• Bulletin of the Korean Mathematical Society
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• v.50 no.4
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• pp.1109-1126
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• 2013

Let $\mathbb{M}^3_q(c)$ denote the 3-dimensional space form of index $q=0,1$, and constant curvature $c{\neq}0$. A curve ${\alpha}$ immersed in $\mathbb{M}^3_q(c)$ is said to be a Bertrand curve if there exists another curve ${\beta}$ and a one-to-one correspondence between ${\alpha}$ and ${\beta}$ such that both curves have common principal normal geodesics at corresponding points. We obtain characterizations for both the cases of non-null curves and null curves. For non-null curves our theorem formally agrees with the classical one: non-null Bertrand curves in $\mathbb{M}^3_q(c)$ correspond with curves for which there exist two constants ${\lambda}{\neq}0$ and ${\mu}$ such that ${\lambda}{\kappa}+{\mu}{\tau}=1$, where ${\kappa}$ and ${\tau}$ stand for the curvature and torsion of the curve. As a consequence, non-null helices in $\mathbb{M}^3_q(c)$ are the only twisted curves in $\mathbb{M}^3_q(c)$ having infinite non-null Bertrand conjugate curves. In the case of null curves in the 3-dimensional Lorentzian space forms, we show that a null curve is a Bertrand curve if and only if it has non-zero constant second Frenet curvature. In the particular case where null curves are parametrized by the pseudo-arc length parameter, null helices are the only null Bertrand curves.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.77-83
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• 2014

The vessel of integral reactor contains its major primary components such as the fuel and core, pumps, steam generators, and a pressurizer, so its size is proportional to the required space for the installation of each component. The steam generators take up the largest volume of internal space of reactor vessel and their volumes is substantial for the overall size of reactor vessel. Reduction of installation space for steam generators can lead to much smaller reactor vessel with resultant decrease of overall cost for the components and related facilities. A printed circuit heat exchanger is one of the compact types of heat exchangers available as an alternative to conventional shell and tube heat exchangers. Its name is derived from the procedure used to manufacture the flat metal plates that form the core of the heat exchanger, which is done by chemical milling. These plates are then stacked and diffusion bonded, converting the plates into a solid metal block containing precisely engineered fluid flow passages. The overall heat transfer area and pressure drops are evaluated for the steam generator based on the concept of the printed circuit heat exchanger in this study. As the printed circuit heat exchanger is known to have much larger heat transfer area density per unit volume, we can expect significantly reduced steam generator compared to former shell and tube type of steam generator. For the introduction of new steam generator, two design requirements are considered: flow area ratio between primary and secondary flow paths, and secondary side parallel channel flow oscillation. The results show that the overall volume of the steam generator can be significantly reduced with printed circuit type of steam generator.

• Journal of The Korean Astronomical Society
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• v.48 no.5
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• pp.299-311
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• 2015

We report first results from KVN and VERA Array (KaVA) VLBI observations obtained in the frame of our Plasma-physics of Active Galactic Nuclei (PAGaN) project. We observed eight selected AGN at 22 and 43 GHz in single polarization (LCP) between March 2014 and April 2015. Each source was observed for 6 to 8 hours per observing run to maximize the uv coverage. We obtained a total of 15 deep high-resolution images permitting the identification of individual circular Gaussian jet components and three spectral index maps of BL Lac, 3C 111 and 3C 345 from simultaneous dual-frequency observations. The spectral index maps show trends in agreement with general expectations – flat core and steep jets – while the actual value of the spectral index for jets shows indications for a dependence on AGN type. We analyzed the kinematics of jet components of BL Lac and 3C 111, detecting superluminal proper motions with maximum apparent speeds of about 5c. This constrains the lower limits of the intrinsic component velocities to ~ 0.98c and the upper limits of the angle between jet and line of sight to ~20°. In agreement with global jet expansion, jet components show systematically larger diameters d at larger core distances r, following the global relation d ≈ 0.2r, albeit within substantial scatter.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.67.2-67.2
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• 2010

We present results of searching for the Very Low Luminosity Objects (VeLLOs; internal luminosity : $L_{int}$ < $0.1(d/140pc)^2\;L\odot$) in the Gould's Belt clouds using observations from 3.6 to 70 micron by the Spitzer Space Telescope. The clouds are California, Chamaeleon I, III, Musca, Lupus V, VI, Scorpius, Serpens, Corona Australis, Cepheus, and IC 5146 having the properties of active low-mass star-forming such as the Taurus cloud. The observing sensitivity of the Spitzer data is estimated to be about $L_{int}\;\geq\;5\times10^{-3}(d/140pc)^2\;L\odot$, a factor of 20 better than that of the Infrared Astronomical Satellite (IRAS). The observing data were processed by the c2d Legacy pipeline. As the criteria to select the VeLLOs, we slightly modified previous ones by Dunham et al. The most important criterion is a flux density at 70 micron that is directly converted to the internal luminosity. Also, we used additional criteria to remove the contamination of evolved stars and extragalaxies which have colors or SEDs very similar to YSOs. We identified a total of 64 new embedded VeLLO candidates with $L_{int}$ < $0.1(d/140pc)^2\;L\odot$, consisting of 8 in California, 15 in Chamaeleon-Musca, 13 in Scorpius-Lupus, 20 in Serpens, 3 in Corona Australis, 3 in Cepheus, and 2 in IC 5146. The classification of the spectral index (${\alpha}$) fitted to the shape of the Ks-24 micron SEDs shows most of VeLLO candidates (89%) are in types of Class I and Flat spectrum. We plot various diagrams based on their 2MASS-Spitzer bands colors and magnitudes to discuss properties of the VeLLOs. This search will lead us new adventure toward a future systematic study of the VeLLOs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.842-849
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• 2010

This paper deals with a TT&C circularly polarized turnstile antenna for LEO satellites. The turnstile antenna consists of radiator for radiating power to free-space and power divider for generating circularly polarized wave. we presents a radiator to tolerate in space environments and a power divider to provide flat phase difference at wide bandwidth. The bandwidth of the proposed antenna covers the frequency bands of up- and down-link. The antenna shows wide beamwidth and enhanced axial ratio for unfavorable space environments.

• The Journal of the Korea Contents Association
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• v.9 no.6
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• pp.104-116
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• 2009

Today's Digital Environment made Typography to enter into a new phase. The Type which is a principal component of Typography is no exception to this aspect. However since the existing two-dimensional space has figurative potential, Visual Communication designers are still striving to explore both X axis and Y axis. In this context, Z axis which signifies 'Depth' is often recognized as an unfamiliar mathematical concept unrelated to Design Sensibility. If Z axis is used, the figurative aspect can be acquired, which was hard to be realized in the flat space, because the additional space of depth allows the expansion of omni-directional expression of target. Most notable is the fact that Z axis provided by Digital Environment has actually long existed and is inseparable from Type. This study, therefore, focuses on the three-dimensional expression of Type in the Visual Communication Design area by taking into account the above characteristics.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.356-361
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• 2006

We present the performance of differential space-time block decoders. which does not require the channel state information. We suggest the structure of the multiple blocks differential space time decoders. which does not require the channel state information, and analyze the Performances. In quasi-static flat fading channels. the Performance of multiple blocks differential detection (MD-STC) outperforms that of 2 blocks(D-STC) by 1.5dB. But in the time-selective fading channels due to Doppler frequency $(f_d)$, the performance of MD-STC degrades as the vehicular speed is greater than 200km/hr in 802.16e systems, where the data transmission rate is 144kbps.

• Journal of Digital Convergence
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• v.12 no.9
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• pp.343-351
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• 2014

This study poses questions on the role of a movie sequences partially deployed in the comic strips style in the movie. Though both the movie and the comic strips's image is expressed in the flat space, it is different to the reciever's manner in the interpretation of the media's narrative. Comic strip has a media's characteristic of the aggressive interpretation. It can be create the objective and critic point of view for an audience as the visual style in the ideology movie. Comic strip Style has a flat frame, a form of comic strip's mise-en-scene, montage and camera working. This paper studies expression of 'La Chinoise' using 'Comic strip style' for the objective point of view.

• Journal of the Korean association of regional geographers
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• v.21 no.3
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• pp.593-607
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• 2015

This study examined the Holocene environmental changes by OSL dating and magnetic susceptibility (MS) in 12 sediment cores from estuarine tidal flat, Mosan Bay Estuary, west coast of Korea. For the complexity of the geomorphic characteristics of estuaries, it is difficult to obtain a series of data. The following significant results were derived using relatively simple methods. First, MS data shows sensitive changes in pattern according to the precipitation change during mid to late Holocene. Second, MS data show periodicity of 250 yr. when they were wavelet transformed. This periodicity is related with the intensifying of solar intensity, the East Asian Summer Monsoon and ENSO. Thus, MS data from estuarine sediments are valuable data which can explain mechanism of climate change in East Asia and worthy as proxy data.

• Journal of architectural history
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• v.22 no.4
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• pp.35-44
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• 2013

This paper looked into the structure of and changes in the building process of Gijang mountain fortress and its receiving reservoir by analyzing data from an excavation investigation. The structure of the receiving reservoir may be classified into a flat form, stone sheath, floor facility, wall facility, and entry and exit facility. The flat form of the Gijang mountain fortress and receiving reservoir is round. Concerning the sectional form, the wall was obliquely excavated in the trapezoid. As a stone sheath building method, it was built by undertaking a range work of oblong stone materials in a clockwise direction on a stamped soil floor. Then, it was treated with stamping using double layers of gray clay and yellowish brown clay on the floor and the wall. Also, in a space between the stamped layers on the floor, herbal plants and a straw mat were laid for waterproofing as well as to prevent sinking. As an entry and exit facility, two facilities were confirmed symmetrically in the southeast and in the northwest. It is believed that they were built additionally during rebuilding after the initial construction. The building process was revealed to have been carried out in 8 stages. Given the structure and excavated remains, the building period is estimated to be the early to mid 7th century for the initial building, the later 9th to 11th centuries for the primary rebuilding, and the later 16th to early 17th centuries for the secondary rebuilding.