• Journal of Korean Ophthalmic Optics Society
• /
• v.13 no.3
• /
• pp.35-43
• /
• 2008

Purpose: This review article was written to investigate how the various factors, such as lacrimal thickness, CL's thickness and Dk, affects the influx of $O_2$ diffusion into the cornea. Methods: A mathematical model was proposed to analyze the oxygen diffusion reaching the cornea through the tear layers and contact lens based on Fick's law and the principle of continuity of the diffusion flux through the each layers. Results: The model predicts how the parameters such as the thickness of tear layer on the cornea, both the Dk and thickness of contact lenses etc., affect the oxygen tension at cornea and oxygen flux entering the cornea. Conclusions: It is found that either too flat or too tightly fitted contact lenses can cause the oxygen deficiency at/inside the periphery of the cornea because of the reduction of oxygen flux resulted from too thickened tear layer.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.5 s.170
• /
• pp.130-137
• /
• 2005

Recently, the importance of CAE research is growing with the advances of the automotive and computer industry. In addition, multi-body dynamics and powertrain analysis are the most important factors in improving the vehicle design. Since engine torque with curve-data was used for analyzing full car simulation in the multi-body dynamics system for many years, it is impossible to assess the concurrent analysis of the engine and powertrain element included in a real full car system. In powertrain, since vehicle are usually modeled as a simple mass and a inertia, they can not be seen as real cars. Moreover, it is hard to obtain additional dynamics data other than the longitudinal velocity value in movement. Because of the reason that was previously discussed, it is necessary to consolidate the two parts as one routine program for design and development through the coordinate system connectivity, and presented here is a program named O-DYN. Using an object-oriented language C++, this program has a good structure with the valuable characteristics of objectivity, inheritance, and reusability. The reliability of this multi-body dynamics program is examined by DADS, which is the general dynamics program, using DAE solver and PECE integral function with the common coordinator separation method. As a result, we can obtain a better solution and total dynamics data in either area through this process. This program will be useful for analyzing full car simulation with powertrain.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.4
• /
• pp.51-59
• /
• 2006

In this paper, the effect of variation of density and uniformity coefficient on shear strength was analyzed from the results of large scale shear test. In addition, the friction coefficient at critical state per vertical load was estimated using the equation proposed by Wood (1998). The test sample fur the test was obtained from the local quarry sites. Tests results show that the shear strength of $2.10g/cm^3$ is relatively larger than that of $1.85g/cm^3$ and uniformity coefficient (5.0) has larger shear strength than that in 10.0. In the meantime, the friction coefficient at critical state shows $1.0{\sim}1.6$ according to the test conditions.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2022.10a
• /
• pp.459-461
• /
• 2022

One of the big differences between Network-on-Chip (NoC) and the existing parallel processing system based on an off-chip network is that data packet routing is performed using a centralized control scheme. In such an environment, the best-effort packet routing problem becomes a real-time assignment problem in which data packet arriving time and processing time is the cost. In this paper, the Hungarian algorithm, a representative computational complexity reduction algorithm for the linear algebraic equation of the allocation problem, is implemented in the form of a hardware accelerator. As a result of logic synthesis using the TSMC 0.18um standard cell library, the area of the circuit designed through case analysis for the cost distribution is reduced by about 16% and the propagation delay of it is reduced by about 52%, compared to the circuit implementing the original operation sequence of the Hungarian algorithm.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2003.05a
• /
• pp.181-186
• /
• 2003

The satellite navigation system is widely used for identifying a user's position regardless of weather or geographic conditions and also make effect on new technology of marine LBS(Location Based Service), which has the technology of geographic information such as the ENC. Generally, there are conceivable systems of marine LBS such as ECDIS, or ECS that use the ENC itself with powerful processor in installed type on ships bridge. Since the ENC is relatively heavy structure with dummy format for data transfer between different systems, we should reduce the ENC to small and compact size in order to use it in mobile platform. In this paper, we assumed that the mobile system like PDA, or Webpad can be used for small capability of mobile platform. However, the ENC should be updated periodically by update profile data produced by HO. If we would reduce the ENC without a consideration of update, we could not get newly updated data furthermore. As summary, we studied considerations for ENC reduction with update capability. It will make the ENC be useful in many mobile platforms for various applications.

• The Journal of Engineering Geology
• /
• v.33 no.1
• /
• pp.105-119
• /
• 2023

Water supply is decreasing due to climate change, and coastal and island regions are highly dependent on groundwater, reducing the amount of available water. For sustainable water supply in coastal and island regions, it is necessary to accurately diagnose the current condition and efficiently distribute and manage water. For a precise analysis of the groundwater flow in the coastal island region, submarine fresh groundwater discharge was calculated for the Seongsan basin in the eastern part of Jeju Island. Two methods were used to estimate the thickness of the fresh groundwater. One method employed vertical interpolation of measured electrical conductivity in a multi depth monitoring well; the other used theoretical Ghyben-Herzberg ratio. The value using the Ghyben-Herzberg ratio makes it impossible to accurately estimate the changing salt-saltwater interface, and the value analyzed by electrical conductivity can represent the current state of the freshwater-saltwater interface. Observed parameter was distributed on a virtual grid. The average of submarine fresh groundwater discharge fluxes for the virtual grid was determined as the watershed's representative flux. The submarine fresh groundwater discharge and flux distribution by year were also calculated at the basin scale. The method using electrical conductivity estimated the submarine fresh groundwater discharge from 2018 to 2020 to be 6.27 × 10⁶ m³/year; the method using the Ghyben-Herzberg ratio estimated a discharge of 10.87 × 10⁶ m³/year. The results presented in this study can be used as basis data for policies that determine sustainable water supply by using precise water budget analysis in coastal and island areas.

• Communications of Mathematical Education
• /
• v.25 no.2
• /
• pp.403-430
• /
• 2011

The purpose of the study was to investigate how the use of graphing calculators influence on forming students' mathematical concept of algebra, students' mathematical connection, and attitude toward mathematics. First, graphing calculators give instant feedback to students as they make students compare their written answers with the results, which helps students learn equations and linear inequalities for themselves. In respect of quadratic inequalities they help students to correct wrong concepts and understand fundamental concepts, and with regard to functions students can draw graphs more easily using graphing calculators, which means that the difficulty of drawing graphs can not be hindrance to student's learning functions. Moreover students could understand functions intuitively by using graphing calculators and explored math problems volunteerly. As a result, students were able to perceive faster the concepts of functions that they considered difficult and remain the concepts in their mind for a long time. Second, most of students could not think of connection among equations, equalities and functions. However, they could understand the connection among equations, equalities and functions more easily. Additionally students could focus on changing the real life into the algebraic expression by modeling without the fear of calculating, which made students relieve the burden of calculating and realize the usefulness of mathematics through the experience of solving the real-life problems. Third, we identified the change of six students' attitude through preliminary and an ex post facto attitude test. Five of six students came to have positive attitude toward mathematics, but only one student came to have negative attitude. However, all of the students showed positive attitude toward using graphing calculators in math class. That's because they could have more interest in mathematics by the strengthened and visualization of graphing calculators which helped them understand difficult algebraic concepts, which gave them a sense of achievement. Also, students could relieve the burden of calculating and have confidence. In a conclusion, using graphing calculators in algebra and function class has many advantages : formulating mathematics concepts, mathematical connection, and enhancing positive attitude toward mathematics. Therefore we need more research of the effect of using calculators, practical classroom materials, instruction models and assessment tools for graphing calculators. Lastly We need to make the classroom environment more adequate for using graphing calculators in math classes.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.13 no.1
• /
• pp.18-29
• /
• 2010

Offshore subsurface storage of $CO_2$ is regarded as one of the most promising options to response severe climate change. Marine geological storage of $CO_2$ is to capture $CO_2$ from major point sources, to transport to the storage sites and to store $CO_2$ into the offshore subsurface geological structure such as the depleted gas reservoir and deep sea saline aquifer. Since 2005, we have developed relevant technologies for marine geological storage of $CO_2$. Those technologies include possible storage site surveys and basic designs for $CO_2$ transport and storage processes. To design a reliable $CO_2$ marine geological storage system, we devised a hypothetical scenario and used a numerical simulation tool to study its detailed processes. The process of transport $CO_2$ from the onshore capture sites to the offshore storage sites can be simulated with a thermodynamic equation of state. Before going to main calculation of process design, we compared and analyzed the relevant equation of states. To evaluate the predictive accuracies of the examined equation of states, we compare the results of numerical calculations with experimental reference data. Up to now, process design for this $CO_2$ marine geological storage has been carried out mainly on pure $CO_2$. Unfortunately the captured $CO_2$ mixture contains many impurities such as $N_2$, $O_2$, Ar, $H_{2}O$, $SO_{\chi}$, $H_{2}S$. A small amount of impurities can change the thermodynamic properties and then significantly affect the compression, purification and transport processes. This paper analyzes the major design parameters that are useful for constructing onshore and offshore $CO_2$ transport systems. On the basis of a parametric study of the hypothetical scenario, we suggest relevant variation ranges for the design parameters, particularly the flow rate, diameter, temperature, and pressure.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.6 no.1
• /
• pp.77-87
• /
• 1996

In order to compare the difference of the measurement of delta aminolevulinic acid(${\delta}$-ALA) in urine between HPLC method(HALA) and colorimetric method(CALA), and also to provide useful information for the new diagnostic criteria of ${\delta}$-ALA in urine in lead poisoning, if at all possible in the future, authors studied 234 male lead workers who were selected from 7 storage battery factories, 3 secondary smelting industries, and 2 litharge making industries. Study subjects were selected on the basis of blood Zinc protoporphyrin(ZPP) level from low to high concentration to cover wide range of lead exposure. Study variables for this study were ${\delta}$-ALA measured by two different methods, blood lead(PbB), and blood ZPP. The results were as follows: 1. There was very high correlation between ${\delta}$-ALA measured by two method(r = 0.989 : HALA = -0.8194 + 0.8110 ${\times}$ CALA), but the value of CALA was measured about 2mg/L greater than HALA. 2. While the correlations of ${\delta}$-ALA by two method with blood lead and blood ZPP were 0.46 and 0.37 respectively, they were increased to 0.63 and 0.57 if ${\delta}$-ALA values were log-transformed. 3. Simple linear regression of ${\delta}$-ALA measured by two method on ZPP were as follows: CALA = 2.0421 + 0.0341 ${\times}$ ZPP ($R^2=0.1385$ p = 0.0001) HALA = 0.8006 + 0.0280 ${\times}$ ZPP ($R^2=0.1389$ p = 0.0001) 4. Simple linear regression of ${\delta}$-ALA measured by two method on PbB were as follows: CALA = - 0.4134 + 0.1545 ${\times}$ PbB ($R^2=0.2085$ p = 0.0001) HALA = -1.2893 + 0.1287 PbB ($R^2=0.2154$ p = 0.0001), 5. Simple linear regression of log-transformed ${\delta}$-ALA by two method on ZPP and PbB were as follows: logHALA = 0.3078 + 0.0060 ZPP ($R^2=0.3329$ p = 0.0001) logCALA = 1.0189 + 0.0044 ZPP ($R^2=0.3290$ p = 0.0001) logHALA = -0.0221 + 0.0246 PbB ($R^2=0.4046$ p = 0.0001) logCALA = 0.7662 + 0.0184 PbB ($R^2=0.4108$ p = 0.0001) 6. The cumulative percent of colorimetric method to detect lead workers whose value of PbS and ZPP were over screening level such as $40{\mu}/dl$ and $100{\mu}/dl$ respectively was higher than HPLC method if cut-off level of ${\delta}$-ALA for screening of lead poisoning was 5 mg/L. But if cut-off level of ${\delta}$-ALA measured by HPLC was reduced to 3 mg/L which is compatible to 5 mg/L of ${\delta}$-ALA measured by colorimetric method, there were good agreement between two methods and showed dose-response relationship with other lead exposure indices such as PbB and ZPP.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.37.3-38
• /
• 2017

우리나라의 천문 관측의 기록의 역사는 삼국시대 이전 선사시대까지 거슬러 올라간다. 선사시대에는 천문 현상을 바위나 건축 유물에 기록을 남기고 역사를 기록하기 시작한 이후에는 일반 역사 기록 속에 항상 함께 기록하고 있다. 특히 동양은 역사기록 자체가 인간이 남긴 자취뿐만 아니라 하늘과 땅에 일어나는 다양한 자연 현상도 함께 동시에 남겼다. 고대로부터 인간은 하늘과 땅과 항상 유기적인 관계를 갖는다고 믿었기 때문이다. 우리나라는 정사로서 가장 오래된 역사 기록인 삼국사기와 삼국유사에 일식, 혜성 출현, 별똥과 유성우, 달과 행성 운행, 초신성 관측 등 250회 이상의 천문 기록이 나타나며 대부분 실제로 일어났던 사실을 그대로 기록하고 있다. 그 후 고려사와 조선왕조실록에는 이루 헤아릴 수 없을 정도로 많은 천문 기록을 남기고 있다. 이러한 천문 기록뿐만 아니라 일찍부터 중국으로부터 역법을 도입하여 천체 운행을 이용하여 우리 생활에 필요한 시각법을 사용하고 달력을 제작하였다. 특히 달과 태양의 운행 원리를 파악하여 일식과 월식을 직접 추산하였다. 역법의 운용은 천체 운행의 원리를 이해하고 수학을 발전시키는데 큰 역할을 하였다. 이러한 천문 관측과 정확한 시각 체계를 유지하고 정밀한 역법을 사용하기 위해서는 끊임없이 천체를 정밀하게 관측할 필요성이 있다. 이를 위해 다양한 천문 관측기기를 개발하고 제작하였다. 천문 의기는 천체의 위치를 측정하고 천체의 운행을 이용하여 시각 체계를 유지 관리를 위해 필수불가결한 기기이다. 우리나라 천문학 발달의 네 가지 축인 천문(天文), 역법(曆法), 의상(儀象), 구루(晷漏)등은 조선 초기 세종시대 완성을 보게 되었다. 이는 단일 왕조가 이룬 업적으로 다른 문화권에서 볼 수 없을 정도의 우수한 과학 기술의 유산이다. 특히 칠정산내편과 외편의 완성은 중국의 역법에서 벗어나 독자적인 역법을 완성하려는 시도였다. 이 모든 것은 당시 이를 주도하던 세종대왕의 지도력과 천문학과 수학에 뛰어난 천문학자가 이룩한 업적이다. 그 후 조선 중기로 접어들면서 쇠퇴하다가 임진왜란과 병자호란을 겪으면서 거의 모든 과학기술의 유산이 파괴되거나 유실되었다. 조선 현종 이후에 세종시대의 유산을 복원하려는 노력 중에 중국을 통하여 서양의 천문학을 도입하게 되었다. 중국에 들어와 있던 서양 선교사들이 주도하여 중국의 역법 체계를 바꾸었다. 즉, 일식과 월식의 예측력이 뛰어난 시헌력을 만들어 사용하기 시작했다. 시헌력에는 서양의 대수학과 기하학을 이용한 다양한 수학적 기법이 사용되었다. 조선 후기에 이 시헌력을 익히기 위한 노력을 하는 과정에서 서양의 수학과 기하학을 접하게 되고 새로운 우주 체계를 도입하게 되었다. 특히 서양의 천문도와 지도 제작에 기하학의 투사법이 사용되어 복잡한 대수학적 계산을 단순화시켜 활용하였다. 조선 후기에 전문 수학자뿐만 아니라 많은 유학자들도 서양의 수학과 기하학에 깊은 관심을 갖고 연구하였다. 고천문학 전체를 조망해 볼 때 핵심은 현대의 천체물리학이 아니라 위치천문학이다. 따라서 고천문학을 연구하는데 필수적인 요소가 지구의 자전과 공전 운동에 의해서 일어나는 현상과 세차운동에 의한 효과를 정확하게 이해하고 있어야 한다. 그중에서도 구면천문학과 천체역학에 대한 원리를 알고 있는 상태에서 접근해야 한다. 고천문학의 중심인 천문(天文), 역법(曆法), 의상(儀象), 구루(晷漏) 등의 내용은 이러한 위치천문학이 그 기본 골격을 이루고 있다. 예를 들어 고려사의 천문 현상을 모아 놓은 천문지(天文志)와 일식과 월식 계산 원리가 들어있는 역지(曆志)를 연구하기 위해서는 위치천문학의 기본 개념 없이는 연구하는데 한계가 있다. 인문학을 전공하는 학자가 고천문을 연구하는데 가장 큰 걸림돌이 되는 점이 위치 천문학의 기본 개념 없이 접근하는 것이다. 심지어 조선시대 유학자들조차 저술한 많은 천문 관련 기록을 보면 상당부분 천체 운행 원리를 모르고 혼란스럽게 기록된 내용이 적지 않다. 우리나라 수학사를 연구할 경우 방정식 해법, 보간법, 삼각법, 일반 기하 원리에 대한 것을 연구하는데 큰 문제가 없다. 그러나 천문 현상이나 천문 의기 제작에 사용되는 수학은 천문 현상에 대한 원리를 모르면 접근하기 어렵게 된다. 수학사를 하더라고 기본적인 위치 천문학의 기본개념을 이해하고 있어야 폭 넓은 수학사 연구에 성과를 거둘 수 있다. 의외로 천문 현상 추산을 위해 사용되는 수학이나 기하학 원리가 수학사 연구에 중요한 요소가 된다. 더구나 한문으로 기록된 천문 내용을 한문 해독이 능숙한 학자라 하더라도 내용을 모르고 번역하면 도무지 무슨 내용인지 알아볼 수 없는 경우가 많다. 그래서 한문으로 된 천문 현상 기록이나 역법 관련 기록의 번역 내용 중에 많은 오역을 발견하게 된다. 문제는 한번 오역을 해 놓으면 몇 십 년이고 그대로 그 내용을 무비판적으로 인용하게 되고 사실로서 인정하는 오류를 범하게 된다. 이 때문에 우리 선조들이 남긴 고천문 관련 기록에 관한 이해는 우리 현대 천문학자의 역할이 대단히 크다.