• Title/Summary/Keyword: angle dependence

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Observation of superparamagnetic behaviors in Co nano dots fabricated by laser irradiation method (레이저 조사 방법으로 제조된 Co 나노닷의 초상자성 현상 관측)

  • 양정엽;윤갑수;도영호;구자현;김채옥;홍진표
    • Proceedings of the Korean Magnestics Society Conference
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    • 2004.12a
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    • pp.219-220
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    • 2004
  • Superparamagnetic regions and magnetic anisotropic properties in randomly orientated Co nano dots(NDs) were investigated as a function of dot diameter, spacing, and density. The Co NDs were fabricated by intentionally exposing a laser source on ultra thin film. Various dot sizes are ultimately realized by changing laser power, scan condition, and intial film thickness. Magnetic hysteresis loops, angle-dependent magnetization, and temperature dependence magnetization of the Co NDs were measured with a superconducting quantum interference device. The analysis of magnetization and hysteresis loops was effectively used to determine superparamagnetic regions of the Co NDs. Up to now, the experimentally observed results repeal that room temperature superparamagnetic limit of our Co NDs was about 30 nm in diameter, with the confirmation of high resolution transmission electron microscope.

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Influence of Surface Morphology and Substrate on Thermal Stability and Desorption Behavior of Octanethiol Self-Assembled Monolayers

  • Ito, Eisuke;Gang, Hun-Gu;Ito, Hiromi;Hara, Masahiko;No, Jae-Geun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.219-219
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    • 2012
  • The formation and thermal desorption behaviors of octanethiol (OT) SAMs on single crystalline Au (111) and polycrystalline Au, Ag, and Cu substrates were examined by X-ray photoelectron microscopy (XPS), thermal desorption spectroscopy (TDS), and contact angle (CA) measurements. XPS and CA measurements revealed that the adsorption of octanethiol (OT) molecules on these metals led to the formation of chemisorbed self-assembled monolayers (SAMs). Three main desorption fragments for dioctyl disulfide (C8SSC8+, dimer), octanethiolate (C8S+), and octanethiol (C8SH+) were monitored using TDS to understand the effects of surface morphology and the nature of metal substrates on the thermal desorption behavior of alkanethiols. TDS measurements showed that a sharp dimer peak with a very strong intensity on single crystalline Au (111) surface was dominantly observed at 370 K, whereas a broad peak on the polycrystalline Au surface was observed at 405 K. On the other hand, desorption behaviors of octanethiolates and octanethiols were quite similar. We concluded that substrate morphology strongly affects the dimerization process of alkanethiolates on Au surfaces. We also found that desorption intensity of the dimer is in the order of Au>>Ag>Cu, suggesting that the dimerization process occurs efficiently when the sulfur-metal bond has a more covalent character (Au) rather than an ionic character (Ag and Cu).

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Elastic-Plastic J Estimations for Pipes with Off-Centred Circumferential Through-Wall Cracks (비대칭 원주방향 관통균열 배관의 탄소성 J-적분 계산식)

  • Shim, Do-Jun;Huh, Nam-Su;Kim, Yun-Jae;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.7
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    • pp.1170-1178
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    • 2003
  • This paper provides approximate J estimates for off-centred, circumferential through-wall cracks in cylinders under bending and under combined tension and bending. The proposed method is based on the reference stress approach, where the dependence of elastic and plastic influence functions of J on the cylinder/crack geometry, the off-centred angle and strain hardening is minimised through the use of a proper normalising load. Based on published limited FE results for off-centred, circumferential through-wall cracks under bending, such normalising load is found, based on which the reference stress based J estimates are proposed for more general cases, such as for a different cylinder geometry and for combined loading. Comparison of the estimated J with extensive FE J results shows overall good agreements for different crack/cylinder geometries and for combined tension and bending, which provides sufficient confidence in the use of the proposed method to fracture mechanics analyses of off-centred circumferential cracks. Furthermore, the proposed method is simple to use, giving significant merits in practice.

Prediction of Poisson's ratio degradation in hygrothermal aged and cracked [θm/90n]s composite laminates

  • Khodjet-Kesb, M.;Adda bedia, E.A.;Benkhedda, A.;Boukert, B.
    • Steel and Composite Structures
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    • v.21 no.1
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    • pp.57-72
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    • 2016
  • The Poisson ratio reduction of symmetric hygrothermal aged $[{\theta}_m/90_n]_s$ composite laminates containing a transverse cracking in mid-layer is predicted by using a modified shear-lag model. Good agreement is obtained by comparing the prediction models and experimental data published by Joffe et al. (2001). The material properties of the composite are affected by the variation of temperature and transient moisture concentration distribution in desorption case, and are based on a micro-mechanical model of laminates. The transient and non-uniform moisture concentration distribution give rise to the transient Poisson ratio reduction. The obtained results represent well the dependence of the Poisson ratio degradation on the cracks density, fibre orientation angle of the outer layers and transient environmental conditions. Through the presented study, we hope to contribute to the understanding of the hygrothermal behaviour of cracked composite laminate.

Lossless Linear Polarization Rotator by Using a ECB Liquid Crystal Cell and a Quarter Wave Plate (ECB 액정 셀과 1/4 파장판을 이용하여 구성한 무손실 선형편광 회전기)

  • Jo, Jae-Heung
    • Korean Journal of Optics and Photonics
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    • v.20 no.1
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    • pp.48-52
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    • 2009
  • We make a simple electrically controllable linear polarization rotator over 360360 without loss by using a thick ECB(electrically controlled birefringence) liquid crystal cell and a quarter wave plate at 514.5 nm wavelength. Its operating principle can be analyzed and explained by using simple polarization analysis and experimental data. We demonstrate that the degree of polarization of the rotator is 0.964 and the temporal variation for 1 week lies within ±1±1 degree. We can easily solve the problem of nonlinearity of the dependence of the rotational angle of linear polarization on the applied voltage by changing the utilized voltage range or its fitting curve.

Near-Infrared Polarization Source Catalog of Northeastern Regions in the Large Magellanic Cloud

  • Kim, Jaeyeong;Jeong, Woong-Seob;Pak, Soojong;Park, Won-Kee;Tamura, Motohide
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.2
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    • pp.31.2-31.2
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    • 2015
  • We present a near-infrared photometric and polarimetric catalog of sources in the 39×69 fields on the northeastern part of the Large Magellanic Cloud (LMC), which was observed using SIRPOL, an imaging polarimeter of the Infrared Survey Facility (IRSF). This catalog contains 1,858 sources brighter than 14 mag at H band with polarization signal-to-noise ratio greater than 3 in at least one of J, H, and Ks bands. We examined the polarization structures around the star-forming regions, where coherent polarization position angle distributions are seen. We also estimated magnetic field strengths in some selected fields using Chandrasekhar and Fermi analysis. The magnetic field strengths are estimated to be 325μG. The wavelength dependence of polarization degrees indicates that the polarization is most likely to be originated from dichroic extinctions by the local interstellar dusts in the LMC. We found that the polarization patterns are well aligned along the molecular clouds around star-forming regions.

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Maturity of the Crater Rim Walls as a function of the Crater Size

  • SIM, Chae Kyung;Kim, Sungsoo S.;Jeong, Minsup
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.2
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    • pp.45.3-46
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    • 2015
  • Space weathering agents such as micrometeoroids and solar wind particles continuously age the uppermost regolith of the lunar surface by comminuting as well as darkening and reddening. Among several maturity indices, we investigate median grain size () and optical maturity (OMAT) of the crater rim walls. Crater rim wall is the most immature place among the impact crater features because the vertical mixing process by mass-movement can enhance the gardening of regolith and the supply of immature materials in the deeper layer to the surface. More than 140 simple and complex craters were considered. Both and OMAT values of the inner rim wall initially increase as the crater size increases until ~10-20 km, then decrease. This transition crater size happens to correspond to the transition diameter from simple to complex craters. For larger craters, i.e., complex craters, it is clear that the inner rim wall of the craters formed in recent eras tend to remain fresh and become mature along with time. For the simple crater case, smaller craters are more mature, which is opposite to the case of complex craters. This is thought to be because smaller craters become flattened more quickly, thus have smaller vertical mixing in the regolith due to mass-movement. We will also discuss on the maturity indices of the crater rim walls at high latitudes as a function of the position angle to see the latitude dependence of the space weathering process.

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Estimation of Polarization Ratio for Sea Surface Wind Retrieval from SIR-C SAR Data

  • Kim, Tae-Sung;Park, Kyung-Ae
    • Korean Journal of Remote Sensing
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    • v.27 no.6
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    • pp.729-741
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    • 2011
  • Wind speeds have long been estimated from C-band VV-polarized SAR data by using the CMOD algorithms such as CMOD4, CMOD5, and CMOD_IFR2. Some SAR data with HH-polarization without any observations in VV-polarization mode should be converted to VV-polarized value in order to use the previous algorithms based on VV-polarized observation. To satisfy the necessity of polarization ratio (PR) for the conversion, we retrieved the conversion parameter from full-polarized SIR-C SAR image off the east coast of Korea. The polarization ratio for SIR-C SAR data was estimated to 0.47. To assess the accuracy of the polarization ratio coefficient, pseudo VV-polarized normalized radar cross section (NRCS) values were calculated and compared with the original VV-polarized ones. As a result, the estimated psudo values showed a good agreement with the original VV-polarized data with an root mean square error by 0.99 dB. We applied the psudo NRCS to the estimation of wind speeds based on the CMOD wind models. Comparison of the retrieved wind field with the ECMWF and NCEP/NCAR reanalysis wind data showed relatively small rms errors of 1.88 and 1.91 m/s, respectively. SIR-C HH-polarized SAR wind retrievals met the requirement of the scatterometer winds in overall. However, the polarization ratio coefficient revealed dependence on NRCS value, wind speed, and incident angle.

Preparation and characterization of proton exchange membranes in non-aqueous conduction (무수 전도성 양성자 교환막 제조 및 특성평가)

  • Park, Jin-Soo;Sekhon, S.S.;Baek, Ji-Suk;Yang, Tae-Hyun;Kim, Chang-Soo;Yim, Sung-Dae;Park, Gu-Gon
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.06a
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    • pp.282-285
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    • 2009
  • This study presents preparation and characterization of composite membranes based on ionic liquids. The ionic liquids act as water in sulfonated membranes. On the behalf of ionic conduction through ionic liquid inside the membranes, non-aqueous membranes showed Arrenhius dependence on temperature with no external humidification. It was implied that hopping mechanism of proton was dominant in the ionic liquid based membranes. In addition, small angle X-ray (SAXS) studies provided the information on morphology of ionic clusters formed by the interaction between sulfonic acid groups of the polymers and ionic liquids. The SAXS spectra showed matrix peaks, ionomer peaks and Prodo's law for Nafion based composite membranes and only matrix peaks for hydrocarbon based ones. However, ionic conductivity and atomic force microscopy (AFM) images showed the clear formation of ionic clusters of the hydrocarbon based composite membranes. It implies for ionic liquid based high temperature membranes that it is important to use sulfonated polymers as solid matrix of ionic liquid which can form clear ionic clusters in SAXS spectra.

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Determination of Specimen Geomery for Estimation of the Complex Modulus of Viscoelas the Materials by the Lumped Mass Model (집중질량 모형화에 의한 점탄성재료의 복소 탄성계수 산출을 위한 시편 크기 의 절정)

  • Kang, Gi-Ho;Shim, Song;Kim, Gwang-Jun
    • Journal of KSNVE
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    • v.1 no.2
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    • pp.121-128
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    • 1991
  • In order to use viscoelastic materials efficiently for noise and vibration control, or th qualify newly developed materials, knowledge of the Young' s modulus and loss factor is essemtial. These material properties, the so-called complex Young' s modulus, are frequently treated as dynamic charicteristics because of their dependence upon the frequency. Many techniques have been developed and verified for measuring complex Young' s modulus of viscoelastic materials. Among them, the impedance method is preferable in order to obtain the frequency information in detail. In this method, a cylindrical or prismatic specimen is excited into longitudinal harmonic vibration at one end, the other being fixed, and the resulting force is measured at the driving or fixed end. The amplitude ratio of the two signals and phase angle between them are then used to compute the material properties using various mathematical models. In this paper, the impedance method is investigated theoretically and experimentally. A way to determine the specimen geometry which is most appropriate for the identification of complex Young' s modulus using the lumped mass model is presented and discussed. Then experimental results supporting the theoretical predictions are presented.

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