• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.3
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• pp.21-28
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• 2009

The precise analysis of soil-pile-structure interaction requires a proper description of soil layer, pile, and structure. In commonly used finite element simulations, mesh boundaries should match the material discontinuity line. However, in practice, the geometry of soil profiles and piles may be so complex that mesh alignment becomes a wasteful and difficult task. To overcome these difficulties, a different integration method is adopted in this paper, which enables easy integration over a regular element with material discontinuity regardless of the location of the discontinuity line. By applying this integration method, the mesh can be generated rapidly and in a highly structured manner, leading to a very regular stiffness matrix. The influence of the shape of the soil profile and piles on the response is examined, and the validity of the proposed soil-pile structure interaction analysis method is demonstrated through several examples. It is seen that the proposed analysis method can be easily used on soil-pile-structure interaction problems with complex interfaces between materials to produce reliable results regardless of the material discontinuity line.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.380-380
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• 2010

Currently, organic light-emitting diodes (OLEDs) have been proven of their readiness for commercialization in terms of lifetime and efficiency. In accordance with emerging new technologies, enhancement of light efficiency and extension of application fields are required. Particularly inverted structures, in which electron injection occurs at bottom and hole injection on top, show crucial advantages due to their easy integration with Si-based driving circuits for active matrix OLED as well as large open area for brighter illumination. In order to get better performance and process reliability, usually a proper buffer layer for carrier injection is needed. In inverted top emission OLED, the buffer layer should protect underlying organic materials against destructive particles during the electrode deposition, in addition to increasing their efficiency by reducing carrier injection barrier. For hole injection layers, there are several requirements for the buffer layer, such as high transparency, high work function, and reasonable electrical conductivity. As a buffer material, a few kinds of transition metal oxides for inverted OLED applications have been successfully utilized aiming at efficient hole injection properties. Among them, we chose 2 nm of $WO_3$ between NPB [N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine] and Au (or Al) films. The interfacial energy-level alignment and chemical reaction as a function of film coverage have been measured by using in-situ ultraviolet and X-ray photoelectron spectroscopy. It turned out that the $WO_3$ interlayer substantially reduces the hole injection barrier irrespective of the kind of electrode metals. It also avoids direct chemical interaction between NPB and metal atoms. This observation clearly validates the use of $WO_3$ interlayer as hole injection for inverted OLED applications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.4
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• pp.1042-1058
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• 2024

Terahertz (THz) communication is becoming a key technology for future 6G wireless networks because of its ultra-wide band. However, the implementation of THz communication systems confronts formidable challenges, notably beam splitting effects and high computational complexity associated with them. Our primary objective is to design a hybrid precoder that minimizes the Euclidean distance from the fully digital precoder. The analog precoding part adopts the delay-phase alternating minimization (DP-AltMin) algorithm, which divides the analog precoder into phase shifters and time delayers. This effectively addresses the beam splitting effects within THz communication by incorporating time delays. The traditional digital precoding solution, however, needs matrix inversion in THz massive multiple-input multiple-output (MIMO) communication systems, resulting in significant computational complexity and complicating the design of the analog precoder. To address this issue, we exploit the characteristics of THz massive MIMO communication systems and construct the digital precoder as a product of scale factors and semi-unitary matrices. We utilize Schatten norm and Hölder's inequality to create semi-unitary matrices after initializing the scale factors depending on the power allocation. Finally, the analog precoder and digital precoder are alternately optimized to obtain the ultimate hybrid precoding scheme. Extensive numerical simulations have demonstrated that our proposed algorithm outperforms existing methods in mitigating the beam splitting issue, improving system performance, and exhibiting lower complexity. Furthermore, our approach exhibits a more favorable alignment with practical application requirements, underlying its practicality and efficiency.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.305-305
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• 2011

Type-II 반도체 나노 구조는 그것의 band alignment 특성으로 인해 광학 소자에 다양한 응용성을 가진다. 특히, 대표적인 Type-II 반도체 나노 구조인 InSb/InAs 양자점의 경우, 약 3~5 ${\mu}m$의 mid-infrared 영역의 spectral range를 가지므로, 장파장을 요하는 소자에 유용하게 적용될 수 있다. 또한, Type-II 반도체 나노 구조의 밴드 구조를 staggered gap 혹은 broken gap 구조로 조절함으로써 infrared 영역 광소자의 전자 구조를 유용하게 바꾸어 적용할 수 있다. 최근, GaSb wafer 위에 InSb/InAsSb 양자점을 이용하여 cutoff wavelength를 6 ${\mu}m$까지 연장한 IR photodetector의 연구도 보고되고 있다. 하지만, GaSb wafer의 경우 그것의 비용 문제로 인해 산업적 적용이 쉽지 않다는 문제가 있다. 이러한 문제를 해결하기 위해 GaAs wafer와 같은 비용 효율이 높은 wafer를 사용한 연구가 필요할 것이다. 본 연구에서는 Molecular Beam Epitaxy(MBE)를 이용하여 undoped InAs wafer 와 semi-insulating GaAs wafer 상에 InSb 양자 구조를 형성한 결과를 보고한다. InSb 양자 구조는 20층 이상의 다층으로 형성되었고, 두 가지 경우 모두 400${\AA}$ spacer를 사용하였다. 단, InAs wafer 위에 형성한 InSb 양자 구조의 경우 InAs spacer를, GaAs wafer 위에 형성한 양자 구조의 경우 InAsSb spacer를 사용하였다. GaAs wafer 위에 양자 구조를 형성한 경우, InSb 물질과의 큰 lattice mismatch 차이 완화 뿐 아니라, type-II 밴드 구조 형성을 위해 1 ${\mu}m$ AlSb 층과 1 ${\mu}m$ InAsSb 층을 GaAs wafer 위에 미리 형성해 주었다. 양자 구조 형성 방법도 두 종류 wafer 상에서 다르게 적용되었다. InAs wafer 상에는 주로 일반적인 S-K 형성 방식이 적용된 것에 반해, GaAs wafer 상에는 migration enhanced 방식에 의해 양자 구조가 형성되었다. 이처럼 각 웨이퍼에 대해 다른 성장 방식이 적용된 이유는 InAsSb matrix와 InSb 물질 간의 lattice mismatch 차이가 6%를 넘지 못하여 InAs matrix에 비해 원하는 양자 구조 형성이 쉽지 않기 때문이다. 두 가지 경우에 대해 AFM과 TEM 측정으로 그 구조적 특성이 관찰되었다. 또한 infrared 영역의 소자 적용 가능성을 보기 위해 광학적 특성 측정이 요구된다.

• Management & Information Systems Review
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• v.32 no.4
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• pp.189-207
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• 2013

Using high-frequency data for 2 years, this study investigates intraday lead-lag relationship between stock index and stock index futures markets in Korea and China. We found that there are some differences in price discovery and volatility transmission between Korea and China after the stock index futures markets was introduced. Following Stoll-Whaley(1990) and Chan(1992), the multiple regression is estimated to examine the lead-lag patterns between the two markets by Newey-West's(1987) heteroskedasticity and autocorrelation consistent covariance matrix(HAC matrix). Empirical results of KOSPI 200 shows that the futures market leads the cash market and weak evidence that the cash market leads the futures market. New market information disseminates in the futures market before the stock market with index arbitrageurs then stepping in quickly to bring the cost-of-carry relation back into alignment. The regression tests for the conditional volatility which is estimated using EGARCH model do not show that there is a clear pattern of the futures market leading the stock market in terms of the volatility even though controlling nonsynchronous trading effects. This implies that information in price innovations that originate in the futures market is transmitted to the volatility of the cash market. Empirical results of CSI 300 shows that the cash market is found to play a more dominant role in the price discovery process after the Chinese index started a sharp decline immediately after the stock index futures were introduced. The new stock index futures markets does not function well in its price discovery performance at its infancy stage, apparently due to high barriers to entry into this emerging futures markets. Based on EGAECH model, the results uncover strong bi-directional dependence in the intraday volatility of both markets.

• Journal of Physiology & Pathology in Korean Medicine
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• v.19 no.1
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• pp.92-97
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• 2005

Inhibition of inflammatory response, acceleration of basal cell growth, and balanced synthesis of extracellular matrix (ECM) are important in healing of cutaneous open wounds. In order to evaluate the healing effects of water extracts of Radix Astragali (the root of Astragalus membranaceus (Fisch.)) on open wound at early stage, the experimental open wounds were generated on the dorsal sides of SD rats under anesthesia. The boiled-water extracts of Radix Astragali $(100{\mu}l)$, soaked into an occlusive film dressing were applied once a day for eleven consecutive days. The healing process was assessed by measuring macroscopic appearance and wound areas of the open wounds. The molecular aspects of healing process by Radix Astragali extracts were also investigated by Hematoxylin-Eosin (H-E) double staining and immunohistological staining of collagen type I in the healed skin area, implying cell density and linear alignment of the granulation tissue, and ECM synthesis and its remodeling, respectively. The Astragali radix extracts were found to significantly accelerate the cutaneous wound healing by suppressing the inflammation and stimulating the basal cell growth in wounded area, as compared to epidermal growth factor (EGF).

• Membrane Journal
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• v.28 no.1
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• pp.75-82
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• 2018

Forward osmosis (FO) desalination system has been highlighted to improve the energy efficiency and drive down the carbon footprint of current reverse osmosis (RO) desalination technology. To improve the trade-off between water flux and salt rejection of thin film composite (TFC) desalination membrane, thin film nanocomposite membranes (TFN), in which nanomaterials as a filler are embeded within a polymeric matrix, are being explored to tailor the separation performance and add new functionality to membranes for water purification applications. The objective of this article is to develop a graphene nanocomposite membrane with high performance of water selective permeability (high water flux, high salt rejection, and low reverse solute diffusion) as a next-generation FO desalination membrane. For advances in fabrication of graphene oxide (GO) membranes, layer-by-layer (LBL) technique was used to control the desirable structure, alignment, and chemical functionality that can lead to ultrahigh-permeability membranes due to highly selective transport of water molecules. In this study, the GO nanocomposite membrane fabricated by LBL dip coating method showed high water flux ($J_w/{\Delta}{\pi}=2.51LMH/bar$), water selectivity ($J_w/J_s=8.3L/g$), and salt rejection (99.5%) as well as high stability in aqueous solution and under FO operation condition.

• Polymer(Korea)
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• v.30 no.5
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• pp.385-390
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• 2006

In this work, the effect of carbon nanofiber (CNF) on thermal properties, and friction and wear behavior of CNF/PMMA composites were examined. While thermal properties of the composites were investigated with differential scanning calorimetry, thermograyimetric analyzer, and dynamic mechanical analyzer friction and wear behaviors were examined using a friction and wear tester. The glass transition temperature (Tg), integral procedural decomposition temperature (IPDT), storage modulus (E'), and tan ${\delta}$ appeared at higher temperatures with increasing CNF content, which were probably attributed to the presence of strong interactions between the carbonaceous fillers and the PMMA resins matrix. The wear loss in the composites decreased at 0.1 wt% CNF and then increased with 5-10 wt% CNF content. This was due to the existence of large aspect ratio CNF in PMMA which led to an alignment of PMMA chains and an increase of mechanical interlocking, resulting in the formation of crosslinked structures between CNF and PMMA in the composite.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.4
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• pp.341-350
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• 2023

The templated grain growth (TGG) method has gained significant attention for its ability to produce highly textured piezoelectric ceramics with significantly enhanced performance, making it a promising method for transducer and actuator applications. However, the texturing process using the TGG method requires the optimization of multiple steps, which can be challenging for beginners in this field. Therefore, in this tutorial, we provide an overview of the TGG method mainly based on our previous published works, including its various processing steps such as synthesizing anisotropic-shaped templates with size and size distribution control using the molten salt synthesis technique, tape casting, and identifying key factors for proper alignment of the templates in the target matrix system. Our goal is to provide a resource that can serve as a basic reference for researchers and engineers looking to improve their understanding and utilization of the TGG method for producing textured piezoelectric ceramics.

• Asia pacific journal of information systems
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• v.19 no.3
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• pp.99-124
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• 2009

Many firms in Korea have adopted and used advanced information technology in an effort to boost efficiency. The process of adapting to the new technology, at the same time, can vary from one firm to another. As such, this research focuses on several relevant factors, especially the roles of social interaction as a key variable that influences the technology adaptation process and the outcomes. Thus far, how a firm goes through the adaptation process to the new technology has not been yet fully explored. Previous studies on changes undergone by a firm or an organization due to information technology have been pursued from various theoretical points of views, evolved from technological and institutional views to an integrated social technology views. The technology adaptation process has been understood to be something that evolves over time and has been regarded as cycles between misalignments and alignments, gradually approaching the stable aligned state. The adaptation process of the new technology was defined as "appropriation" process according to Poole and DeSanctis (1994). They suggested that this process is not automatically determined by the technology design itself. Rather, people actively select how technology structures should be used; accordingly, adoption practices vary. But concepts of the appropriation process in these studies are not accurate while suggested propositions are not clear enough to apply in practice. Furthermore, these studies do not substantially suggest which factors are changed during the appropriation process and what should be done to bring about effective outcomes. Therefore, research objectives of this study lie in finding causes for the difference in ways in which advanced information technology has been used and adopted among organizations. The study also aims to explore how a firm's interaction with social as well as technological factors affects differently in resulting organizational changes. Detail objectives of this study are as follows. First, this paper primarily focuses on the appropriation process of advanced information technology in the long run, and we look into reasons for the diverse types of the usage. Second, this study is to categorize each phases in the appropriation process and make clear what changes occur and how they are evolved during each phase. Third, this study is to suggest the guidelines to determine which strategies are needed in an individual, group and organizational level. For this, a substantially grounded theory that can be applied to organizational practice has been developed from a longitudinal comparative case study. For these objectives, the technology appropriation process was explored based on Structuration Theory by Giddens (1984), Orlikoski and Robey (1991) and Adaptive Structuration Theory by Poole and DeSanctis (1994), which are examples of social technology views on organizational change by technology. Data have been obtained from interviews, observations of medical treatment task, and questionnaires administered to group members who use the technology. Data coding was executed in three steps following the grounded theory approach. First of all, concepts and categories were developed from interviews and observation data in open coding. Next, in axial coding, we related categories to subcategorize along the lines of their properties and dimensions through the paradigm model. Finally, the grounded theory about the appropriation process was developed through the conditional/consequential matrix in selective coding. In this study eight hypotheses about the adaptation process have been clearly articulated. Also, we found that the appropriation process involves through three phases, namely, "direct appropriation," "cooperate with related structures," and "interpret and make judgments." The higher phases of appropriation move, the more users represent various types of instrumental use and attitude. Moreover, the previous structures like "knowledge and experience," "belief that other members know and accept the use of technology," "horizontal communication," and "embodiment of opinion collection process" are evolved to higher degrees in their dimensions of property. Furthermore, users continuously create new spirits and structures, while removing some of the previous ones at the same time. Thus, from longitudinal view, faithful and unfaithful appropriation methods appear recursively, but gradually faithful appropriation takes over the other. In other words, the concept of spirits and structures has been changed in the adaptation process over time for the purpose of alignment between the task and other structures. These findings call for a revised or extended model of structural adaptation in IS (Information Systems) literature now that the vague adaptation process in previous studies has been clarified through the in-depth qualitative study, identifying each phrase with accuracy. In addition, based on these results some guidelines can be set up to help determine which strategies are needed in an individual, group, and organizational level for the purpose of effective technology appropriation. In practice, managers can focus on the changes of spirits and elevation of the structural dimension to achieve effective technology use.