자성 디스크 배열 내 결합된 자기 소용돌이의 동적 거동 연구

학위논문(박사)--서울대학교 대학원 :공과대학 재료공학부,2020. 2. 김상국.자기 소용돌이는 수 마이크로미터 크기 혹은 그 이하의 강자성 구조체에서 안정적으로 형성되는 특이한 배열 구조를 말한다. 자기 소용돌이는 박막면에 수직한 수십 나노미터 크기의 자기 소용돌이 핵과, 그 주위의 평면 내 회전하는 모양으로 배열된 스핀들로 구성된다. 자기 소용돌이에 외부 자기장 혹은 전류 등을 인가하면 자기 소용돌이 핵이 회전운동을 하는 성질이 있다. 이러한 자기 소용돌이는 핵의 두 가지 자화방향과 주변에 배열된 스핀들의 두 가지 회전방향의 조합으로 네 개의 동일한 기저 에너지 준위를 가질 수 있고, 열적으로 매우 안정하기 때문에 비휘발성 정보저장 소자로 응용 가능하다. 또한 여러 개의 결합된 자기 소용돌이 사이에서 나타나는 자기 소용돌이 핵의 집단적 회전운동은 새로운 신호전달의 매개체로 이용될 수 있어 정보처리 소자로의 응용성에 대한 연구가 진행되어왔다. 본 학위 논문에서는 미소자기 전산모사 및 실험을 이용하여 자기 소용돌이의 동적 거동과 자기 소용돌이 간의 동적 상호작용 연구에 초점을 두고있다. 자기 디스크 배열에서 자기 소용돌이 결합 모드, 자기 소용돌이 핵 반전 방법 및 자기 소용돌이 핵의 회전운동 신호 전달의 제어에 관한 연구가 주 내용이다. 이러한 자기 소용돌이의 동적 거동 제어 방법을 이용해 새로운 개념의 RS 래치 논리 소자, 시분할 및 주파수 분할 디멀티플렉서 소자를 제안하고 그 동작 특성을 연구하였다. 자기 소용돌이를 이용한 소자들은 비휘발성이며, 거의 무제한의 수명을 가지고, 에너지가 적게 드는 등 많은 장점을 가지고 있다. 또한 자기 소용돌이는 그 특성의 제어가 매우 용이해서 향후 개발될 스핀트로닉스 소자로 응용될 수 있는 가능성을 가지고 있다. 본 연구 결과는 차세대 스핀트로닉스 기술로서 자기 소용돌이에 기반한 논리 소자 및 정보 처리 장치의 구현 가능성을 보여준다.In the sub-micrometer-size ferromagnetic structure, the magnetic vortex is in a strongly stable ground state characterized by an in-plane curling magnetization around and an out-of-plane magnetization in the central region. The magnetic vortex is characterized by clockwise (CW) or counter-clockwise (CCW) curling in-plane magnetizations around a single vortex core in which region magnetizations are perpendicularly oriented either upward or downward. In isolated disks, applied external forces induce vortex excitations, among which a translational mode exists in which the vortex core gyrates around its equilibrium position at a characteristic eigenfrequency. Vortex-core switching can be accomplished with low power consumption when vortex gyrations are resonantly excited. Moreover, the gyration modes of individual vortex cores in a periodic array of patterned vortex-state disks are coupled with each other, thus yielding collectively coupled motions of the individual cores. On the basis of such novel dynamic characteristics, non-volatile memory and information processing devices using magnetic vortex have been proposed. This work focused on dynamic interaction between vortex-state ferromagnetic structures and its applications, utilizing micromagnetic simulations, analytical calculations, and experiments. The dynamic behaviors of vortex-gyration-coupled modes, vortex-core switching, and propagation of vortex-core gyration signal in magnetic-disk-network devices are investigated. Based on the combinations of the novel dynamic characteristics of vortices in dipolar-coupled disks, a new concept RS latch logic, time- and frequency-division demultiplexer device operations are explored. Magnetic vortex has many advantages such as non-volatility, almost unlimited endurance, and low power operation. Furthermore, a rich tunability of magnetic vortices makes them adoptable as future spintronics devices. This work can pave the way for possible implementation of logic gates and information processing devices based on coupled magnetic vortices.1. Introduction 1 2. Research Background 5 2.1. Magnetization dynamics and micromagnetics 5 2.1.1. Landau-Lifshitz-Gilbert equation 5 2.1.2. Effective fields in the LLG equation 8 2.2. Vortices in magnetic microstructures and their dynamics 10 2.2.1. Vortex core gyration 15 2.2.2. Vortex core switching 18 2.2.3. Interaction between magnetic vortices 18 2.3. Experimental methods 20 2.3.1. Photo lithography 20 2.3.2. Electron beam lithography 20 2.3.3. Anisotropic magneto resistance in vortex 21 3. Vortex Core Switching by Propagation of a Gyration-Coupled Mode 23 3.1. Micromagnetic simulation conditions 23 3.2. Coupled modes of gyration for the two types of vortex-state configurations 26 3.3. Concept design of reset-set latch device 32 3.4. Magnitude of oscillating magnetic field and radius of disks dependent switching behavior 36 3.5. Reset-set latch logic operation 39 4. Control of Gyration Signal Propagation in Coupled Magnetic Vortices 43 4.1. Dynamics of the single and coupled disk array 43 4.2. Control of gyration signal propagation by in-plane bias field 50 4.3. Control of gyration signal propagation by vortex core switching 53 4.4. Concept design of time-division demultiplexer device and its operation 60 4.5. Concept design of frequency-division demultiplexer device and its operation 65 5. Electrical Measurement of the Gyrotropic Resonance of a Magnetic Vortex in Circular and Chopped Disks. 68 5.1. Sample fabrication 68 5.2. DC AMR measurement 73 5.3. AC AMR measurement by rectification technique 78 6. Summary 88 Bibliography 90 Publication List 100 Patent List 102 Presentations in Conferences 103Docto

조선후기 綿紬廛 大房의 齋錢과 禮錢 운영: 護喪所 자료의 실증 분석

Taebang was at the center of the management of myŏnjujŏn. Taebang received money from its members and paid money to them through hosangso, chobigye, paeksagye, and sujuiso. The money was both chaetton and yejŏn. In this study, in order to examine the management of chaetton and yejŏn, three types of account books written by Taebang in relation to hosangso, such as hosangso sangyongch’aek, hosangso ch’ahach’aek, and hosangso chŏnjangtŭngnok, were empirically analyzed. The volume of chaetton and yejŏn and their long-term trend was identified from 1863 to 1900, when hosangso of myŏnjujŏn was disappeared into history. Hosangso sangyongch’aek was the account book of chaetton management and hosangso ch’ahach’aek was the account book of yejŏn management. Calculation in red letters was made every six months, but in order to know the specific calculation process, we must check hosangso chŏnjangtŭngnok. The management of hosangso by myŏnjujŏn can be commonly applied to chobigye, paeksagye, and sujuiso. The management of chaetton and yejŏn did not change significantly even after the amendment of regulations in 1878 and the Kabo Reform in 1894. Considering that both chaetton and yejŏn were applied internally to the members of myŏnjujŏn, it can be evaluated that myŏnjujŏn had been continued as a cooperative association regardless of its procurement function or the aspect of a merchant organization

Differential Biases and Variabilities of Deep Learning-Based Artificial Intelligence and Human Experts in Clinical Diagnosis: Retrospective Cohort and Survey Study

Background: Deep learning (DL)-based artificial intelligence may have different diagnostic characteristics than human experts in medical diagnosis. As a data-driven knowledge system, heterogeneous population incidence in the clinical world is considered to cause more bias to DL than clinicians. Conversely, by experiencing limited numbers of cases, human experts may exhibit large interindividual variability. Thus, understanding how the 2 groups classify given data differently is an essential step for the cooperative usage of DL in clinical application. Objective: This study aimed to evaluate and compare the differential effects of clinical experience in otoendoscopic image diagnosis in both computers and physicians exemplified by the class imbalance problem and guide clinicians when utilizing decision support systems. Methods: We used digital otoendoscopic images of patients who visited the outpatient clinic in the Department of Otorhinolaryngology at Severance Hospital, Seoul, South Korea, from January 2013 to June 2019, for a total of 22,707 otoendoscopic images. We excluded similar images, and 7500 otoendoscopic images were selected for labeling. We built a DL-based image classification model to classify the given image into 6 disease categories. Two test sets of 300 images were populated: balanced and imbalanced test sets. We included 14 clinicians (otolaryngologists and nonotolaryngology specialists including general practitioners) and 13 DL-based models. We used accuracy (overall and per-class) and kappa statistics to compare the results of individual physicians and the ML models. Results: Our ML models had consistently high accuracies (balanced test set: mean 77.14%, SD 1.83%; imbalanced test set: mean 82.03%, SD 3.06%), equivalent to those of otolaryngologists (balanced: mean 71.17%, SD 3.37%; imbalanced: mean 72.84%, SD 6.41%) and far better than those of nonotolaryngologists (balanced: mean 45.63%, SD 7.89%; imbalanced: mean 44.08%, SD 15.83%). However, ML models suffered from class imbalance problems (balanced test set: mean 77.14%, SD 1.83%; imbalanced test set: mean 82.03%, SD 3.06%). This was mitigated by data augmentation, particularly for low incidence classes, but rare disease classes still had low per-class accuracies. Human physicians, despite being less affected by prevalence, showed high interphysician variability (ML models: kappa=0.83, SD 0.02; otolaryngologists: kappa=0.60, SD 0.07). Conclusions: Even though ML models deliver excellent performance in classifying ear disease, physicians and ML models have their own strengths. ML models have consistent and high accuracy while considering only the given image and show bias toward prevalence, whereas human physicians have varying performance but do not show bias toward prevalence and may also consider extra information that is not images. To deliver the best patient care in the shortage of otolaryngologists, our ML model can serve a cooperative role for clinicians with diverse expertise, as long as it is kept in mind that models consider only images and could be biased toward prevalent diseases even after data augmentation.ope

Usefulness of serial measurement of the mean platelet volume to predict multiple organ dysfunction syndrome in patients with severe trauma

Objective: The early prediction of multiple organ dysfunction syndrome (MODS) in trauma patients and provision of prompt treatment may improve their outcomes. We investigated the efficacy of the mean platelet volume (MPV) for predicting MODS in cases of severe trauma. Methods: This retrospective, observational cohort study was performed with patients prospectively integrated in a critical pathway of TRAUMA. We analyzed the severe trauma patients admitted to the emergency department (ED), based on the Advanced Trauma Life Support guideline, between January 1, 2011 and May 31, 2017. The outcomes were developed from MODS at least 48 hours after ED admission. Results: A total of 348 patients were enrolled. An increase in the MPV at 12 hours (odds ratio [OR], 2.611; P8.6 fL (OR, 4.831; P<0.001). The area under the receiver operating characteristic curve (AUROC) value of the MPV at 12 hours (0.751; 95% confidence interval [CI], 0.687-0.818; P<0.01) was not inferior than that of Acute Physiology and Chronic Health Evaluation II score, injury severity score, lactate, and total CO2 for predicting MODS. Conclusion: MPV was an independent predictor of MODS development in severe trauma patients. Emergency physicians can use the MPV as an ancillary biomarker for predicting MODS.ope

The usefulness of lactate as an early predictor of the severity of emergency department patients with postpartum hemorrhage

Objective: Only a few studies have examined the role of lactate reflecting on tissue hypoperfusion determining the severity of postpartum hemorrhage (PPH) patients in the emergency department (ED). This study evaluated the utility of the arterial lactate level as a prognostic marker of severity in PPH patients admitted to an ED. Method: This retrospective, observational cohort study was conducted on patients integrated prospectively in a critical pathway of SPEED (Severance Protocol to save postpartum bleeding through Expeditious care Delivery). Adult primary PPH patients admitted to the ED between July 1, 2010 and March 31, 2017 were analyzed. The outcomes were the development of severe PPH including death, hysterectomy, surgical treatment, and massive transfusion. Results: A total of 112 patients were enrolled in this study. An increase in the arterial lactate value was a strong independent predictor of severe PPH. The increasing predictability of severe PPH was closely associated with an arterial lactate ≥3.15 mL/L at admission (odds ratio, 13.870; P<0.001). Conclusion: Lactate is an independent predictor of severe PPH and is suitable for a rapid and simple estimation of the severity of PPH. Emergency physicians can use lactate to determine the initial treatment strategies more precisely.ope

農林市場에서의 商人團體에 관한 硏究 : 忠南 洪城 一帶의 褓負商團을 中心으로

학위논문(석사)--서울대학교 대학원 :경제학부 경제학전공,2004.Maste

Coastal Trade Brokers and their Rights in Traditional Korea Revisited Using a Document Database from the Kyujanggak Collection

In the 1980s, a series of lists and research of Changt"o Munjŏk, a unique collection of royal properties at Kyujanggak Institute, were published. Despite the rapid improvement in the understanding of Yŏgaek Chuin, or coastal trade brokers in traditional Korea, no additional progress has been made since the 1990s. This paper attempts to conduct a critical review of existing research and present a novel method of analysis for Korean economic history research through the introduction of a database of Changt"o Munjŏk related to Yŏgaek Chuin in the provincial areas of Kyŏnggi and Ch"ungch"ŏng. Three hypotheses are developed in this study. First, the coastal trade brokers did not become major merchants or accumulate huge commercial capital. Second, the rights of coastal trade brokers were converged, standardized, and even concentrated into the royal force in the nineteenth century, while such rights were disputed in the eighteenth century. Lastly, the purchasing price, which is a key indicator of the secondary market of those rights, did not seem to rise sharply, unlike that depicted in existing research.朝鮮의 대표적 상업기관중 客王는 客商의 主人이고，旅閣은 旅商의 宿屋이라는 설명이 20세기 초에 제시된 바 있다. 이와 같이 객주와 여각을인위적으로 구분한 것은 객주가 수행하는 여러 업무가 조선 후기 王人權에서 파생되어 다양 하게 분화，발전된 사정을 이해하지 못한 결과 발생한 오류였음이 21세기 초에 들어 지적되었다. 약 100년이 경과한 시점에서나마 이와 같은 인식이 가능하게 된 것은 1980년대에 집중적으로 수행되었던 일련의 旅客主人 연구에 힘입은 바 크다. 여객주인을 내륙의 도시나 상업중심지들에서 활동하던 상업자본으로，선상주인을 강가나 바다가의 포구들에 형성된 도시나 상업중심지들에서 활동하던 상업자본으로 구분하는 견해도 있으나，이는 어디까지나 각종 年代記에 나타나는 부실하고도 단편적인 기사에 의존한 것이다. 여객주인에 관한 전면적 연구가 개시되고 난 후에는 여객주인의 범주를 浦口商業과 관계된 것으로 한정하여 이해하는 것이 일반적이며，이는 각종 古文書에 기재된 표현에 근거한다.이 논문은 2008년도 정부(교육과학기술부)의 재원으로 한국연구재단의 지원을 받아 연구되었음(NRF-2008-361-A00007)

체험의 관점에서 본 J.W. von Goethe의 교양소설『Wilhelm Meisters Lehrjahre』연구

학위논문(석사)--서울대학교 대학원 :독어독문학과,1995.Maste

확률분포를 이용한 복합재료의 강도예측

학위논문(석사)--서울대학교 대학원 :섬유고분자공학과,1999.Maste