• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.24 no.2
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• pp.161-197
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• 2020

Total variation minimization is standard in mathematical imaging and there have been numerous researches over the last decades. In order to process large-scale images in real-time, it is essential to design parallel algorithms that utilize distributed memory computers efficiently. The aim of this paper is to illustrate recent advances of domain decomposition methods for total variation minimization as parallel algorithms. Domain decomposition methods are suitable for parallel computation since they solve a large-scale problem by dividing it into smaller problems and treating them in parallel, and they already have been widely used in structural mechanics. Differently from problems arising in structural mechanics, energy functionals of total variation minimization problems are in general nonlinear, nonsmooth, and nonseparable. Hence, designing efficient domain decomposition methods for total variation minimization is a quite challenging issue. We describe various existing approaches on domain decomposition methods for total variation minimization in a unified view. We address how the direction of research on the subject has changed over the past few years, and suggest several interesting topics for further research.

• Journal of The Korean Astronomical Society
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• v.41 no.2
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• pp.17-22
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• 2008

We present an analysis of the soft X-ray emission of MRK 841 to investigate its long-term variation. The light variation of MRK 841 for three different energy bands of soft, medium, and hard values were studied. The maximum variability with a factor of 5 for about two years was confirmed at all three different bands. The light curves exhibit a gradual variation of brightness. In addition to a gradual variation, the short- term or micro variation was also confirmed with a factor of about two for all three different bands. The light variation of each band did not exhibit a correlation between them, but the flare event is strongest in the soft band. The hardness ratio for hard and soft bands shows irregular variation but there was no correlation between them. It was confirmed that there is a gradual decrease of the photon index. Results of our analysis are discussed within the framework of the accretion disk phenomenon.

• The Korean Journal of Ecology
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• v.26 no.2
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• pp.82-86
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• 2003

We investigated the variation in adaptation to growth for four ecotypically-differentiated population of Taraxacum officinale found naturally in temporal environmental heterogeneity. Seeds collected from the four seasons were germinated in incubators and were grown for four months in greenhouse to test genetic variation among biotypes. Biotypes, segregated by seeds collected seasonally, were the part of natural population in Mokpo, South Korea. Each biotype was different in total dry weight of seeds, biomass, and leaf area, confirming previous finding. Differences between biotypes grown under a common environment indicated a genetic basis to their distinct demographic rates. Therefore, biotypes with similar annual rates of growth and contrasting seasonal rates should persist in the population. This differential response suggests that temporal variation in environment may be responsible, in part, for the maintenance of genetic variation within populations.

• Journal of Environmental Science International
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• v.12 no.9
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• pp.943-948
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• 2003

Variation of the polar front in the East Sea is studied using temperature and dissolved oxygen data obtained from Japan Meteorological Agency from 1972 to 1999. Variation of the polar front in the East Sea has a close relation to the variation of the Tsushima Warm Current (TWC). When the TWC spreads widely in the East Sea, polar front moves northward. The spatial variation of the polar front is greater in the southwestern area of the East Sea and the northern area of Tsugaru Strait where the variation of the TWC's distribution area is greater than those in others of the East Sea. Hence, in the southeastern area of the East Sea, that is, between near Noto peninsula and Tsugaru Strait, the spatial variation of the polar front is not so wide as in the southwestern area because the flow of TWC is stable.

• Journal of the Korean Society for Railway
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• v.7 no.1
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• pp.26-31
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• 2004

A study is conducted to clarify internal and external pressure variation of passenger cabin for KTX. These pressure variation may give rise to the ear-discomfort for passenger and fatigue for carbody. In this study, the pressure variation of interior, gangway and exterior of KTX passenger car is measured by using the atmospheric pressure sensors and portable data acquisition system. The tunnel from 4000m to 200m in length are chosen far the investigation of tunnel length effects. From the results of experiment, the pressure variation of interior per second is under the ear-discomfort limitation in all of tunnel. And, We found that there are similar patterns of exterior pressure variation for each critical tunnel length. These results generally agree to RTRI's experimental result fur Shinkansen.

• Phonetics and Speech Sciences
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• v.11 no.1
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• pp.19-27
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• 2019

Lateral approximants are well known as having complex articulatory characteristics, which vary cross-linguistically, across speakers, and across utterances. However, less attention has been paid to the articulation of Korean laterals, which do not contrast with a rhotic and may thus exhibit greater-than-normal variability. The focus of this study is to investigate the general articulatory characteristics of the Korean lateral [l] as well as the articulatory variation using novel 3D ultrasound imaging methods. The results of this study revealed significant between-speaker variation and some vowel-dependent variation with regard to the articulation of the Korean lateral [l], which has not been reported previously. Even though all participants in this study showed an anterior occlusion, the place of articulation and the size of the occlusion varied greatly across speakers. The data also revealed that left-right asymmetry is present in the articulation of the Korean lateral. The individual variation of the Korean lateral [l] suggests that it has a large articulatory-acoustic space for variation, since it has no contrasting sound that causes perceptual confusion.

• Journal of the Korean Statistical Society
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• v.30 no.1
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• pp.99-113
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• 2001

This paper deals with the problem of estimating the means in two inverse Gaussian populations with equal but unknown coefficient of variation. The maximum likelihood estimators are derived by solving a cubic equation and their asymptotic variances are presented for comparative purpose. Monte-Carlo simulation is conducted to investigate the efficiency of the estimators relative to the sample means over a wide range of values for the sample size and the coefficient of variation. The effect on this efficiency under the departure from the assumption of common coefficient of variation is also studied.

• Bulletin of the Korean Mathematical Society
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• v.61 no.1
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• pp.207-216
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• 2024

This note is devoted to establishing the variation continuity of the one-dimensional discrete uncentered multilinear maximal operator. The above result is based on some refine variation estimates of the above maximal functions on monotone intervals. The main result essentially improves some known ones.

• Smart Structures and Systems
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• v.19 no.2
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• pp.137-149
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• 2017

Under the interference of the temperature effect, the alternation of cable force due to damages of a cable-stayed bridge could be difficult to distinguish. Considering the convenience and applicability in engineering practice, simple air or cable temperature measurements are adopted in the current study for the exclusion of temperature effect from the variation of cable force. Using the data collected from Ai-Lan Bridge located in central Taiwan, this work applies the ensemble empirical mode decomposition to process the time histories of cable force, air temperature, and cable temperature. It is evidently observed that the cable force and both types of temperature can all be categorized as the daily variation, long-term variation, and high-frequency noise in the order of decreasing weight. Moreover, the correlation analysis conducted for the decomposed variations of all these three quantities undoubtedly indicates that the daily and long-term variations with different time shifts have to be distinguished for accurately evaluating the temperature effect on the variation of cable force. Finally, consistent results in reducing the range of cable force variation after the elimination of temperature effect confirm the validity and stability of the developed method.

• Journal of Ecology and Environment
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• v.31 no.3
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• pp.207-211
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• 2008

We investigated the leaf demography of a temperate woody liana, Akebia trifoliata, in a temperate forest in Japan, Akebia is semi-evergreen: some leaves are shed before winter, while others remain through the winter. Previous studies of semi-evergreen species found that variation in leaf life span was caused by variation in the timing of leaf emergence, Leaves that appeared just before winter over-wintered, while leaves appearing earlier were shed, However, it is unclear whether leaves of the same cohort (i.e., leaves that appear at the same time within a single site) show variation in life span under the effect of strong seasonality. To separate variation in life span among the leaves in each cohort from variation among cohorts, we propose a new method - the single leaf diagram, which shows the emergence and death of each leaf. Using single leaf diagrams, our study revealed that Akebia leaves within a cohort showed substantial variation in life span, with some over-wintering and some not. In addition, leaves on small ramets in the understory showed great variation in life span, while leaves on large ramets, which typically reach higher positions in the forest canopy, have shorter lives, As a result, small ramets were semi-evergreen, whereas large ramets were deciduous, The longer lives of leaves on small ramets can be interpreted as a shade-adaptive strategy in understory plants.