• Title/Summary/Keyword: grain angle

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Microprobe EELS Study of Oxygen Non-Stoichiometry in High Tc $YBa_2Cu_3O_{7-\delta}$ Grain Boundaries (전자에너지손실분광법(EELS)을 이용한 $YBa_2Cu_3O_{7-\delta}$ 고온초전도체 쌍결정 경계에서의 산소 조성변화 연구)

  • ;S. E. Babcock
    • Journal of the Korean Vacuum Society
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    • v.4 no.2
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    • pp.194-200
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    • 1995
  • 2-3nm의 공간분해능을 갖는 전자에너지손실분광법(Electron Energy Loss Spectroscopy, EELS)을 이용하여, 전기적 특성조사된 YBa2Cu3O7-$\delta$ 고온초전도체 쌍결정의 결정경계(grain boundary)에서 산소의 조성변화를 조사하였다. Misorientation angle이 $14^{\circ}$, $28^{\circ}$,$ 30^{\circ}$인 3개의 쌍결정 중에서 Josephson junction 특성을 보인 $28^{\circ}$$30^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서의 oxygen 1s absorption edge와 매우 다름을 알 수 있었다. 이는 결정경계에서의 산소조성이 결정내부에 비해 낮음을 의미하며, 그 영역이 결정경계 부근 20-40nm로, coherence length에 비해 큼을 알 수 있다. 반면에, flux pinningxmr성을 보인 $14^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서와 별 차이를 보이지 않았다. 따라서 일반적으로 관찰되어온, misorientation angle이 큰 결정경계에서의 Josephson junction 특성은 결정경계 부근에서 산소의 조성이 낮아지는데에 기인하며, 그 원인은 결정경계면을 통해 산소가 out-diffusion되기 때문인 것으로 생각된다.

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Effect of Equal Channel Angular Pressing Temperature on the Fracture and Mechanical Properties of Magnesium (마그네슘의 등통로각압축 시 파괴 및 기계적 특성에 미치는 공정온도 효과)

  • Yoon, S.C.;Bok, C.H.;Kwak, E.J.;Jeong, Y.G.;Kim, T.S.;Kim, H.S.
    • Transactions of Materials Processing
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    • v.17 no.1
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    • pp.13-18
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    • 2008
  • Mg and Mg alloys are promising materials for light weight high strength applications. In this paper, grain refinement of pure Mg using severe plastic deformation was tried to enhance the mechanical properties of the hard-to-deform metallic material. The microstructure and the mechanical properties of Mg processed by equal channel angular pressing(ECAP) at various processing temperatures were investigated experimentally. ECAP with channel angle of $90^{\circ}$ and corner angle of $0^{\circ}$ was successful at $300^{\circ}C$ without fracture of the samples during the processing. The hardness of the ECAP processed Mg decreased with increasing ECAP processing temperature. The effect of temperature on the hardness and microstructure of the ECAP processed Mg were explained by the dislocation glide in the basal plane and non-basal slip systems and by the dynamic recrystallization and recovery.

LABORATORY SIMULATION OF LIGHT SCATTERING FROM REGOLITH ANALOGUES: EFFECT OF POROSITY

  • KAR, AMRITAKSHA;DEB, SANJIB;SEN, A.K.;GUPTA, RANJAN
    • Publications of The Korean Astronomical Society
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    • v.30 no.2
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    • pp.65-67
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    • 2015
  • The surfaces of most atmosphereless solar system objects are referred to as regolith, layers of loosely connected fragmentary debris, produced by meteorite impacts. Measurements of light scattered from such surfaces provides information about the composition and structure of the surface. A suitable way to characterize the scattering properties is to consider how the intensity and polarization of scattered light depends on the particle size, composition, porosity, roughness, wavelength of incident light and the geometry of observation. In the present work, the effect of porosity on bidirectional reflectance as a function of phase angle is studied for alumina powder with grain size of $0.3{\mu}m$ and olivine powder with grain size of $49{\mu}m$ at 543.5 nm. The optical constants of the alumina sample for each porosity were calculated with Maxwell Garnett effective medium theory. On using each of the optical constants of alumina sample in Mie theory with the Hapke model the variation of bidirectional reflectance is obtained as a function of phase angle with porosity as a parameter. Experimental reflectance data are in good agreement the model. For the olivine sample the effect of porosity is studied using Hapke (2008).

Shear Behavioral Characteristics of Weathered Residual Soil for the Change Water Content (풍화잔적토의 함수비 변화에 따른 전단거동특성)

  • Yoo, Nam-Jae;Kim, Young-Gil;Lee, Jong-Ho
    • Journal of Industrial Technology
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    • v.17
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    • pp.119-124
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    • 1997
  • This thesis is an experimental research of shear behavioral characteristics and shear behavioral coefficient of weathered residual soil which is mostly contained in soil of Korea. Using the weathered residual soil from mountain near Kangwon National University, this experimental research were contained the physical properties of sample in term of the basic test method such as specific gravity, plastic and liquid limit, grain-size distribution, density and water content. Experimental results obtained from direct shear test sand triaxial compression tests show that according to step loading, linear strain and linear stress increase continually and angle of internal friction decreases just little according to incresing of water content in case of ignoring the cohesion, and angle of internal friction appears the maximum angle near a optimum moisture content in case of considering the cohesion.

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Efficiency of Photovoltaic Cell with Random Textured Anti Glare (RTAG) Glass

  • Kim, Geon Ho;Jeon, Bup Ju
    • Applied Science and Convergence Technology
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    • v.25 no.6
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    • pp.133-137
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    • 2016
  • The surface treatment of cover glass for conversion efficiency of photovoltaic cell is important to reduce reflectivity and to increase the incident light. In this work, random textured anti glare (RTAG) glass was prepared by wet surface coating method. Optical properties due to the changes of surface morphology of RTAG glass were compared and conversion efficiency of photovoltaic cell was researched. Grain size and changes of surface morphologies formed with surface etching time greatly affected optical transmittance and transmission haze. Current density (Jsc) were high at the condition when surface morphologies reflection haze were low and transmission haze were high. Jsc was $40.0mA/cm^2$ at glancing angle of $90^{\circ}$. Incidence light source was strongly influenced by surface treatment of cover glass at high incidence angle but was hardly affected light source at the low angle of incidence.

Dependancy of Internal Friction Angle of Rock Materials on Confining Pressure (Rock재료의 내부마찰각의 구속압 의존성)

  • 신동훈;이경필;구방서
    • Proceedings of the Korean Geotechical Society Conference
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    • 2002.10a
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    • pp.253-258
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    • 2002
  • In this study the confining pressure dependancy of internal friction angle of rock materials are discussed based on the results of a series of large triaxial tests under consolidated-drained condition. The rock materials tested are two kinds of grain-size distribution ;one is well graded, the other poorly graded(a uniform distribution). The obtained results shows that the internal friction angle of rock materials decreases more sharply in low stress level than in high stress level, and the test constants A and b in De Mello's failure criterion on rockfill materials are A =0.683∼l.584, b=0.712∼l.015 for the well graded and A=1.145∼l.523, b=0.788∼0.880 for the poorly graded.

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Bulk and Surface of Al2O3 doped ZnO Films at Different Target Angles by DC magnetron sputtering

  • Kang, Junyoung;Park, Hyeongsik;Yi, Junsin
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.345.2-345.2
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    • 2016
  • Alumina (Al2O3) doped zinc oxide (ZnO) films (AZO) have been prepared from 2 wt.% Al2O3 doped ZnO target by DC magnetron sputtering at a 2 mTorr (0.27 Pa) chamber pressure in (15 sccm) argon ambient. We obtained films of various opto-electronic properties by variation of target angle from 32.5o to 72.5o. At lower target angle deposited films show higher values in optical gap, mobility of charge carrier, carrier concentration, crystallite grain size, transmission range of wavelength, which are favorable characteristics of AZO as a transparent conducting oxide (TCO). At higher target angle the sheet resistance, work function, surface roughness for the AZO films increases. Measured haze ratio of the films changed lower to higher and size of characteristic surface structure of as deposited film ranges from ~40 nm to ~300 nm. By a combination of low and high target angle we obtained a textured TCO film with high conductivity.

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A Study on Fatigue Crack Retardation and Retardation Mechanism in Variable Loading (변동하중하에서의 피로크랙 지연현상과 지연기구에 관한 연구 - 균열성장 지연현상에 미치는 균열 가지의 영향 -)

  • Song, S.H.;Kwon, Y.K.
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.6
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    • pp.83-89
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    • 1997
  • In order to study on fatigue crack retardation and retardation mechanism in variable loading, the effects of crack tip branching in fatigue crack growth retardation were examined. The characteristics of crack tip banching behavior was considered to micro structure. It was examined that the variation of crack tip branching angle. Crack tip branching was observed along the grain boundary of ferrite and pearlite structure. It was found that the abanching angle ranges from 25 to 53 degrees. Using the finite element method, the variable of crack driving force to branching angle was examined. The effective crack driving force ( $K_{\eff}$ ) decreased as the braching angle increases. The rate of decrease was 33% for the kinked type and 29% for the forked one. It was confirmed that the effect of crack tip branching is a very important factor in fatigue crack growth retardation. Therefore, crack branching effect should be considered building the hypoth- etical model to predict crack growth retardation.

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Microstructural Evolution Analysis in Thickness Direction of An Oxygen Free Copper Processed by Accumulative Roll-Bonding Using EBSD Measurement (EBSD측정에 의한 반복겹침접합압연된 무산소동의 두께방향으로의 미세조직 변화 분석)

  • Lee, Seong-Hee;Lim, Cha-Yong
    • Korean Journal of Materials Research
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    • v.24 no.11
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    • pp.585-590
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    • 2014
  • Microstructural evolution in the thickness direction of an oxygen free copper processed by accumulative rollbonding (ARB) is investigated by electron back scatter diffraction (EBSD) measurement. For the ARB, two copper alloy sheets 1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stacked and roll-bonded by about 50% reduction rolling without lubrication at an ambient temperature. The bonded sheet is then cut to the two pieces of the same dimensions and the same procedure was repeated on the sheets up to eight cycles. The specimen after 1 cycle showed inhomogeneous microstructure in the thickness direction so that the grains near the surface were finer than those near the center. This inhomogeneity decreased with an increasing number of ARB cycles, and the grain sizes of the specimens after 3 cycles were almost identical. In addition, the aspect ratio of the grains decreased with an increasing number of ARB cycles due to the subdivision of the grains by shear deformation. The fraction of grains with high angle grain boundaries also increased with continuing process of the ARB so that it was higher than that of the low angle grain boundaries in specimens after 3 cycles. A discontinuous dynamic recrystallization occurred partially in specimens after 5 cycles.

Dynamic Analysis of Shattering of Tongil Paddy (통일(統一)벼의 탈립(脱粒)에 관(關)한 역학적(力學的) 분석(分析))

  • Kang, Young Sun;Chung, Chang Joo
    • Journal of Biosystems Engineering
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    • v.9 no.1
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    • pp.11-21
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    • 1984
  • This study was intended to analyze the dynamic force system which induced the shattering of paddy grains. A model to predict the shattering of paddy grains was developed, and physical quantities, such as mass distribution and rigidity of rice plant, needed for evaluating the minimum shattering forces were also measured. Under the assumption that rice plant right before harvesting is a vibratory system, the mathematical model of the vibratory system was developed and solved with the varied conditions of forcing functions. The results of the study were summarized as follows: 1. The shattering of grain occurred at the abscission layer of grain by the bending moments resulted from the impact force due to the collision of panicles of rice plant. 2. The vibratory model developed for milyang 23 rice variety was analyzed to give the natural frequencies of 7-9 Hz, which were closely related with the excitation frequencies of 4-10 Hz caused by various machine parts besides engine. Thus, avoiding the resonance should be taken into consideration in the design of the harvesting machinery. 3. It was analyzed to predict the lowest frequency that could develop the shattering when the excitation force was applied to the lower end of stem. The lowest frequency for the Milyang 23 rice variety ranged from 8.33 Hz to 11.66 Hz as the amplitude varied from 1 cm to 2.5 cm. 4. The degree of shattering depended upon the magnitude of the impact force and its application point. For Milyang 23 rice variety, the minimum impact force developing the shattering was $5g_f$ when it was applied at 1 cm above the lower end of stern and $1g_f$ when applied at 5 cm above the lower end of stem. 5. The minimum colliding velocity of the panicle, when it was on the ground that would just develop the shattering, was given as follows, $$V=\sqrt{\frac{K_t}{m_g}{\cdot}{{\phi}^2}}$$ where V : The colliding velocity of the panicle against ground to cause the shatteering of rice grain. (cm/sec) $K_t$ : The minimum spring constant for bending at the abscission layer of grain. (dyne-cm/rad) ${\phi}$ : The minimum shattering angle of grain (rad) $m_g$ : The maximum mass of grain. (g).

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