• 천문학회지
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• 제34권4호
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• pp.285-287
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• 2001

We have studied the nonlinear evolution of a magnetized disk of isothermal gas, which is sustained by its self-gravity. Our objective is to investigate how the Jeans, Parker, and convective instabilities compete with each other in structuring/de-structuring large scale condensations in such disk. The Poisson equation for the self-gravity has been solved with a fourth-order accurate Fourier method along with the Green function, and the MHD part has been handled by an isothermal TVD code. When large wavelength perturbations are applied, the combined action of the Jeans and Parker instabilities suppresses the development of the convection and forms a dense core of prolate shape in the mid-plane. Peripheral structures around it are filamentary. The low density filaments connect the dense core to the diffuse upper region. On the other hand, when small wavelength perturbations are applied, the disk develops into an equilibrium state which is reminiscent of the Mouschovias's 2-D non-linear equilibrium of the classical Parker instability under an externally given gravity.

• 천문학회지
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• 제37권4호
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• pp.249-255
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• 2004

Here we present a linear stability analysis and an MHD 2D model for the Parker-Jeans instability in the Galactic gaseous disk. The magnetic field is assumed parallel to a Galactic spiral arm, and the gaseous disk is modelled as a multi-component, magnetized, and isothermal gas layer. The model employs the observed vertical stratifications for the gas density and the gravitational acceleration in the Solar neighborhood, and the self-gravity of the gas is also included. By solving Poisson's equation for the gas density stratification, we determine the vertical acceleration due to self-gravity as a function of z. Subtracting it from the observed gravitational acceleration, we separate the total acceleration into self and external gravities. The linear stability analysis provides the corresponding dispersion relations. The time and length scales of the fastest growing mode of the Parker-Jeans instability are about 40 Myr and 3.3 kpc, respectively. In order to confirm the linear stability analysis, we have performed two-dimensional MHD simulations. These show that the Parker-Jeans instability under the self and external gravities evolves into a quasi-equilibrium state, creating condensations on the northern and southern sides of the plane, in an alternate manner.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2004년도 한국우주과학회보 제13권2호
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• pp.290-292
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• 2004

Near-IR observations of the central few parsecs of our Galaxy from the HST/NICMOS have been analyzed to produce H, K photometry. We have cross-identified our photometry with the Keck high-resolution spectrometry of the central 0.5 pc of our galaxy to distinguish evolved late-type stars from early-type stars, and use late-type stars as tracer population. We perform several statistical tests to find the best fitting parameters of stellar density distribution and velocity dispersion models, then derive volume number densities and velocity dispersions. The volume number density distribution has power law index $1.55\~1.7$. We then derive the mass distribution in the Central region of our Galaxy using the Jeans equation.

• 천문학회보
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• 제36권2호
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• pp.111.2-111.2
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• 2011

While many astrophysical disks are vertically stratified and obey a polytropic equation of state, most studies on gravitational instability (GI) of flattened systems consider isothermal, razor-thin disks by taking vertical averages of disk properties. We investigate local GI of rotating pressure-confined polytropic disks with resolved vertical stratification by performing linear stability analysis. We find that the GI of vertically-stratified disks is in general a combination of conventional razor-thin Jeans modes and incompressible modes. The incompressible modes that dominate in the limit of the maximal disk compression require surface distortion and are an unstable version of terrestrial water waves. Disks with a steeper equation of state are found to be more Jeans unstable because they tend to have a smaller vertical scale height as well as a steeper temperature gradient corresponding to lower pressure support. GI depends more sensitively on the vertical temperature than density distribution. The density-weighted, harmonic mean, rather than the simple mean, of the adiabatic sound speed well describes the dispersion relation of horizontal modes, and thus is appropriate in the expression for Toomre Q stability parameter of razor-thin disks. We generalize Q into vertically-stratified disks, and discuss astrophysical application of our work.

• 한국의류학회지
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• 제26권5호
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• pp.606-617
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• 2002

The purpose of this study is to develop a decision model that helps manufacturers and retailers determine the optimal timing of markdown in order to maximize their profit. An optimal timing decision model was developed based on three steps; conjoint measurement, scenario analysis and simulation. Data were collected from the sample of 149 out of 170 undergraduate and graduate students in Seoul in 1997. From the Jeans market, 8 brands; Levi's, lee, Guess, Calvin Klein, Pintos, Get used, MFG, and Basic, were selected as competitors for this study. In the conjoint measurement, respondents estimated the level of preference, from 1 to 100, for each item in which brand, price, style, and colors were used to explain product characteristics. Then, in order to reflect competitive situation in Jeans market, four types of scenarios were developed. In each scenario, simulations were applied to decide optimal timing of markdowns that leads to maximal profitability and sales volume. The profit was calculated based on the equation; Profit = Jean's market volume x market share of each brand - cost, where market volume was obtained by integral calculus for market utility function, and market share by logit value of part-worth from the conjoint analysis. For the purpose of the parsimony of the research, costs and the level of markdown were fixed to 30% of the regular price. In results, the optimal timing decision model identified 3 different types of brands. The brands that do not need to take markdown were Ievi's, MFG, and Basic Jeans characterized by the highest brand power and the highest price zone. The brands that needed to take early markdowns were Guess, Lee, Calvin Klein, and Get Used with the intermediate level of brand power and price. The brand that need late markdown was Pintos with the weakest brand power among the competitors and the lowest price. The optimal range of markdown remains for further research.

• 천문학회지
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• 제42권2호
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• pp.17-26
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• 2009

We estimate the enclosed mass profile in the central 10 pc of the Milky Way by analyzing the infrared photometry and the velocity observations of dynamically relaxed stellar population in the Galactic center. HST/NICMOS and Gemini Adaptive Optics images in the archive are used to obtain the number density profile, and proper motion and radial velocity data were compiled from the literature to find the velocity dispersion profile assuming a spherical symmetry and velocity isotropy. From these data, we calculate the the enclosed mass and density profiles in the central 10 pc of the Galaxy using the Jeans equation. Our improved estimates can better describe the exact evolution of the molecular clouds and star clusters falling down to the Galactic center, and constrain the star formation history of the inner part of the Galaxy.

• 마케팅과학연구
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• 제20권1호
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• pp.98-109
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• 2010

对于品牌资产的组成, 测量和管理的研究开始于David A.Aaker (1991) 和Kevin Lane Keller(1993). 最近, 很多的研究都集中于品牌资产的组成: 品牌意识, 质量预期, 产品形象和品牌忠诚度. 本文主要针对于这些成分间相互关系, 而且特别主意产品种类(实用或者享受)的调节作用. 基于以上所提及的关系所建立的模型可以参看图1. 本文的假设如下: 顾客的品牌意识对于顾客的忠诚度和品牌形象有积极的影响; 顾客的质量预期对于品牌忠诚度和品牌形象有积极的影响; 品牌形象对于品牌忠诚度有积极影响; 这些品牌资产成分间的关系可以被产品种类所调节. 具体说明就是, 对于实用性产品, 质量预期对于品牌忠诚度的作用会增强, 而对于享受产品品牌形象对于品牌忠诚度的作用会更强. 为了确定适用于本研究的产品, 58名首尔的大学生参加了前测. 结果是计算机被选择成为实用性产品, 而牛仔裤被选定成为享受产品. 每一种产品各选择了两个品牌: 三星和惠普以及李维斯和NIX. 在研究中, 首尔地区的237名大学生回答了问卷. 研究对象被划分为两组: 一组(121名)回答关于计算机的问卷, 其他的116名回答关于牛仔裤的问卷. 搜集的数据通过AMOS 7来验证可信度, 效度以及变量间的相互关系. 验证性因子分析证明本研究的模型是可以用来进一步研究的. 品牌资产成分间的相互关系也通过AMOS 7 来验证. 结果模型的结果展现在图2中. 质量预期对于品牌的形象有积极的影响, 但是品牌意识却没有. 但是品牌意识, 质量预期, 以及品牌形象都对品牌忠诚度有积极的影响. 并且, 这些关系受到产品种类的调节. 本文的研究结果可以增进我们对于品牌资产成分间相互关系的了解, 并且可以支撑对于品牌资产的测量. 本文也对于产品种类的作用进行了阐述. 在现实的营销管理中, 这些结果可以提供一些建议来有效保持品牌资产.

• 마케팅과학연구
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• 제18권4호
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• pp.245-276
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• 2008

본 연구는 상표자산의 구성요소에 대한 선행요인을 분석하고 이를 토대로 하여 상표자산 구성요소와 상표자산 영향요인간의 관계 그리고 상표자산 구성요소와 구매의도간의 관계를 규명하고 한국과 영국을 중심으로 비교하여 상표자산관리 방안을 도출해보고자 하였다. 연구결과, 정보탐색은 제품지식에 정(+)의 영향을 미치며, 상표태도와 상표지식은 상표 충성도와 상표 가치에 정(+)의 영향을 미치는 것으로 나타났다. 그리고 상표충성도와 상표가치는 구매의도에 정(+)의 영향을 미치는 것으로 나타났다. 정보원천의 경우, 한국에서는 제품지식에 정(+)의 영향을 미치고 있는 반면, 영국에서는 영향을 미치지 않는 것으로 나타났다.