• 제목/요약/키워드: Kepler

검색결과 76건 처리시간 0.022초

REGULAR MAPS-COMBINATORIAL OBJECTS RELATING DIFFERENT FIELDS OF MATHEMATICS

  • Nedela, Roman
    • 대한수학회지
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    • 제38권5호
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    • pp.1069-1105
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    • 2001
  • Regular maps and hypermaps are cellular decompositions of closed surfaces exhibiting the highest possible number of symmetries. The five Platonic solids present the most familar examples of regular maps. The gret dodecahedron, a 5-valent pentagonal regular map on the surface of genus 5 discovered by Kepler, is probably the first known non-spherical regular map. Modern history of regular maps goes back at least to Klein (1878) who described in [59] a regular map of type (3, 7) on the orientable surface of genus 3. In its early times, the study of regular maps was closely connected with group theory as one can see in Burnside’s famous monograph [19], and more recently in Coxeter’s and Moser’s book [25] (Chapter 8). The present-time interest in regular maps extends to their connection to Dyck\`s triangle groups, Riemann surfaces, algebraic curves, Galois groups and other areas, Many of these links are nicely surveyed in the recent papers of Jones [55] and Jones and Singerman [54]. The presented survey paper is based on the talk given by the author at the conference “Mathematics in the New Millenium”held in Seoul, October 2000. The idea was, on one hand side, to show the relationship of (regular) maps and hypermaps to the above mentioned fields of mathematics. On the other hand, we wanted to stress some ideas and results that are important for understanding of the nature of these interesting mathematical objects.

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서울 도심지에서의 QZSS를 이용한 GPS 확장시스템의 가용도 평가 (Availability Assessment of GPS Augmentation System Using QZSS at Urban Environment of seoul)

  • 유경호;성상경;강태삼;이영재;이은성;이상욱
    • 한국항공우주학회지
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    • 제36권8호
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    • pp.761-766
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    • 2008
  • 본 논문에서는 사용자 위치결정에 널리 사용되는 GPS를 일본의 QZSS (Quasi-Zenith Satellite System)과 결합하여 서울 도심지역에서의 위성항법시스템의 가용도 및 DOP (Dilution Of Precision)성능을 분석하였다. QZSS 궤도 파라메터를 이용한 궤도 시뮬레이터를 구현하였다. 3D GIS 수치지도를 기반으로 서울 도심의 3차원 모델을 생성하고, 위성 관측 알고리즘을 이용하여 구성한 가시위성 시뮬레이션 시스템에 대해 기술하였다. 서울 도심지에서 GPS와 QZSS의 결합을 통한 가용도와 DOP 성능 향상을 보였다.

On the static and dynamic stability of beams with an axial piezoelectric actuation

  • Zehetner, C.;Irschik, H.
    • Smart Structures and Systems
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    • 제4권1호
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    • pp.67-84
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    • 2008
  • The present contribution is concerned with the static and dynamic stability of a piezo-laminated Bernoulli-Euler beam subjected to an axial compressive force. Recently, an inconsistent derivation of the equations of motions of such a smart structural system has been presented in the literature, where it has been claimed, that an axial piezoelectric actuation can be used to control its stability. The main scope of the present paper is to show that this unfortunately is impossible. We present a consistent theory for composite beams in plane bending. Using an exact description of the kinematics of the beam axis, together with the Bernoulli-Euler assumptions, we obtain a single-layer theory capable of taking into account the effects of piezoelectric actuation and buckling. The assumption of an inextensible beam axis, which is frequently used in the literature, is discussed afterwards. We show that the cited inconsistent beam model is due to inadmissible mixing of the assumptions of an inextensible beam axis and a vanishing axial displacement, leading to the erroneous result that the stability might be enhanced by an axial piezoelectric actuation. Our analytical formulations for simply supported Bernoulli-Euler type beams are verified by means of three-dimensional finite element computations performed with ABAQUS.

케플러궤도운동과 카울라의 인공위성궤도 섭동이론의 상세한 재유도 (Detailed Re-derivation of Keplerian Orbit and Kaula's Satellite Orbit Perturbation Theory)

  • 나성호;배태석;조중현;박종욱
    • 한국지구과학회지
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    • 제33권1호
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    • pp.11-31
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    • 2012
  • 카울라에 의해 완성되었던 인공위성궤도이론과 케플러의 법칙을 다시 다루었다. 카울라의 원문에서는 생략되었던 부분을 포함한 모든 수식유도과정을 상세히 기술하였다. 특히 15개의 독립적인 라그랑지 괄호들을 계산하는 데에 변환행렬의 직교성을 사용하여, 간결성과 명확성을 이루었다. 여러 중간단계에서 중요한 물리적인 개념들에 대한 설명도 추가하였다. 카울라의 개념적 오류 한 개를 정정하였다.

스윕 기반 인체 형상 모델링 및 변형 (Sweep-based Human Modeling and Deformation)

  • 현대은;윤승현;성준경;장정우;김명수
    • 한국컴퓨터그래픽스학회논문지
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    • 제10권2호
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    • pp.27-34
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    • 2004
  • 본 논문에서는 스윕에 기반하여 인체 형상을 모델링하고 변형하는 방법을 제시한다. 본 방법은 다각형 메쉬 형태로 주어진 3차원 인체 형상을 스윕 기반의 형상 구조로 재구성하여, 형상을 모델링하고 변형한다. 인체 형상의 팔, 다리, 몸통 등 각 부분을 근사하는 스윕 곡면을 생성하고 다각형 메쉬 상의 꼭지점들을 인접한 스윕 곡면과 연결하며, 스윕 곡면이 만나는 팔, 다리와 몸통 사이에서는 꼭지점마다 연결된 스윕 단면들을 블렌딩한다. 이를 통해 스윕을 제어하여 이와 연결된 인체 형상의 자연스러운 변형을 얻어낼 수 있다. 본 논문에서는 몇 개의 애니메이션 예들을 통하여 제시한 인체 변형 방법이 자연스러운 인체 동작 생성에 효과적임을 보인다. 본 논문의 결과들은 스윕 기반의 인체 형상 변형 방법이 실시간에 상당히 사실적이고 자연스러운 형상 변형이 가능함을 보여주어, 캐릭터 skinning 방법으로서 적절한 대안임을 보여준다.

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An exosolar planetary system N-body simulator II

  • Hong, ChaeLin;van Putten, Maurice
    • 천문학회보
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    • 제43권1호
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    • pp.46.3-47
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    • 2018
  • We present a general N-body exasolar system simulator in anticipation of upcoming searches for exoplanets and even exomoons by next generation telescopes such as James Webb Space Telescope. For habitable zones, traditionally defined by temperature, we here address the essential problem of dynamical stability of planetary orbits. Illustrative examples are presented on P-type orbits in stellar binary systems, that should be fairly common as in Kepler 16b. Specific attention is paid to reduced orbital lifetimes of exoplanets in the habitable zone by the stellar binary, that is propoesed by Maurice van Putten (2017). Especially, we focused on a classic work of complex three-body problem that is well known by Dvorak(1986). We charge his elliptic restricted three-body problem to extend unrestricted three-body problem to look into dynamical motions in view of circumbinary planet, furthermore, we suggest that opposite angular orientation of the planet is relative to the stability of orbits. In here, counter-rotation case is relatively more faster than co-rotation case for being stable. As a result, we find that various initial conditions and thresholds to approach dynamical stability and unstability with unexpectable isolated islands over enormous parameter space. Even, superkeplerian effect of binary is important to habitability of the exoplanet and we can verify that superfaster binary doesn't effect on th planet and increases survivality of planet around the binary.

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WFIRST ULTRA-PRECISE ASTROMETRY II: ASTEROSEISMOLOGY

  • Gould, Andrew;Huber, Daniel;Penny, Matthew;Stello, Dennis
    • 천문학회지
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    • 제48권2호
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    • pp.93-104
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    • 2015
  • WFIRST microlensing observations will return high-precision parallaxes, σ(π) . 0.3 µas, for the roughly 1 million stars with H < 14 in its 2.8 deg2 field toward the Galactic bulge. Combined with its 40,000 epochs of high precision photometry (∼ 0.7 mmag at Hvega = 14 and ∼ 0.1 mmag at H = 8), this will yield a wealth of asteroseismic data of giant stars, primarily in the Galactic bulge but includindvvvvvg a substantial fraction of disk stars at all Galactocentric radii interior to the Sun. For brighter stars, the astrometric data will yield an external check on the radii derived from the two asteroseismic parameters, the large-frequency separation <∆νnl> and the frequency of maximum oscillation power νmax, while for the fainter ones, it will enable a mass measurement from the single measurable asteroseismic parameter νmax. Simulations based on Kepler data indicate that WFIRST will be capable of detecting oscillations in stars from slightly less luminous than the red clump to the tip of the red giant branch, yielding roughly 1 million detections.

구아리노 구아리니의 종교 건축에서 나타나는 생성 다이어그램에 관한 연구 (A Study on the Generative Diagram in Guarino Guarini's Religious Buildings)

  • 김홍수;정인하
    • 건축역사연구
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    • 제14권4호
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    • pp.157-175
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    • 2005
  • Guarino Guarini(1624-1683) is one of great Baroque architects who developed new spatial concept in architecture. He refused to static space typically appeared in Renaissance architecture. Instead, to make it possible to generate complicate form and moving space, he made use of generative diagram. It provide him with an abstract machine to generate automatically architectural inferiority. His generative diagram consists of three types: single circle diagram, matrix diagram and longitudinal diagram. The first diagram uses single circle as primary generator and develop this by means of overlap and equiangular division. La Cappella della Santissima Sindone, Sanctuary of Chiesa di Oropa, Chiesa dei Padri Somaschi, San Gaetano are designed according to this diagram. The generator of the second diagram is nine circles in $3{\times}3$ matrix, which provide the base for the interpenetration of space in Guarini's architecture. He inspired this diagram from Kepler's $\ulcorner$Harmonices mundi$\lrcorner$. The Churches of San Lorenzo, Ste-Anne-la-Royale, San Filippo Neri, San Gaetano are generated by this diagram. The third diagram has several circles in Lantin-cross plan. Guarini adopted this diagram because he had chances to design several churches in Northern Europe. The churches of Santa Maria di Ettinga, Immacolata Concezione, San Maria della Divina Providenza, Church without Name, San Filippo Neri are representative examples for this diagram.

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Orbital stability study and transit-timing variations of the extrasolar planetary system: K2-3

  • Choi, Beom-Kyu;Hinse, Tobias C.;Yoon, Tae Seog
    • 천문학회보
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    • 제41권1호
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    • pp.79.1-79.1
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    • 2016
  • We investigated the dynamical properties of the K2-3 multi-planet system. Recently three transiting planets are discovered using the extended Kepler2 (K2) mission (Crossfield et al. 2015). We extended their preliminary stability study by considering a substantial longer integration time. Since planet mass is not known from photometry we calculated exoplanets masses using empirical mass-radius relations (Weiss & Marcy 2014). Forward numerical integration was done using the MERCURY integration package (Chambers 1999). Our results demonstrate that this system is stable over a time scale of $10^8years$. Furthermore, we investigated the dynamical effects of a hypothetical planet in the semi-major axis vs eccentricity space. For stable orbits of the hypothetical planet we calculated transit-timing variation (TTV) and radial velocity signals. We find that for a hypothetical perturber with mass 1-13 Mjup, semi-major axis 0.2 - 0.8 AU and eccentricity 0.00-0.47 the following timing signals for the planet K2-3 b is ~ 5 sec, K2-3 c is ~ 130 sec and for K2-3 d is ~ 190 sec. The radial velocity signal of the hypothetical planet is ~ 4 m/s. Using typical transit-timing errors from the K2 mission, we find that the above hypothetical planet would not be detectable. Its radial velocity signal, however, would be detectable using the APF 2.4m telescope or HARPS at the ESO/La Silla Observatory in Chile.

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Design of piezoelectric transducer arrays for passive and active modal control of thin plates

  • Zenz, Georg;Berger, Wolfgang;Gerstmayr, Johannes;Nader, Manfred;Krommer, Michael
    • Smart Structures and Systems
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    • 제12권5호
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    • pp.547-577
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    • 2013
  • To suppress vibration and noise of mechanical structures piezoelectric ceramics play an increasing role as effective, simple and light-weighted damping devices as they are suitable for sensing and actuating. Out of the various piezoelectric damping methods this paper compares mode based active control strategies to passive shunt damping for thin plates. Therefore, a new approach for the optimal placement of the piezoelectric sensors/actuators, or more general transducers, is proposed after intense theoretical investigations based on the Kirchhoff kinematical hypotheses of plates; in particular, modal and nilpotent transducers are discussed in detail. Based on the proposed distribution a discrete design for modal transducers is implemented, tested and verified on an experimental setup. For active control the modal sensors clearly identify the eigenmodes, whereas the modal actuators impose distributed eigenstrains in order to reduce the transverse plate vibrations. In contrast to the modal control, passive shunt damping works without requiring additional actuators or auxiliary power and can therefore act as an autonomous system, but it is less effective compensating the flexible vibrations. Exemplarily, an acryl glass plate disturbed by an arbitrary force initialized by a loudspeaker is investigated. Comparing the different methods their specific advantages are highlighted and a significant broadband reduction of the vibrations of up to -20dB is obtained.