• Current Optics and Photonics
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• 제2권6호
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• pp.589-594
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• 2018

We have investigated the dimensional nature of center-of-mass exciton confinement states in a CdMnTe/CdTe/CdMnTe heterostructure, where the CdTe well is too wide (144 nm) to confine both electrons and holes but able to confine whole excitons in the center-of-mass coordinate. Fine multiple photoluminescence spectra with a few meV separation were observed at 6 K. From the thickness dependence of the transition rate, they were attributed to even numbered center-of-mass exciton confinement states (N = 2, 4, 6, ${\cdots}$, 18). Dimensionality of the center-of-mass exciton confinement states was also investigated in terms of temperature dependence of radiative decay time. At low temperatures (${\leq}12K$), we found that the ground state excitons are likely localized possibly due to the barrier interface fluctuation, resulting in a constant decay time (~350 ps). With increased temperature (${\geq}12K$), localized excitons are thermally released, giving rise to a linear temperature dependence of radiative decay time as an evidence of two-dimensional nature.

• Steel and Composite Structures
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• 제32권2호
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• pp.199-212
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• 2019

This paper presents an investigation on seismic behavior of out-of-code Q690 circular high-strength concrete-filled thin-walled steel tubular (HCFTST) columns made up of high-strength (HS) steel tubes (yield strength $f_y{\geq}690MPa$). Eight Q690 circular HCFTST columns with various diameter-to-thickness (D/t) ratios, concrete cylinder compressive strengths ($f_c$) and axial compression ratios (n) were tested under the constant axial loading and reversed cyclic lateral loading. The obtained lateral load-displacement hysteretic curves, energy dissipation, skeleton curves and ductility, and stiffness degradation were analyzed in detail to reflect the influences of tested parameters. Subsequently, a simplified shear strength model was derived and validated by the test results. Finally, a finite element analysis (FEA) model incorporating a stress triaxiality dependent fracture criterion was established to simulate the seismic behavior. The systematic investigation indicates the following: compared to the D/t ratio and axial compression ratio, improving the concrete compressive strength (e.g., the HS thin-walled steel tube filled with HS concrete) had a slight influence on the ductility but an obvious enhancement of energy dissipation and peak load; the simplified shear strength model based on truss mechanism accurately predicted the shear-resisting capacity; and the established FEA model incorporating steel fracture criterion simulated well the seismic behavior (e.g., hysteretic curve, local buckling and fracture), which can be applied to the seismic analysis and design of Q690 circular HCFTST columns.

• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1364-1371
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• 2018

An extensive investigation of photon interaction properties has been made for $Zn_xTe_{100-x}$ alloys (where x = 5, 20, 30, 40, 50) to explore its possible use in sensing and shielding gamma radiations. The results show better and stable response of ZnTe alloys for various photon interaction properties over the wide energy range, with an additional benefit of ease in fabrication due to lower melting points of Zn and Te. Mass attenuation coefficient values show strong dependence on photon energy as well as composition. Effective atomic number has maximum value for $Zn_5Te_{95}$ and lowest for $Zn_{50}Te_{50}$ in the entire energy region. The alloy sample with maximum $Z_{eff}$ shows minimal value of $N_e$ and vice versa. Mean free path follows inverse trend as observed for mass attenuation coefficient. The exposure and energy absorption buildup factors depend upon photon energy, penetration thickness and composition (effective atomic number) of $Zn_xTe_{100-x}$ alloys. It finds its application for sensing and shielding from highly energetic and highly penetrating photons at sites where radioactive materials were used and visibility of material is not a big constraint. Further, energy down conversion property of ZnTe alloys with subsequent emission in green band suggests its potential use in sensing gamma photons.

• 소성∙가공
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• 제31권4호
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• pp.179-185
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• 2022

The influence of post-roll bonding heat treatment conditions such as temperature and time on the variation in the diffusion layer, generated at the bonding interface and the subsequent mechanical properties of the roll-bonded Ti grade 1/Al1050/Ti grade 1 sheets, was systematically investigated. The intermetallic compound (IMC) phase generated by post heat treatment conditions adopted in this study was obviously indexed as monolithic TiAl₃. Whereas the thickness of IMC layer generated by annealing at 500 ℃ was approximately 100 nm scale, it drastically increased above 1.5 ㎛ when annealed at 600 ℃. Uniaxial tensile and peel tests were then performed to compare mechanical properties. As a result, the bonding strength drastically increased above 7.9 N/mm by annealing at 600 ℃, which implies that proper annealing condition was a prerequisite, to improving interface bonding strength as well as global elongation properties for Ti/Al/Ti 3-ply sheet.

• 한국항행학회논문지
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• 제19권6호
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• pp.623-629
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• 2015

본 논문에서 CDMA (1.85~2.12 GHz) 및 2.4 GHz WLAN (2.4~2.484 GHz) 이중대역 사용이 가능하면서 무지향성 방사패턴을 가질 수 있도록 역 L-형 슬롯을 가진 CPW (coplanar waveguide) 급전 인쇄형 모노폴 안테나를 새롭게 제안하였다. 제안된 안테나는 2.4 GHz WLAN (wireless local area network) 대역에서 임피던스 대역폭을 증가시키기 위해 기존의 n-형 슬롯을 대신하여 역 L-형 슬롯이 인쇄된 방사 모노폴에 에칭 된다. 제안된 안테나는 크기가 $50{\times}25mm^2$이고 두께가 1.6 mm, 유전상수가 4.4인 FR4 기판의 한쪽 면에서 설계 및 제작되었다. 제작된 안테나의 측정결과, 임피던스 대역폭($S_{11}{\leq}-10dB$)이 CDMA (code division multiple access) 주파수 대역에서는 280 MHz (1.84~2.12 GHz), WLAN 주파수 대역에서는 420 MHz (2.38~2.8 GHz)인 대역폭을 얻을 수 있었다. 역 L-형 슬롯 사용의 결과로 WLAN 대역에서 기존의 n-형 슬롯의 사용결과 140 MHz (2.39~2.53 GHz)에 비해 대역폭이 3배가량 증가된 점은 주목할 만한 결과이다. 또한 사용 주파수 전 대역에서 좋은 무지향성 방사패턴을 얻을 수 있었다.

• 한국양식학회지
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• 제17권3호
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• pp.215-220
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• 2004

돌돔, Oplegnathus fasciatus의 소화관은 식도, 위, 장 및 항문이 일련의 관을 이루고 있고,전체적으로 지방 덩어리가 싸고 있다. 어체 체장에 대한 식도에서 항문까지의 소화관 길이의 비(relative length of gut: RLG)는 일반적인 잡식성 어류와 비슷한 평균 1.78 (n=30)의 값을 가진다. 식도는 근육층이 잘 발달되어 있으며, 점막주름의 상피층은 입방상피 또는 원주상피로 구성되고 상피세포 사이에는 다수의 산성 점액분비세포들이 분포하며, 상피세포의 정단부에서 미세융모의 관찰은 어렵다. 위의 근육층은 외부로부터 종주근, 환상근층으로 구성된다. 위의 점막주름은 규칙적인 형태로서 상피층에는 pit, 상피 및 위선이 아주 잘 발달되어 있으며, 점막상피 세포질의 정단부에서는 영양분 흡수계통의 물질들이 관찰된다. 50∼60개의 유문수를 가지는 돌돔 유문수의 점막상피층에서는 원주형의 상피세포와 중성의 점액분비세포들이 관찰되며, 상피세포의 정단면에는 미세융모가 발달되어 있다. 장의 점막상피층에서는 원주상피세포와 중성과 산성의 점액분비세포들이 관찰되며, 종주근층의 두께가 전장, 중장, 후장으로 갈수록 두꺼워진다. 산성의 점액분비세포의 출현빈도는 중장부에서 가장 발달된 양상을 보이며 후장부로 갈수록 감소하는 경향을 보인다.

• 한국결정성장학회지
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• 제13권5호
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• pp.241-246
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• 2003

ATO(antimony-doped tin oxide) 투명전도막을 sol-gel dip coating 방법에 의해 $SiO_2$/glass 기판 위에 성공적으로 제조하였다 ATO막의 결정상은 $SnO_2$상임을 확인하였고, 막의 두께는 withdrawal speed를 50 mm/minute로 코팅시 약 100 nm/layer였다. $SiO_2$/glass 기판 위에 코팅한 400 nm두께의 ATO 박막을 질소분위기에서 annealing한 후, 측정한 광 투과율과 전기 저항치는 각각 84%와 $5.0\times 10^{-3}\Omega \textrm{cm}$였다. 이러한 특성은 $SiO_2$막이 Na 이온의 확산을 제어하여 $Na_2SnO_3$ 및 SnO와 같은 불순물의 형성을 억제하고, 막 내부의 Sb의 농도와 $Sb^{3+}$에 대한 $Sb^{5+}$의 비를 증가시키는데 기여했기 때문으로 확인되었다. 또한, $N_2$ annealing은 $Sb^{5+}$뿐만 아니라 $Sn^{4+}$를 환원시킴으로써 전기전도도를 향상시킴을 확인하였다.

• International Journal of Concrete Structures and Materials
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• 제8권1호
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• pp.83-97
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• 2014

This paper presents the results of an investigation aimed at developing reinforced concrete beams consisting of precast permanent U-shaped reinforced mortar forms filled with different types of core materials to be used as a viable alternative to the conventional reinforced concrete beam. To accomplish this objective, an experimental program was conducted and theoretical model was adopted. The experimental program comprised casting and testing of thirty beams of total dimensions $300{\times}150{\times}2,000mm$ consisting of permanent precast U-shaped reinforced mortar forms of thickness 25 mm filled with the core material. Three additional typical reinforced concrete beams of the same total dimensions were also cast to serve as control specimens. Two types of single-layer and double-layers steel meshes were used to reinforce the permanent U-shaped forms; namely welded wire mesh and X8 expanded steel mesh. Three types of core materials were investigated: conventional concrete, autoclaved aerated lightweight concrete brick, and recycled concrete. Two types of shear connections between the precast permanent reinforced mortar form and the core material were investigated namely; adhesive bonding layer between the two surfaces, and mechanical shear connectors. The test specimens were tested as simple beams under three-point loadings on a span of 1,800 mm. The behavior of the beams incorporating the permanent forms was compared to that of the control beams. The experimental results showed that better crack resistance, high serviceability and ultimate loads, and good energy absorption could be achieved by using the proposed beams which verifies the validity of using the proposed system. The theoretical results compared well with the experimental ones.

• Steel and Composite Structures
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• 제22권5호
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• pp.937-974
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• 2016

While extensive efforts have been made in the past to develop finite element models (FEMs) for concrete-filled steel tubular columns (CFSTCs), these models may not be suitable to be used in some cases, especially in view of the utilisation of high strength steel and high strength concrete. A method is presented herein to predict the complete stress-strain curve of concrete subjected to tri-axial compressive stresses caused by axial load coupled with lateral pressure due to the confinement action in square and rectangular CFSTCs with normal and high strength materials. To evaluate the lateral pressure exerted on the concrete in square and rectangular shaped columns, an accurately developed FEM which incorporates the effects of initial local imperfections and residual stresses using the commercial program ABAQUS is adopted. Subsequently, an extensive parametric study is conducted herein to propose an empirical equation for the maximum average lateral pressure, which depends on the material and geometric properties of the columns. The analysis parameters include the concrete compressive strength ($f^{\prime}_c=20-110N/mm^2$), steel yield strength ($f_y=220-850N/mm^2$), width-to-thickness (B/t) ratios in the range of 15-52, as well as the length-to-width (L/B) ratios in the range of 2-4. The predictions of the behaviour, ultimate axial strengths, and failure modes are compared with the available experimental results to verify the accuracy of the models developed. Furthermore, a design model is proposed for short square and rectangular CFSTCs. Additionally, comparisons with the prediction of axial load capacity by using the proposed design model, Australian Standard and Eurocode 4 code provisions for box composite columns are carried out.

• 치과방사선
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• 제23권1호
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• pp.103-114
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• 1993

The purpose of this study was to determine whether any difference existed in craniofacial morphology between parents of children with cleft lip and/or palate and parents of children without cleft lip and/or palate as well as the characteristics of craniofacial morphology in parents of children with cleft lip and/or palate. Thirty three measurements of the various regions of cranium and face were obtained from lateral cephalometric radiograms in parents of 28 children with cleft lip and palate, 18 children with cleft lip, and 22 children with cleft palate. There were 28 couples and 40 single parents in this sample. There were 92 individuals including 41 males and 51 females. The measurements were compared with those in control subjects, including 40 adult males and 40 adult females, who had no history of craniofacial abnormalities. The total sample was compared for the sex independently. The obtained results were as follows. 1. In the cranium, both parents of cleft children had significantly shorter posterior cranial base length(S-Ba). 2. In the upper face, a significantly shorter anteroposterior length of maxilla(A'-Ptm'), particularly in the anterior region (A'-K), anterior facial depth(A-SBaL), posterior facia! height(Ptm'-SNL) and relation of subnasale to the cranial base (∠BaN'Sn) were noted in fathers of cleft children. But, all measurements were not found to be significantly different between experimental group and control group in all mothers. 3. In the lower face, both parents of cleft children showed a significantly greater Y axis angle(∠NSGn) and ramal plane angle(∠SNL-RP) in fathers of cleft children. Thus both patents showed a posteriorly rotation of mandible. The thickness of the lower lip(B-B') was significantly thicker in fathers of cleft children. 4. In the facial profile, a significantly shorter posterior facial height(S-Go) and greater angle of soft tissue facial convexity (∠BaN'Pog') were noted in the fathers of cleft children. But, all measurements were not found to be significantly different between experimental group and control group in all mothers.