주석이 도핑된 SrRuO3 페로브스카이트 산화물의 반쪽금속 강자성체 연구

학위논문 (박사)-- 서울대학교 대학원 : 협동과정 계산과학전공, 2015. 2. 유재준.In this thesis, we investigate the electronic structure and properties of SrRuO3 as a candidate of half-metallic ferromagnets. We will suggest two methods modulating the band structure of SrRuO3 to become half-metallic ground states. The first method is the doping of Sn atoms as substitute for Ru atoms. Due to the excellent band positioning between Ru 4d t2g bands and Sn 5s bands, only small decrease of Ru 4d t2g majority bandwidth can induce the half-metallic band structure of SrRuO3. We carried out first-principles electronic structure calculations for the series of solid solutions Sr(Ru1-xSnx)O3 of orthorhombic perovskite adopting LSDA+U scheme with 1 eV of the effective value of on-site Coulomb interaction Ueff for Ru d-orbitals. We present the electronic structure and analysis of projected density-of-states of Sr(Ru1-xSnx)O3 for x = 1/8, 1/4, 1/2, 5/8, 3/4, 7/8. From the result, we can observe that the band width of Ru t2g majority band decreased with Sn-doping. Since Sn 5s band has no overlap with Ru 4d band, the decreased hopping by B-site substituted Sn atoms narrows the bandwidth of Ru 4d t2g band. And we also analyzed for the disorder in B-site atoms at fixed Sn-doping ratio. In the super-cell of 2×2×2 times cubic perovskite unit cell, we calculated all the possible B-site configurations of Ru atoms and Sn atoms. The Ru t2g band in clustering types of defects are more dispersive than that in homogeneous types of defects. The averaged density-of-states over all possible B-site configurations at fixed Sn-doping ratio can suggest more reliable prediction for the phase transition to the half-metallic ground state. The calculated density-of-states shows half-metallic ferromagnetic ground states in the range of 0.6 < x < 0.75 of Sn-doping. And the metal-insulator transition occurs at x ~ 0.75. The calculation including the spin-orbit coupling showed that the checker-boarded type of B-site defects has non-collinear spin structures but the total energy of the checker-boarded type is larger by 0.6 eV than the plane type. The second method is an epitaxial strain on SrRuO3. The change of lattice parameter can modulate the bandwidth of the material and we found that the expansion of volume by 9% can induce the half-metallic ground state of SrRuO3. In experiments, the wide range of epitaxial strain can be given by the selection of substrate materials having different size of lattice. For better accuracy of calculated lattice parameters with experimental value, we used the PBEsol functional which can give improved bulk properties than PBE and LSDA. The band structure for 2.5% tensile epitaxial strain showed the maximally decreased Ru 4d t2g bandwidth in LSDA+U and PBEsol+U calculations. Accidentally the best fitting substrate to the lattice size of 2.5% tensile strained SrRuO3 was SrSnO3 that is previously used by the doping material. Our study is a new revenue in search of half-metallic materials in the perovskite family. Considering the potential application of half-metal in spintronics applications, we expect that the half-metallic Sn-doped SrRuO3, when realized, can contribute to the development of devices and technology in spintronics.Abstract vii 1. Introduction 1 2. Half-metallic Ferromagnetism in Perovskite SrRuO3 5 2.1 Possibility to Half-metallicity in SrRuO3 5 2.2 Electronic Structure of SrRuO3 6 2.2.1 Crystal Structure of SrRuO3 6 2.2.1.1 Goldschmidt Tolerance Factor 7 2.2.1.2 Irregular Lattice Distortion 8 2.2.2 LSDA Calculation 8 2.2.2.1 Cubic SrRuO3 9 2.2.2.2 Orthorhombic SrRuO3 11 2.2.3 LSDA+U Calculation 13 2.2.3.1 U-dependent Half-metallicity 15 2.2.3.2 Determination of Ueff parameter 18 2.2.4 GGA and GGA+U Calculation 19 2.3 Sn-doped SrRuO3 20 2.3.1 Crystal Structure of SrSnO3 20 2.3.2 Electronic structure of SrSnO3 22 2.3.3 LSDA Calculation of Sr(Ru1-xSnx)O3 23 2.3.4 LSDA+U Calculation of Sr(Ru1-xSnx)O3 26 2.3.5 Half-metallic and Metal-Insulator Transitions in Sr(Ru1-xSnx)O3 29 2.3.6 B-site Configuration Dependency 31 2.3.6.1 Total Energy and Spin state 34 2.3.6.2 Spin-orbit Coupling 35 2.3.7 Lattice Expansion vs. Sn-doping 36 2.4 Epitaxial Strain on SrRuO3 38 2.4.1 Structural Distortion by Epitaxial Strain 38 2.4.2 LSDA and LSDA+U Calculation 40 2.4.3 PBEsosl and PBEsol+U Calculation 47 3. Summary and Perspectives 50 Bibliography 53 Abstract in Korean 56Docto

The effect of epilepsy on autistic symptom severity assessed by the social responsiveness scale in children with autism spectrum disorder.

BACKGROUND: As the prevalence of autism spectrum disorders in people with epilepsy ranges from 15 to 47 % (Clarke et al. in Epilepsia 46:1970-1977, 2005), it is speculated that there is a special relationship between the two disorders, yet there has been a lack of systematic studies comparing the behavioral phenotype between autistic individuals and autistic individuals with epilepsy. This study aims to investigate how the co-occurrence of epilepsy and Autism Spectrum Disorder (ASD) affects autistic characteristics assessed by the Social Responsiveness Scale (SRS), which has been used as a measure of autism symptoms in previous studies. In this research we referred to all individuals with Autism or Autistic Disorder as individuals with ASD. METHODS: We reviewed the complete medical records of 182 participants who presented to a single tertiary care referral center from January 1, 2013 to July 28, 2015, and subsequently received complete child and adolescent psychiatric assessments. Of the 182 participants, 22 were diagnosed with Autism Spectrum Disorder and epilepsy. Types of epilepsy observed in these individuals included complex partial seizure, generalized tonic-clonic seizure, or infantile spasm. Using 'Propensity Score Matching' we selected 44 children, diagnosed with only Autism Spectrum Disorder, whose age, gender, and intelligence quotient (IQ) were closely matched with the 22 children diagnosed with Autism Spectrum Disorder and epilepsy. Social functioning of participants was assessed by the social responsiveness scale, which consists of five categories: social awareness, social cognition, social communication, social motivation, and autistic mannerisms. Bivariate analyses were conducted to compare the ASD participants with epilepsy group with the ASD-only group on demographic and clinical characteristics. Chi square and t test p values were calculated when appropriate. RESULTS: There was no significant difference in age (p = 0.172), gender (p > 0.999), IQ (FSIQ, p = 0.139; VIQ, p = 0.114; PIQ, p = 0.295) between the two groups. ASD participants with epilepsy were significantly more impaired than ASD participants on some measures of social functioning such as social awareness (p = 0.03) and social communication (p = 0.027). ASD participants with epilepsy also scored significantly higher on total SRS t-score than ASD participants (p = 0.023). CONCLUSIONS: Understanding the relationship between ASD and epilepsy is critical for appropriate management (e.g. social skills training, seizure control) of ASD participants with co-occurring epilepsy. Results of this study suggest that mechanisms involved in producing epilepsy may play a role in producing or augmenting autistic features such as poor social functioning. Prospective study with larger sample sizes is warranted to further explore this association.ope

Characteristics of Brains in Autism Spectrum Disorder: Structure, Function and Connectivity across the Lifespan

Autism spectrum disorder (ASD) is a highly prevalent neurodevelopmental disorder characterized by impaired social communication and restricted and repetitive behaviors (RRBs). Over the past decade, neuroimaging studies have provided considerable insights underlying neurobiological mechanisms of ASD. In this review, we introduce recent findings from brain imaging studies to characterize the brains of ASD across the human lifespan. Results of structural Magnetic Resonance Imaging (MRI) studies dealing with total brain volume, regional brain structure and cortical area are summarized. Using task-based functional MRI (fMRI), many studies have shown dysfunctional activation in critical areas of social communication and RRBs. We also describe several data to show abnormal connectivity in the ASD brains. Finally, we suggest the possible strategies to study ASD brains in the future.ope

Pontryagin 최소 원리에 기반한 하이브리드 전기 자동차의 동력원 제어 전략

Thesis(doctors) --서울대학교 대학원 :기계항공공학부,2009.8.Docto

Fundamental Study of Light Rare-earth Element Separation for Radioactive Isotope Analysis using Gas Pressurized Extraction Chromatography

MasterA new method for chemical separation of light rare-earth elements (LREEs) using gas-pressurized extraction chromatography (GPEC) is described. GPEC is a microscale column chromatography system that features a constant flow of solvents, which is created by pressurized nitrogen gas. The flow rate of the system can be easily modified by changing Nitrogen gas pressure, which enhances column stability. The separation column with a Teflon tubing was packed with LN resin. The column can be easily switched using different resin for other targeted elements. The proposed GPEC method facilitates production of lesser chemical wastes and faster separation owing to the use of low solvent volume compared to traditional column VI chromatography. We evaluated the separation of Ba, La, Ce, and Nd using various elution solvents. The reproducibility of the proposed GPEC system ranged from 2.4% to 4.9% with RSDs of recoveries, and the reproducibility of column-to-column ranged from 3.1% to 6.3% with RSDs of recoveries. The proposed technique is robust, and it can be useful for the fast separation of LREEs. Such trait can enable the technique to be utilized in other radioactive isotope separation

An Adaptive Concept of PMP-Based Control for Saving Operating Costs of Extended-Range Electric Vehicles

The fuel efficiencies of Hybrid Electric Vehicles (HEVs) depend heavily on the control concepts, especially on energy management strategies, because the system efficiency of the vehicle is determined by the exploitation of the electric energy. Control concepts based on optimal control theories like Dynamic Programming (DP) or Pontryagin&rsquo;s Mminimum Principle (PMP) have been widely studied over the last two decades, and it has been proven that these control concepts provide near-optimal solutions if future driving conditions are given prior to actual driving. However, it is difficult to apply to real vehicles unless the future driving conditions are known. In this paper, a well-known control strategy based on PMP has been developed, which needs only current driving conditions. The significance of the study is that the control concept introduced herein was evaluated in the IEEE VTS Challenge 2018 competition. It produced the best results in terms of the total energy consumption, where 52 controllers had been competing to minimize the energy consumption in unknown driving cycles. Although the control system was designed from traditional PMP-based control, it becomes a practicable and effective solution by using an adaptive concept for balancing State Of Charge (SOC) of a battery. This study is an extended version of the study presented during IEEE VPPC 2018 and provides the development process of the control concept used in the controller during the IEEE VTS Challenge 2018

Adjunctive α-lipoic acid reduces weight gain compared with placebo at 12 weeks in schizophrenic patients treated with atypical antipsychotics: a double-blind randomized placebo-controlled study

α-Lipoic acid (ALA) has been reported to be effective in reducing body weight in rodents and obese patients. Our previous open trial showed that ALA may play a role in reducing weight gain in patients with schizophrenia on atypical antipsychotics. The present study evaluated the efficacy of ALA in reducing weight and BMI in patients with schizophrenia who had experienced significant weight gain since taking atypical antipsychotics. In a 12-week, double-blind randomized placebo-controlled study, 22 overweight and clinically stable patients with schizophrenia were randomly assigned to receive ALA or placebo. ALA was administered at 600-1800?mg, as tolerated. Weight, BMI, abdomen fat area measured by computed tomography, and metabolic values were determined. Adverse effects were also assessed to examine safety. Overall, 15 patients completed 12 weeks of treatment. There was significant weight loss and decreased visceral fat levels in the ALA group compared with the placebo group. There were no instances of psychopathologic aggravation or severe ALA-associated adverse effects. ALA was effective in reducing weight and abdominal obesity in patients with schizophrenia who had experienced significant weight gain since beginning an atypical antipsychotic regimen. Moreover, ALA was well tolerated throughout this study. ALA might play an important role as an adjunctive treatment in decreasing obesity in patients who take atypical antipsychotics.restrictio