• Journal of applied mathematics & informatics
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• v.26 no.1_2
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• pp.395-400
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• 2008

Although the properties of flatness and condition (E) for Sacts over a monoid S are incomparable, Liu([10]) showed that necessary and sufficient condition for a monoid S over which all left S-acts that satisfy condition (E) are flat is the regularity of S. But the problem of describing a monoid over which all cyclic flat left S-acts satisfy condition (E) is still open. Thus the purpose of this paper is to characterize monoids over which all cyclic flat right S-acts satisfy condition (E).

• Korean Journal of Mathematics
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• v.20 no.4
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• pp.423-431
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• 2012

There have been some study characterizing monoids by homological classification using the properties around projectivity, injectivity, or regularity of acts. In particular Kilp and Knauer([4]) have analyzed monoids over which all acts with one of the properties around projectivity or injectivity are regular. However Kilp and Knauer left over problems of characterization of monoids over which all regular right S-acts are (weakly) at, (weakly) injective or faithful. Among these open problems, Liu([3]) proved that all regular right S-acts are (weakly) at if and only if es is a von Neumann regular element of S for all $s{\in}S$ and $e^2=e{\in}T$, and that all regular right S-acts are faithful if and only if all right ideals eS, $e^2=e{\in}T$, are faithful. But it still remains an open question to characterize over which all regular right S-acts are weakly injective or injective. Hence the purpose of this study is to investigate the relations between regular right S-acts and weakly injective right S-acts, and then characterize the monoid over which all regular right S-acts are weakly injective.

• Journal of the Korean Mathematical Society
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• v.56 no.3
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• pp.723-738
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• 2019

A property of reduced rings is proved in relation with centers, and our argument in this article is spread out based on this. It is also proved that the Wedderburn radical coincides with the set of all nilpotents in symmetric-over-center rings, implying that the Jacobson radical, all nilradicals, and the set of all nilpotents are equal in polynomial rings over symmetric-over-center rings. It is shown that reduced rings are reversible-over-center, and that given reversible-over-center rings, various sorts of reversible-over-center rings can be constructed. The structure of radicals in reversible-over-center and symmetric-over-center rings is also investigated.

• Korean Journal of Mathematics
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• v.22 no.4
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• pp.725-742
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• 2014

In this paper, we find all inequivalent classes of self-orthogonal codes over $Z_{p^2}$ of lengths $l{\leq}3$ for all primes p, using similar method as in [3]. We find that the classification of self-orthogonal codes over $Z_{p^2}$ includes the classification of all codes over $Z_p$. Consequently, we classify all the codes over $Z_p$ and self-orthogonal codes over $Z_{p^2}$ of lengths $l{\leq}3$ according to the automorphism group of each code.

• Communications for Statistical Applications and Methods
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• v.7 no.2
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• pp.415-426
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• 2000

Hader and Park (1978) introduced the idea of slope rotatability, and Park (1987) introduced the concept of slope rotatability over all directions, and gave necessary and sufficient conditions. Park and Kim (1992) proposed a measure that represent the extent of slope rotatability for a given response surface design. Kim (1993) proposed a measure that represent the extent of slope rotatavility over all directions. In this paper, we embodied the measure of slope rotatability over all directions. Examples of applying this measure to some response surface designs are also given. In this response surface design of slope rotatavility over all directions, we obtain the mean slope variances on the spherical surface to select better experimental design varying the number of center points and radius.

• Ocean and Polar Research
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• v.24 no.3
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• pp.263-266
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• 2002

Gravity waves have been searched for with a new all-sky camera system over Korean Peninsular. The all-sky camera consists of a 37mm/F4.5 Mamiya fisheye lens with a 180 dog field of view, interference filters and a 1024 by 1024 CCD camera. The all-sky camera has been tested near Daejeon city, and moved to Mt. Bohyun where the largest astronomical telescope is operated in Korea. A clear wave pattern was successfully detected in OH filter images over Mt. Bohyun on July 18, 2001, indicating that small scale coherent gravity waves perturbed OH airglow near the mesopause. Other wave features are since then observed with Na 589.8nm and OI 630.0nm filters. Since a Japanese all-sky camera network has already detected traveling ionospheric disturbances (TID) over the northeast-southwest range of Japanese islands, we hope our all-sky camera extends the coverage of the TID's observations to the west direction. We plan to operate our all-sky camera all year around to study seasonal variation of wave activities over the mid-latitude upper atmosphere.

• Acta Via Serica
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• v.7 no.2
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• pp.39-64
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• 2022

Ancient Iranians highly esteemed the horse and horse tacks, one of which is the jul (saddlecloth). It is a felt, sheepskin, or woven pad placed between the horse's back and saddle. The aim of this paper is to identify and categorize jul designs in the Sāsānian period. The research questions are about the variety of jul designs and how to categorize them. This is fundamental research and the method is descriptive and analytical. Neither a jul nor a saddle-cover remains from the Sāsānian period, therefore the statistical population includes all available items, such as metal and stone items and parget and plasterworks, in which juls are recognizable. Due to the scarcity of such items, all the available samples were studied; so the sampling method is a total enumeration. This is documentary research by means of note-taking and using reliable websites; the data has been analyzed qualitatively. The results show that jul designs were not diverse in the Sāsānian period. All-over designs were dominant. In terms of pattern types, these designs are classified into five groups, each of which has its own formal and aesthetic characteristics: all-over design with a four-petal flower pattern, allover design with a checkered pattern, all-over design with a spotted pattern, allover design with a tiger stripe pattern, and all-over design with a zigzag pattern.

• The Research Journal of the Costume Culture
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• v.24 no.4
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• pp.431-440
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• 2016

The purpose of this research is to revive the colors of combination dyeing and mixed dyeing with natural dyestuffs. The fabrics used were cotton and rayon. The natural dyestuffs used in this research were indigo, Phellodendron amurense, and Caesalpinia sappan. The effects of combination dyeing were as follows. First, all samples showed deeper colors. Second, according to the results of the surface K/S measurement, while the surface K/S of cotton was over 15, that of rayon was over 17. Third, the results of the light fastness measurement showed the superiority (by over grade 4) of all the samples, except in the case of rayon fiber sample no. 6 (which had been pre-dyed with indigo five times before being dyed with P. amurense once and then being dyed with C. sappan once). In the color fastness to washing measurement, all fibers showed superiority (by over grade 3~4). In addition, the color fastness to dry cleaning of all fibers was satisfactory or excellent (by over grade 3). Fourth, according to the results of the tensile strength measurement, it tended to decrease in the case of cotton and increase in the case of rayon. Fifth, the results of the density measurement showed that the density of cotton decreased by about 15~20% in the case of warp and 10% in the case of weft for all samples. The density of rayon decreased 20% in the case of warp for all samples and increased 30% in the case of weft for all samples.

• 전기의세계
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• v.25 no.1
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• pp.87-94
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• 1976

The characteristic of flashover electric discharge has been brought to light in this paper for the situation in which the space and creeping gaps are laid out in series. The result of this study has disclosed the facts that the over all flashover characteristics have three kind of features such as unilateral increase after increase, and increase after decrease in compliance with varied layout method and relative magnitude of gap length, and accordingly there exist a ratio among the magnitudes of gap length and a proper layort method through which the over all flashover voltage reaches the highest. Also involved with this study is the theoretic analysis of flashover characteristics even in the case of creeping electric discharge from hand tip of the gauge, where the over all value of flashover voltage can be estimated from the peculiar value of flashover voltage and flicker voltage for the space and creeping gap within the extent of 5% error.

• Communications for Statistical Applications and Methods
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• v.11 no.1
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• pp.121-137
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• 2004

Kim(2002) proposed a second type of central composite design (CCD2), in which the positions of the axial points are indicated by two numbers. In this paper, we study properties of CCD2 when we are interested in estimating the slope of a response surface. Conditions are obtained for CCD2 to be slope-rotatable over axial directions, and some CCD2's are presented that have slope rotatability over axial directions. Also values of a measure of slope rotatability over axial directions are tabulated for various CCD2's. Finally, it is shown that CCD2 is always slope-rotatable over all directions.