in addition, the explanatory power of one variable in variations of the other appears to remain time invariant. The outcome is proved to be valid as the hypothesis test for no structural change in their relationship fails to be rejected.

• Korean Journal of Remote Sensing
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• v.37 no.6_2
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• pp.1819-1827
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• 2021

Land-use/cover change caused by rapid urbanization in South Korea is one of the concerns in flood risk management because groundwater recharge by precipitation hardly occurs due to an increase in impermeable surfaces in urban areas. This study investigated the hydrologic effects of land-use/cover on groundwater recharge in the Yeonje-gu district of Busan, South Korea. A statistical time series analysis was conducted with temporal variations of precipitation and groundwater level to estimate lag-time based on correlation coefficients calculated from auto-correlation function (ACF), cross-correlation function (CCF), and moving average (MA) at five sites. Landform and land-use/cover within 250 m radius of the monitoring wells(GW01, GW02, GW03, GW04, and GW05) at five sites were identified by land cover and digital map using Arc-GIS software. Long lag-times (CCF: 42-71 days and MA: 148-161 days) were calculated at the sites covered by mainly impermeable surfaces(GW01, GW03, and GW05) while short lag-times(CCF: 4 days and MA: 67 days) were calculated at GW04 consisting of mainly permeable surfaces. The results suggest that lag-time would be one of the good indicators to evaluate the effects of land-use/cover on estimating groundwater recharge. The results of this study also provide guidance on the application of statistical time series analysis to environmentally important issues on creating an urban green space for natural groundwater recharge from precipitation in the city and developing a management plan for hydrological disaster prevention.

• Journal of Pharmaceutical Investigation
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• v.22 no.1
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• pp.49-54
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• 1992

This study was carried out for the purpose of developing an effective temazepam soft elastic gelatin capsule (softgel) which exhibits an excellent bioavailability and of comparing the rate and extent of absorption of temazepam from the marked elixir and prepared softgel using hydrophilic liquid such as polyethylene glycol 400 as a suspending agent by rotary die method. Both softgel and elixir containing 3 mg of temazepam were given to 7 healthy male New Zealand White rabbits in a single oral dose cross-over study. Plasma temazepam concentrations were measured by HPLC. The mean peak concentrations of temazepam following a single oral dosing as softgel and elixir dosage form were 13.84 and 13.25 ng/ml, respectively. And the mean time to peak concentration was 1.29 hr for the softgel and 1.07 hr for the elixir. There was no significant difference in the extent of drug absorption (AUC) for the two different dosage froms (p>0.05). While the softgel exhibited mean lag time of 0.63 hr, the elixir did not show any lag time. Statistical moment parameters such as the mean residence time and variance of the mean residence time did not differ significantly for the two formulations.

• Journal of Astronomy and Space Sciences
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• v.28 no.2
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• pp.123-132
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• 2011

It is generally believed that the occurrence of a magnetic storm depends upon the solar wind conditions, particularly the southward interplanetary magnetic field (IMF) component. To understand the relationship between solar wind parameters and magnetic storms, variations in magnetic field polarity and solar wind parameters during magnetic storms are examined. A total of 156 storms during the period of 1997~2003 are used. According to the interplanetary driver, magnetic storms are divided into three types, which are coronal mass ejection (CME)-driven storms, co-rotating interaction region (CIR)-driven storms, and complicated type storms. Complicated types were not included in this study. For this purpose, the manner in which the direction change of IMF $B_y$ and $B_z$ components (in geocentric solar magnetospheric coordinate system coordinate) during the main phase is related with the development of the storm is examined. The time-integrated solar wind parameters are compared with the time-integrated disturbance storm time (Dst) index during the main phase of each magnetic storm. The time lag with the storm size is also investigated. Some results are worth noting: CME-driven storms, under steady conditions of $B_z$ < 0, represent more than half of the storms in number. That is, it is found that the average number of storms for negative sign of IMF $B_z$ (T1~T4) is high, at 56.4%, 53.0%, and 63.7% in each storm category, respectively. However, for the CIR-driven storms, the percentage of moderate storms is only 29.2%, while the number of intense storms is more than half (60.0%) under the $B_z$ < 0 condition. It is found that the correlation is highest between the time-integrated IMF $B_z$ and the time-integrated Dst index for the CME-driven storms. On the other hand, for the CIR-driven storms, a high correlation is found, with the correlation coefficient being 0.93, between time-integrated Dst index and time-integrated solar wind speed, while a low correlation, 0.51, is found between timeintegrated $B_z$ and time-integrated Dst index. The relationship between storm size and time lag in terms of hours from $B_z$ minimum to Dst minimum values is investigated. For the CME-driven storms, time lag of 26% of moderate storms is one hour, whereas time lag of 33% of moderate storms is two hours for the CIR-driven storms. The average values of solar wind parameters for the CME and CIR-driven storms are also examined. The average values of ${\mid}Dst_{min}{\mid}$ and ${\mid}B_{zmin}{\mid}$ for the CME-driven storms are higher than those of CIR-driven storms, while the average value of temperature is lower.