• Journal of Engineering Education Research
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• v.7 no.2
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• pp.51-59
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• 2004

The signs have been used as the world-wide common language. Because all units have their own meanings, their usage should be kept correctly. This paper shows how middle school students know and keep the usage of SI units. And this paper shows the necessity of teaching the students correct units in their schools.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.2
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• pp.66-74
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• 1997

현재 세계 대부분의 나라에서 사용하는 국제단위계는 우리가 그동안 미터법이라고 부르던 단위계가 현대화 된 것이라고 보면 된다. 이 국제단위계를 보통 'SI'라고 하는데 이는 불어 Le Sys- teme International d'Unites에서 온 약어로 국제 공통으로 이렇게 표시하기로 했다. 즉 이 단위계의 이름을 우리나라 말로는 '국제단위계'이지만 영어로는 'The International System of Unit's로 표시 하는 등 각 나라마다 다를 수 있으나 전 세계 모든 나라가 공통으로 'SI'라고 부르기로 한 것이다. 국제단위계(SI)의 시초는 1790년경 프랑스에서 발명된 '미터계'이며, 이 미터계는 1875년 17개국 이 미터협약(Meter Convention)에 조인함으로써 공시화되었다. 이 미터계로부터 분야에 따라 여러 개의 하부 단위가 생겼으며 이에 따라 많은 단위들이 나타나게 되었는데, 그 한 예가 1881년 과학분 야에서 사용하기 위해 만든 CGS계이며, 이는 센티미터, 그램 및 초에 바탕을 두고 있다.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.19-25
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• 2002

Ternary $xSrO-yB_2O_3-0.1Al_2O_3$ and $xSrO-yB_2O_3-0.1SiO_2$ glasses were prepared as a function of R(${\equiv}x/y$). The fraction of four-coordinated brans ($N_4$), symmetric three-coordinated barons ($N_{3S}$), and asymmetric three-coordinated barons ($N_{3A}$) were determined quantitatively to study the structures of these glasses by $^{11}B$ NMR. The values of $Q_{cc}$ and ${\eta}$ for $BO_3$ unit in the glasses were 2.74MHz and 0.22, those for $BO_3{^-}$ unit were 2.54MHz and 0.55, and those for $BO_4$ unit 0.60~0.75MHz and 0.00, respectively. The structure of SrBAl glass at $R_{1st}$ consisted of tetraborate ($[B_8O_{13}]^{-2}$) units and 1st-modified diborate ($[B_2Al_2O_7]^{-2}$) units, and those for the glass at $R_{max}$consisted of diborate ($[B_4O_7]^{-2}$) units, metaborate ($[BO_2^{-1}]$), 1st-modified diborate units, and 2nd-modified diborate ($[B_2Al_2O_8]^{-4}$) units. Due to the oxygens introduced from the strontium oxide. $AlO_4$ units were preferably formed rather than $BO_4$ units. And, the structure of SrBSi glasses in the region $R{\leq}0.5$ could be viewed as binary $SrO-B_2O_3$ glasses structure diluted by silicate oxide: therefore, the Si atoms of the glasses did not contributed to the change the configuration around the boron atoms. The silicate oxide was formed the $SiO_4{^-}$ units rather than the $BO_3{^-}$ units by the oxygens introduced from the storntium oxide in the region of $R{\geq}R_{max}$, and structure of those glass at $R_{max}$ consisted of diborate units, metaborate units loose $BO_4([BO_2]^{-1})$, and $SiO_4{^-}([SiO_{2.5}]^{-1})$ units.

• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.37-44
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• 2006

The homoepitaxy of Si(5 5 12) at $495^{\circ}C$ has been studied by Scanning Tunneling Microscopy under ultrahigh vacuum. A Si-dimer is the basic building-block and preferentially adsorbs on a unique site, that is, the Si-dimer/adatom site at the (337) and the (225) subsections within the Si(5 5 12) unit cell. The Si(5 5 12) unit cell is faceted to $3\times(337)$ subsections filled with Si-addimers and $1\times(113)$ subsection. In this step the tetramer at the other (337) section within the unit cell is transformed to a dimer/adatom site which can accept Si-dimers. Each (337) section is faceted to $1\times(112)\;and\;1\times(113)$, and then finally the unit cell of Si(5 5 12) is faceted to $3\tiems(112)\;and\;4\times(113)$ and forms the facet of effective height, $2.34{\AA}$. In this step, mutual transformation between the honeycomb chain and the dimer/adatom occurs. Finally, the valley between (112) and (113) facets is filled. If once the last step is completed, the uniform and planar Si(5 5 12) terrace is recovered. From the present study, therefore, it can be concluded that the homoepitaxy on Si(5 5 12) is periodically achieved and such growth mode is quite unique since faceting of the substrate-unit-cell plays a critical role for controlling uniformity of the overlayer.

• Korean Journal of Optics and Photonics
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• v.30 no.4
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• pp.133-141
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• 2019

Revision of the International System of Units (SI) in terms of fundamental constants was achieved by the 26th General Conference on Weights and Measures (CGPM) in November 2018. Four base units (kilogram, ampere, kelvin, and mole) of SI were redefined by fixing the values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant $N_A$ respectively. In this paper the scientific principle for redefining the kilogram from the Planck constant with the Kibble balance is explained as an example. The revised SI takes effect on May 20, 2019.

• 전기의세계
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• v.58 no.11
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• pp.51-56
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• 2009

산업이 고도로 발달함에 따라 자기장의 정밀 측정 및 발생 등에 대한 관심이 증대되고 있다. 정밀 자기장 측정기를 이용하여 생체.의료공학, 지하광물 및 매설물 탐사, 지진 및 전파방해 예측, 지구물리탐사 및 우주 자기장 분포 측정, 항법장치, 국방 및 우주항공분야, 송유관 부식 연구 등에 활용되고 있다. KRISS에서는 첨단 자기분야의 표준/정밀측정 보급 지원을 위해 자기장 범위 $20\;{\mu}T$ ~ 1.2 mT에서 비자성 실험실, 지구자기장 상쇄장치 등을 이용하여 불확도 (4 ~ 21) ${\mu}T$/T, 자기장 범위 1 mT ~ 2.5 T에서는 헬름홀스 코일, 전자석, NMR 자기장 측정기 등을 사용하여 불확도 (10 ~ 80) ${\mu}T$/T의 표준을 유지하고 있다. 자기장는 자속(magnetic flux) 및 자속밀도(magnetic flux density)로 나눌수 있으며, 그 SI 단위는 웨버(Wb, weber)와 테슬러(T, tesla)이다. 그러나 아직까지 자성재료 등의 특성을 측정하는 전문가들은 SI 단위보다는 지금까지 널리 사용되어온 cgs 단위인 맥스웰(Mx, maxwell), 가우스(G, gauss), 외르스테드(Oe, oersted) 등에 익숙해져 있다. 앞으로 자기분야 전문가들도 기본 SI 단위로부터 소급이 유지되는 SI 자기단위의 사용을 기대해 본다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.670-677
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• 2012

In this paper, mechanical property of biomorphic C/SiC composite was calculated by unit cell analysis. The microstructural arrangements of carbonized pine and radiata pine which were impregnated with silicon, were idealized as square and hexagonal arrays. Unit cell was then defined and equivalent elastic constants were calculated. A single and double unit cell structures were considered. The effect of void distribution was also studied by monte carlo simulation.

• Journal of the Korea Computer Graphics Society
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• v.16 no.3
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• pp.11-19
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• 2010

This paper describes how to define and implement the schema for 3D virtual objects with physical units so that the objects can be compared in virtual environments based on physical properties, such as length, according to the specified units. We define physical units for virtual objects using the International System of Units and based on the X3D (Extensible 3D) specification. The schema must be defined with validation so that it does not violate the original X3D data structure. In this paper, we have extended the original X3D schema with a physical unit specification, and demonstrate the difference between units-specified and non-units-specified 3D scenes using an X3D browser that we developed.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.27-31
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• 2002

Quarternary $Li_2O-B_2O_3-Al_2O_3-SiO_2$ glasses were fabricated by the function of $R({\equiv}Li_2Omole%/B_2O_3mole%)$ and $K({\equiv}(Al_2O_3mole%+SiO_2mole%/B_2O_3mole%)$. The structures of these glasses were investigated through refractive index and Vicker's hardness. The refractive index increased as the increase of the polarizability in the glass network. In the region of low $Li_2O$ content, the refractive index increased due to the increase of the polarizability in the glass network but, in the region of high $Li_2O$ content, the rate of increase of the refractive index decreased due to the increase of the molar volume caused by the formation of $BO_3{^-}$ units with relatively high molar volume. And, the refractive index decreased as the increase of $Al_2O_3+SiO_2$ content with the molar volume in the glass network. The increase and decrease of vicker's hardness values for those glasses depended on the fraction of tetrahedral $BO_4$ units and it of triangle $BO_3{^-}$ units with non-bridging oxygen, respectively.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.97.2-97.2
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• 2010

유리기판을 이용하여 제조되는 미세 결정질 실리콘 박막 태양전지에서 진성 반도체층(i ${\mu}c$-Si:H layer, i층)은 태양전지의 광 흡수층으로 사용되기 때문에 그 특성은 매우 중요하다. 특히, i층의 결정분율 변화는 태양광의 흡수파장 및 효율을 결정하여 준다. 본 연구에서는 i층 증착시 $SiH_4$ 가스의 농도 변화 및 $SiH_4$ 가스 profiling을 통하여 i층의 결정분율을 변화하였으며, 이에 따른 i층 단위박막과 미세결정질 태양전지 특성변화를 분석 하였다. i층의 $SiH_4$ 가스 농도가 증가함에 따라 i층 단위박막의 결정분율은 증가하였으며, 전기 전도도는 감소하였다. 또한, i층의 $SiH_4$ 가스 농도를 점차 증가하며 profiling 하여 증착한 박막은 동일 가스 농도로 증착한 박막보다 전기 전도도가 감소하였고, 증착속도는 증가하였다. 이와 같은 다양한 i층들은 'Raman spectroscopy'를 통하여 결정분율 변화를 측정하였다. 또한, 이 박막들을 광 흡수층으로 사용하는 미세결정질 태양전지를 제조하고, 태양전지의 효율, 양자효율, 암전류 특성들을 단위박막 특성과 연계하여 분석하였다.