• 천문학회지
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• 제56권2호
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• pp.201-212
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• 2023

The inscription of Cheonsang Yeolcha Bunyajido (天象列次分野之圖) has the sun's locations at the equinoxes, which must have been copied from the astronomical treatises in Chinese historical annals, Songshu (宋書) and Jinshu (晉書). According to the treatises, an astronomer Wang Fan (王蕃, 228-266 CE) referred those values from a calendrical system called Qianxiangli (乾象曆, 223 CE), from which it is confirmed that it adopted the sun's location at the winter solstice of the $(21{\frac{1}{4}})^{th}$ du of the 8th lunar lodge Dou (斗) as the reference direction for equatorial lodge angles. This indicates that the sun's locations at equinoxes and solstices in the calendrical system are the same as those in Jingchuli (景初曆, 237 CE). Hence, we propose that the sun's location at the autumnal equinox in Cheonsang Yeolcha Bunyajido should be corrected from 'wu du shao ruo' (五度少弱), meaning the $(5{\frac{1}{6}})^{th}$ du, to 'wu du ruo' (五度弱), meaning the $(4{\frac{11}{12}})^{th}$ du, of the first lunar lodge Jiao (角), as seen in Jingchuli. We reconstruct the polar coordinate system used in circular star charts, assuming that the mean motion rule was applied and its reference direction was the sun's location at the winter solstice. Considering the precession, we determined the observational epoch of the sun's location at the winter solstice to be t_o = -18.3 ± 43.0 adopting the observational error of the so-called archaic determinatives (古度). It is noteworthy that the sun's locations at equinoxes inscribed in Cheonsang Yeolcha Bunyajido originated from Houhan Sifenli (後漢 四分曆) of the Latter Han dynasty (85 CE), while the coordinate origin in the star chart is related to Taichuli (太初曆) of the Former Han dynasty (104 BCE).

• Journal of Magnetics
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• 제17권1호
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• pp.19-26
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• 2012

This paper deals with the performance analysis and estimation of the electrical parameters of a permanent magnet synchronous generator (PMSG) for hydrokinetic energy conversion applications using vortex induced vibration (VIV). The analytical solutions for the magnetic fields produced by permanent magnets (PMs) and stator winding currents are obtained using a 2D polar coordinate system and a magnetic vector potential. An analytical expression for the 2D permeance is also derived, which takes into account stator skew effects. Based on these magnetic field solutions and the 2D permeance function, electrical circuit parameters such as the backemf constant and the air-gap inductance are obtained analytically. The performances of the PMSG are investigated using the estimated electrical circuit parameters and an equivalent circuit (EC). All analytical results are validated extensively using 2D finite element (FE) analyses. Experimental measurements for parameters such as the back-emf and inductance are also presented to confirm the analyses.

• Ocean and Polar Research
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• 제23권2호
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• pp.181-188
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• 2001

We describe here the Korea ocean prediction system that closely resembles operational numerical weather prediction systems. This prediction system will be served for real-time forecasts. The core of the system is a three-dimensional primitive equation numerical circulation model, based on ${\sigma}$-coordinate. Remotely sensed multi-channel sea surface temperature (MCSST) is imposed at the surface. Residual subsurface temperature is assimilated through the relationship between vertical temperature structure function and residual of sea surface height (RSSH) using an optimal interpolation scheme. A unified grid system, named as [K-E-Y], that covers the entire seas around Korea is used. We present and compare hindcasting results during 1990-1999 from a model forced by MCSST without incorporating RSSH data assimilation and the one with both MCSST and RSSH assimilated. The data assimilation is applied only in the East Sea, hence the comparison focuses principally on the mesoscale features prevalent in the East Sea. It is shown that the model with the data assimilation exhibits considerable skill in simulating both the permanent and transient mesoscale features in the East Sea.

• 한국인터넷방송통신학회논문지
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• 제15권4호
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• pp.105-117
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• 2015

본 논문에서는 PRC (polar-rectangular coordinate) 에 대한 2 tier 19 셀에 대해 고려해보고, BS 와 같은 셀 중앙으로 부터의 거리에 기반해 셀룰러 망의 셀 에지(edge) 성능을 제시한다. BS 들은 하향링크 다중 셀 시스템에서 ICI (intercell interference) 제거를 위한 자신들의 SINR (signal-to-interference-noise ratio) 을 개선하기 위해 셀 에지 user 와 협력하여 송신한다. 제안한 새로운 모델은 다중 셀 시스템의 MIMO DC sum rate 용량을 계산한다. 이 모델은 협력 하향 링크 다중 셀 시스템에서 셀 간 간섭을 제거해 셀 에지 user의 성능을 개선시킨다. 모의실험 결과 제안한 방법이 망 경로 지수에 최소 영향을 주어 셀 에지 SINR 관점에서 기존 방법들보다 좋은 성능을 보였다. 경로손실 지수가 3.6인 경우에는 reuse-1에 비해 reuse-3을 사용한 결과 셀 에지 SINR에서 대략 13 dB가 개선되었다.

• Ocean and Polar Research
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• 제42권1호
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• pp.77-88
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• 2020

This paper presents the coordinate systems used for trawl doors modeling, and provides matrix equations of connection between these systems. The projections of the forces acting on the door into axes of various coordinate systems were obtained, which were used in the door equilibrium equations. Six equilibrium conditions for the door as a solid were obtained: formulas that allow for the door area in plan to be determined; its weight in water; its mass; three moment equations for determining the position of the warp and backstrops fastening points to the door with triangular and quadrangular backstrop arrangements. It was found that the moment equilibrium equations of trawl doors are generally incompatible, which was not found by any of the authors who have previously conducted research into trawl doors. Using the Kronecker-Capelli theorem, the compatibility equation is obtained. This equation includes the coordinates of the backstrop fastening points to the door, which means that these points cannot be randomly selected. The technique of determining the warp and backstrops' fastening points position to the door is described. Conditions of directional (by angle of attack) and roll (in angle of roll) stability of the doors' equilibrium are presented. The equations presented in this paper comprise a mathematical model that allows, when designing the doors, to select optimal parameters, as well as to carry out adjustments for trawling purposes to ensure the stable movement of the doors and the entire trawl system.

• 대한전기학회논문지
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• 제41권7호
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• pp.712-722
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• 1992

Several voltage instability/collapse problems that have occurred in the electric utility industry worldwide have gained the attention of engineers and researchers of electric power systems. This paper proposes an effective calculation scheme of the extreme loading point and nose curves(P-V curves) using modified Newton-Raphson(N-R) load flow method and the Continuation Method. This method provides detail and visual information of the power system voltage profile and operating margin ro operators and planners. In this paper, a modified load flow claculation method for ill-conditioned power systems is introduced for the purpose of seeking more precise load flow solutions and nose curves, and the Continuation Method is also used as a part of the solution algorithm for the calculation of extreme loading point and nose curves. The conventional polar coordinate based N-R load flow program is modified to avoid numerical difficulties caused by the singularity of the Jacobian matrix occuring in the vicinity of extreme loading point of heavily loaded systems. Application results of the proposed method to Klos-Kerner 11-bus system and modified IEE-30-bus system are presented to assure the usefulness of the approach.

• 예술인문사회 융합 멀티미디어 논문지
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• 제8권3호
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• pp.945-953
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• 2018

본 논문은 무인수상정의 자율운항을 위한 장애물 탐지 및 회피기동을 위해 3차원 라이다를 사용하였다. 단일센서만을 사용해서 해상조건에서의 무인수상정 장애물 회피운항을 하는데 목적이 있다. 3차원 라이다는 Quanergy사의 M8센서를 사용하여 주변 환경 장애물 데이터를 (r, ��, ��)로 수집하며 장애물 정보에는 Layer 정보와 Intensity 정보를 포함한다. 수집된 데이터를 3차원 직각좌표계로 변환을 하고, 이를 2차원 좌표계로 사상한다. 2차원 좌표계로 변환한 장애물 정보를 포함하는 데이터는 수면위의 잡음데이터를 포함하고 있다. 그래서 기본적으로 무인수상정을 기준으로 가상의 관심영역을 정의하여서 규칙적으로 생성되는 잡음데이터에 대해서 삭제를 하였으며, 그 이후에 발생하는 잡음데이터는 Vector Field Histogram으로 계산된 히스토그램 데이터에서 Threshold를 정해 밀도값에 비례하여 잡음데이터를 제거하였다. 제거된 데이터를 이용하여 무인수상정의 움직임에 따른 상대물체를 탐색하여 가상의 격자지도에 1 Cell씩 저정하면서 데이터의 밀도 지도를 작성하였다. 작성된 장애물 지도를 폴라 히스토그램을 생성하고, 경계값을 이용하여 회피방향을 선정하였다.

• 대한화학회지
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• 제23권3호
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• pp.125-131
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• 1979

한 쌍의 slater type orbitals에 대한 two overlap integrals을 계산하는 방법이 Mulliken등에 의하여 발전되었다. 이 방법으로 two center integrals을 계산하기 위해서는 한쌍의 Slater type orbital,에 대한 극좌표들 타원좌표로 변환해야한다. 두 점에 위치한 Slater type orbital을 공통좌표상에 전개시키는 새로운 방법 즉 spherical harmonics의 전개방법이 two center overlap integrals, 을 계산하는데 응용되었다. 이 새로운 방법에서는 Slater type orbitals, 을 기준점에 대해 전개시키는 것이 필요하다. 본 연구에서는 two center overlap integral을 계산하기 위한 spherical harmonics 전개방법을 $|3s{\g}$, $|5s{\g}$및 $|5s{\g}$에 까지 확장시켰다. 이들 원자궤도함수의 전개식을 사용하여 two center overlap integrals의 기본식을 유도하였으며, 이 기본식을 사용하여 가상적인 NO 분자에 대한 two cunter overlap integrals의 계산값이 이미 보고된 값과 일치하였다.

• 천문학회보
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• 제40권1호
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• pp.66.1-66.1
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• 2015

We present the first observational detection of radial and azimuthal oscillations in full halo coronal mass ejections (HCMEs). We analyze nine HCMEs well-observed by LASCO from Feb 2011 to Jun 2011. Using the LASCO C3 running difference images, we estimated the instantaneous apparent speeds of the HCMEs in different radial directions from the solar disk center. We find that the development of all these HCMEs is accompanied with quasi-periodic variations of the instantaneous radial velocity with the periods ranging from 24 to 48 mins. The amplitudes of the instant speed variations reach about a half of the projected speeds. The amplitudes are found to anti-correlate with the periods and correlate with the HCME speed, indicating the nonlinear nature of the process. The oscillations have a clear azimuthal structure in the heliocentric polar coordinate system. The oscillations in seven events are found to be associated with distinct azimuthal wave modes with the azimuthal wave number m=1 for six events and m=2 for one event. The polarization of the oscillations in these seven HCMEs is broadly consistent with those of their position angles with the mean difference of $42.5^{\circ}$. The oscillations may be connected with natural oscillations of the plasmoids around a dynamical equilibrium, or self-oscillatory processes, e.g. the periodic shedding of Alfvenic vortices. Our results indicate the need for advanced theory of oscillatory processes in CMEs.

• 한국정보과학회논문지:소프트웨어및응용
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• 제26권1호
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• pp.157-157
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• 1999

Researches on the gesture recognition have become a very interesting topic in the computer vision area, Gesture recognition from visual images has a number of potential applicationssuch as HCI (Human Computer Interaction), VR(Virtual Reality), machine vision. To overcome thetechnical barriers in visual processing, conventional approaches have employed cumbersome devicessuch as datagloves or color marked gloves. In this research, we capture gesture images without usingexternal devices and generate a gesture trajectery composed of point-tokens. The trajectory Is spottedusing phase-based velocity constraints and recognized using the discrete left-right HMM. Inputvectors to the HMM are obtained by using the LBG clustering algorithm on a polar-coordinate spacewhere point-tokens on the Cartesian space .are converted. A gesture vocabulary is composed oftwenty-two dynamic hand gestures for editing drawing elements. In our experiment, one hundred dataper gesture are collected from twenty persons, Fifty data are used for training and another fifty datafor recognition experiment. The recognition result shows about 95% recognition rate and also thepossibility that these results can be applied to several potential systems operated by gestures. Thedeveloped system is running in real time for editing basic graphic primitives in the hardwareenvironments of a Pentium-pro (200 MHz), a Matrox Meteor graphic board and a CCD camera, anda Window95 and Visual C++ software environment.