• Kyungpook Mathematical Journal
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• 제60권3호
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• pp.535-549
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• 2020

In this paper, we introduce the geometry of contact CR submanifolds and radical transversal lightlike submanifolds of Sasaki-like almost contact manifolds with B-metric. We obtain some new results that establish a relationship between these two submanifolds.

• 대한수학회보
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• 제52권3호
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• pp.1027-1034
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• 2015

As a natural generalization of the contact metric manifolds, Kim, Park and Sekigawa discussed quasi contact metric manifolds based on the geometry of the corresponding quasi $K{\ddot{a}}hler$ cones. In this paper, we show that a quasi contact metric manifold is a contact manifold.

• 대한수학회보
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• 제53권4호
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• pp.1095-1103
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• 2016

B. Y. Chen introduced a series of curvature invariants, known as Chen invariants, and proved sharp estimates for these intrinsic invariants in terms of the main extrinsic invariant, the squared mean curvature, for submanifolds in Riemannian space forms. Special classes of submanifolds in Sasakian manifolds play an important role in contact geometry. F. Defever, I. Mihai and L. Verstraelen [8] established Chen first inequality for C-totally real submanifolds in Sasakian space forms. Also, the differential geometry of slant submanifolds has shown an increasing development since B. Y. Chen defined slant submanifolds in complex manifolds as a generalization of both holomorphic and totally real submanifolds. The slant submanifolds of an almost contact metric manifolds were defined and studied by A. Lotta, J. L. Cabrerizo et al. A Chen first inequality for slant submanifolds in Sasakian space forms was established by A. Carriazo [4]. In this article, we improve this Chen first inequality for special contact slant submanifolds in Sasakian space forms.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.1483-1487
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• 2006

In electric railway, image monitoring using high speed camera provides reliable, timely information of wear and geometry status, important in taking decisions for overhead contact wire maintenance. The contribution of this research is the development of a simple real-time monitoring system for use in measurement subsystem of contact wire and geometry of overhead contact wire in electric railway. The system has been consists of a high speed CMOS camera with resolution $1024{\times}1280$ pixels, line type laser source and PC-based image acquisition system with PCI Express slot. Vision acquisition software have been used in application programming interface for image acquisition, display, and storage with a frequency of sampling of 500 acquisitions per second.

• Kyungpook Mathematical Journal
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• 제62권3호
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• pp.485-495
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• 2022

The aim of this paper is to characterize K-contact and Sasakian manifolds whose metrics are generalized quasi-Einstein metric. It is proven that if the metric of a K-contact manifold is generalized quasi-Einstein metric, then the manifold is of constant scalar curvature and in the case of a Sasakian manifold the metric becomes Einstein under certain restriction on the potential function. Several corollaries have been provided. Finally, we consider Sasakian 3-manifold whose metric is generalized quasi-Einstein metric.

• Journal of applied mathematics & informatics
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• 제9권2호
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• pp.543-559
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• 2002

In this paper we formulate the linear theory for compressible fluids in cylindrical geometry with small perturbation at the material interface. We derive the first order equations in the smooth regions, boundary conditions at the shock fronts and the contact interface by linearizing the Euler equations and Rankine-Hugoniot conditions. The small amplitude solution formulated in this paper will be important for calibration of results from full numerical simulation of compressible fluids in cylindrical geometry.

• 한국안광학회지
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• 제18권1호
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• pp.75-84
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• 2013

목적: 연령에 따라 역기하콘택트렌즈(reverse geometry contact lens), MC렌즈(myopia control lens)를 착용 한 후 근시진행억제 효과에 대한 굴절교정값의 변화를 단초점렌즈(single vision lens)와 비교해 알아보고자 한다. 방법: 6세에서 15세 사이의 아동에게 역기하콘택트렌즈 57안, MC렌즈 56안, 단초점렌즈 78안을 각각 착용시킨 후 연령에 따라 Group 1은 10세 이하, Group 2는 11세에서 15세 이하, Group 3은 연구 대상을 모두 포함하여 3그룹으로 나눴다. 이를 바탕으로 12개월 이하, 13~24개월, 25~36개월 까지 굴절교정값의 변화를 통한 근시 진행 억제 효과를 알아보고 통계적 유의성을 검증하고자 하였다. 결과: 착용기간에 따른 굴절교정값의 변화는 Group 3에서 12개월 이하에서는 역기하콘택트렌즈를 착용한 아동에서 변화가 없었고, MC렌즈는 $-0.36{\pm}0.10$ D, 단초점렌즈는 $-0.67{\pm}0.52$ D가 유의하게 변화되었다(P<0.05). 13~24개월에서 역기하콘택트렌즈는 $0.18{\pm}0.49$ D, MC렌즈는 $0.60{\pm}0.42$ D, 단 초점렌즈는 $1.37{\pm}0.72$ D로 유의(P<0.05)하게 변화되었다. 25~36개월에서 역기하콘택트렌즈는 $0.29{\pm}0.61$ D, MC렌즈는 $0.93{\pm}0.57$ D, 단초점렌즈는 $1.72{\pm}0.78$ D로 유의(P<0.05)하게 변화되었다. Group 1에서는 36개월 까지 역기 하콘택트렌즈는 $0.29{\pm}0.73$ D로 MC렌즈는 $1.07{\pm}0.59$ D로 단초점 렌즈는 $1.75{\pm}0.74$ D로 유의(P<0.05)하게 증가하였으며 Group 2에서는 36개월 까지 역기하콘택트렌즈는 $0.28{\pm}0.42$ D로 MC렌즈는 $0.75{\pm}0.49$ D로 단초점 렌즈는 $1.70{\pm}0.84$ D로 유의(P<0.05)하게 증가하여 굴절교정값의 변화는 10세 이하가 11세 이상보다 유의(P<0.05)하게 큰 것으로 나타났다. 결론: 본 연구 결과 12개월 이하의 착용시 역기하콘택트렌즈는 모든 연령에서 굴절교정값의 변화가 없었고, MC렌즈는 모든 연령에서 단초점렌즈보다 더 낮은 시력변화폭을 나타내 근시진행의 억제효과가 있으며, 13~36개월 착용시 역기하콘택트렌즈와 MC렌즈는 모든 연령에서 단초점렌즈보다 낮은 시력변화를 보여 근시진행의 억제효과가 있는 것으로 사료된다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권2호
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• pp.59-64
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• 2001

The distribution of current in the conductors influenced by the armature geometry and velocity is an important parameter for determining performance of an electromagnetic launcher(EML). the electric current in the early launching stage tends to flow on the outer surfaces of the conductors, resulting in very high local electric current density. However, the tendency for current to concentrate on the surface is driven by the velocity skin effect later in launching stage. The high current density produces high local heating and, consequently, increases armature wear which causes several defects on EML system. This paper investigates the effects of rail/armature geometry on current density distribution, launcher inductance gradient (L'), and contact force. Three geometrical parameters are used here to characterize the railgun system. These are the ratio of contact length to root length, relative position of contact leading edge to root trailing edge, and the ratio of rail overhang to the rail height. The distribution of current density, L', contact force between various configurations of the armature and the rail are analyzed and compared by using the EMAP3D program.

• 호남수학학술지
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• 제44권1호
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• pp.62-77
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• 2022

This study presents an 𝛼-Sasakian structure on the product manifold M₁ × 𝛽(I), where M₁ is a Kähler manifold with an exact 1-form, and 𝛽(I) is an open curve. It then defines a new type warped product metric to study the warped product of almost Hermitian manifolds with almost contact metric manifolds, contact metric manifolds, and K-contact manifolds.

• Journal of Computational Design and Engineering
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• 제1권1호
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• pp.27-36
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• 2014

Similar to the essential components of many mechanical systems, the geometrical properties of the teeth of spiral bevel gears greatly influence the kinematic and dynamic behaviors of mechanical systems. Logarithmic spiral bevel gears show a unique advantage in transmission due to their constant spiral angle property. However, a mathematical model suitable for accurate digital modeling, differential geometrical characteristics, and related contact analysis methods for tooth surfaces have not been deeply investigated, since such gears are not convenient in traditional cutting manufacturing in the gear industry. Accurate mathematical modeling of the tooth surface geometry for logarithmic spiral bevel gears is developed in this study, based on the basic gearing kinematics and spherical involute geometry along with the tangent planes geometry; actually, the tooth surface is a parametric surface defined on a parallelogrammic domain. Equivalence proof of the tooth surface geometry is then given in order to greatly simplify the mathematical model. As major factors affecting the lubrication, surface fatigue, contact stress, wear, and manufacturability of gear teeth, the differential geometrical characteristics of the tooth surface are summarized using classical fundamental forms. By using the geometrical properties mentioned, manufacturability (and its limitation in logarithmic spiral bevel gears) is analyzed using precision forging and multiaxis freeform milling, rather than classical cradle-type machine tool based milling or hobbing. Geometry and manufacturability analysis results show that logarithmic spiral gears have many application advantages, but many urgent issues such as contact tooth analysis for precision plastic forming and multiaxis freeform milling also need to be solved in a further study.