• 경영과정보연구
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• 제31권2호
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• pp.61-87
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• 2012

조직 구성원들은 자신의 가치와 조직의 성과를 높이기 위해 인적자본의 향상을 위한 노력뿐만 아니라 사회적 자본의 확충을 위해서 많은 노력을 하고 있는 추세이다. 이에 따라 본 연구의 목적은 조직 구성원 개인의 사적인 인맥으로 구성된 개인적 친밀네트워크가 성과에 어떠한 영향을 미치는 가에 대하여 검증하는 것이다. 본 연구에서 독립변수로 개인의 친밀 네트워크 특성을, 결과변수로 직무성과와 네트워크에의 협력의도로 설정하여 검증하였다. 본 연구에서 개인적 친밀네트워크가 개인성과에 미치는 영향을 분석한 결과 사회적 네트워크의 특성 중 크기, 강도, 지위가 협력행동에 긍정적인 영향을 미치는 것으로 나타났으며 직무성과에는 크기와 강도만 유의미한 영향을 미치는 것으로 나타났다.

• 한국초전도ㆍ저온공학회논문지
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• 제15권2호
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• pp.20-23
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• 2013

For sensitive measurements of micro-Tesla nuclear magnetic resonance (${\mu}T$-NMR) signal, a low-noise superconducting quantum interference device (SQUID) system is needed. We have fabricated a liquid He dewar for an SQUID having a large diameter for the pickup coil. The initial test of the SQUID system showed much higher low-frequency magnetic noise caused by the thermal magnetic noise of the aluminum plates used for the vapor-cooled thermal shield material. The frequency dependence of the noise spectrum showed that the noise increases with the decrease of frequency. This behavior could be explained from a two-layer model; one generating the thermal noise and the other one shielding the thermal noise by eddy-current shielding. And the eddy-current shielding effect is strongly dependent on the frequency through the skin-depth. To minimize the loop size for the fluctuating thermal noise current, we changed the thermal shield material into insulated thin Cu mesh. The magnetic noise of the SQUID system became flat down to 0.1 Hz with a white noise of 0.3 $fT/{\surd}Hz$, including the other noise contributions such as SQUID electronics and magnetically shielded room, etc, which is acceptable for low-noise ${\mu}T$-NMR experiments.

• 경영과학
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• 제32권2호
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• pp.91-109
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• 2015

The M&A of firms has been emerged as the effective means of fast diversification and growth in dynamic environment. However, the empirical research about M&A in Korea has not been implemented rich due to the difficulty of obtaining M&A data. In this research, we empirically investigate the relationships among M&A, environment and firms' performance focused on Korean manufacturing firms, understanding the current practice of M&A in Korea. We use the Manufacturing Productivity Panel Survey Data, which are collected by Korea Productivity Center in 2013. The sample size is 575 and the sample is divided into M&A group and non-M&A group. We conduct logit analysis with the independent variables of environment factors (munificence, dynamic, uncertainty), and firms' performance (sales growth, ROS, labor productivity and Inventory turnover), and dependent variable of M&A group or non M&A group. The results show that M&A is closely related to environment feature and firm performance: M&A firms are likely to be the higher munificence and dynamic and the lower sales growth and higher profitability than non-M&A group. In addition, we also examine the characteristics of firms by M&A types (competitors, customer/supplier and firms from unrelated industry). These results imply that if firms confront the pressure of uncertainty (dynamic) and the lower growth, they tend to choose M&A. Futhermore, to profoundly understand the behavior of firms about M&A, it is required to classify the M&A firms by merge types.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1831-1843
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• 2001

In this study, convective boiling tests were conducted for enhanced tube bundles. The surface geometry consists of pores and connecting gaps. Tubes with three different pore sizes (d$_{p}$ = 0.20, 0.23 and 0.27 mm) were tested using R-123 and R-l34a for the following range: 8 kg/m$^2$s G 26 kg/m$^2$s, 10 kW/m$^2$ q0 40 kW/m$^2$and 0.1 $\chi$ 0.9. The convective boiling heat transfer coefficients were strongly dependent on heat flux with negligible dependency on mass flux or quality. For the present enhanced geometry (pores and gaps), the convective effect was apparent. The gaps of the present tubes may have served routes for the passage of two-phase mixtures, and enhanced the boiling heat transfer. The convective effect was more pronounced at a higher saturation temperature. More bubbles will be generated at a higher saturation temperature, which will lead to enhanced convective contribution. The pore size where the maximum heat transfer coefficient was obtained was larger for R-l34a (d$_{p}$ = 0.27 mm) compared with that for R-123 (d$_{p}$ = 0.23 mm). This trend was consistent with the previous pool boiling results. For the enhanced tube bundles, the convective effect was more pronounced for R-134a than for R-123. This trend was reversed for the smooth tube bundle. Possible reasoning is provided based on the bubble behavior on the tube wall. Both the modified Chen and the asymptotic model predicted the present data reasonably well. The RMSEs were 14.3% for the modified Chen model and 12.7% for the asymptotic model.model.

• 한국진공학회지
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• 제16권4호
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• pp.298-304
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• 2007

rf 플라즈마 소스가 장착된 분자선 에피택시 장비를 이용하여 Si(111) 기판위에 GaN 나노로드를 성장할 때, N2의 흐름양을 조절하여 나노로드의 구조 및 광학적인 특성을 조사하였다. $N_2$의 양이 1.1sccm에서 2.0sccm으로 변할 때 육각형 모양의 나노로드가 성장되었으며, 평균 직경이 80nm에서 190nm 까지 변화 하였다. 그러나 나노로드와 compact한 영역의 길이 (두께)비는 $N_2$의 양이 1.7sccm 까지는 증가하지만 그 이상에서는 변화지 않았다. PL 측정으로부터, $N_2$의 양이 적은 나노로드에서 자유 엑시톤의 피이크가 더욱 뚜렷하게 관측되었고, 모든 PL 피이크의 위치는 직경이 적을수록 나노로드의 크기 효과에 의해서 고에너지 쪽으로 이동하였다. $N_2$의 양이 1.7sccm 인 시료에서는 온도에 따른 PL의 피이크의 위치가 온도가 증가함에 따라서 "S-형"의 거동을 나타내었다.

• Computers and Concrete
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• 제26권1호
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• pp.75-94
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• 2020

The aim of this research is to investigate free vibration of a novel five layer Timoshenko microbeam which consists of a transversely flexible porous core made of Al-foam, two graphen platelets (GPL) nanocomposite reinforced layers to enhance the mechanical behavior of the structure as well as two piezo-magneto-electric face sheets layers. This microbeam is subjected to a thermal load and resting on Pasternak's foundation. To accomplish the analysis, constitutive equations of each layer are derived by means of nonlocal strain gradient theory (NSGT) to capture size dependent effects. Then, the Hamilton's principle is employed to obtain the equations of motion for five layer Timoshenko microbeam. They are subsequently solved analytically by applying Navier's method so that discretized governing equations are determined in form of dynamic matrix giving the possibility to gain the natural frequencies of the Timoshenko microbeam. Eventually, after a validation study, the numerical results are presented to study and discuss the influences of various parameters such as nonlocal parameter, strain gradient parameter, aspect ratio, porosity, various volume fraction and distributions of graphene platelets, temperature change and elastic foundation coefficients on natural frequencies of the sandwich microbeam.

• 대한화학회지
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• 제34권3호
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• pp.267-279
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• 1990

Amberlite XAD-2 및 XAD-7 수지에 대한 페놀과 그 할로겐 일치환체들에 대한 흡착성을 분포계수를 측정하여 조사하였다. XAD 수지에 대한 페놀의 흡착은 Langmuir 등온흡착으로 설명될 수 있었으며, 이 때의 흡착은 분자의 크기에 따르는, 즉 분산상호작용에 기인하는 전형적인 물리흡착임을 알았다. 고분자 합성수지에 대한 페놀류의 흡착에너지는 Lennard-Jones potential로 계산하였다. 이 때 고분자 수지의 반지름은 수지의 최소기본단위의 van der Waals 부피로부터 계산하였으며 페놀류의 분자 반지름도 같은 방법으로 구하였다. 페놀유도체들의 흡착성은 각 수지에 대한 시료의 Stacking factor (F)-고분자 수지와 페놀류사이의 van der Waals 부피로부터 구한 평형거리의 보정인자-로부터 흡착에너지를 구하고 뱃치법으로 측정한 흡착엔탈피값과 비교함으로써 설명할 수 있었다. 각 수지에 대한 페놀이온의 흡착엔탈피는 쌍극자 작용력이나 하전-쌍극자 상호작용보다 분산상호작용이 주 요인인 것으로 나타났다.

• Smart Structures and Systems
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• 제20권6호
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• pp.709-728
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• 2017

This disquisition proposes a nonlocal strain gradient beam theory for thermo-mechanical dynamic characteristics of embedded smart shear deformable curved piezoelectric nanobeams made of porous electro-elastic functionally graded materials by using an analytical method. Electro-elastic properties of embedded curved porous FG nanobeam are assumed to be temperature-dependent and vary through the thickness direction of beam according to the power-law which is modified to approximate material properties for even distributions of porosities. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Since variation of pores along the thickness direction influences the mechanical and physical properties, so in this study thermo-mechanical vibration analysis of curve FG piezoelectric nanobeam by considering the effect of these imperfections is performed. Nonlocal strain gradient elasticity theory is utilized to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field. The governing equations and related boundary condition of embedded smart curved porous FG nanobeam subjected to thermal and electric field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved piezoelectric nanobeam resting on Winkler and Pasternak foundation. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, electric voltage, coefficient of porosity, elastic foundation parameters, thermal effect, gradient index, strain gradient, elastic opening angle and slenderness ratio on the natural frequency of embedded curved FG porous piezoelectric nanobeam are successfully discussed. It is concluded that these parameters play important roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• 대한조선학회논문집
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• 제53권2호
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• pp.85-91
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• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• 보건행정학회지
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• 제29권2호
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• pp.160-171
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• 2019

Background: This study purposed to compare the difference on medical utilization and health expenditure of baby boomer generation by depression between gender. Methods: Korea Welfare Panel Survey 2016, provided by the Korea Institute for Health and Social Affairs, was used for the analysis. For the research, we used the two-part model, yes or no of use (part 1), and frequency of use (part 2) for medical utilization. The dependent variables are the whether or not to use of hospitalization services, outpatient services, length of stay, outpatient service visits, and health expenditure. And the independent variables are used as the predisposing (education, spouse presence), enabling (insurance type, private insurance, economic activity, income), and need (chronic disease, self-rated health, disability) factors in the Andersen behavior model. Depression was used as intervening variables. Structural equation model and multiple group analysis by gender were used. Results: There were differences in the medical care usage and cost between men and women in baby boomer. For men, mediating effects of depression were present at the hospitalization (yes/no), length of stay, and health expenditure. On the other hand, for women, the mediating effect of depression was found only at the outpatient visits. Specially, depression was working at the medical services by the different way between gender. The size of effect (multiple group analysis) was affected by significant differences between men and women. Conclusion: This study found that the mediating effect of depression is increased medical usage and health expenditure and the effect factors are different by gender. Therefore, it is necessary to establish a medical care policy considering the socio-economic characteristics of baby boomers.