• 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.

• 한국심리학회지 : 문화 및 사회문제
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• 제28권3호
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• pp.373-392
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• 2022

본 연구는 Donnelly 등(2016)의 물질주의 추구에 대한 도피이론을 적용하여 대학생의 물질주의 추구 과정을 경험적으로 검증하였다. 도피이론에서 제시된 6단계 중 높은 삶의 기준에 비추어 자신의 부족함을 느끼는 1단계를 외적 자기가치 수반성으로, 부족한 자신을 비난하는 2단계를 실제-이상적 자기 간 불일치로, 자신을 혐오적으로 인식하는 3단계를 낮은 자존감 안정성으로 개념화하였다. 이상의 도피이론 3단계에 따라 외적 자기가치 수반성이 자기불일치와 자존감 안정성을 매개로 물질주의를 예측할 것으로 예상하였다. 가설 확인을 위해 대학생 465명(여 262명)을 대상으로 자기보고식 설문조사를 실시하고 구조방정식 모형을 통해 검증하였다. 연구 결과, 외적 자기가치 수반성과 물질주의 간 관계에서 자기 불일치의 매개효과 및 자기 불일치와 자존감 안정성의 순차적 매개효과가 유의하였다. 물질주의에 대한 외적 자기가치 수반성의 직접효과 또한 유의하게 나타났다. 이 연구는 능력주의 한국사회에서 대학생이 물질을 좇게 되는 과정을 도피이론을 적용하여 경험적으로 밝힌 의의가 있다.

• Advances in concrete construction
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• 제7권2호
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• pp.97-105
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• 2019

In this paper, the workability and static stability were evaluated using a proposed test method. Workability and static stability represent a key property of self-compacting concrete (SCC) in fresh state. A number of standardized test methods were developed to assess these properties. However, no accelerated test method reliably predicts both workability and static stability of SCC. In the present work, a modified K-slump test method was developed to evaluate workability and static stability of SCC. In order to take implicit mixture variations of SCC constituents that can affect fresh SCC properties, a central composite design was adopted to highlight the effect of gravel to sand ratio (G/S), gravel 3/8 to gravel 8/15 ratio (G1/G2), water to cement ratio (W/C), marble powder to cement ratio (MP/C) and superplasticizer content (SP) on workability measured with slump and flow time (T50) tests and static stability measured with sieve stability test (Pi), segregation test index (SSI), Penetration test (Pd) and the proposed K-slump test (Km). The obtained results show that G/S ratio close to 1 and G1/G2 ratio close to 60% can be considered as optimal values to achieve a good workability while ensuring a sufficient static stability of SCC. Acceptable relationships were obtained between Slump flow, Pi, Pd and Km. Results show that the proposed K-slump test allow to assess both workability and static stability of fresh SCC mixtures.

• 통합자연과학논문집
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• 제3권2호
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• pp.96-102
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• 2010

It is still controversial where the improved stability of n-octadecyltriethoxysilane self-assembled monolayer (OTE SAM) on plasma-pretreated mica surface exactly originates from. To date, it has been well known that the extensive cross-polymerization between silane headgroups is a crucial factor for the outstanding mechanical strength of the monolayer. However, this study directly observed that the stability comes not only from the cross-links but also, far more importantly, from the direct chemical bonds between silane headgroups and mica surface. To observe this phenomenon, n-octadecyltrichlorosilane monolayers were self-assembled on both untreated and plasma treated mica surfaces, and their adhesion properties at various stress conditions and force profiles in pure water were investigated and compared through the use of the surface forces apparatus technique. It revealed that, in pure water, there is a substantial difference of stability between untreated and plasma treated cases and the plasma treated surface is mechanically much more stable. In particular, the protrusion behavior of the monolayer during contact repetition experiment was always observed in the untreated case, but never in the plasma treated case. It directly demonstrates that the extensive chemical bonds indeed exist between silane head-groups and plasma treated mica surface and dramatically improve the mechanical stability of the OTE monolayer-coated mica substrate.

• 통합자연과학논문집
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• 제3권2호
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• pp.89-95
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• 2010

It is still controversial where the improved stability of n-octadecyltriethoxysilane self-assembled monolayer (OTE SAM) on plasma-pretreated mica surface exactly originates from. To date, it has been well known that the extensive cross-polymerization between silane head-groups is a crucial factor for the outstanding mechanical strength of the monolayer. However, this study clearly showed that the stability comes not only from the cross-links but also, far more importantly, from the direct chemical bonds between silane headgroups and mica surface. To examine this phenomenon, n-octadecyltrichlorosilane monolayers were self-assembled on both untreated and plasma treated mica surfaces, and their adhesion properties at various physical conditions (relative humidity, high stress, and contact repetition) were investigated and compared through the use of the surface forces apparatus technique. It revealed that, in highly humid conditions (>90%RH), there is a substantial difference of stability between untreated and plasma treated cases and the plasma treated surface is mechanically much more stable. It obviously proves that the extensive chemical bonds indeed exist between silane head-groups and plasma treated mica surface and dramatically improve the mechanical stability of the OTE monolayer-coated mica substrate.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.231-238
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• 2010

75톤급 기술검증용 연소기의 저압 조건 연소안정성 시험이 수행되었다. 동일한 추진제 유량을 연소실에 공급하면서 분사기 수량이 감소된 연소기 헤드의 경우 연소압력 30 bar에서 자발 불안정이 발생하였으나, 분사기 수량이 증가된 연소기 헤드에서는 동일한 연소압력 조건에서 고주파 연소안정성이 유지됨을 보였다. 30 bar에서 연소안정성을 보인 연소기 헤드는 연소압력 20 bar에서 자발 불안정이 발생하여 안정성 경계 영역을 보여주었다.

• 한국응급구조학회지
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• 제25권1호
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• pp.49-56
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• 2021

Purpose: This experimental study aimed to solve the problem of discomfort and stably fix the bandage. A new self-adhesive bandage was manufactured to reduce the inconveniences associated with the plaster bandage. We compared the associated stability between the plaster bandage and the new self-adhesive bandage. Methods: The traditional elastic bandage (traditional EB; i.e., plaster bandage) and modified elastic bandage (modified EB; i.e., new self-adhesive bandage) were applied to 30 people each. We measured the time of preparation and attachment for traditional TB and attachment for modified TB. A 4kg cattle bell was fixed to each bandage to compare their respective stability levels. Results: The speed for the traditional EB was 28.93(±9.28)sec (mean 25.56s) and 6.13(±1.81)sec for the modified EB (mean 5.95sec). The stability values were 1.49(±.77)min for the traditional EB (mean 1.31min) and 26.22(±9.04)min for modified EB (mean 1.31min). The differences in speed and stability were statistically significant. Conclusion: Compared to the traditional EB, applying the modified EB could solve the attachment inconvenience and provide stable maintenance.

• 제어로봇시스템학회논문지
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• 제5권2호
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• pp.189-199
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• 1999

This paper presents an optimization algorithm for a stable Self Dynamic Neural Network(SDNN) using genetic algorithm. Optimized SDNN is applied to a problem of controlling nonlinear dynamical systems. SDNN is dynamic mapping and is better suited for dynamical systems than static forward neural network. The real-time implementation is very important, and thus the neuro controller also needs to be designed such that it converges with a relatively small number of training cycles. SDW has considerably fewer weights than DNN. Since there is no interlink among the hidden layer. The object of proposed algorithm is that the number of self dynamic neuron node and the gradient of activation functions are simultaneously optimized by genetic algorithms. To guarantee convergence, an analytic method based on the Lyapunov function is used to find a stable learning for the SDNN. The ability and effectiveness of identifying and controlling a nonlinear dynamic system using the proposed optimized SDNN considering stability is demonstrated by case studies.

• 한국생활과학회지
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• 제12권3호
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• pp.275-286
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• 2003

The purposes of this study were to identify the relationship between children's personality traits and self-esteem, and to find out if there were any differences in the relationship patterns in terms of children's sex. The questionnaire were collected from 984 subjects in 5th grade of elementary schools located in cities of Seoul, Suwon, Daejeon, and Daegu. Results showed that personality factors such as stability, sociability, responsibility, and superiority had stronger correlations with self-esteem factors whereas masculinity, activity level, and reflectivity did so to a less degree. Children's personality factors such as superiority, sociability and responsibility were better predictors of their self-esteem factors such as scholastic competence, social acceptance and general self-worth. Girls showed higher level of stability, sociability, responsibility and superiority, however there was no sex difference in the self-esteem such as scholastic competence, social acceptance and general self-worth. Children's behavioral conduct were mainly explained by masculinity, activity level, and responsibility. Responsibility turned out to be the strongest predictor of behavioral conduct among boys, while the activity level did among girls.

• 대한가정학회지
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• 제44권12호
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• pp.53-64
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• 2006

The purpose of this study was to investigate the variables on employees' retirement expectations divided into imposed frustration, new beginning, transition to rest, and continuing. Independent variables were individual(gender, age, occupation, income, education, and health condition), psychological(self-esteem, locus of control, attitude of leisure, and attitude of family), and job-related variables(job attitude, job satisfaction, and job stability). In order to achieve this purpose, a survey was conducted with 515 employees from Daegu and Kyungpook. Retirement expectations were measured with questionnaire based on several studies. The data analyzed by frequency, percentage, mean, factor analysis, Cronbach's $\alpha$, correlation, and multiple regression. The major findings were as follows. First, imposed frustration was affected by income, self-esteem, locus of control, job satisfaction, job attitude, and job stability. Second, new beginning was affected by self-esteem, locus of control, attitude toward leisure and family, and job stability. Individual variables were not statistically significant predictors of new beginning. Third, transition to rest was affected by locus of control, attitude toward family, job satisfaction, job attitude, and job stability. Individual variables were not statistically significant predictors of transition to rest. Finally, continuing was affected by age, education, job satisfaction. Psychological variables were not statistically significant predictors of continuing.