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Department of PhysicsPolymeric materials have a wide range of scientific and technological applications especially in the field of nanoscience. For example, in the design of well-arranged nanostructures, block copolymers are popular for the control of various material properties because they can phase-separate and self-assemble into periodic structures on nanoscale due to the connectivity and incompatibility of the blocks. In past decades, the major principles of polymer physics have been established, and many theoretical tools investigating the polymeric system have been developed. One of the most successful theoretical tools to describe polymer behavior is self-consistent field theory (SCFT). The theory calculates mean field solutions of polymer statistics under self-consistently determined potential fields, and the phase diagram for self-assembly of block copolymers has been successfully obtained by this tool. In standard SCFT simulation, it is important to improve numerical algorithms for exploring wide ranges of polymeric systems. When investigating some polymeric systems related with interesting physical problems, there remains the SCFT problems waiting for development of numerical method to accurately solve the target system. On the other hand, there are some cases when standard SCFT is inappropriate to apply because of its fundamental assumption of polymer modeling. While a new group of SCFT method with alternative polymer models has been introduced recently, there are many numerical issues to be solved for practical implementation of this SCFT method due to its limitation in applicability and speed. Regarding those numerical challenges of SCFT, I conducted two independent studies of SCFT, and this thesis consists of two parts. The first part of this thesis is about two particle interaction in long homopolymer melts. It has been well known that efficient dispersion of the nanoparticles (NPs) in polymer melts is an important factor in yielding high performance nanocomposites. One of the strategies to achieve good dispersion of the NPs is grafting the nanoparticle surface with stretched brush polymers which is chemically identical to the matrix. According to the scaling analysis made by Leibler, when the matrix homopolymers are relatively short, the free homopolymers penetrate and wet the brush by maximizing the translational entropy. This favorable interaction promotes stable dispersion of NPs. In contrast, when the matrix chains are relatively long, there is additional entropy loss associated with deep penetration of free homopolymers into the brush. This effect results in aggregation of NPs, and it is well known as autophobic dewetting behavior. Many experimental and theoretical studies confirmed that the entropically driven wetting/dewetting transition is not only dependent on ?? (the length ratio of free to grafted chains), but also on particle curvature. In addition, it has been reported that autophobic dewetting can be suppressed by using polydisperse grafted chains, which means that higher value of ?? may be necessary to observe autophobic dewetting phenomenon. Most theoretical studies about the effect of polydisperse brush on the NP dispersion are limited at a moderate length ratio ?? less than 4. It is usually hard for most simulation methods to achieve high grafting density of brush and large ?? at the same time because increase of simulation components results in high computational demand. Because of the problem, no theoretical research has been conducted for the direct comparison of monodisperse and polydisperse brush behaviors especially in completely autophobic dewetting regime with ?? = 8 or beyond. In order to theoretically investigate the autophobic dewetting phenomenon, I calculate two particle interaction using SCFT with the newly developed numerical scheme, adopting two-dimensional finite volume method (FVM) and multi-coordinate-system (MCS) scheme which makes use of the reflection symmetry between the two NPs. By calculating the polymer density profile and interparticle potential, I identify the effects of parameters such as brush thickness, particle radius, ??, brush chain polydispersity, and chain end mobility. It was found that increasing ?? is the most efficient method for promoting autophobic dewetting phenomenon, and the attraction keeps increasing up to ?? = 20. At small ?? values, high polydispersity in brush may completely nullify the autophobic dewetting, while at intermediate ?? values, its effect is still significant in that the interparticle attractions are heavily reduced. The calculation also revealed that the grafting type is not a significant factor affecting the NP aggregation behavior. The second part of this thesis concerns implementation of discrete chain SCFT for low molecular weight polymers. In recent nanoscience, block copolymers with low molecular weight and high interaction parameter are known as promising material for the creation of nanostructure with domain of sub-10 nm period. In the standard SCFT, however, the most widely used polymer model is the Gaussian chain model in which a long polymer is approximated as an infinitely flexible chain. In the formulation of SCFT, the partition function of polymer chain is calculated by solving a partial differential equation in the form of modified diffusion equation. One of the limitations of Gaussian chain model is that it is only applicable to long enough polymer chain, and it may produce unphysical results when applied to the calculation of the mean field statistics of short polymer chains. Recently, the discrete chain SCFT has been suggested as an alternative method. In this formulation, discrete segment chain model is adopted, and the partition functions are obtained through successive integrals calculating the probability distribution. However, the shape of the partition function integral makes the calculation of this method much slower than the standard SCFT when calculated in the real space. Even though the formulation of the discrete chain SCFT has been already established, the numerical implementation of the method is still in the developing stage. In this study, I implement the pseudo-spectral method for the discrete chain SCFT adopting bead-spring or freely-jointed chain (FJC) model, and a few issues such as the accurate discretization of the FJC bond function are settled in this process. With the adoption of the pseudo-spectral method, the calculation becomes as fast as that of the standard SCFT. The integral equation introduces a new boundary condition, the neutral boundary, which is not available in the standard SCFT solving the differential equation. This interesting physical situation is combined with the finite-range interaction model for the study of symmetric block copolymers within thin films. I find that the surface-perpendicular block copolymer lamellar phase becomes preferable to the surface-parallel one when both the top and bottom surfaces are neutral.clos

Improved docking, screening and selectivity prediction for small molecule nuclear receptor modulators using conformational ensembles

Nuclear receptors (NRs) are ligand dependent transcriptional factors and play a key role in reproduction, development, and homeostasis of organism. NRs are potential targets for treatment of cancer and other diseases such as inflammatory diseases, and diabetes. In this study, we present a comprehensive library of pocket conformational ensembles of thirteen human nuclear receptors (NRs), and test the ability of these ensembles to recognize their ligands in virtual screening, as well as predict their binding geometry, functional type, and relative binding affinity. 157 known NR modulators and 66 structures were used as a benchmark. Our pocket ensemble library correctly predicted the ligand binding poses in 94% of the cases. The models were also highly selective for the active ligands in virtual screening, with the areas under the ROC curves ranging from 82 to a remarkable 99%. Using the computationally determined receptor-specific binding energy offsets, we showed that the ensembles can be used for predicting selectivity profiles of NR ligands. Our results evaluate and demonstrate the advantages of using receptor ensembles for compound docking, screening, and profiling

Do lifestyle factors influence risk of breast cancer recurrence in Korean women?: a cross-sectional survey

Purpose This study aimed to investigate the influencing factors of breast cancer recurrence by comparing the risk factors and lifestyle patterns related to breast cancer in Korean women with and without recurrence. Methods This cross-sectional survey comprised 241 Korean women diagnosed with breast cancer who had received follow-up treatment. Participants were recruited from a university hospital in Seoul and an online social media platform for breast cancer patients. Data were collected either via online or a paper survey, using a structured questionnaire that included general and disease-related characteristics and lifestyle behaviors. Data were analyzed using descriptive statistics, univariate analysis, and logistic regression. Results Recurrence of breast cancer was influenced by four factors; childbirth experience, consumption of green/yellow vegetables, drinking behavior, and recovery from fatigue after sleep.Prevalence of recurrent breast cancer was associated with no childbirth experience (OR=2.29, p=.010), fewer green/yellow vegetables (OR=0.71, p=.008), drinking behavior (OR=0.24, p=.001), and a lower level of recovery from fatigue after sleep (OR=0.51, p<.001). Conclusion Aside from having experienced childbirth, this study identified several modifiable factors that influence breast cancer recurrence. Increasing green/yellow vegetable intake, alleviating fatigue, and reducing alcohol intake are important. Intervention strategies in clinical research and practice can be applied to address risk factors and reduce the prevalence of recurrent breast cancer

The Analysis of Antecedents for the Video Telephony Service Adoption: From the Value-Based Perspective

Korean Telecommunications Industry has a large scale market and boasts on high service quality and high technologies enough to provide the Video Telephony Service (VTS) satisfactorily. For many years, Korean telephone companies have been investing enormous sums to advertise their services widely and to allow their customers to change their cell phones for the third-generation (3G) devices indispensable for the service. However, despite their efforts, the VTS adoption rate in Korea is very low and it seems that customers seldom feel the necessity to use. From this viewpoint, it becomes necessary to find the antecedents influencing the intention to use for the VTS empirically. For this purpose, we proposed several hypotheses from the perspective of the Value-based Adoption Model (VAM). VAM is a conceptual model suggested to overcome some limitations of the Technology Acceptance Model (TAM) in explaining the adoption of new Information and Communication Technology (ICT) such as Mobile Internet where customers play the role of service consumer rather than simply technology users. We conducted a survey on 125 samples and found that customers perceive the value of VTS when they can recognize the service is functionally useful (Perceived Usefulness) and when they feel they can put themselves forward by using it (Self-Expression). On the other hand, the other factors including Technical Complexity, Privacy Concern and Perceived Price (Fee) don’t have statistically significant influences on the Perceived Value of VTS

Fingerprints of Multiple Electron Scatterings in Single-Layer Graphene

The electrons in graphene exhibit unusual behaviours, which can be described by massless Dirac quasiparticles. Understanding electron scattering in graphene has been of significant importance for its future application in electronic devices because electron scattering determines electrical properties such as resistivity and electron transport. There are two types of electron scatterings in graphene: intervalley scattering and intravalley scattering. In single-layer graphene, to date, it has been difficult to observe intravalley scattering because of the suppression of backscattering resulting from the chiral nature of the electrons in graphene. Here, we report the multiple electron scattering behaviours in single-layer graphene on a metallic substrate. By applying one- and two-dimensional Fourier transforms to maps of the local density of states, we can distinguish individual scattering processes from complex interference patterns. These techniques enable us to provide direct evidence of intravalley scattering, revealing a linear dispersion relation with a Fermi velocity of ???7.4 ?? 105 m/s.open

A system dynamics computer model to assess the effects of developing an alternate water source on the water supply systems management

AbstractThe purpose of developing alternate water sources is to secure water sources of sufficient quantity and high quality due to water quality and/or quantity problems of an existing water source and, thereby, raise the level of consumer satisfaction. Considering the enormous costs and the effects to the consumers and operation of water supply enterprises, a technique to support long term management of water supply systems is needed. In this paper a System Dynamics computer simulation model was developed to evaluate the effects of alternate water source development. The System Dynamics model was used for the simulation of the effects of the alternate water source development project in Busan, South Korea

Fabrication of a spherical inclusion phantom for validation of magnetic resonance-based magnetic susceptibility imaging

© 2019 Kim et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Fabrication of a spherical multi-compartment MRI phantom is demonstrated that can be used to validate magnetic resonance (MR)-based susceptibility imaging reconstruction. The phantom consists of a 10 cm diameter gelatin sphere that encloses multiple smaller gelatin spheres doped with different concentrations of paramagnetic contrast agents. Compared to previous multi-compartment phantoms with cylindrical geometry, the phantom provides the following benefits: (1) no compartmental barrier materials are used that can introduce signal voids and spurious phase; (2) compartmental geometry is reproducible; (3) spherical susceptibility boundaries possess a ground-truth analytical phase solution for easy experimental validation; (4) spherical geometry of the overall phantom eliminates background phase due to air-phantom boundary in any scan orientation. The susceptibility of individual compartments can be controlled independently by doping. During fabrication, formalin crosslinking and water-proof surface coating effectively blocked water diffusion between the compartments to preserve the phantom’s integrity. The spherical shapes were realized by molding the inner gel compartments in acrylic spherical shells, 3 cm in diameter, and constructing the whole phantom inside a larger acrylic shell. From gradient echo images obtained at 3T, we verified that the phantom produced phase images in agreement with the theoretical prediction. Factors that limit the agreement include: air bubbles trapped at the gel interfaces, imperfect magnet shimming, and the susceptibility of external materials such as the phantom support hardware. The phantom images were used to validate publicly available codes for quantitative susceptibility mapping. We believe that the proposed phantom can provide a useful testbed for validation of MR phase imaging and MR-based magnetic susceptibility reconstructio

Premixed Calcium Silicate-Based Root Canal Sealer Reinforced with Bioactive Glass Nanoparticles to Improve Biological Properties

Recently, bioactive glass nanoparticles (BGns) have been acknowledged for their ability to promote interactions with the periapical tissue and enhance tissue regeneration by releasing therapeutic ions. However, there have been no studies on calcium silicate sealers with bioactive glass nanoparticle (BGn) additives. In the present study, a premixed calcium silicate root canal sealer reinforced with BGn (pre-mixed-RCS@BGn) was developed and its physicochemical features and biological effects were analyzed. Three specimens were in the trial: 0%, 0.5%, and 1% bioactive glass nanoparticles (BGns) were gradually added to the premixed type of calcium silicate-based sealer (pre-mixed-RCS). To elucidate the surface properties, scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy were used and flowability, setting time, solubility, and radiopacity were analyzed to evaluate the physical properties. Chemical properties were investigated by water contact angle, pH change, and ion release measurements. The antibacterial effects of the bioactive set sealers were tested with Enterococcus faecalis and the viability of human bone marrow-derived mesenchymal stem cells (hMSCs) with this biomaterial was examined. In addition, osteogenic differentiation was highly stimulated, which was confirmed by ALP (Alkaline phosphatase) activity and the ARS (Alizarin red S) staining of hMSCs. The pre-mixed-RCS@BGn satisfied the ISO standards for root canal sealers and maintained antimicrobial activity. Moreover, pre-mixed-RCS@BGn with more BGns turned out to have less cytotoxicity than pre-mixed-RCS without BGns while promoting osteogenic differentiation, mainly due to calcium and silicon ion release. Our results suggest that BGns enhance the biological properties of this calcium silicate-based sealer and that the newly introduced pre-mixed-RCS@BGn has the capability to be applied in dental procedures as a root canal sealer. Further studies focusing more on the biocompatibility of pre-mixed-RCS@BGn should be performed to investigate in vivo systems, including pulp tissue