• Smart Structures and Systems
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• 제17권2호
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• pp.297-311
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• 2016

Based on the distributed fiber optic sensing (DFOS) technique, plastic optical fibers (POFs) are attractive candidates to measure deformations of geotechnical structures because they can withstand large strains before rupture. Understanding the mechanical interaction between an embedded POF and the surrounding soil or rock is a necessary step towards establishing an effective POF-based sensing system for geotechnical monitoring. This paper describes a first attempt to evaluate the feasibility of POF-based soil deformation monitoring considering the POF-soil interfacial properties. A series of pullout tests were performed under various confining pressures (CPs) on a jacketed polymethyl methacrylate (PMMA) POF embedded in soil specimens. The test results were interpreted using a fiber-soil interaction model, and were compared with previous test data of silica optical fibers (SOFs). The results showed that the range of CP in this study did not induce plastic deformation of the POF; therefore, the POF-soil and the SOF-soil interfaces had similar behavior. CP was found to play an important role in controlling the fiber-soil interfacial bond and the fiber measurement range. Moreover, an expression was formulated to determine whether a POF would undergo plastic deformation when measuring soil deformation. The plasticity of POF may influence the reliability of measurements, especially for monitored geo-structures whose deformation would alternately increase and decrease. Taken together, these results indicate that in terms of the interfacial parameters studied here the POF is feasible for monitoring soil deformation as long as the plastic deformation issue is carefully addressed.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.643-657
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• 2020

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

• 대한전자공학회논문지SD
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• 제41권8호
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• pp.1-8
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• 2004

두께가 3nm인 게이트 산화막을 사용한 n-MOSFET에 정전압 스트레스를 가하였을 때 관찰되는 SILC 및 soft breakdown 열화 및 이러한 열화가 소자 특성에 미치는 영향에 대해 실험하였다. 열화 현상은 인가되는 게이트 전압의 극성에 따라 그 특성이 다르게 나타났다. 게이트 전압이 (-)일 때 열화는 계면 및 산화막내 전하 결함에 의해 발생되었지만, 게이트 전압이 (＋)일 때는 열화는 주로 계면 결함에 의해 발생되었다. 또한 이러한 결함의 생성은 Si-H 결합의 파괴에 의해 발생할 수 있다는 것을 중수소 열처리 및 추가 수소 열처리 실험으로부터 발견하였다. OFF 전류 및 여러 가지 MOSFET의 전기적 특성의 변화는 관찰된 결함 전하(charge-trapping)의 생성과 직접적인 관련이 있다. 그러므로 실험 결과들로부터 게이트 산화막으로 터널링되는 전자나 정공에 의한 Si 및 O의 결합 파괴가 게이트 산화막 열화의 원인이 된다고 판단된다. 이러한 물리적 해석은 기존의 Anode-Hole Injection 모델과 Hydrogen-Released 모델의 내용을 모두 포함하게 된다.

• Molecules and Cells
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• 제37권4호
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• pp.322-329
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• 2014

N-acetylglucosamine kinase (GlcNAc kinase or NAGK; EC 2.7.1.59) is highly expressed and plays a critical role in the development of dendrites in brain neurons. In this study, the authors conducted structure-function analysis to verify the previously proposed 3D model structure of GlcNAc/ATP-bound NAGK. Three point NAGK mutants with different substrate binding capacities and reaction velocities were produced. Wild-type (WT) NAGK showed strong substrate preference for GlcNAc. Conversion of Cys143, which does not make direct hydrogen bonds with GlcNAc, to Ser (i.e., C143S) had the least affect on the enzymatic activity of NAGK. Conversion of Asn36, which plays a role in domain closure by making a hydrogen bond with GlcNAc, to Ala (i.e., N36A) mildly reduced NAGK enzyme activity. Conversion of Asp107, which makes hydrogen bonds with GlcNAc and would act as a proton acceptor during nucleophilic attack on the ${\gamma}$-phosphate of ATP, to Ala (i.e., D107A), caused a total loss in enzyme activity. The overexpression of EGFP-tagged WT or any of the mutant NAGKs in rat hippocampal neurons (DIV 5-9) increased dendritic architectural complexity. Finally, the overexpression of the small, but not of the large, domain of NAGK resulted in dendrite degeneration. Our data show the effect of structure on the functional aspects of NAGK, and in particular, that the small domain of NAGK, and not its NAGK kinase activity, plays a critical role in the upregulation of dendritogenesis.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.4-5
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• 2010

The surface phonon is defined as a coherent vibrational excitation of surface atoms propagating along the surface. It is characterized by a phonon dispersion curves, which were extensively studied in 1990's using helium atom scattering and high-resolution electron-energy-loss spectroscopy (HREELS)[1].The understanding is mainly based on the theoretical framework of a classical bond model or cluster calculations. The recent sample preparation and first principles calculations open the naval way to deep insight for surface phonon problems. The surface phonon dispersion on the hydrogen-terminated Si(111)-($1{\times}1$) surface [H:Si(111)] is the typical system and already reported experimentally [2] and theoretically [3], although the understandingis incomplete. The sample contaminated by the oxygen atoms on the surface and the calculations were also classical. In this study, firstly, we have prepared an ultra-clean H:Si(111) surface [4] and measured the surface phonon dispersion curvesusing HREELS. Secondly, we have performed first-principles density functional calculations with the projector augmented wave functionals, as implemented in VASP, using generalized gradient approximations. We used aslab of six silicon layers and both top and bottom surfaces were terminated with hydrogen atoms. Finally, we have compared with the surface phonon dispersion of deuterium-terminatedSi(111)-($1{\times}1$) surface[5] and led to our conclusions. The Si-H stretching and the bending modes are observed at 258.5 and 78.2 meV, respectively. These energies are the same as the previously reported values [2], but the energy-loss peaks at the lower energy regions are dramatically shifted. Through this combination study, we have formulated the procedure of preparing ultra-clean H:Si(111)/D:Si(111), which was confirmed by HREELS vibrational analysis. The Si surface will be utilized for further nano-physics research as well as for the materials for nano-fubrication.

• Steel and Composite Structures
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• 제23권4호
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• pp.409-420
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• 2017

This paper theoretically studies the cyclic behavior of hybrid connections between steel coupling beams and concrete shear walls with embedded steel columns. Finite element models of connections with long and short embedded steel columns are built in ABAQUS and validated against the test results in the companion paper. Parametric studies are carried out using the validated FE model to determine the key influencing factors on the load-bearing capacity of connections. A close-form solution of the load-bearing capacity of connections is proposed by considering the contributions from the compressive strength of concrete at the interface between the embedded beam and concrete, shear yielding of column web in the tensile region, and shear capacity of column web and concrete in joint zone. The results show that the bond slip between embedded steel members and concrete should be considered which can be simulated by defining contact boundary conditions. It is found that the loadbearing capacity of connections strongly depends on the section height, flange width and web thickness of the embedded column. The accuracy of the proposed calculation method is validated against test results and also verified against FE results (with differences within 10%). It is recommended that embedded steel columns should be placed along the entire height of shear walls to facilitate construction and enhance the ductility. The thickness and section height of embedded columns should be increased to enhance the load-bearing capacity of connections. The stirrups in the joint zone should be strengthened and embedded columns with very small section height should be avoided.

• 한국학교보건학회지
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• 제24권2호
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• pp.199-209
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• 2011

Purpose: The aim of this study was to investigate the structural relationships between functional deficiency of Family and self-esteem, depression, suicidal inclination of adolescents. Methods: The data in this study came from the Korea Youth Panel Survey Data (N=3,449) for 2005~2007. To investigate the causal relationship between each variable presented in the research model, structural equation modeling (SEM) was carried out by using AMOS 7.0. And all data were analyzed by using SPSS/WIN 12.0. Results: The main analytical results of this study were as follows; First, the family function made a positive impact on the self-esteem of adolescents. Second, the severe functional deficiency in family appeared to have a negative effect on the suicidal inclination and depression of adolescents. Third, the higher the adolescents' self-esteem, the lower depression and suicidal ideation. Fourth, the more severe the depression, the higher occurrence of suicidal inclination. Conclusion: In conclusion, functional deficiency in adolescents' family impacted negatively on self-esteem, and this contributed to increased depression and anxiety, and to suicidal inclination finally. These findings confirmed that the strength of family function, the closeness with parents, forming a stable relationship and strength of the emotional bond are very important factors to form self-esteem and reduce depression and suicidal inclination.

• Structural Engineering and Mechanics
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• 제78권2호
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• pp.163-174
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• 2021

Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCST-bridge system.

• 한국프랜차이즈경영연구
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• 제7권1호
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• pp.13-20
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• 2016

Purpose - In the past, the chain hotel chefs only serve food to their customers. However recently, the hotel chefs play a pivotal role in hotel including considering various customer preferences, safety and nutrition of food, and increasing profits through effective human resource management and inventory control. With the change of the chain hotel chef's' roles, pygmalion leadership, one of new leadership styles, focuses on the effect that leader's positive expectation let subordinates have motivation and more engage in work. This study investigates the effect of chain hotel chef's pygmalion leadership on leader trust and organizational trust. Research design, data, and methodology - This study was to investigate the structural relationships among chain hotel restaurant chefs' pygmalion leadership, hotel restaurant cooks' leader trust, organizational trust, and teamwork, and how leader trust and organizational trust play mediating roles in the relationship between pygmalion leadership and teamwork. In this model, pygmalion leadership includes 4 dimensions: Climate, Feedback, Input, and Output. Data were collected using self-administered questionnaire survey on cooks of Deluxe hotel restaurants located in Seoul and Gyonggi-Do. The samples for data analyses were 243 excepting unusable responses. Result - The findings can be summarized as follows: First, climate and feedback had a positive effect on leader trust, respectively. Second, feedback and output had a statistically positive effect on organizational trust, respectively. Third, leader trust had positive effects on organizational trust and teamwork. Fourth, organizational trust had a significant effect on teamwork. Conclusions - As a chain hotel chef treats his/her staffs sincerely, they will be more engaged in work by establishing trust in their leader. Ultimately, it leads to higher sales profit and customer satisfaction. In addition, a hotel can encourage chefs and other staffs to treat each other as if the student-instructor relations, not just commanding staffs. Then, cooks build up their trust to their leader and organization for its sustained growth and development, and the internal bond in organization including teamwork is strengthened. Therefore, to strengthen teamwork and organizational trust, there should be active communication, knowledge sharing, goal sharing, and cooperation between chefs and cooks.

• 품질경영학회지
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• 제51권2호
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• pp.171-184
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• 2023

Purpose: First, this paper suggests an alternative approach to find optimal portfolio (stocks, bonds and ESG stocks) under the maximizing utility of investors. Second, we include ESG stocks in our optimal portfolio, and compare improvement of welfares in the case with and without ESG stocks in portfolio. Methods: Our main method of analysis follows Brennan et al(2002), designed under the continuous time framework. We assume that the dynamics of stock price follow the Geometric Brownian Motion (GBM) while the short rate have the Vasicek model. For the utility function of investors, we use the Power Utility Function, which commonly used in financial studies. The optimal portfolio and welfares are derived in the partial equilibrium. The parameters are estimated by using Kalman filter and ordinary least square method. Results: During the overall analysis period, the portfolio including ESG, did not show clear welfare improvement. In 2017, it has slightly exceeded this benchmark 1, showing the possibility of improvement, but the ESG stocks we selected have not strongly shown statistically significant welfare improvement results. This paper showed that the factors affecting optimal asset allocation and welfare improvement were different each other. We also found that the proportion of optimal asset allocation was affected by factors such as asset return, volatility, and inverse correlation between stocks and bonds, similar to traditional financial theory. Conclusion: The portfolio with ESG investment did not show significant results in welfare improvement is due to that 1) the KRX ESG Leaders 150 selected in our study is an index based on ESG integrated scores, which are designed to affect stability rather than profitability. And 2) Korea has a short history of ESG investment. During the limited analysis period, the performance of stock-related assets was inferior to bond assets at the time of the interest rate drop.