• Journal of the Korean Vacuum Society
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• v.10 no.4
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• pp.424-430
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• 2001

An electron Boltzmann equation is solved numerically to calculate the electron energy distribution functions in plasma discharge which is generated by radio-frequency (RF) and microwave frequency electric field. The maintenance field strengths are determined self-consistently by solving the homogeneous electron Boltzmann equation in the Lorentz approximation expressed by 2nd order differential equation and an additional particle balance equation expressed by integro-differential equation. By using this numerical code, the electron energy distribution functions in argon discharge are calculated in the range from RF to microwave frequency. The influence of frequency of the HF electric field on the electron energy distribution functions and ionization rate are investigated.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.4
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• pp.437-444
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• 2009

A bi-directional, multi-step numerical integrator is developed to determine the GPS (Global Positioning System) orbit based on a dynamic approach, which shows micrometer-level accuracy at GPS altitude. The acceleration due to the planets other than the Moon and the Sun is so small that it is replaced by the empirical forces in the Solar Radiation Pressure (SRP) model. The satellite orbit parameters are estimated with the least-squares adjustment method using both the integrated orbit and the published IGS (International GNSS Service) precise orbit. For this estimation procedure, the integration should be applied to the partial derivatives of the acceleration with respect to the unknown parameters as well as the acceleration itself. The accuracy of the satellite orbit is evaluated by the RMS (Root Mean Squares error) of the residuals calculated from the estimated orbit parameters. The overall RMS of orbit error during March 2009 was 5.2 mm, and there are no specific patterns in the absolute orbit error depending on the satellite types and the directions of coordinate frame. The SRP model used in this study includes only the direct and once-per-revolution terms. Therefore there is errant behavior regarding twice-per-revolution, which needs further investigation.

• School Mathematics
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• v.19 no.1
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• pp.171-187
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• 2017

To engineering students, calculus is essential knowledges and skills as a mathematical model and give a perspective to observe phenomenon in the future industrial field. However, engineering students' calculus study tends to solve problems by only applying the mechanical calculation and mathematical results. This study aimed to make engineering students realize the importance of calculus and untypical problems, by suggesting problems that could apply the mathematical concepts and principles and even solve the actual conditions of the problems. Students conjectured the anti-derivative graphs by interpreting the given derivate problems. They showed errors in this process and the errors are contributed by their mathematics leaning styles. As a result, the task would be helpful to engineering students.

• Communications of Mathematical Education
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• v.21 no.4
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• pp.613-620
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• 2007

We made an investigation into basic mathematical abilities and made university freshmen an object of this study in order to find out the reason why their capabilities are remarkably behind in studies year by year. According to the survey, we confirmed that recent university freshmen's basic abilities to attend calculus class, right away after entering university, are insufficient for that class. In particular, a matter of grave concern is that score variations are so big despite the equal major of the same university. The aim of the study is to evaluate university freshmen's basic mathematical abilities in nationwide university and to figure out the real situation, then to give assistance to the proper calculus curriculum of university by reflecting the result in it. And also we wish to be helpful to propose proper policy plan in natural science system of highschool.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.283-292
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• 2009

Considering an integral equation governing the motion of unfolding fin, an algebraic equation was acquired to get estimated minimum deployment energy required for the successful fin unfolding under the given wind condition. To complete the integration of moment, some approximations had to be introduced particularly to frictional moment and aerodynamic damping for which deployment angular speed of the unfolding fin was modelled as a function of deployment angle only with assumed profile using expected maximum angular speed. Technique for the estimation of the minimum required deployment energy was finalized by introducing the ideal deployment angular speed representing work done by the fin unfolding device alone during fin unfolding and was confirmed by comparing results from simulation with various aerodynamic conditions and profiles of the hinge torque.

• School Mathematics
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• v.8 no.4
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• pp.417-439
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• 2006

Many studies indicate the emerging crisis of education of calculus even though the emphasis of calculus have been widely recognized. In our classrooms, the education of calculus also has been faced with its bounds. Most instructions of calculus is too much emphasis on the algebraic approach, thus students solve mathematical problems without truly understanding the underlying concept. The purpose of this study is to develop mathematization teaching and learning materials and methods in caculus based on the mathematization teaching and learning theories by Freudenthal and the variability principles of conceptual learning by Dienes, In order to this purpose, first, we analyzed the high school mathematics II textbook of 7th curriculum in Korea. Second, we developed mathematization teaching and learning materials and methods in highschool calculus. Consequently, the following conclusions have been drawn: we have reorganized and reconstructed the context problem in calculus based on concepts of tangent line and instantaneous rate of change.

• Journal for History of Mathematics
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• v.17 no.3
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• pp.33-42
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• 2004

${\varrho}$ is the real constant number that appears not only in calculus but also in a real life. The concept of the number ${\varrho}$ first appeared in an appendix of Napier's work on logarithms in 1618. The early developments on the logarithm became part of an understanding of the number ${\varrho}$. In 1727, the number ${\varrho}$ was studied by Euler explicitly. It ton14 almost 100 years to understand the number ${\varrho}$ which we learn in high school nowadays. By studying the origin of the number ${\varrho}$, we can guess that many mathemetician's research in our time will have significant meaning in the future although it looks like just some calculations of cohomology or K-theory etc.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.65-74
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• 2005

It is required for getting the ring laser gyro output purely related to the input rotation to eliminate the output of the modulated angular vibration from the ring laser signal. In this paper we discuss the dither stripping methods of compensating the ring laser signal by converting the rate signal of dither detector from voltage to frequency for a dither type ring laser gyro. We discuss the differential methods for getting rid of the offset of the V-F signal. And we develope the methods of compensating the phase differences between the ring laser signals and the V-F differential signals by using analog integrator and digital time delays. And also, we develope the gain calculation method by comparing the standard deviations of the ring laser signals with V-F differential signals. We implemented these methods and analyzed the effectiveness of these methods by comparing the dither trapping methods.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.75-81
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• 2002

In the re-entry comtrol system, errors apt to induce because the time deriviative of drag acceleration is analytically estimated. Still more, the difficulty of estimation of th exact drag coefficient in hypersonic velocity and the non-reality of the scale height cause a steady-state drag errer. In the Space-Shuttle, a steady-state drag error is reduced by the addition of the integral term of drag acceleation error into the control system. This method, however, induces a difficulties in respect to the modern controller composition due to the multi-poles in a closed-loop system. Thus, this paper proposes the additional method of the disturbance observer. This reduces the steady-state drag error according to the following by the analytic calculation, and then creates the new drag acceleration time derivative using the estimated error. The performance of the re-entry control system is verified about 32 refernce trajectories.

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.296-298
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• 2009

Ac-dc 싸이리스터 컨버터에서 전류기준값의 부호가 변화할 경우에 적분항 초기값을 통해 전류제어 과도특성을 개선하는 연구가 있었다. 이 논문에서는 전류기준값의 기울기에 변화가 있을 때 그 변화를 일으키기 위한 전압을 계산하고 그 값을 점호각 $\alpha$로 환산하여 시스템에 적용시켜 변곡점 부근에서의 전류제어 특성을 개선하는 방법을 제시하였다. 또한 전류기준값에 노이즈가 포함된 경우 LPF 유/무에 따른 특성변화와 노이즈가 포함되지 않은 경우 LPF 유/무에 따른 특성변화를 관찰하였다.