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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 73/122
721
- JONES T. W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.231-235
- 2001
- 원문 바로보기
Cosmic-ray acceleration, although physically important in many astrophysical contexts, is difficult to incorporate into numerical models,. because it involves microphysics that is generally far from thermodynamic equilibrium, and also because the length and time scales for that physics typically range over many orders of magnitude, reflecting the huge range of particle rigidities that must be represented. The most common accelerator models are stochastic in nature and involve nonequilibrium plasma properties that are also often poorly understood. Still, nature clearly finds a way to produce simple, robust and almost scale-free energy distributions for the cosmic-rays. Their importance has inspired a number of approaches to examining the production and transport of cosmic-ray particles in numerical simulations. I offer here a brief comparison of some of the methods that have been introduced.
722
- MOLTENI D.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.247-249
- 2001
- 원문 바로보기
The accretion disks are usually supposed symmetric to reflection on the Z=0 plane. Asymmetries in the flow are be ver-y small in the vicinity of the compact accretor. However their existence can have a important role in the case of subkeplerian accretion flows onto black holes. These flows lead to strong heating and even to the formation of shocks close to the centrifugal barrier. Large asymmetries are due to the development of the KH instability triggered by the small turbulences at the layer separating the incoming flow from the out coming shocked flow. The consequence of this phenomenon is the production of asymmetric outflows of matter and quasi periodic oscillations of the inner disk regions up and down the Z=0 plane.
723
- KIM HUN-DAE
- Journal of the Korean astronomical society = 천문학회지
- 34, n.3
- pp.167-179
- 2001
- 원문 바로보기
A molecular line survey towards the UC H II region G34.3+0.15 from 155.3 to 165.3GHz has been conducted with the TRAO 14-m radio telescope. Combined with our previous observations from 84.7 to 115.6GHz and 123.5 to 155.3GHz (Paper I), the spectral coverage of this survey in G34.3+0.15 now runs from 85 to 165 GHz. From these latest observations, a total of 18 lines from 6 species were detected. These include four new lines corresponding to <TEX>${\Delta}$</TEX>J = 0, <TEX>${\Delta}$</TEX>K = 1 transitions of the <TEX>$CH_3OH$</TEX> E-type species, and two new lines corresponding to transitions from <TEX>$SO_2$</TEX> and <TEX>$HC_3N$</TEX>. These 6 new lines are <TEX>$CH_3OH$</TEX>[1(1) - 1(0)E], <TEX>$CH_3OH$</TEX>[2(1) - 2(0)E], <TEX>$CH_3OH$</TEX>[3(1) - 3(0)E], <TEX>$CH_3OH$</TEX>[4(1) - 4(0)E], <TEX>$SO_2$</TEX>[14(1, 13) -14(0, 14)] and <TEX>$HC_3N$</TEX>[18 -17]. We applied a rotation diagram analysis to derive rotation temperatures and column densities from the methanol transitions detected, and combined with NRAO 12-m data from Slysh et al. 1999. Applying a two-component fit, we find a cold component with temperature 13-16K and column density <TEX>$3.3-3.4 {\times} 10^{14} cm^{-2}$</TEX>, and a hot component with temperature 64 - 83K and column density <TEX>$9.3{\times}10^{14} - 9.7 {\times} 10^{14} cm^{-2}$</TEX>. On the other hand, applying just a one-component fit yields temperatures in the 47 -62 K range and column densities from <TEX>$7.5-1.1 {\times} 10^{15} cm^{-2}$</TEX>.
724
- KIM JONGSOO
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.333-335
- 2001
- 원문 바로보기
We study the properties of supernova (SN) driven interstellar turbulence with a numerical magnetohydrodynamic (MHD) model. Calculations were done using the RIEMANN framework for MHD, which is highly suited for astrophysical flows because it tracks shocks using a Riemann solver and ensures pressure positivity and a divergence-free magnetic field. We start our simulations with a uniform density threaded by a uniform magnetic field. A simplified radiative cooling curve and a constant heating rate are also included. In this radiatively-cooling magnetized medium, we explode SNe one at a time at randomly chosen positions with SN explosion rates equal to and 12 times higher than the Galactic value. The evolution of the system is basically determined by the input energy of SN explosions and the output energy of radiative cooling. We follow the simulations to the point where the total energy of the system, as well as thermal, kinetic, and magnetic energy individually, has reached a quasi-stationary value. From the numerical experiments, we find that: i) both thermal and dynamical processes are important in determining the phases of the interstellar medium, and ii) the power index n of the <TEX>$B-p^n$</TEX> relation is consistent with observed values.
725
- MATHEWS GRANT J.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.265-269
- 2001
- 원문 바로보기
We present preliminary numerical simulations of tilted-disk accretion around a rotating black hole. Our goal is to explore whether hydrodynamic instabilities near the Bardeen-Petterson radius could be responsible for generating moderate-frequency quasi-periodic oscillations in X-ray binaries. We review the relevant general relativistic hydrodynamic equations, and discuss preliminary results on the structure and dynamics of a thin, Keplerian disk.
726
- 문봉곤
- Journal of the Korean astronomical society = 천문학회지
- 34, n.1
- pp.35-40
- 2001
- 원문 바로보기
For the planned experiments of Korea Sounding Rocket-III (KSR-III), we have constructed a model of MUV dayglow in the mid-latitude. The model computes relative intensities of individual emission lines in the Vegard-Kaplan and 2PG band systems of <TEX>$N_2$</TEX> in the wavelength range of 2500-3500<TEX>${\AA}$</TEX>. In addition to the emission lines, solar scattered continuum was computed by an extended LOWTRAN7 code, in which we have included solar scattering in altitudes higher than 100 km by using MSIS90 thermosphere model. Ratios among vibrational bands of VK and 2PG system, were computed from the observed MUV dayglow spectra of Cleary et al. (1995). The model provides MUV dayglow intensitiy profiles with a wavelength resolution of 3.13<TEX>${\AA}$</TEX> as a function of altitude. The computed intensity profiles have been utilized in designing the KSR-III airglow photometers.
727
- 한수련
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.67-80
- 2001
- 원문 바로보기
Chemical evolution of galaxies can be understood by studying the spatial distribution of heavy elements. We selected two nearby galaxies, M31 and M33 and investigated spectrum of their HII regions: a) the elec-tron densities have been derived from the [S II] 6717/6731 ratio along with the most recent atomic constants (Hyung & Aller 1996); b) the electron temperatures were determinated from the Pagel's empirical method. Nebula Model (Hyung 1994) has been employed to predict the spectral line intensities which gives the proper chemical abundances. The model would predict the line intensities correctly only when various input parameters such as the effective central star temperatures, gravity log g, model atmosphere as well as the geometry and the nebula physical condition are appropriate. Thus, the determination of chemical abundances of O, S, N of the two nearby galaxies M31 and M33 has been done, which shows a radial dependance of O/H and N/H: decrease with the distance, or increasing electron temperature due to the elemental deficiency. Abundances of M31 appear to be enhanced than those of M33.
728
- KOVALENKO ILYA G.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.271-273
- 2001
- 원문 바로보기
We present a 4-parameter implicit Lagrangean code which satisfies conservation of mass, linear and angular momenta, energy and entropy simultaneously. The primary advantage of this scheme is possibility to control dissipative properties of the scheme avoiding the effects of numerical viscosity.
729
- KO CHUNG-MING
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.289-291
- 2001
- 원문 바로보기
To study the structure and dynamics of a cosmic-ray-plasma system, hydrodynamic approach is a fairly good approximation. In this approach, there are three basic energy transfer mechanisms: work done by the plasma flow against pressure gradients, cosmic ray streaming instability and stochastic acceleration. The interplay between these mechanisms gives a range of structures. We present some results of different version of the hydrodynamic approach, e.g., flow structure, injection, instability, acceleration with and without shocks.
730
- LANZAFAME GIUSEPPE
- Journal of the Korean astronomical society = 천문학회지
- 34, n.4
- pp.313-315
- 2001
- 원문 바로보기
Some authors have concluded that spiral structures and shocks do not develop if an adiabatic index <TEX>$\gamma$</TEX> > 1.16 is adopted in accretion disc modelling, whilst others have claimed that they obtained well defined spirals and shocks adopting a <TEX>$\gamma$</TEX> = 1.2 and a <TEX>$M_2/ M_1$</TEX> = 1 stellar mass ratio. In our opinion, it should be possible to develop spiral structures for low compressibility gas accretion discs if the primary component is a black hole. We considered a primary black hole of 8M0 and a small secondary component of 0.5M<TEX>$\bigodot$</TEX> to favour spiral structures formations and possible spiral shocks via gas compression due to a strong gravitational attraction. We performed two 3D SPH simulations and two 2D SPH simulations and characterized a low compressibility model and a high compressibility model for each couple of simulations. 2D models reveal spiral structures existence. Moreover, spiral shocks are also evident in high compressibility 2D model at the outer disc edge. We believe that we could develop even well defined spiral shocks considering a more massive primary component.