• Title/Summary/Keyword: end of the century

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Fundamental Background for 3T MRI/MRS

  • Choe, Bo-Young
    • Proceedings of the KSMRM Conference
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    • 2002.11a
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    • pp.47-49
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    • 2002
  • At present, the trend of magnetic field strength in MRI system is dramatically changing. In early 70, the only low field (<0.5T) was developed. It was technically difficult to develop the high field system. At that time, people believed that the fine MR imaging could not be obtained in the high field MR system due to the magnetic susceptibility effect. However, 1.5T system was evolved at the end of 80, and used for clinical usage. Thus, it was proved that the signal to noise ratio (SNR) could be greatly contribute to enhance the image quality. And, the results of functional MRI and MR spectroscopy could be improved in the higher field MR system. So, 8T system was eventually developed in Ohio State University Hospital at the end of 90. Therefore, there is no doubt that the system with the ultra high magnetic field strength will be developed near future in 21 century.

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조선시대의 산학서에 관하여

  • 이창구
    • Journal for History of Mathematics
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    • v.11 no.1
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    • pp.1-9
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    • 1998
  • This article explores what is the genuine Koreanness in Korean arithmetic by examining what kind of influence the Chinese arithmetic had on the Korean arithmetic and how the Korean arithmetic scholars had accepted and utilized it. Because the main stream of Korean culture before the end of Chosun dynasty was located under the umbrella of the Chinese philosophy, technique, and culture, it is necessary to make researches on the historical documents and materials in order to establish the milestone in the Korean arithmetic history for the Korean arithmetic scholars. For this research, the arithmetic books published in between the sixteenth century and the end of Chosun dynasty are mainly consulted and discussed, dealing with the bibliographical introduction in the arithmetic Part in Re Outline History of the Korean Science & Technology written by Prof. Yong-Woon Kim.

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Experimental and analytical study on prestressed concrete hollow slabs with asymmetric boundary conditions

  • Ma, Haiying;Lai, Minghui;Xia, Ye
    • Structural Engineering and Mechanics
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    • v.81 no.1
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    • pp.59-68
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    • 2022
  • Prestressed prefabricated hollow core concrete slabs with spans of 5 m and 10 m are commonly used since last century and still in service due to the advantage of construction convenience and durability. However, the end slabs are regularly subjected to cracks at the top and fail with brittleness due to the asymmetric boundary conditions. To better maintain such widely used type of hollow core slabs, the effect of asymmetric constraint in the end slabs are systematically studied through detailed nonlinear finite element analyses and experimental data. Experimental tests of slabs with four prestressed tendons and seven prestressed tendons with different boundary conditions were conducted. Results observe three failure modes of the slabs: the bending failure mode, shear and torsion failure mode, and transverse failure mode. Detailed nonlinear finite element models are developed to well match the failure modes and to reveal potential damage scenarios with asymmetric boundary conditions. Recommendations regarding ultimate capacity of the slabs with asymmetric boundary conditions are made to ensure a safe and rational design of prestressed concrete hollow slabs for short span bridges.

State of the Art of Taenia solium as Compared to Taenia asiatica

  • Flisser, Ana
    • Parasites, Hosts and Diseases
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    • v.51 no.1
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    • pp.43-49
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    • 2013
  • Three species of tapeworms infect humans in their adult stage (Taenia solium, Taenia saginata and Taenia asiatica). The 3 are flat, opaque white or yellowish, and exceptional long segmented parasites, measuring 1 to 12 m in their adult stage. In this review, the development of the knowledge regarding the first species, mainly focused on understanding how the larval stage or cysticercus is transmitted to humans, is described. The second species is a cosmopolitan parasite that only causes taeniosis and not cysticercosis; therefore, it will not be included. Information on the third species, which is presently being produced, since this species was recognized as such only at the end of the 20th century, will be discussed at the end of this review.

A study of the classic Sijo(時調) concerning the productive life (생활 표현의 고시조 연구)

  • Jeon, Jae-Gang
    • Sijohaknonchong
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    • v.26
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    • pp.151-185
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    • 2007
  • The main industry of the Chosun dynasty was farming, which was related to the people's lives in every respect. By the end of the Chosun dynasty commerce was a new industry becoming increasingly more beneficial. I study how these two industries were being expressed in the classic Sijo. The classic Sijo is a main literary genre created by the upper-class. Even though industry was very important for sustaining the Chosun dynasty, Confucian scholars and government officials(members of the upper class) didn't actually work in the industries of farming and commerce. But sometimes they returned to their rural hometowns, because they owed large amounts of land which they let the servants farm for themselves. As the main composers of Sijo were these Confucian scholars and government officials, I study a collection of their Sijo which expresses the life of industry. In order to achieve this goal, I analyze several sides of the classic Sijo : for example, its writers(along with their personalities) throughout different periods: the point of view of persona; and the specific life of industry and the way it is expressed in the Sijo. First, I look at the writers of the different periods and their personalities. During the fourteenth century to the seventeenth century, the main writers of Sijo on the life of farming were Confucian scholars and government officials. During the eighteenth century to the nineteenth century, the main writers of Sijo on the life of farming were Confucian scholars, government officials, and also commoner singers-the unnamed writers. Second, I look at the point of view of persona. During the fourteenth century to the seventeenth century, the personas were the country man(one's lord and master) and the farmer, who was of two kinds of people : i.e., those trying to work together and those really working together. During the eighteenth century to the nineteenth century, the personas were the country man, who was satisfied with his rural life as overseer to farming, and two kinds of farmers : those who farmed very hard by themselves, or those who criticized the failed tax system. Third, I discuss the specific life of industry and the way it is expressed in the Sijo. During the fourteenth century to the seventeenth century, the writers of Sijo expressed, in a general way together in one Sijo, different kinds of work for example, plowing a dry field and a rice field, picking wild vegetables, and cutting rice and weed. During the eighteenth century to the nineteenth century, the writer of Sijo expressed different kinds of work in a more specific way, each in its own Sijo : for example, buying and selling, bringing land under cultivation for farming. weaving, digging for water, and heavy taxation. I look at three aspects of Sijo concerning industry, but there still remain several aspects of Sijo to study, such as those concerning worship of the king, and those concerning high officials, the common people, and the being of things.

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Elastohydrodynamic Lubrication Analysis of a Tilted Tapered Roller (Tilting 상태인 테이퍼 로울러의 탄성유체윤활 해석)

  • Park, Tae-Jo
    • Tribology and Lubricants
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    • v.31 no.4
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    • pp.177-182
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    • 2015
  • Tapered roller bearings are widely used in equipment where high combined thrust and radial loads are experienced. A certain amount of tilting between the tapered rollers and the races always occurs because of bending moment load conditions and shaft deflection. It is now well understood that a coherent elastohydrodynamic lubrication (EHL) film separates the rollers and races. In spite of extensive study on EHL problems for over half a century, relatively few studies have focused on the finite line contacts problem. This study presents a complete numerical analysis of the effects of roller tilting on the EHL characteristics in a tapered roller bearing. We systematically analyze this highly nonlinear problem using finite differences with fully non-uniform grids and the Newton-Raphson method. Detailed EHL pressure distributions and film shapes are presented under moderate loads and material parameters. A very small roller tilting significantly affects the pressure distributions and film shapes near both ends of the roller. Moreover, the effect of tilting on the EHL characteristics at the small end is much greater than that at the large end. Therefore, in designing optimum profiles for tapered roller bearings, the profile radius should be larger at the small end.

A Study of Similarity between hair Styles of Chosun and france at the End of Eighteenth century (18세기 미 조성과 프랑스 두발양식의 유사성 연구)

  • 구남옥
    • Journal of the Korean Society of Costume
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    • v.42
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    • pp.207-222
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    • 1999
  • This study is a thesis based on the fact that at the end of eighteenth century similar change in hair style appeared in Chosun and France which are located very far almost the opposite side of the earth. We can see that very exaggerated and big hair styles of those days in both countries became exceptionally reduced and changed to practical shapes through (an order prohibiting to make large hair style using wigs) is case of Chosun and through the France Revolution in case of France. Outwardly the abobe mentioned change may seem to be caused by such brave and outward convention as the prohibition order and the revolution. however I think that more basic cause of such change from big and splendid hair styles of those days to simple styles was because of many people's sympathy with the necessity of improving various social and economical problems caused by the luxurious and even prodigal situation of those days before the change and additionally because of such pragmatic thought as Positivism of chosun and illuminism of france. In case of france the change in hair style occurred for such a short period of time around the France Revolution(1789) that we can even that the change occurred in a day. However in case of Chosun such change became fixed at the time of king Suncho prohibiting to make large hair style using wigs (1756-1788) was announced. in case of France such change in hair style was mainly because of change of thought caused by people's self-consciousness. But in case of Chosun under the situation where common people's way of thinking about sumptuous moods and beauty was not changed unvoluntary and compulsory change was asked by the King's order so a lot of time seemed to have been necessary for the change in hair style to become fixed as a nationwide common and general custom.

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Changes in the Low Latitude Atmospheric Circulation at the End of the 21st Century Simulated by CMIP5 Models under Global Warming (CMIP5 모델에서 모의되는 지구온난화에 따른 21세기 말 저위도 대기 순환의 변화)

  • Jung, Yoo-Rim;Choi, Da-Hee;Baek, Hee-Jeong;Cho, Chunho
    • Atmosphere
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    • v.23 no.4
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    • pp.377-387
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    • 2013
  • Projections of changes in the low latitude atmospheric circulation under global warming are investigated using the results of the CMIP5 ensemble mean. For this purpose, 30-yr periods for the present day (1971~2000) and the end of the $21^{st}$ century (2071~2100) according to the RCP emission scenarios are compared. The wintertime subtropical jet is projected to strengthen on the upper side of the jet due to increase in meridional temperature gradient induced by warming in the tropical upper-troposphere and cooling in the stratosphere except for the RCP2.6. It is also found that a strengthening of the upper side of the wintertime subtropical jet in the RCP2.6 due to tropical upper-tropospheric warmings. Model-based projection shows a weakening of the mean intensity of the Hadley cell, an upward shift of cell, and poleward shift of the Hadley circulation for the winter cell in both hemispheres. A weakening of the Walker circulation, which is one of the most robust atmospheric responses to global warming, is also projected. These results are consistent with findings in the previous studies based on CMIP3 data sets. A weakening of the Walker circulation is accompanied with decrease (increase) in precipitation over the Indo-Pacific warm pool region (the equatorial central and east Pacific). In addition, model simulation shows a decrease in precipitation over subtropical regions where the descending branch of the winter Hadley cell in both hemispheres is strengthened.

Impact of predicted climate change on groundwater resources of small islands : Case study of a small Pacific Island

  • Babu, Roshina;Park, Namsik
    • Proceedings of the Korea Water Resources Association Conference
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    • 2018.05a
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    • pp.145-145
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    • 2018
  • Small islands rely heavily on groundwater resources in addition to rainwater as the source of freshwater since surface water bodies are often absent. The groundwater resources are vulnerable to sea level rise, coastal flooding, saltwater intrusion, irregular pattern of precipitation resulting in long droughts and flash floods. Increase in population increases the demand for the limited groundwater resources, thus aggravating the problem. In this study, the effects of climate change on Tongatapu Island, Kingdom of Tonga, a small island in Pacific Ocean, are investigated using a sharp interface transient groundwater flow model. Twenty nine downscaled General Circulation Model(GCM) predictions are input to a water balance model to estimate the groundwater recharge. The temporal variation in recharge is predicted over the period of 2010 to 2099. A set of GCM models are selected to represent the ensemble of 29 models based on cumulative recharge at the end of the century. This set of GCM model predictions are then used to simulate a total of six climate scenarios, three each (2010-2039, 2040-2069, and 2070-2099) under RCP 4.5 and RCP 8.5. The impacts of predicted climate change on groundwater resources is evaluated in terms of freshwater volume changes and saltwater ratios in pumping wells compared to present conditions. Though the cumulative recharge at the end of the century indicates a wetter climate compared to the present conditions the large variability in rainfall pattern results in frequent periods of groundwater drought leading to saltwater intrusion in pumping wells. Thus for sustaining the limited groundwater resources in small islands, implementation of timely assessment and management practices are of utmost importance.

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Effects of Continental Evaporation for Precipitation Over East Asia in the Past and the Future of HadGEM2-AO Climate Model (HadGEM2-AO 기후모델에 따른 과거와 미래의 동아시아 강수량에 대한 육지 증발량의 영향)

  • Kim, Jin-Uk;Lee, Johan;Boo, Kyung-On;Shim, Sungbo;Kim, Jee-Eun;Byun, Young-Hwa
    • Atmosphere
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    • v.26 no.4
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    • pp.553-563
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    • 2016
  • Land evaporation contribution to precipitation over East Asia is studied to understand terrestrial moisture source of continental precipitation. Moisture recycling of precipitation relying on terrestrial evaporation is estimated based on the analysis method of Van der Ent et al. (2010). We utilize HadGEM2-AO simulations for the period of 1970~1999 and 2070~2099 from RCP8.5. Globally, 46% of terrestrial precipitation is depending from continental evaporation. 58% of terrestrial evaporation returns as continental precipitation. Over East Asia, precipitation has been affected by local evaporation and transported moisture. The advection of upwind continental evaporation results from the prevailing westerlies from the midwestern of Eurasian continent. For the present-day period, about 66% of the precipitation over the land of East Asia originates from land evaporation. Regionally, the ratios change and the ratios of precipitation terrestrial origin over the Northern inland and Southern coast of East Asia are 82% and 48%, respectively. Seasonally, the continental moisture recycling ratio is larger during summer (JJA) than winter (DJF). According to RCP8.5, moisture recycling ratio is expected to change. At the end of the 21st century, the impact of continental moisture sources for precipitation over East Asia is projected to be reduced by about 5% compared to at the end of 20th century. To understand the future changes, moisture residence time change is investigated using depletion and replenishment time.