• Title/Summary/Keyword: micro-voids

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Evaluation of Void Distribution on Lightweight Aggregate Concrete Using Micro CT Image Processing (Micro CT 이미지 분석을 통한 경량 골재 콘크리트의 공극 분포 분석)

  • Chung, Sang-Yeop;Kim, Young-Jin;Yun, Tae Sup;Jeon, Hyun-Gyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.2A
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    • pp.121-127
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    • 2011
  • Spatial distribution of void space in concrete materials strongly affects mechanical and physical behaviors. Therefore, the identification of characteristic void distribution helps understand material properties and is essential to estimate the integrity of material performance. The 3D micro CT (X-ray microtomography) is implemented to examine and to quantify the void distribution of a lightweight aggregate concrete using an image analysis technique and probabilistic approach in this study. The binarization and subsequent stacking of 2D cross-sectional images virtually create 3D images of targeting void space. Then, probability distribution functions such as two-point correlation and lineal-path functions are applied for void characterization. The lightweight aggregates embedded within the concrete are individually analyzed to construct the intra-void space. Results shows that the low-order probability functions and the density distribution based on the 3D micro CT images are applicable and useful methodology to characterize spatial distribution of void space and constituents in concrete.

In vitro Estimation of The Hounsfield Units and The Volume and Void of Canine Struvite Stones as Predictors of Fragility in Extracorporeal Shock Wave Lithotripsy

  • Wang, Ji-hwan;Hwang, Tae-sung;Jung, Dong-in;Yeon, Seong-chan;Lee, Hee-chun
    • Journal of Veterinary Clinics
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    • v.34 no.3
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    • pp.178-184
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    • 2017
  • The aim of this study was to determine whether Hounsfield units (HUs), volume, and various void parameters can predict stone fragility in extracorporeal shock wave lithotripsy (ESWL). HU, volume, porosity, number of voids/stone volume, and void distribution of 30 struvite stones were estimated using helical computed tomography (CT) and micro-CT. The number of shock waves necessary for full fragmentation was accepted as a measure of the stone fragility in ESWL. The correlations between the number of shock waves and the HU, volume, porosity, and number of voids/stone volume were examined. The number of shock waves of the two groups according to the void distribution was also compared. Stone volume correlated with the number of shock waves. Shell-patterned struvite stones were significantly less susceptible to fragmentation in ESWL than non-shell-patterned struvite stones. Stone volume and void distribution may be predictors of the outcome of ESWL treatment.

Laboratory tests for studying the performance of grouted micro-fine cement

  • Aflaki, Esmael;Moodi, Faramarz
    • Computers and Concrete
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    • v.20 no.2
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    • pp.145-154
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    • 2017
  • In geological engineering, grouting with Portland cement is a common technique for ground improvement, during which micro-fine cement is applied as a slurry, such that it intrudes into soil voids and decreases soil porosity. To determine the utility and behavior of cements with different Blaine values (index of cement particle fineness) for stabilization of fine sand, non-destructive and destructive tests were employed, such as laser-ray determination of grain size distribution, and sedimentation, permeability, and compressive strength tests. The results of the experimental study demonstrated a suitable mix design for the upper and lower regions of the cement-grading curve that are important for grouting and stabilization. Increasing the fineness of the cement decreased the permeability and increased the compressive strength of grouted sand samples considerably after two weeks. Moreover, relative to finer (higher Blaine value) or coarser (lower Blaine value) cements, cement with a Blaine value of $5,100cm^2/g$ was optimal for void reduction in a grouted soil mass. Overall, study results indicate that cement with an optimum Blaine value can be used to satisfy the designed geotechnical criteria.

Development of lightweight concrete using the PCM II : Investigation on Foam Volume/Fly Ash Relationship of Foam Concrete, and Effect of High Content Micro Polypropylene Fiber and Microstructure

  • Lim, Myung-Kwan;Enkhbold, odontuya;Choi, Dong-Uk
    • KIEAE Journal
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    • v.15 no.4
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    • pp.45-52
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    • 2015
  • Purpose: Foam concrete is the concrete that contains large amount of air voids inside. In general, the density of foam concrete depends on parameters like water/binder ratio, foam volume, aggregate and pozzolan content, etc. Method: In this study, the effect of foam volume and fly ash content on dry density is investigated intensively in order to find the relationship between each parameter and their abilities to counteract with each other. According to the above information, though there are quite a number of studies on the effect micro fiber on foam concrete at low volume fractions, there is still lack of information especially on the high fiber content side. The objective of the second study is to investigate further on the use of micro fiber at higher volume fraction and fill in the lacking information. Beside from this study, the investigation of the effect of micro-fiber (polypropylene) to enhance the properties of foam concrete is also carried out. Result: Of the two variables that are investigated in this study, the foam volume and the fly ash content, show significant effect on the properties of foam concrete. The foam volume tends to decrease the density and strength of foam concrete. In the second part of our study, a large fibre volume fraction is proved to be able to evidently increase the flexural strength of foam concrete up to about 40% due to the effect of fibre bridging over the crack and a significant number of fibres that intercepts the crack surfaces. However, the compressive strength is found to decrease severely due to the occurrence of large pores as the result of fibre being added into concrete mixture.

Bacterial leakage and micro-computed tomography evaluation in round-shaped canals obturated with bioceramic cone and sealer using matched single cone technique

  • Yanpiset, Kallaya;Banomyong, Danuchit;Chotvorrarak, Kanet;Srisatjaluk, Ratchapin Laovanitch
    • Restorative Dentistry and Endodontics
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    • v.43 no.3
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    • pp.30.1-30.12
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    • 2018
  • Objectives: To evaluate sealing ability of root canals obturated with bioceramic-impregnated gutta percha cone (BCC) or gutta percha (GP), with bioceramic sealer (BCS) or AH Plus (AH; Dentsply-Maillefer), in roundly-prepared canals using matched single-cone technique, based on bacterial leakage test, and to analyze obturation quality using micro-computed tomography (CT) analysis. Materials and Methods: Ninety-two distobuccal roots of maxillary molars were prepared using nickel-titanium files to apical size 40/0.06. The roots were divided into 4 groups (n = 20) that were obturated with a master cone and sealer: GP/AH, BCC/AH, GP/BCS, and BCC/BCS. Bacterial leakage model using Enterococcus faecalis was used to evaluate sealing ability for 60-day period. Obturated samples from each group (n = 4) were analyzed using micro-CT. Results: All groups showed bacterial leakage at 20%-45% of samples with mean leakage times of 42-52 days. There were no significant differences in bacterial leakage among the groups. Micro-CT showed minimal gaps and voids in all groups at less than 1%. Conclusions: In roundly-prepared canals, the single cone obturation with BCC/BCS was comparable to GP/AH for bacterial leakage at 60 days.

Preparation and Properties of ZnSe/Zn3P2 Heterojunction Formed by Surface Selenization of Zn3P2 Film Deposited on ZnTe Layer

  • Park, Kyu Charn;Cha, Eun Seok;Shin, Dong Hyeop;Ahn, Byung Tae;Kwon, HyukSang
    • Current Photovoltaic Research
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    • v.2 no.1
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    • pp.8-13
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    • 2014
  • ZnSe/$Zn_3P_2$ heterojunctions with a substrate configuration were fabricated using a series of cost-effective processes. Thin films of ZnTe and $Zn_3P_2$ were successively grown by close-spaced sublimation onto Mo-coated glass substrates. ZnSe layers thinner than 100nm were formed by annealing the $Zn_3P_2$ films in selenium vapor. Surface selenization generated a high density of micro-cracks which, along with voids, provided shunt paths and severely deteriorated the diode characteristics. Annealing the $Zn_3P_2$ film at $300^{\circ}C$ in a $ZnCl_2$ atmosphere before surface selenization produced a dense microstructure and prevented micro-crack generation. The mechanism of micro-crack generation by the selenization was described and the suppression effect of $ZnCl_2$ treatment on the micro-crack generation was explained. ZnSe/$Zn_3P_2$ heterojunctions with low leakage current ($J_0$ < $1{\mu}A/cm^2$) were obtained using an optimized surface selenization process with $ZnCl_2$ treatment. However, the series resistance was very high due to the presence of an electrical barrier between the ZnTe and $Zn_3P_2$ layers.

Mechanical Characteristics and Macro-and Micro-structures on Friction Stir Welded Joints with 5083O Al Alloys (Al 5083O합금의 마찰교반용접부의 조직과 특성평가)

  • Jang, Seok-Ki;Park, Jong-Seek
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.1
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    • pp.104-111
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    • 2009
  • This paper shows the behaviors of macro- and micro-structures and mechanical properties for specimen's welding region welded by FSW. according to welding conditions with 5mm thickness aluminum 5083O alloy plate. It apparently results in defect-free weld zone in case traverse speed was changed to 32 mm/min under conditions of anti-clockwise direction and tool rotation speed such as 800 and 1250 rpm with tool's pin diameter of 5 ${\Phi}mm$ and shoulder diameter of 20 ${\Phi}mm$, pin length of 4.5 mm and tilting angle of $2^{\circ}$. The ultimate stress of ${\sigma}_T=331$ MPa and the yield point of 147 MPa are obtained at the condition of the travel speed of 32 mm/min with the tool rotation speed of 1250 rpm. There is neither voids nor cracks on bended surface of $180^{\circ}$ after bending test. The improvement of toughness after impact test was found. The lower rotating and traverse speed became, the higher were yield point, maximum stress and elongation(%) with the stresses and the elongation(%) versus the traverse speed diagram. Vickers hardness for cross section of welding zone were also presented. The typical macro-structures such as dynamically recrystallized zone, thermo-mechanically affected zone and heat affected zone and the micro-structures of the transverse cross-section were also showed. However, the author found out that the region of 6mm far away from shoulder circumference was affected by friction heat comprehensively, that is, hardness softened and that part of micro-structures were re-solid-solution or recrystallized, the author also knew that there is no mechanically deformation on heat affected zone but there are the flow of plastic deformation of $45^{\circ}$ direction on thermo-mechanically affected zone and the segregation of Al-Mg on nugget. The solid solution wt(%) of parent material as compared against of friction stir welded zone was comprehensively changed.

A Study on Selection Capability and Investment Efficiency of Korean Venture Capitals (한국 벤처캐피탈의 선별력에 대한 분석)

  • Sohn, Dong-Won;Hur, Wonchang
    • Korean Management Science Review
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    • v.29 no.3
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    • pp.91-105
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    • 2012
  • This paper examines the investment efficiency of Korean venture capitals during 1987~2006 (20 years), focusing on their selection capability. Despite the Korean government's efforts, venture capital industry has evolved in a slow speed. Since the genesis of venture paradigm in Korea at 1997, venture capital industry as a macro unit has been fully discussed in Korean contexts. But venture capital's activities at micro level regarding each investment's outcome have not been examined. This study attempts to fill the voids of micro knowledge about each investment success rates by venture capitals. We analyzed venture investment records in 4,791 venture startups and their success rates. Their investment criteria were relevant to high potential industries and amount of tangible assets. But their criteria were not relevant to R&D intensity and financial growth of venture firms, which may indicate low level of maturity about Korean venture capital industry. We found that Korean venture capital's investment pattern may be originated from the low return of investment, so that efficiency of IPO markets is a prerequisite for the upgrade of venture capitals' efficiency. Some policy implications are discussed.

The Detection of the Internal Defect in the Glass Using Auto Focusing Method (자동 초점 기법을 이용한 유리 내부 결함 검출)

  • Jy, Yong-Woo;Jhang, Kyung-Young;Jung, Ji-Hwa;Kim, Suk-Jun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.1047-1054
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    • 2004
  • Internal defects in the glass, like-as micro-voids, micro-cracks, or inclusions, easily cause the failure when the glass is exposed to the shock or the thermal variation. In order to produce the highly reliable glass product, the precision inspection of the defect in the glass is required. For this purpose, this paper proposes a machine vision technique based on the auto-focusing method, which searches the defect and measures the location under the fact that the edge image of defect must be the most clear when the focal plane of CCD camera is coincided with the defect. As for the search index, the gradient indicator is presented. The basic principles are verified through the simulations for the computer-generated defect images, where the affects of defect shape, gray level of background, and the brightness of the defect image are also analyzed. Finally, experimental results for actual glass specimens are shown to confirm the applicability of this method to the actual field.

Deterioration of tensile behavior of concrete exposed to artificial acid rain environment

  • Fan, Y.F.;Hu, Z.Q.;Luan, H.Y.
    • Interaction and multiscale mechanics
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    • v.5 no.1
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    • pp.41-56
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    • 2012
  • This study is focused on evaluation of the tensile properties of concrete exposed to acid rain environment. Acid rain environment was simulated by the mixture of sulfate and nitric acid in the laboratory. The dumbell-shaped concrete specimens were submerged in pure water and acid solution for accelerated conditioning. Weighing, tensile test, CT, SEM/EDS test and microanalysis were performed on the specimens. Tensile characteristics of the damaged concrete are obtained quantitatively. Evolution characteristics of the voids, micro cracks, chemical compounds, elemental distribution and contents in the concrete are examined. The deterioration mechanisms of concrete exposed to acid rain are well elucidated.