• 한국전기전자재료학회논문지
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• 제16권12S호
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• pp.1165-1174
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• 2003

The responses of hypothetical silicon nanotubes under torsion have been investigated using an atomistic simulation based on the Tersoff potential. A torque, proportional to the deformation within Hooke's law, resulted in the ribbon-like flattened shapes and eventually led to a breaking of hypothetical silicon nanotubes. Each shape change of hypothetical silicon nanotubcs corresponded to an abrupt energy change and a singularity in the strain energy curve as a function of the external tangential force, torque, or twisted angle. The dynamics o silicon nanotubes under torsion can be modelled in the continuum elasticity theory.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1140-1141
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• 2006

Maglev is a non-contact traffic system in which cars are supported by magnetic force instead of wheels. This is a ground-breaking traffic system providing superior environmental friendliness and cost efficiency due to the minimal noise and vibration offered by its non-contacting nature. We study the present specification and performance of the low speed urban maglev system in Korea and other countries. After set up the test line, to success the "Commercialization of Korean Urban Maglev System" project, we establish proper requirement of maglev system in Korean environment on base of "Daejeon National Science Museum Maglev Establish Project".

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권8호
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• pp.381-389
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• 2003

Nowadays, Vacuum Circuit Breaker(VCB) is used in the most medium voltage level because vacuum has environment-friendly characteristics as well as excellent dielectric strength. In order to elevate the breaking performance, the improvement of vacuum interrupters and the driving mechanism should be proceeded. In this paper, the development of a Permanent Magnet Actuator could replace the mechanical spring mechanism which is the driving mechanism of existing VCB. The holding force and opening characteristics of magnetic actuator are analysed with FEM and the result is verified through experiment.

• 한국항해학회지
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• 제15권3호
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• pp.73-97
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• 1991

The analysis and investigation are described for White's[2] equations compared to the equations of Runeburg[3] and Milano[5] for continuous icebreaking mode, Tunik[8-1] and Ghoneim[8-2] for ramming icebreaking mode. Calculation results compare reasonably well with published model-scale and full-scale icebreaker data by Baker[1] and Dick[11]. During continuous and ramming mode operation, using characteristics of an incebreaker, down ward force on ice and standard ice thickness broken are predicted. Additionally draft, trim and extraction difficulty are also predicted. The bow part line of an icebreakin $g^{ply}$ vessel is designed aiming to maximize the ice breaking capabiltiy as following conditions-low bow angle[20 degrees] at designed waterline, small spread angle complement [6 degrees] at designed waterline, small spread angle complement [6 degrees] and high propeller thrust [220tons]. with plow, two reamers and wave type bumper.

• 한국표면공학회지
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• 제53권5호
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• pp.265-270
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• 2020

We investigated mechanochemical radical, which is concomitant with chemical lift-off lithography(CLL), on the self-assembled monolayer(SAM)/electrodes and a polydimethylsiloxane(PDMS) using a colorimetric and a spectroscopic method. The 11-mercaptoundecanol(MUO)/Au or the 11-hydroxyundecylphosphonic acid (HUPA)/ITO were contacted with bare or activated PDMS. After contact, the each of SAM/substrates and the PDMS were immersed in a 2,2 Diphenyl-1-picrylhydrazyl(DPPH) radical scavenger. The color of the DPPH exposed to the PDMS was changed from purple to yellow and the absorbance decreased definitely at 515 nm wavelength. The SAM/substrates, however, have caused small changes in spectroscopic property, indicating no existence of radical species. We concluded that mechanochemical radicals were formed by homolytic cleavage of PDMS molecules upon external force and hardly transferred on the SAM/substrates.

• Restorative Dentistry and Endodontics
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• 제26권5호
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• pp.418-435
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• 2001

Root canal preparation process is of utmost importance in successful treatment of root canal. Also, one of the most important purpose of the root canal preparation is to enlarge the root canal three dimensionally without changing the curvature of the root canal However as the curvature of the root canal increases, there are many difficulties involved in formation of optimum root canal. Therefore in order to solve the above mentioned problems, new developments in methods of root canal preparation and equipments for such purposes were made. Recently, vigorous studies about newly introduced engine-driven nickel-ti-tanium rotary file are conducted. As shown in research results to dates, it is well established that the use of nickel-titanium file is better suited for curved root canal than stainless steel file in maintaining the curvature or root canal and reducing the deformation of root canal. However it is also acknowledged that there are a few discrepancies in research results according to protocol, due to failure to remove variables in experiments. In addition, although it is recommended by the manufacturer that the GT rotary file should maintain a low rotational speed of 150~350rpm and 'light pressure' as light as not to break the lead of a pencil, academic studies about the vertical force which is not yet standardized are not sufficiently explored. Therefore, this research devised and utilized a special research equipment to standardize the appropriate range of vertical force for GT rotary file through experiments by breaking of the lead of a pencil as expressed by the manufacturer and to accurately measure factors involved through repeating and recreating the environment of root canal preparation. Forming nine experimental groups by varying the vertical forces (150g. 220g, 300g) and rpm (150rpm, 250rpm, 350rpm), the effects of changing vertical forces and rpm on working efficiency were measured in terms of time expended in root canal preparation by crown-down method using a transparent resin block with 35 degree curvature and GT rotary file (z-test). The following research using this special research equipment that involved nine experimental groups and varying the vertical force for root canal preparation from 300g which is within the normal vertical force range to 700g and 1000g which fall outside the normal rpm range. The results were as follows : 1. Analysis of the experiment results revealed that the time spent in root canal preparation decreased as the vertical forces and rpm increased (p<0.05). Also, the effects of rpm were greater than those of the vertical forces within the normal vertical force range ($\beta$-weight test). 2. Observation of the deformation of GT rotary file revealed that deformation increases in a direct correlation with the vertical force increase and in a reverse correlation with the rpm decrease. In the case of the vertical forces close to the normal range, the probability of GT rotary file deformation were quite different depending on the rpm changes. In the case of greater vertical forces, the occurrences of deformation of the file were more frequent regardless of the rpm changes. 3. Deformation and breakage of file were also commonly observed in the expended time measurement experiments and GT rotary file deformation experiments in which low speed rpm (150rpm) was used and at the curved portion of the resin block.

• Asian-Australasian Journal of Animal Sciences
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• 제18권4호
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• pp.545-551
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• 2005

A feeding trial was conducted to determine whether dietary vitamin C (200 mg/kg) and vitamin E (250 mg/kg) prevent any drops in egg shell quality under heat stress in broiler breeder hens. One hundred and sixty molted Ross broiler breeders were housed randomly in an individual cage at 83 weeks of age. Four dietary treatments with forty hens and four replications per treatment were control (no additional vitamins), vitamin C-, or vitamin E-supplemented and combined supplementation of the two vitamins. After a tenday-adaptation period at 25$^{\circ}C$, the ambient temperature was kept at 32$^{\circ}C$ for a three-week-testing period. Egg production dropped dramatically over week but it did not show a significant change among treatments (p<0.05). However, egg quality parameters such as egg weight, specific gravity, shell thickness, SWUSA, puncture force and shell breaking strength from the birds fed the diet with the combined vitamins C and E were significantly improved over those of the control group during the heat stress period (p<0.05). The hens fed the vitamin C diet improved tibia breaking strength (37.16 kg), statistically higher than the birds fed the control and the vitamin E diets (p<0.05). The hens fed the control diet showed higher serum corticosterone levels, a mean of 5.97 ng/ml, than those of the other treatments (p<0.05). The heat stress resulted in elevated heterophils and decreased lymphocytes in serum, increasing the H/L ratios for all the treatments. However, the increases in H/L ratios were alleviated by feeding the diets containing vitamin C alone or together with vitamin E, although there were no significant differences in the ratio between the two groups (p<0.05). In conclusion, vitamins C (200 mg/kg) and/or E (250 mg/kg) supplemented to the diets for broiler breeder hens could prevent drops in egg shell quality and tibia bone strength under highly stressful environmental temperatures.

• Design & Manufacturing
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• 제10권1호
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• pp.41-45
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• 2016

Electrical equipment in factories, buildings, etc. with the development of the industry has become a large capacity. By the development, electric load also become diversified and there is also highly functional requirements being electrical equipment. Particularly in the small and medium-sized circuit breakers, tend to preferentially consider the economy stands out and improvements in safety, ease of mounting and connection through the modularity of the basic dimensions compact and cost to block expansion of the scope of the development of capacity, etc. The product having a competitive has been strongly required. In order to implement the circuit breakers of breaking capacity and compact at the same time taking into account the economic development of this technology applied to the current-limiting mechanism is essential budget or the current limiting mechanism is currently available mechanisms applicable to small and medium-sized frame (frame) can not do it. In this paper, at the same time satisfying the economic efficiency, by minimizing the load force of the moving contactor (moving contactor) to be applied to small and medium frame other hand to secure the economical efficiency without using high speed contact parting acceleration of the moving contactor conventional current-limiting mechanism, and to develop a current-limiting mechanism that can be satisfied with the same or higher performance to meet the needs of the market.

• 대기
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• 제16권2호
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• pp.67-83
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• 2006

The statistical analysis for the springtime windstorm in Korea shows that Yeongdong region has the highest occurrence frequency during recent 10 years. The objective of this study is to find possible mechanisms for the downslope windstorm formation in the Yeongdong region by using a mesoscale numerical model, WRF. Dynamical process, wave breaking (hereafter WB), is qualitatively investigated as the candidate mechanism for a windstorm event occurred in 5 April, 2005. WB is developed in upper troposphere downstream, since stable air is lifted by the Taebaek mountain. This process can cause and maintain the severe downslope windstorm by drawing the upper flow down to the surface. And the intensified downslope wind leads the hydraulic jump (hereafter HJ) in downstream region. Froude numbers at Chuncheon (upslope side), Seorak Mountain (crest), Yangyang (lee side), and the East Sea (distant downstream position) are estimated by about 0.4, 1.0, 1.6, and 0.6, respectively. This result implies that the accelerated and supercritical (Fr>1) flow adjusts to the ambient subcritical (Fr<1) conditions in the turbulent HJ. In addition, we find the formation of upstream inversion near top level of the mountain cause the intensification of HJ. Experiments to examine the orographic effect on the mechanisms suggest that the magnitudes of WB and HJ are larger in the experiment of higher topography, but there is no significant difference of windstorm magnitude among the experiments. Another important result from these sensitivity experiments is that the intensity of downslope windstorm strongly depends on the magnitude of upper (2~4 km) wind in upstream side.

• 풍력에너지저널
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• 제14권2호
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• pp.26-33
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• 2023

In this study, the global response characteristics of floater and mooring for floating offshore wind turbine with a detachable mooring system are performed. Global motion and structural response result extracted from the coupled motion analysis of 10MW DTU floating offshore wind turbine with detachable mooring system modeled by high-order boundary element model and finite element mesh, were used to study the characteristics of tension on mooring lines subjected to three different types of ocean loads. Breaking limit of mooring line characterized by wind, current and wave load has a major effect on the distribution of mooring tension found in time domain analysis. Based on the numerical results of coupled motion analysis, governing equation for calculating the motion response of a floater under ocean loads, and excitation force and surge motion and tension respectively are presented using excursion curve. It is found that the response of floater is reliable and accurate for calculating the tension distributions along the mooring lines under complex loadings. This means that the minimun breaking limit of mooring system satisfied a design criteria at ultimate ocean environmental loading condtions.