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Conformal Frame Dependence on Cosmological Observations in Scalar-Tensor Theories of Gravity
현영환,김윤배,이석천 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.12
Cosmological observations provide more accurate values both for the background evolution of the Universe and for the structure formation. These values are given by the so-called dark energy equation of state, $\omega$, and the growth index parameter, $\gamma$. From these observed parameters, one can reconstruct the model functions in scalar-tensor gravity theories. However, there is a long-standing debate about the (in)equality between conformally transformed frames in scalar-tensor gravity models and some cosmological observables have been shown to be frame independent and others frame dependent. We focus on the cosmological evolutions of the frame-dependent observables, which are functions of the frame-independent parameter, the redshift. Thus, if one measures the cosmological parameters $\omega$ and $\gamma$ from the frame-dependent cosmological observables in one specific frame, then all of the other observables should also be interpreted in that frame with the same cosmological parameters obtained from that measurement. If one analyzes the same observables in another frame, then the obtained cosmological parameters should be different from those of the original frame. This explicitly shows the frame dependence of cosmological observables. Also, our method provides a model-independent analysis of scalar-tensor theories of gravity models about various observables in both frames.
Fe(II)/과황산/전기화학적 산화 공정에 의한 2,4-D의 제거
현영환,최지연,신원식 한국지하수토양환경학회 2021 지하수토양환경 Vol.26 No.1
The removal of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution by coupled electro-oxidation and Fe(II) activatedpersulfate oxidation process was investigated. The electrochemical oxidation was performed using carbon sheet electrode andpersulfate using Fe(II) ion as an activator. The oxidation efficiency was investigated by varying current density (2 - 10 mA/cm2), electrolyte (Na2SO4) concentration (10 - 100 mM), persulfate concentration (5 - 20 mM), and Fe(II) concentration (10 -20 mM). The 2,4-D removal efficiency was in the order of Fe(II) activated persulfate-assisted electrochemical oxidation(Fe(II)/PS/ECO, 91%) > persulfate-electrochemical oxidation (PS/ECO, 51%) > electro-oxidation (EO, 36%). The persulfatecan be activated by electron transfer in PS/ECO system, however, the addition of Fe(II) as an activator enhanced 2,4-Ddegradation in the Fe(II)/PS/ECO system. The 2,4-D removal efficiency was not affected by the initial pHs (3 - 9). Thepresence of anions (Cl and HCO3) inhibited the 2,4-D removal in Fe(II)/PS/ECO system due to scavenging of sulfateradical. Scavenger experiment using tert-butyl alcohol (TBA) and methanol (MeOH) confirmed that although both sulfate(SO4•−) and hydroxyl (•OH) radicals existed in Fe(II)/PS/ECO system, hydroxyl radical (SO4•−) was the predominant radical.
발파 굴착에 의한 주방식 지하구조물의 굴착공기 분석 연구
이철호,현영환,송준호,장수호,Lee, Chulho,Hyun, Younghwan,Song, Junho,Chang, Soo-Ho 한국터널지하공간학회 2015 한국터널지하공간학회논문집 Vol.17 No.6
주방식 지하구조물은 여러 개의 암주의 룸으로 구성된 격자 형태의 구조물로 굴착순서에 따라 주방식 지하구조물의 시공성과 경제성이 좌우될 수 있다. 본 연구에서는 주방식 지하구조물의 굴착공정에서 중요하게 다뤄질 수 있는 발파굴착 공정을 장비 운영과 현행 발파 규정 및 건설공사 표준품셈에 근거하여 검토하였다. 굴착공법으로는 점보드릴을 이용한 발파공법을 가정하였으며, 기존연구에서 제시한 가로 세로 순차시공방식으로 검토하였다. 주방식 지하구조의 계획부지 크기에 따라 굴착공기와 장비운영 등을 고려하여 전체 굴착공정을 예상할 수 있었으며 막장운영 계획에 따라 운영가능한 장비수를 고려하여 전체 굴착공기를 예상할 수 있었다. A room-and-pillar underground structure is characterized by its grid-type array of room and pillar. As a result, its construction and economical efficiency can be governed by excavation sequence. In this study, the construction period by the drill and blast method which can be treated as a main sequence for excavation was examined by considering the regulation for blasting and construction standard of estimation in Korea. To evaluate the construction period for the room-and-pillar underground structure constructed in 4 kinds of square-type area ($30{\times}30{\sim}57{\times}57m$), the concurrent excavation pattern which was suggested in the previous researches was used. From the suggested condition, the total construction period by drill-and-blast method can be estimated with the consideration of the construction area, number of jumbo drill and faces in operation.
이철호,현영환,황제돈,최순욱,강태호,장수호,Lee, Chul-Ho,Hyun, Young-Hwan,Hwang, Je-Don,Choi, Soon-Wook,Kang, Tae-Ho,Chang, Soo-Ho 한국터널지하공간학회 2016 한국터널지하공간학회논문집 Vol.18 No.6
주방식 지하구조물은 룸과 암주로 이루어진 격자 형태의 지하구조물로 굴착순서에 따라 주방식 지하구조물의 시공성과 경제성이 좌우될 수 있다. 선행연구에서는 주방식 지하구조물의 굴착공정에서 중요하게 다뤄질 수 있는 발파굴착 공정을 장비 운영과 현행 발파 규정 및 건설공사 표준품셈에 근거하여 검토하였다. 굴착공법으로는 점보드릴을 이용한 발파공법을 가정하였으며, 기존 연구에서 제시한 가로 세로 병행시공방식으로 검토하였다. 연구에서 고려한 단면의 크기에 따라 필요한 착암 공정에 대한 천공시간을 산정하였으며 기존 도로터널 사례를 통해 버력처리 및 지보재 설치 공정의 소요시간을 산정하였다. 굴진면 운용 수를 고려하여 굴착 사이클을 산출하였으며 이를 통해 운영가능한 천공장비의 최대 대수와 최소 대수를 수식화하여 제시하였다. Since a room-and-pillar underground structure is characterized by its grid-type array of room and pillar, its economical efficiency can be governed by excavation sequence. In this study, the construction period by the drill-and-blast method as a excavation method for a room-and-pillar underground structure was examined. In addition, the parallel excavation sequence was considered as the main sequence of a room-and-pillar underground structure. Sequences of mucking and support installation were derived to estimate the total excavation cycle by taking the case of a road tunnel into consideration. From the excavation cycle of room-and-pillar underground structure, the relationship between available maximum and minimum numbers of jumbo drill machines depending on the number of faces in operation was suggested.