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          Differences in the relationship between traumatic experiences, self-esteem, negative cognition, and Internet addiction symptoms among North Korean adolescent defectors and South Korean adolescents: A preliminary study

          Park, Subin,Lee, Yeeun,Jun, Jin Yong Elsevier/North Holland Biomedical Press 2017 Psychiatry research Vol.257 No.-

          <P><B>Abstract</B></P> <P>North Korean adolescent defectors experience adaptation difficulties along with a wide range of psychosocial problems, but no study has yet examined their Internet addiction symptoms. We compared early traumatic experiences, self-esteem, negative cognition, and Internet addiction symptoms, as well as the relationships between these variables, between North Korean adolescent defectors and South Korean adolescents. Fifty-six North Korean adolescent defectors and 112 age- and sex- matched South Korean adolescents participated. The analyses examined the relationship between traumatic experiences and Internet addiction symptoms, with negative automatic thoughts or low self-esteem as mediators of these relations. North Korean adolescent defectors tended to have higher levels of negative automatic thoughts and more severe Internet addiction symptoms, as well as better self-esteem, than did South Korean adolescents. Furthermore, only among North Korean adolescent defectors, traumatic experiences were positively associated with Internet addition symptoms via increasing negative automatic thoughts. North Korean adolescent defectors are more susceptible to Internet addiction, negative cognitions, and early traumatic experiences compared to South Korean adolescents. However, the cross-sectional design of this study precludes consideration of the causality of these relationships. Interventions aiming to correct negative cognitions and increase self-esteem may be helpful for North Korean adolescent defectors with problematic Internet use.</P> <P><B>Highlights</B></P> <P> <UL> <LI> North Korean adolescent defectors had higher trauma and Internet addiction (IA). </LI> <LI> North Korean defectors also had greater self-esteem and negative automatic thoughts. </LI> <LI> Self-esteem and negative thoughts were mediators in the relation of trauma and IA. </LI> <LI> Country of origin (North vs. South Korea) moderated the mediating effects. </LI> </UL> </P>


          Development of the loss coefficient correlation for cross flow between graphite fuel blocks in the core of prismatic very high temperature reactor-PMR200

          Lee, J.H.,Cho, H.K.,Park, G.C. North-Holland Pub. Co 2016 Nuclear engineering and design Vol.307 No.-

          The core of the very high temperature reactor (VHTR) PMR200 (a prismatic modular reactor rated at 200MW of thermal power) consists of hexagonal prismatic fuel blocks and reflector blocks made of graphite. If the core bypass flow ratio increases, the coolant channel flow is decreased and can then lower the heat removal efficiency, resulting in a locally increased fuel block temperature. The coolant channels in the fuel blocks are connected to bypass gaps by the cross gap, complicating flow distribution in the VHTR core. Therefore, reliable estimation of the bypass flow is highly important for the design and safety analysis of the VHTR core. Because of the complexity of the core geometry and gap configuration, it is challenging to predict the flow distribution in the VHTR core. To analyze this flow distribution accurately, it is necessary to determine the cross flow phenomena, and the loss coefficient across the cross gap has to be evaluated to determine the flow distribution in the VHTR core when a lumped parameter code or a flow network analysis code that uses the correlation of the loss coefficient is employed. The purpose of this paper is to develop a loss coefficient correlation applicable to the cross gap in the PMR200 core. The cross flow was evaluated experimentally using the difference between the measured inlet and outlet mass flow rates. Next, the applicability of a commercial computational fluid dynamics (CFD) code, CFX 15, was confirmed by comparing the experimental data and CFD analysis results. To understand the cross flow phenomena, the loss coefficient was evaluated; in the high Reynolds number region, the cross flow loss coefficient on Reynolds number is nearly constant regardless of the Reynolds number, whereas it varies with the gap size in the low Reynolds number region. Finally, the loss coefficient correlation was proposed on the basis of experiments and the CFD analysis. The developed correlation was compared with existing correlations, and the developed one shows better agreement with the experimental results than the existing ones. Hence, the developed correlation will be applied to the flow network code to analyze flow distribution in the PMR200 core.

        • Information transfer network of global market indices

          Kim, Y.,Kim, J.,Yook, S.H. North-Holland Pub. Co 2015 PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIO Vol.430 No.-

          We study the topological properties of the information transfer networks (ITN) of the global financial market indices for six different periods. ITN is a directed weighted network, in which the direction and weight are determined by the transfer entropy between market indices. By applying the threshold method, it is found that ITN undergoes a crossover from the complete graph to a small-world (SW) network. SW regime of ITN for a global crisis is found to be much more enhanced than that for ordinary periods. Furthermore, when ITN is in SW regime, the average clustering coefficient is found to be synchronized with average volatility of markets. We also compare the results with the topological properties of correlation networks.


          Surface/state correspondence and bulk local operators in pp-wave holography

          Kim, N.,Shin, H. North-Holland Pub. Co 2015 Physics letters. Section B Vol.751 No.-

          We apply the surface/state correspondence proposal of Miyaji et al. to IIB pp-waves and propose that the bulk local operators should be instantonic D-branes. In line with ordinary AdS/CFT correspondence, the bulk local operators in pp-waves also create a hole, or a boundary, in the dual gauge theory as pointed out by H. Verlinde, and by Y. Nakayama and H. Ooguri. We also present simple calculations which illustrate how to extract the spacetime metric of pp-waves from instantonic D-branes in boundary state formalism.


          Power maximization method for land-transportable fully passive lead-bismuth cooled small modular reactor systems

          Cho, J.,Shin, Y.H.,Hwang, I.S. North-Holland Pub. Co 2015 Nuclear engineering and design Vol.289 No.-

          Although current pressurized water reactors (PWRs) have significantly contributed to global energy supply, PWR technology has not been considered a trustworthy energy solution owing to its problems of spent nuclear fuels (SNFs), nuclear safety, and nuclear economy. In order to overcome these problems, a lead-bismuth eutectic (LBE) fully passive cooling small modular reactor (SMR) system is suggested. This technology can not only provide the solution for the problems of SNFs through the transmutation feature of the LBE coolant, but also strengthen safety and economy through the concept of natural circulation cooling SMRs. It is necessary to maximize the advantages, namely safety and economy, of this type of nuclear power plants for broader applications in the future. Accordingly, the objective of this study is to maximize the reactor core power while satisfying the limitations of shipping size, materials endurance, and criticality of a long-burning core as well as safety under beyond design basis events. To achieve these objectives, the design limitations of natural circulating LBE-cooling SMRs are derived. Then, the power maximization method is developed based on obtaining the design limitations. The results of this study are expected to contribute to the effectiveness of the reactor design stage by providing insights to designers, as well as by formulating methods for the power maximization of other types of SMRs.

        • Enhancement of variational mode decomposition with missing values

          Choi, G.,Oh, H.S.,Kim, D. North-Holland Pub. Co 2018 Signal processing Vol.142 No.-

          This paper considers an improvement of variational mode decomposition (VMD) in the presence of missing values. VMD developed by Dragomiretskiy and Zosso (2014) efficiently decomposes a signal into some meaningful modes according to their frequency information. It is well known that VMD is useful for tone detection and denoising of noisy signals. However, VMD may not be efficient for analyzing missing data since it is based on discrete Fourier transform (DFT). This paper proposes a new VMD procedure that can effectively handle problems caused by missing values. The proposed method is based on an estimation of spectral density that reflects frequency information of a signal properly with removing the effects of missing samples; hence, it is able to produce stable decomposition results. Results from numerical studies including simulation study and real data analysis demonstrate the promising empirical properties of the proposed method.

        • Ab initio study of adsorption properties of hazardous organic molecules on graphene: Phenol, phenyl azide, and phenylnitrene

          Lee, J.,Min, K.A.,Hong, S.,Kim, G. North Holland 2015 Chemical physics letters Vol.618 No.-

          Phenol, phenyl azide, and phenylnitrene are hazardous organic molecules; therefore, the fabrication of sensors or filters with high sorption capabilities for the chemicals is necessary. Considering van der Waals interaction, we perform first-principles density functional theory calculations to investigate the adsorption properties of the hazardous molecules on graphene. For parallel stacking configurations, AB stacking is slightly more favorable than AA stacking for all the adsorbates that we considered. We find that phenyl azide has a higher adsorption energy than phenol. Phenylnitrene forms covalent bonds with graphene in oblique stacking structures, resulting in a bandgap opening in graphene.

        • Using link-preserving imputation for logistic partially linear models with missing covariates

          Chen, Q.,Paik, M.C.,Kim, M.,Wang, C. North-Holland Pub. Co ; Elsevier Science Ltd 2016 Computational statistics & data analysis Vol.101 No.-

          <P>To handle missing data one needs to specify auxiliary models such as the probability of observation or imputation model. Doubly robust (DR) method uses both auxiliary models and produces consistent estimation when either of the model is correctly specified. While the DR method in estimating equation approaches could be easy to implement in the case of missing outcomes, it is computationally cumbersome in the case of missing covariates especially in the context of semiparametric regression models. In this paper, we propose a new kernel-assisted estimating equation method for logistic partially linear models with missing covariates. We replace the conditional expectation in the DR estimating function with an unbiased estimating function constructed using the conditional mean of the outcome given the observed data, and impute the missing covariates using the so called link-preserving imputation models to simplify the estimation. The proposed method is valid when the response model is correctly specified and is more efficient than the kernel-assisted inverse probability weighting estimator by Liang (2008). The proposed estimator is consistent and asymptotically normal. We evaluate the finite sample performance in terms of efficiency and robustness, and illustrate the application of the proposed method to the health insurance data using the 2011-2012 National Health and Nutrition Examination Survey, in which data were collected in two phases and some covariates were partially missing in the second phase. (C) 2016 Elsevier B.V. All rights reserved.</P>


          Identifying codes and searching with balls in graphs

          Kim, Y.,Kumbhat, M.,Nagy, Z.L.,Patkos, B.,Pokrovskiy, A.,Vizer, M. North Holland ; Elsevier Science Ltd 2015 Discrete Applied Mathematics Vol.193 No.-

          Given a graph G and a positive integer R we address the following combinatorial search theoretic problem: What is the minimum number of queries of the form ''does an unknown vertex v@?V(G) belong to the ball of radius r around u?'' with u@?V(G) and r@?R that is needed to determine v. We consider both the adaptive case when the jth query might depend on the answers to the previous queries and the non-adaptive case when all queries must be made at once. We obtain bounds on the minimum number of queries for hypercubes, the Erdos-Renyi random graphs and graphs of bounded maximum degree.


          AMS02 positron excess from decaying fermion DM with local dark gauge symmetry

          Ko, P.,Tang, Yong North-Holland Pub. Co 2015 Physics letters. Section B Vol.741 No.-

          <P><B>Abstract</B></P> <P>Positron excess observed by PAMELA, Fermi and AMS02 may be due to dark matter (DM) pair annihilation or decay dominantly into muons. In this paper, we consider a scenario with thermal fermionic DM (<I>χ</I>) with mass ∼ O ( 1 – 2 ) TeV decaying into a dark Higgs (<I>ϕ</I>) and an active neutrino ( <SUB> ν a </SUB> ) instead of the SM Higgs boson and <SUB> ν a </SUB> . We first present a renormalizable model for this scenario with local dark U <SUB> ( 1 ) X </SUB> gauge symmetry, in which the DM <I>χ</I> can be thermalized by Higgs portal and the gauge kinetic mixing. Assuming the dark Higgs (<I>ϕ</I>) mass is in the range 2 <SUB> m μ </SUB> < <SUB> m ϕ </SUB> < 2 <SUB> m <SUP> π 0 </SUP> </SUB> , the positron excess can be fit if a proper background model is used, without conflict with constraints from antiproton and gamma-ray fluxes or direct detection experiments. Also, having such a light dark Higgs, the self-interaction of DM can be enhanced to some extent, and three puzzles in the CDM paradigm can be somewhat relaxed.</P>

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