• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.137-142
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• 2004

The aim of this study is to investigate the characteristics and quantity of the noise reduction by floor coverings. The characteristics on the reduction of the lightweight impact sound level by floor coverings is as follows. The insulation level attained by floor coverings tends to be smaller in actual buildings than in public laboratories. The reduction of the impact sound level to the tape is similar to the method of adhesives. For this reason, the reduction of impact sound level by floor coverings in public laboratories can be utilized to tape. And the reduction of impact sound level by floor coverings is not influenced by the size of specimen except the specific frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.419-422
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• 2014

Floor impact sound level is affected by various factors. This study was examined about impact sources and floor coverings influenced at floor impact sound. So this study wishes to get method to reduce sound pressure level of receiving room. Light-weight impact sound in mid frequency and Heavy-weight impact sound in low frequency was affected by floor coverings. Therefore, method to reduce floor impact sound level is to use proper floor coverings. Some coverings can amplify the heavy-weight impact sound in low frequency. Floor impact sound sources used measurement and analysis were standard heavy-impact source(Tapping, Bang, Ball) and living impact sources(Cleaner, Chair, Toy-car, Soccer ball). And Floor coverings used measurements were various thickness vinyl, laminate(or ply-wood) floor. Especially vinyl floor coverings were very effective method to reduce floor impact.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.439-440
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• 2008

Five floor coverings were tested with three different types of floor structures in the standard test building in order to evaluate the effectiveness of the floor impact sound reduction. The level of floor impact sound reduction is influenced by not only the types of floor coverings but interrelationship between the floor coverings and floor structures. From the tests, it was found that floor coverings were effective in reducing the floor impact sound using the light impact source. In addition, proper mixtures of the floor structure and the floor covering have shown effectiveness to a certain extent in reducing the floor impact sound using the heavy impact source.

• Journal of the Korean Mathematical Society
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• v.39 no.2
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• pp.289-317
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• 2002

We associate binary codes to polynomials over fields of characteristic two and show that the binary Golay codes are associated to the Mathieu group polynomials in characteristics two. We give two more polynomials whose Galois group in $M_{12}$ but different self-orthogonal binary codes are associated. Also, we find a family of $M_{24}$-coverings which includes previous ones.

• Bulletin of the Korean Mathematical Society
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• v.49 no.6
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• pp.1199-1211
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• 2012

In this paper we give an introduction to the theory of universal central extensions of perfect Lie algebras. In particular, we will provide a model for the universal coverings of Lie tori and we show that automorphisms and derivations lift to the universal coverings. We also prove that the universal covering of a Lie ${\Lambda}$-torus of type ${\Delta}$ is again a Lie ${\Lambda}$-torus of type ${\Delta}$.

• Bulletin of the Korean Mathematical Society
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• v.54 no.5
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• pp.1851-1857
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• 2017

We study relations between two descriptions of closed orientable 3-manifolds: as branched coverings and as Heegaard splittings. An explicit relation is presented for a class of 3-manifolds which are branched cyclic coverings of connected sums of lens spaces, where the branching set is an axis of a hyperelliptic involution of a Heegaard surface.

• Bulletin of the Korean Mathematical Society
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• v.40 no.1
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• pp.101-108
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• 2003

In this paper we study the connections between cyclic presentations of groups and cyclic branched coverings of (1, 1)- knots. In particular, we prove that every π-fold strongly-cyclic branched covering of a (1, 1)-knot admits a cyclic presentation for the fundamental group encoded by a Heegaard diagram of genus π.

• Journal of the Korean Mathematical Society
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• v.53 no.2
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• pp.263-286
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• 2016

We discuss relations between Galois coverings of compact Riemann surfaces and their Jacobi varieties. We prove a theorem of a kind of Galois correspondence for Abelian subvarieties of Jacobi varieties. We also prove a theorem on the sets of points in Jacobi varieties fixed by Galois group actions.

• East Asian mathematical journal
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• v.17 no.2
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• pp.239-251
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• 2001

We construct a family of 3-manifolds by pairwise identifications of faces in the boundary of certain polyhedral3-balls and prove that all these manifolds are cyclic branched coverings of the 3-sphere over the double link.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.425-430
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• 2014

Floor coverings and Mats are for children are economical and has excellent workability, as well as they can reduce floor impact noise effective. "When these floorings contact to impact source, they are deformed and change impact force characteristics that strikes floor structure. It is important to measure the impact force spectrum of floorings in order to evaluate reduction of floor impact noise for floorings. In experimental test of floor impact noise and impact force for 14 PVC vinyl floor coverings and 16 mats for children, we confirmed that the impact force spectrum directly related to the floor impact noise spectrum.