• Animal Systematics, Evolution and Diversity
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• v.23 no.2
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• pp.169-173
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• 2007

Two new marine sponges in the family Chalinidae, Haliclona (Haliclona) uljinensis n. sp. and Haliclona (Reniera) hongdoensis n. sp., are collected from Uljin and Hongdo Island, Korea during 2004-2007. H. (H.) uljinensis n. sp. is closely related to H. (H.) oculata in type of spicules. However, ectosomal skeleton of H. (H.) uljinensis n. sp. is reticulated and isodictyal reticulated type but H. (H.) oculata has not any dermal specialization in skeleton. The growth form of H. (H.) uljinensis n. sp. is thin encrusting with numerous cylindrical tubes on the surface but H. (H.) oculata is solid branch form. Haliclona (R.) hongdoensis n. sp. is closely related to H. (R.) aquaeductus in skeletal structure and growth form. However, oxeas of H. (R.) hongdoensis n. sp. are larger than H. (R.) aquaeductus's.

• Animal Systematics, Evolution and Diversity
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• v.24 no.2
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• pp.205-208
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• 2008

Two new marine sponges in family Halichondriidae, Halichondria ulleungensis n. sp. and H. hongdoenesis n. sp. are collected from Ulleungdo Island and Hongdo Island, Korea by SCUBA diving during 2003-2004. H. ulleungensis n. sp. is similar to H. corrugata Diaz, Pomponi and van Soest, 1993 in the type of spicule, but it is different in growth form and choanosomal skeleton. The growth form is encrusting, with numerous erected cylindrical tube, comparing with massive-lobate of H. corrugata. The choanosomal skeleton is confused with loosely arranged oxea tract, comparing with densely tracts with many spicules of H. corrugata. H. hongdoenesis n. sp. is similar to H. surrubicunda Hoshino, 1981 in type of spicule and growth form, but this species has two kinds (thick and thin) of oxea.

• Animal Systematics, Evolution and Diversity
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• v.35 no.2
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• pp.57-62
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• 2019

Eutima japonica Uchida, 1925, a bivalve-inhabiting hydrozoan was collected for the first time in Korea, associating with Mytilus galloprovincialis. The morphology of male medusae of this hydrozoan is clarified by culture and described as well as other developmental stages. As the present material from Korea is in good accord with that of the northern Japanese form of E. japonica, so the geographical distribution of the northern form of this species is widened, Japan, China and Korea. Green fluorescent protein distribution pattern of this medusa is also described and compared with that of the most related species Eutima sapinhoa Narchi and Hebling, 1975.

• Animal Systematics, Evolution and Diversity
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• v.36 no.4
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• pp.400-407
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• 2020

An epialtid spider crab, Naxioides robillardi (Miers, 1882), is known as widely distributed in Indo-West Pacific region include Japanese waters. Four specimens of epialtid crabs were collected from adjacent waters of Jejudo Island and identified as N. robillardi. This species can be grouped into two forms such as N. robillardi form typical and N. robillardi form mammillata according to morphological features of carapace, gastric spine, and chela. Morphological characters of all Korean specimens well agree with the form mammillata in general. In this paper, morphological diagnosis and illustrations of newly collected N. robillardi are provided. DNA barcode sequence of COI region is also determined for the first time.

• Computers and Concrete
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• v.25 no.1
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• pp.15-27
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• 2020

During the past decades, the application of acoustic emission techniques (AET) through the diagnosis and monitoring of the fracture process in materials has been attracting considerable attention. AET proved to be operative among the other non-destructive testing methods for various reasons including their practicality and cost-effectiveness. Concrete and rock structures often demand thorough and real-time assessment to predict and prevent their damage nucleation and evolution. This paper presents an overview of the work carried out on the use of AE as a monitoring technique to form a comprehensive insight into its potential application in brittle materials. Reported properties in this study are crack growth behavior, localization, damage evolution, dynamic character and structures monitoring. This literature review provides practicing engineers and researchers with the main AE procedures to follow when examining the possibility of failure in civil/resource structures that rely on brittle materials.

• The Journal of Engineering Research
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• v.3 no.1
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• pp.131-138
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• 1998

In this paper, we investigate the direction of LAN evolution. We focus rather on the philosophical changes than on the advances of technologies. In terms of topology, channel structure, and medium access control, we categorize major local area networks widely used in the past. We then investigate new directions in the concept and advances in the technology of local area networks. The idea of collapsed backbone is shown to be the most fundamental factor influencing the evolution of local area networks. Asynchronous Transfer Mode that is radically different form the existing LAN technology is now actively applied to LAN. In order to compete with ATM, conventional LANs should evolve to support quality of service for multimedia application

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.21 no.1
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• pp.1-16
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• 2017

The Allen-Cahn equation is solved numerically by operator splitting Fourier spectral methods. The basic idea of the operator splitting method is to decompose the original problem into sub-equations and compose the approximate solution of the original equation using the solutions of the subproblems. The purpose of this paper is to characterize higher order operator splitting schemes and propose several higher order methods. Unlike the first and the second order methods, each of the heat and the free-energy evolution operators has at least one backward evaluation in higher order methods. We investigate the effect of negative time steps on a general form of third order schemes and suggest three third order methods for better stability and accuracy. Two fourth order methods are also presented. The traveling wave solution and a spinodal decomposition problem are used to demonstrate numerical properties and the order of convergence of the proposed methods.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.177-187
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• 2003

Active galactic nuclei (AGNs) are distant, powerful sources of radiation over the entire electromagnetic spectrum, from radio waves to gamma-rays. There is much evidence that they are driven by gravitational accretion of stars, dust, and gas, onto central massive black holes (MBHs) imprisoning anywhere from $\~$1 to $\~$10,000 million solar masses; such objects may naturally form in the centers of galaxies during their normal dynamical evolution. A small fraction of AGNs, of the radio-loud type (RLAGNs), are somehow able to generate powerful synchrotron-emitting structures (cores, jets, lobes) with sizes ranging from pc to Mpc. A brief summary of AGN observations and theories is given, with an emphasis on RLAGNs. Preliminary results from the imaging of 10000 extragalactic radio sources observed in the MITVLA snapshot survey, and from a new analytic theory of the time-variable power output from Kerr black hole magnetospheres, are presented. To better understand the complex physical processes within the central engines of AGNs, it is important to confront the observations with theories, from the viewpoint of analyzing the time-variable behaviours of AGNs - which have been recorded over both 'short' human ($10^0-10^9\;s$) and 'long' cosmic ($10^{13} - 10^{17}\;s$) timescales. Some key ingredients of a basic mathematical formalism are outlined, which may help in building detailed Monte-Carlo models of evolving AGN populations; such numerical calculations should be potentially important tools for useful interpretation of the large amounts of statistical data now publicly available for both AGNs and RLAGNs.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.54.1-54.1
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• 2011

Formation of self-gravitating gas clouds and hence stars in galaxies is a consequence of both thermal and dynamical evolution of a gaseous medium. Using hydrodynamics simulations including cooling and heating explicitly, we follow simultaneously thermal and dynamical evolution of galactic gas disks to study dynamics and structures of galactic spiral shocks with thermal instability and regulation of the star formation rates (SFRs). We first perform one-dimensional simulations in direction perpendicular to spiral arms. The multiphase gas flows across the arm soon achieve a quasi-steady state characterized by transitions from warm to cold phases at the shock and from cold to warm phases in the postshock expansion zone, producing a substantial fraction of intermediate-temperature gas. Next, we allow a vertical degree of freedom to model vertically stratified disks. The shock front experiences unsteady flapping motions, driving a significant amount of random gas motions, and self-gravity promotes formation of bound clouds inside spiral arms. Finally, we include the star formation feedback in both mechanical (due to supernova explosion) and radiative (due to FUV heating by young stars) forms in the absence of spiral arms. At saturation, gravitationally bound clouds form via thermal and gravitational instabilities, which are compensated by disruption via supernova explosions. We find that the FUV heating regulates the SFRs when gas surface density is low, confirming the prediction of the thermal and dynamical equilibrium model of Ostriker et al. (2010) for star formation regulation.

• Journal of Korea Foundry Society
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• v.28 no.3
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• pp.129-135
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• 2008

The reheating stage of electromagnetically stirred Al billet is a critical factor in the thixoforming process. When reheated to the solid-liquid state, the microstructure evolves to a more globular and more homogeneous structure by a coarsening mechanism, the kinetics depending on the initial microstructure. Microstructural evolution has been characterized by conventional parameters (mean size of particle and shape factor) as a function of holding time in the solid-liquid state. The aim of this study is to report experimental results concerning microstructural evolution in the solid-liquid state of electromagnetically stirred Al billet. The material was elaborated in the form of continuously cast bars solidified with electromagnetic stirring to degenerate the dendritic structure. The choice of the reheating conditions is determined by a dendritic ripening and coalescence mechanism, involving variations of both the shape and size of the particles. The reheating time has to be long enough to allow a minimum degree of spheroidizing, but has to be limited as much as possible in order to avoid excessive ripening. The optimum microstructure was obtained at the reheating temperature of near $584^{\circ}C$ and the holding time of 5 min. The only means of combining high productivity with good casting quality was to use feedstock billets whose microstructure showed rapid transformation characteristics.