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Magnetohydrodynamics Code Basics
RYU DONGSU The Korean Astronomical Society 2001 Journal of The Korean Astronomical Society Vol.34 No.4
This paper describes the numerical solution to the hyperbolic system of magnetohydrodynamic (MHD) equations. First, by pointing out the approximations involved, the deal MHD equations are presented. Next, the MHD waves as well as the associated shocks and discontinuities, are presented. Then, based on the hyperbolicity of the ideal MHD equations, the application of upwind schemes, which have been developed for hydrodynamics, is discussed to solve the equations numerically. As an definite example, one and multi-dimensional codes based on the Total Variation Diminishing scheme are presented. The treatment in the multi-dimensional code, which maintains ${\nabla}{\cdot}$B = 0, is described. Through tests, the robustness of the upwind schemes for MHDs is demonstrated.
Dynamical Influence of Cosmic Rays on Cosmic Structures
Dongsu Ryu 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III
There are growing interests in the roles of relativistic particles, or cosmic-rays (CRs), in cosmology. Those CRs may provide not only unique and vital diagnostic information through their emissions, but may also influence the formation and dynamics of cosmic structures if they constitute a dynamically significant component. We report here simulations of cosmic structure formation that include CRs explicitly. Two origins of CRs are considered: diffusive acceleration at cosmic shock waves and injection from black holes in active galactic nuclei. We describe the dynamical influence of CRs and its cosmological implications.
COSMIC SHOCK WAVES ON LARGE SCALES OF THE UNIVERSE
RYU DONGSU,KANG HYESUNG The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
In the standard theory of the large scale structure formation, matter accretes onto high density perturbations via gravitational instability. Collision less dark matter forms caustics around such structures, while collisional baryonic matter forms accretion shocks which then halt and heat the infalling gas. Here we discuss the characteristics. roles, and observational consequences of these accretion shocks.
CLUSTERS OF GALAXIES: SHOCK WAVES AND COSMIC RAYS
RYU DONGSU,KANG HYESUNG The Korean Astronomical Society 2003 Journal of The Korean Astronomical Society Vol.36 No.3
Recent observations of galaxy clusters in radio and X-ray indicate that cosmic rays and magnetic fields may be energetically important in the intracluster medium. According to the estimates based on theses observational studies, the combined pressure of these two components of the intracluster medium may range between $10\%{\~}100\%$ of gas pressure, although their total energy is probably time dependent. Hence, these non-thermal components may have influenced the formation and evolution of cosmic structures, and may provide unique and vital diagnostic information through various radiations emitted via their interactions with surrounding matter and cosmic background photons. We suggest that shock waves associated with cosmic structures, along with individual sources such as active galactic nuclei and radio galaxies, supply the cosmic rays and magnetic fields to the intracluster medium and to surrounding large scale structures. In order to study 1) the properties of cosmic shock waves emerging during the large scale structure formation of the universe, and 2) the dynamical influence of cosmic rays, which were ejected by AGN-like sources into the intracluster medium, on structure formation, we have performed two sets of N-body /hydrodynamic simulations of cosmic structure formation. In this contribution, we report the preliminary results of these simulations.
COSMIC RAYS ACCELERATED AT SHOCK WAVES IN LARGE SCALE STRUCTURE
RYU DONGSU,KANG HYESUNG The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5
Shock waves form in the intergalactic space as an ubiquitous consequence of cosmic structure formation. Using N-body/hydrodynamic simulation data of a ACDM universe, we examined the properties of cosmological shock waves including their morphological distribution. Adopting a diffusive shock acceleration model, we then calculated the amount of cosmic ray energy as well as that of gas thermal energy dissipated at the shocks. Finally, the dynamical consequence of those cosmic rays on cluster properties is discussed.
INTERGALACTIC MAGNETIC FIELD AND ARRIVAL DIRECTION OF ULTRA-HIGH-ENERGY PROTONS
Ryu, Dongsu,Das, Santabrata,Kang, Hyesung IOP Publishing 2010 The Astrophysical journal Vol.710 No.2
<P>We studied how the intergalactic magnetic field (IGMF) affects the propagation of super-Greisen-Zatsepin-Kuz'min (GZK) protons that originate from extragalactic sources within the local GZK sphere. To this end, we set up hypothetical sources of ultra-high-energy cosmic rays (UHECRs), virtual observers, and the magnetized cosmic web in a model universe constructed from cosmological structure formation simulations. We then arranged a set of reference objects mimicking active galactic nuclei (AGNs) in the local universe, with which correlations of simulated UHECR events are analyzed. With our model IGMF, the deflection angle between the arrival direction of super-GZK protons and the sky position of their actual sources is quite large with a mean value of <theta > similar to 15 degrees and a median value of (0) over tilde similar to 7 degrees-10 degrees. On the other hand, the separation angle between the arrival direction and the sky position of nearest reference objects is substantially smaller with < S > similar to 3 degrees.5-4 degrees, which is similar to the mean angular distance in the sky to nearest neighbors among the reference objects. This is a direct consequence of our model that the sources, observers, reference objects, and the IGMF all trace the matter distribution of the universe. The result implies that extragalactic objects lying closest to the arrival direction of UHECRs are not necessarily their actual sources. With our model for the distribution of reference objects, the fraction of super-GZK proton events, whose closest AGNs are true sources, is less than 1/3. We discussed implications of our findings for correlation studies of real UHECR events.</P>
Quality, Product Quality, and Market Share Increase: A Perspective for Management Decisions
Ryu, Dongsu The Korean Reliability Society 2001 International Journal of Reliability and Applicati Vol.2 No.3
Starting with the meaning of the word quality, diverse concepts connoted by the term are examined. Instead of a bathtub curve, the desirable shape of a failure rate covering the entire life of a good product, which might be called hockey-stick line, is introduced. From the hockey-stick line and the definition of reliability, two measurements are extracted. The terms reliability, failure rate, product life, and durability are explained. From the customer's standpoint, the concept of product quality is classified in five factors, according to related technology: performance, reliability, conformance to specifications, customer perception, and fundamentals advantage. The correlation of the five factors for a first-class product is discussed, Since the market share of a company is determined as the competition result of its product value, defined as product quality and price, the market share increase is derived mathematically from the increment of product value. The market share increase, $\Delta$S, can be calculated from the present market share, S, and the oriented relative value increment of new product, R, to the current product in the same company for the same market target: $\Delta$S : $\Delta$(1-S). R/(1+S.R). Finally, the importance of separating warranty cost from the profit equation for the durables is explained.