Study of electron bunching in vacuum devices: Electron gun, Linear accelerator

Department of Electrical EngineeringElectron bunching is an interesting issue with practical and scientific applications. In this thesis, I will present two topics of electron bunching in vacuum devices: electron gun, linear accelerator. For the electron gun, I will present a theoretical approach of bunching condition in dc-biased ac-driven vacuum devices. There are two different approaches. The one is electron bunching from a DC-biased single surface multipactor. Generation of electron bunch from a dc biased, single surface multipactor was studied theoretically and by PIC simulations. The condition for a spatially narrow bunch was obtained and verified by PIC simulations. This kind of multipactor is proposed to be used as a compact electron gun for various applications, such as linear accelerators. The other one is a theoretical correlation between the periodicity of an electron micro-bunch train and the transit phase of each electrons passing through a vacuum gap in a dc-biased ac-driven diode was derived. The upper frequency limitation by the transit time effect could be explained by abnormal exclusion of a certain range of transit phase analyzed for the first time by our theory. In a particle-in-cell simulation guided by our theory to evade the deficiency, a micro-bunch train with 1.41 picosecond periodicity (0.707 THz) could be obtained from a gap of 50 ??m regarded as excessively large owing to severe suffering from the transit time effect. For the linear accelerator, A 9.3 GHz 6 MeV linear accelerator (LINAC) was analyzed by using three-dimensional (3D) particle-in-cell (PIC) simulations with 3D time-domain electromagnetic simulations. In the 3D PIC simulations, field data of a p /2 standing wave mode extracted from the 3D time-domain field calculations were injected into a side-coupled LINAC composed of 25 acceleration and 24 coupling cavities. Acceleration of an electron beam of 20 kV, 300 mA in the 3D full LINAC structure was analyzed without spatial or time segmentations, which resulted in maximum energy of 6 MeV and average current of 68.5 mA when 9.3 GHz, 1.6 MW radio frequency (RF) power was assumed. By virtue of in-depth data from the 3D electromagnetic and PIC simulations aided by a one-dimensional (1D) particle code developed by ourselves, the analysis for a full LINAC structure being reported first in this paper, may be informative and useful because experimental reports about an X-band (9.3 GHz) 6 MeV side-coupled LINAC have been rare until now.ope

The Impact of Network Neutrality Violation on the Streaming Platform Ecosystem : Evidence from Twitch TV

The widespread use of media streaming services has resulted in a surge in network traffic, triggering debates on network usage fees between Internet service providers (ISPs) and content providers (CPs). As a response to network usage fees imposed by ISPs, CPs have opted to provide discriminatory service quality as a means of mitigating costs associated with high traffic volume. In 2022, a leading Korean ISP charged discriminatory network usage fees to Twitch TV, the media streaming platform, due to its excessive network traffic. In response, Twitch implemented a discriminatory service quality reduction policy. Our study examines the impact of this policy on the streaming platform ecosystem. Our results indicate that the implementation of the service quality reduction led to a remarkable decline in the number of viewers, which then resulted in adverse effects for streamers. This study contributes to the literature on network neutrality violation by offering empirical evidence

Stringent Nucleotide Recognition by the Ribosome at the Middle Codon Position.

Accurate translation of the genetic code depends on mRNA:tRNA codon:anticodon base pairing. Here we exploit an emissive, isosteric adenosine surrogate that allows direct measurement of the kinetics of codon:anticodon University of California base formation during protein synthesis. Our results suggest that codon:anticodon base pairing is subject to tighter constraints at the middle position than at the 5'- and 3'-positions, and further suggest a sequential mechanism of formation of the three base pairs in the codon:anticodon helix

Design and Application of a Collocated Capacitance Sensor for Magnetic Bearing Spindle

This paper presents a collocated capacitance sensor for magnetic bearings. The main feature of the sensor is that it is made of a specific compact printed circuit board (PCB). The signal processing unit has been also developed. The results of the experimental performance evaluation on the sensitivity, resolution and frequency response of the sensor are presented. Finally, an application example of the sensor to the active control of a magnetic bearing is described

How Did the Clinical Medicine Progress during the Unified Silla Era: Installment of the Medical Education Center ‘Uihak 醫學’, and Its Effects

In this research, I aimed to recognize the historical meaning of installing the medical education center, ‘Uihak 醫學’, during the Silla 新羅 dynasty. ‘Uihak’ was installed in 692, in the first year of King Hyoso 孝昭 ’s rule. ‘Uihak’ was founded by using various Chinese medical classics as its textbooks for medical education, such as the Classic of Plain Questions 素問經.The wooden prescriptions excavated from Anapji 雁鴨池, which is thought to have been created in the middle of the 8th century, and the Chinese medical book Prescriptions for Universal Benefit 廣利方, which the envoy of Silla tried to acquire in 803, reflect the idea on medicine during that period in Silla. By this time, the field of medicine began to develop the idea to discern the locations and mechanism of disease patterns by centering on the viscera and bowels 臟腑 while making use of the herbal prescriptions based on various drugs. This means that clinical medicine founded upon the medical education achieved in ‘Uihak’ was being realized in the medical fields as well. According to the Chronicles of the Three States 三國史記, for the illness of Queen Sunduk 善德 in 636, medicine, praying, and the method of esoteric Buddhism 密敎 was tried out as a means of her cure. Comparatively, for the treatment of the first rank Chunggong 忠公 in 822, the Kingdom’s representative doctor 國 醫 with professional medical knowledge was sought out to fine a cure. The analyses of the human disease, diagnosis, treatment method, etc., given by the kingdom’s representative doctor were identical to those recommended in the medical textbooks used in ‘Uihak’. As such, we can posit that his academic background was ‘Uihak’ and the education given there.The Classic of Materia Medica 本草經, which was also used in ‘Uihak’, was a book professionally centered on the drug branch of medicine. The Classic of Materia Medica is a terminology referring to various books on drugs, including the Shennong’s Classic of Materia Medica 神農本草經, the Variorum of the Classic of Materia Medica 本草經集注, the Newly Revised Materia Medica 新修本草, etc. Thus, we cannot specify what the classic of Materia Medica actually taught, based on only its terminology. However, based on the wooden prescriptions excavated from Anapji, and from the terminology of drugs recorded in the drug trading document Purchase List for Silla goods 買新羅物解 preserved in Shosoin 正倉院 of Japan, we can hypothesize that in the middle of the 8th century, the Newly Revised Materia Medica was indeed being circulated. Based on these evidences, we can also hypothesize that Silla was part of the network of drug trading that encompassed the entire region of Asia.After unifying the Korean peninsula, the Kingdom of Silla actively adopted the medical educational system of Tang 唐 China. By using the obtained medical knowledge, Silla cured illnesses and used the medical knowledge on various drugs recorded in the Newly Revised Materia Medica to pursue trade with China, Japan, and other countries. Through the installation of ‘Uihak’, the same medicine has now begun to be officially used in East Asia, including Silla

Characteristics of Using Oriental Medicine Clinics during the Japanese Occupation: An Analysis of the 1931 Seoul Bochun Clinic Account Book

This article analyzes the “account book” of Kim Young-hoon (1882-1974), which summarizes information about patients at his Bochun Clinic in Seoul (then Gyeongseong) in 1931. Kim Young-hoon was a pivotal figure in the medical scene throughout the Korean Empire, the Japanese occupation, and the early years of the Republic of Korea. He left behind a large amount of documentation during his 60 years of practice at the Bochun Clinic, which he opened in the spring of 1909. In particular, the 1931 “account book” offers an insight into the daily life histories of his patients.Among the patient-visitors recorded in the account book, there were many influential people of the time, ranging from privileged individuals to anti-Japanese independence activists, from those in political and economic fields to those in academic and entertainment fields. At the same time, a significant number of lower-class people also visited the Clinic. Geographically, patients were centered in the city center of the capital, Gyeongseong, but were also widely distributed throughout the country. There are indications that those from the rural areas stayed in the homes of their acquaintances in Seoul. As such, the account book provides a tangible, concrete picture of the clinic’s management for the year 1931, including visitor demographics, visiting diagnoses, telephone consultations, and the total cost of medicinal prescriptions.Because the account book is a one-year statistic, it has its limitations; however, it is the smallest unit that can be analyzed statistically. It provides insights into how many people came in over the course of a year and how much they spent. The expenditures are kept per individual family. The patient's name, prescribed medication, and the price of the medicine are mandatorily included, and in many cases, the place of residence and family relationships are also noted. The account book shows several layers of householders, servants, and employees in the extended family; it also shows people in various occupations. A few privileged families accounted for nearly half of the total expenditures, and the powerful visited frequently, utilizing Oriental medicine for many of their daily needs. For some, the Bochun Clinic is reminiscent of the royal temples of the dynasties. Patients come from the center and suburbs of Seoul, as well as from all over the country.In one year, more than one thousand types of prescriptions are issued and the total cost of medicines is about 33 seom (≒180 liters of rice). Although there is a concentration of high-frequency prescriptions, more than a thousand prescriptions are prescribed only once, which shows that the practice is specialized for each individual. Patient visits, consultations, and telephone use are observed, and the use of new drugs, quinine, and special ginseng as one-herb medication (danbang) are also noticeable.The statistical analysis of the 1931 Bochun Clinic “account book” can serve as a milestone for comparative analysis of the patterns of herbal medicine use before and after that year. Meanwhile, the Bochun Clinic “account book” shows the continuation of traditional practices of herbal medicine by both the powerful and the masses. On the one hand, Koreans responded to the coercive tide of modernity symbolized by the Imperial Governorate of Japan, but on the other hand, they were unwilling to let go of tradition and their own authority. While actively embracing the tide of civilization, Koreans also internalized their own rationality and sought to open a new path forward, a sentiment discernible between the lines of the “account book.

Phase stability of hafnium oxide and zirconium oxide on silicon substrate

Phase stabilities of Hf-Si-O and Zr-Si-O have been studied with first-principles and thermodynamic modeling. From the obtained thermodynamic descriptions, phase diagrams pertinent to thin film processing were calculated. We found that the relative stability of the metal silicates with respect to their binary oxides plays a critical role in silicide formation. It was observed that both the HfO$_2$/Si and ZrO$_2$/Si interfaces are stable in a wide temperature range and silicide may form at low temperatures, partially at the HfO$_2$/Si interface.Comment: 5 pages, 3 figure