• Kyungpook Mathematical Journal
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• v.57 no.1
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• pp.145-161
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• 2017

If a virtual knot diagram can be transformed to another virtual one by a finite sequence of crossing changes, Reidemeister moves and virtual moves then the two virtual knot diagrams are said to be homotopic. There are infinitely many homotopy classes of virtual knot diagrams. We give necessary conditions by using polynomial invariants of virtual knots for two virtual knots to be homotopic. For a sequence S of crossing changes, Reidemeister moves and virtual moves between two homotopic virtual knot diagrams, we give a lower bound for the number of crossing changes in S by using the affine index polynomial introduced in [13]. In [10], the first author gave the q-polynomial of a virtual knot diagram to find Reidemeister moves of virtually isotopic virtual knot diagrams. We find how to apply Reidemeister moves by using the q-polynomial to show homotopy of two virtual knot diagrams.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.3
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• pp.1-10
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• 2021

This study examines the dynamic pattern of the exchange rate volatilities of the ASEAN-5 currencies from January 2006 to August 2020. The exchange rates applied in this study comprise bilateral and effective exchange rates in order to investigate the influence of the US dollar on the stability of the ASEAN-5 currencies. Since a volatility model employed in this study is a natural cubic spline volatility model, the Monte Carlo simulation is consequently conducted to determine an appropriate criterion to select a number of quantile knots for this model. The simulation results reveal that, among four candidate criteria, Generalized Cross-Validation is a suitable criterion for modeling the ASEAN-5 exchange rate volatilities. The estimated volatilities showed the inconstant dynamic patterns reflecting the uncertain exchange rate risk arising in international transactions. The bilateral exchange rate volatilities of the ASEAN-5 currencies to the US dollar are more variable than their corresponding effective exchange rate volatilities, indicating the influence of the US dollar on the stability of the ASEAN-5 currencies. The findings of this study suggest that the natural cubic spline volatility model with the quantile knots selected by Generalized Cross-Validation is practical and can be used to examine the dynamic patterns of the financial volatility.

• Journal of Navigation and Port Research
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• v.32 no.8
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• pp.577-582
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• 2008

In order to ascertain the effect of ship's speeds, in maneuver under the condition of strong cross current in the breakwater channel of Busan port, this paper is to deal with the analyses of vessel proximity measures, vessel controllability measures, and ship handlers' subjective evaluation measures of simulated maneuvers, which were carried out by 76 ship handlers who conned Panamax bulk carrier of 60,000 DWT, The set and drift of current are southwesterly and 2 knots. The speeds of the model ship are 5 knots & 10 knots respectively. The followings are concluded. ${(1)}$ In the approaches of the breakwater of Busan port, ship handlers psychologically tend not to give the drift angle of more than $10^{\circ}$ bemuse ship's head points out of the entrance. ${(2)}$ Ship handlers' subjective evaluation, vessel proximity and controllability measures are relatively larger under the speed of 5 knots than under that of 10 knots. due to direct pressure of strong current. ${(3)}$ A single index of controllability measures was suggested, by removing their units.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.3
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• pp.208-215
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• 2011

A full-scale field trial in ice-covered sea is one of the most important tasks in the design of icebreaking ships. The first Korean icebreaking research vessel 'ARAON', after her delivery in late 2009, had a sea ice field trial in the Arctic Sea during July-August, 2010. This paper describes the test procedures and data analysis on the icebreaking performance of the IBRV ARAON. The data gathered from the icebreaking performance test in the Chukchi Sea and the Beaufort Sea during the Arctic voyage of ARAON includes the speed and engine power of the ship as well as sea ice thickness and strength data. The air temperature, wind speed and heading of the ship were also measured during each sea ice trial. The ARAON was designed to break 1 m thick level ice with a flexural strength of 630kPa at a continuous speed of 3knots. She is registered as a KR POLAR 10 class ship. The principal dimensions of ARAON are 110 m, 19 m and 6.8 m in length, breadth and draft respectively. She is equipped with four 3,500kW diesel-electric main engines and two Azipod type propulsion motors. Four sea ice trials were carried out to understand the relationship between the engine power and the ship speed, given the Arctic ice condition. The analysis shows that the ARAON was able to operate at 1.5knots in a 2.5m thick medium ice floe condition with the engine power of 5MW, and the speed reached 3.1 knots at the same ice floe condition when the power increased to 6.6MW. She showed a good performance of speed in medium ice floe compared to the speed performance in level ice. More detailed analysis is summarized in this paper.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.65.2-66
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• 2021

Observational studies of supernova (SN) feedback are limited. In our galaxy, most supernova remnants (SNRs) are located in the Galactic plane, so there is contamination from foreground/background sources. SNRs located in other galaxies are too far, so we cannot study them in detail. The Large Magellanic Cloud (LMC) is a unique place to study the SN feedback due to their proximity, which makes possible to study the structure of individual SNRs in some detail together with their environment. Recently, we carried out a systematic study of 13 LMC SNRs using [P II] (1.189 ㎛) and [Fe II] (1.257 ㎛) narrowband imaging with SIRIUS/IRSF, four SNRs (SN 1987A, N158A, N157B and N206), show [P II]/[Fe II] ratio much higher than the cosmic abundance. While the high ratio of SN 1987A could be due to enhanced abundance in SN ejecta, we do not have a clear explanation for the other cases. We investigate the [P II] knots found in SNRs N206, N157B and N158A, using optical spectra obtained last November with GMOS-S mounted on Gemini-South telescope. We detected several emission lines (e.g., H I, [O I], He I, [O III], [N II] and [S II]) that are present in all three SNRs, among other lines that are only found in some of them (e.g., [Ne III], [Fe III] and [Fe II]). Various line ratios are measured from the three SNRs, which indicate that the ratios of N157B tend to differ from those of other two SNRs. We will use the abundances of He and N (from the detection of [N II] and He I emission lines), together with velocity measurements to tell whether the origin of the [P II] knots are SN ejecta or CSM/ISM. For this purpose we have built a family of radiative shock with self-consistent pre-ionization using MAPPINGS 5.1.18, with shock velocities in the range of 100 to 475 km/s. We will compare the observed and modeled line fluxes for different depletion factors.

• Journal of the Korean Mathematical Society
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• v.47 no.1
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• pp.113-122
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• 2010

In [4], we gave a condition for a pair of unknotting tunnels of a non-trivial tunnel number one link to give a genus three Heegaard splitting of the link complement. In this paper we prove the corresponding result for tunnel number one knots.

• Journal of the Korean Institute of Navigation
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• v.8 no.2
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• pp.51-70
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• 1984

In the North Pacific Ocean a lot of large waves set up in winter, affected by continued winds and swells owing to severe extratropical cyclones. Under this sea condition, if the ship is about 100,000L/T (in deadweight capacity tonnage), we can't find the danger involved in the ship at sea apparently. But when we compare the seaworthiness of ship's building strength with the stress given to the hull by waves, we can't insist that the former be more stronger than the latter. As a result, VLCC is in danger of destroying and cutting for lack of longitudinal strength in heavy weather. Up to this time, Naval Architects have actively studied the relation between ship's longitudinal strength and waves as a ship's projector; however, actually, they have never made more profound study on the problem of longitudinal strength in relation to navigation. The main puprpose of this thesis is to clarify these vivid actual states of ship's trouble unknown to ship's masters. In this thesis we picked up VLCC Pan Yard, a vessel of Pan Ocean Bulk Carrier company's, as a model ship. And in the North Pacific Ocean, we have chosen for this research the basins where the wind speed and the wave height are greater than average. The data used this thesis are quotes from the "winds and waves of the North Pacific Ocean('64-'73)", and wind speed more than 30 knots was made use of as an ocject of this study. By usinh the ITTC wave spectrum, we found out the significant waves for every 5 knots within the range of 20 knots to 45 knots of wind speed. According to this H1/1000 was calculated. The stress of ship's hull is determined by ship's speed and wave height. We compared the ship's longitudinal strength with a planned wave height by rules of several famous classification societies in the world. In the last analysis, we found out that ship's present planned strength in heavy weather is not enough. Finally we made a graph for avoiding heavy weather, with which we studied safe ship's handling in the North pacafic Ocean in winter.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.3
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• pp.278-286
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• 2019

The Port of Pyeong Taek is located on the west coast, meaning that the difference between the rise and fall of tide is great (flood tide 1.8 to 2.9 knots, ebb tide 1.6 to 2.9 knots). Due to mainly N~NW'ly strong winds & high waves during winter, navigating as well as loading & discharging vessels must focus on cargo handling. The strong tidal and wind forces in the Port of Pyeong Taek can push an LNG carrier away from its berth, which will end up causing forced disconnection between the vessel's cargo line and shore-side loading arm. The primary consequence of this disconnection will be LNG leakage, which will lead to tremendous physical damage to the hull and shore-side equipment. In this study, the 125K LNG Moss Type ship docked at No. 1 Pier of the Pyeong Taek is observed, and the tension of the mooring line during cargo handling is calculated using a combination of wind and waves to determine effective mooring line and mooring line priority management. As a result if the wind direction is $90^{\circ}$ to the left and right of the bow, it was found that line monitoring should be performed bearing special attention to the Fore Spring Line, Fore Breast Line, and Aft Spring Line.

• Journal of the Korean Wood Science and Technology
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• v.16 no.4
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• pp.40-47
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• 1988

Our plywood manufacturing industries which entertained prosperous stage in late 1970's have come to be in face of the problems of conceedingly obtaining good quality logs and yield up-grading, which is considered by future-replaceable forest resources. In view of this point, manufacturing characteristic on softwood plywood using Japanese larch, pitch pine as domestic plantation species, and western hemlock as foreign species was studied. In this study, veneer- and plywood manufacturing yields were discussed in relation to log properties and veneer defects (knots). The summarized conclusions were as follows: 1. The majority of sample logs belonged to second grade on the standard. And, eccentricity of larch was the highest 11%, about 2 times those of pitch pine, hemlock. 2. Knot frequency of occurrence of larch reached 19% within log height 8m, and pitch pine 13% within 4m. Correspondingly, the log height of larch available for plywood manufacture was higher by about 2 times that of pitch pine. 3. In the knot types, most of knots of larch appeared dead, whereas those of pitch pine and hemlock appeared live. In size of knots, larch and hemlock showed relatively small 1-2cm dia. by 70% or more and pitch pine did the larger 24cm by 65%. Generally the more knot emerged in the inner side of veneer than the outer. 4. Plywood manufacturing yields by peeling with spindle revolution lathe were 37% in larch > 32% in hemlock> 26% in pitch pine. S. Jointed core veneer yields by peeling with outer perimeter back-up lathe were 55% in hemlock> 53% in larch> and 48% in pitch pine.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.4
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• pp.347-354
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• 2007

This paper describes on the real-time monitoring of net setting and hauling process for fishing operations of Danish seine vessels in the southern waters of Korea as an application of a PC based ECDIS system. Tracking of fishing process was performed for the large scale Danish seine vessel of G/T 90 and 350 PS class using the fishing gear which the length of net, ground rope, head rope and sweep line including warp in both sides were 86m, 104m, 118m and 3,200m, respectively. Tracking information for net setting and hauling process was continuously recorded for 23 fishing operations performed on November and December, 2003. All measurement data, such as trawl position, heading, towing course and past track which was individually time stamped during data acquisition, was processed in real time on the ECDIS and displayed simultaneously on the ENC chart. The results indicated that after the separation of a marker buoy from Danish seiner, the averaged running speed of vessel and the averaged setting period while shooting the seine on the course of diamond shape to surround the fish school in the 23 fishing operations were 8.3 knots and 13.1 minutes, respectively. And with the maker buoy taken on board, the averaged running speed of vessel and the averaged towing period while closing the seine on the straight route was 1.0 knots and 47.0 minutes, respectively. After the closing stage of hand rope, the hand rope was towed by the averaged speed of 2.2 knots during the 13.0 minutes. The average area for route of diamond shape swept by sweep lines of the seine in 23 fishing grounds was $709,951.6m^2$. Further investigation is also planed to provide more quantitative tracking information and to achieve more effective surveillance and control of Danish seine vessels in EEZ fishing grounds.