• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.327-334
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• 2013

The purpose of this study is to develop an observation program for obtaining effective flat images that are necessary for photometric observation. The development of the program was achieved by improving the existing method for obtaining twilight flat images. The existing method for obtaining twilight flat images acquires flat images by observing the sky light after sunset or light before sunrise. The decision of when to observe flat images at each night is solely dependent on the judgment of an observer, and thus the obtained flat images for particular nights may not be clean. Especially, in the case of the observatories where an automated observation system is in operation, there is a difficulty that an observer should pay attention during sunrise and sunset in order to obtain flat images. In this study, a computer program is developed to improve this inconvenience and to efficiently perform photometric observation in the observatories where an automated observation system is applied. This program can obtain flat images by calculating the time for obtaining flat images automatically and the exposure time using a numerically calculated function. When obtaining twilight flat images at dusk and at dawn, the developed program performs automated observation and provides effective flat images by acquiring appropriate exposure time considering the sunrise and sunset times that vary depending on the day of observation. The code for performing this task was added to Obs Tool II (Yoon et al. 2006), which is the automated observation system of the Chungbuk National University Observatory, and the usefulness of the developed program was examined by performing an actual automated observation. If this program is applied to other observatories where automated observation is in operation, it is expected that stable and high-quality flat images could be obtained, which can be used for the pre-processing of photometric observation data.

• Communications of the Korean Mathematical Society
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• v.12 no.4
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• pp.999-1006
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• 1997

We proved that if a fibred Riemannian space $\tilde{M}$ with cosymplectic structure is conformally flat, then $\tilde{M}$ is the locally product manifold of locally Euclidean spaces, that is locally Euclidean. Moreover, we investigated the fibred Riemannian space with cosymplectic structure when the Riemannian metric $\tilde{g}$ on $\tilde{M}$ is Einstein.

• Bulletin of the Korean Mathematical Society
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• v.50 no.6
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• pp.2089-2101
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• 2013

The aim of this paper is to introduce the notion of Lie recurrent structure Jacobi operator for real hypersurfaces in non-flat complex space forms and to study such real hypersurfaces. More precisely, the non-existence of such real hypersurfaces is proved.

• Journal of applied mathematics & informatics
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• v.7 no.1
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• pp.297-303
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• 2000

We investigate the conformally flat warped product manifolds and study the geometric structure of the base space and each fibre. Moreover we find the conditions that the base space and each fibres to be the space of constant curvatures.

• Journal of the Korean Geographical Society
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• v.51 no.6
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• pp.799-817
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• 2016

This article aims to reveal the ways in which a "space of difference" is produced and interpret the space as a heterotopic space, drawing the case of Filipino elderly care-givers in Israel. The in-betweens and temporariness of the migrants'experiences in the Israeli society lead to the creation of a heterotopic space. Paying attention to their particular life rhythm as live-in care-givers, namely weekdays-workplace and weekend-flat, this article explores how the migrant care-givers build their own society through a variety of spatial practices and multiple social relations based on the flat. In making the flat a perfect form of a lifestyle for their own, the migrants inscribe their presence in the flat in unique ways for different purposes, in a way different to that which surrounds it. However, the structure of flat not only signifies the migrants' marginality but also reflects the challenging position. The flat has functions in relation to all other space that remains, even if such connection often creates effects of contrast and difference. In this light, the flat is not merely an alienated and circumscibed exotic migrant enclave but a heterotopic space which is dynamically constructed in relation to other sites in the wider societal order.

• Journal of the Korean Mathematical Society
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• v.55 no.3
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• pp.735-747
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• 2018

Let M be a real hypersurface of a complex space form with constant curvature c. In this paper, we study the hypersurface M admitting Miao-Tam critical metric, i.e., the induced metric g on M satisfies the equation: $-({\Delta}_g{\lambda})g+{\nabla}^2_g{\lambda}-{\lambda}Ric=g$, where ${\lambda}$ is a smooth function on M. At first, for the case where M is Hopf, c = 0 and $c{\neq}0$ are considered respectively. For the non-Hopf case, we prove that the ruled real hypersurfaces of non-flat complex space forms do not admit Miao-Tam critical metrics. Finally, it is proved that a compact hypersurface of a complex Euclidean space admitting Miao-Tam critical metric with ${\lambda}$ > 0 or ${\lambda}$ < 0 is a sphere and a compact hypersurface of a non-flat complex space form does not exist such a critical metric.

• Journal of applied mathematics & informatics
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• v.24 no.1_2
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• pp.541-545
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• 2007

In this paper, we study the infinitesimal transformation on the fibred Riemannian space. The conharmonic curvature tensor is invariant under the conharmonic transformation. We have proved that the conharmonically flat fibred Riemannian space with totally geodesic fibre is locally the Riemannian product of the base space and a fibre.

• Communications of the Korean Mathematical Society
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• v.17 no.1
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• pp.57-69
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• 2002

We study a unifying method to obtain nondegenerate isometric immersions of manifolds of constant sectional curvatures c with flat normal bundles into the space forms of curvature c for c= -1,0,1.

• Communications of the Korean Mathematical Society
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• v.11 no.2
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• pp.407-413
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• 1996

The $(\alpha, \beta)$-metric is a Finsler metric which is constructed from a Riemannian metric $\alpha$ and a differential 1-form $\Beta$; it has been sometimes treat in theoretical physics. In particular, the projective flatness of Finsler space with a metric $L^2 = 2\alpha\beta$ is considered in detail.

• East Asian mathematical journal
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• v.19 no.2
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• pp.261-271
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• 2003

We deal with two metrics of Randers type, which are characterized by the solution of certain differential equations respectively. Furthermore, we will give the condition for a Finsler space with such a metric to be a locally Minkowski space or a conformally flat space, respectively.