• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.829-834
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• 2005

A series of reinforced G109 type specimens was fabricated and pended with a 15 weight percent NaCl solution. Mix design variables included 1) two cement alkalinities (equivalent alkalinities of 0.32 and 1.08), 2) w/c 0.50 and 3) two rebar surface conditions (as-received and wire-brushed). Potential and macro-cell current between top and bottom bars were monitored to determine corrosion initiation time. Once corrosion was initiated, the specimen was ultimately autopsied to perform visual inspection, and the procedure included determination of the number and size of air voids along the top half of the upper steel surface. This size determination was based upon a diameter measurement assuming the air voids to be half spheres or ellipse. The followings were reached based upon the visual inspection of G109 specimens that were autopsied to date. First, voids at the steel-concrete interface facilitated passive film breakdown and onset of localized corrosion. Based upon this, the initiation mechanism probably involved a concentration cell with contiguous concrete coated and bare steel serving as cathodes and anodes, respectively. Second, the corrosion tended to initiate at relatively large voids. Third, specimens with wire-brushed steel had a lower number of voids at the interface for both cement alkalinities, suggesting that air voids preferentially formed on the rough as-received surface compared to the smooth wire brushed one.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.315-321
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• 2004

The void evolution in direct bonding process of $Si/Si_3$$N_4$ ∥ $SiO_2$/Si silicon wafer pairs has been investigated with an infrared camera. The voids that formed in the premating process grew in the conventional furnace annealing process at a temperature of $600^{\circ}C$. The voids are never shrunken even with the additional annealing process at the higher temperatures. We observed that the voids became smaller and disappeared with sequential scanning by our newly proposed fast linear annealing(FLA). FLA irradiates the focused line-shape halogen light on the surface while wafer moves from one edge to the other. We also propose the void shrinking mechanism in FLA with the finite differential method (FDM). Our results imply that we may eliminate the voids and enhance the yield for the direct bonding of wafer pairs by employing FLA.

• KIEE International Transactions on Electrophysics and Applications
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• v.3C no.1
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• pp.10-14
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• 2003

The occurrence of partial discharge (PD) in solid dielectrics is very harmful because it leads to the deterioration of insulation by electrical, chemical, and thermal reactions as a combined action of the discharged ions bombarding the surface and by the action of chemical compounds that are formed by the discharge. Consequently, if any defects are present in the solid insulation system, performance decreases until the system breaks down. Therefore, removing or suppressing the defect is very important. Voids are a typical defect in the solid insulation system and are very harmful because they deteriorate insulation. As a basic step, studying the properties of PD in voids is important because an accurate knowledge of these properties is required to estimate the deterioration of voids. In this paper, the correlation between the size of voids and internal PD is discussed as a function of the time of the applied voltage and its magnitude. Magnitude, repetition rate, average discharge power, and average discharge current of PD in specimens with large voids were found to be larger than the others in this experiment. The smaller specimens had voids when the magnitude and number of PDs were reduced.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.2
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• pp.146-156
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• 2001

The purpose of this study was twofold. One was to evaluate the wettability of 4 elastomeric impression materials on tooth and different kinds of filling materials. The other was to identify the effect of topical surfactants sprayed on the surface of each impression. The elastomeric impression mate rials used in this experimental study were one polyether(Impregum F) and three polyvinyl siloxanes(Provil novo, Zerosil, Imprint). The abutments were prepared for 3/4 crown or onlay on the extracted human first molar. The filling materials used in this study for the duplication of prepared abutment were composite resin, amalgam, and casting metal. Impression was taken by manufacturer's recommendations and the number of voids on the impression surface was counted. The topical surfactants were Spannex $II^{(R)}$ and $Cohere^{(R)}$. The wettability was evaluated by comparing the number of voids between non-treated group and treated groups. The results were as follows : 1. $Zerosil^{(R)}$ showed the least number of voids on the impression surface. The number of voids increased in order of Provil $novo^{(R)}$, Impregum $F^{(R)}$, and $Imprint^{(R)}$. 2. Impregum $F^{(R)}$ and $Zerosil^{(R)}$ showed the least number of voids on the surface of dental stone master cast. The number is inclosed in order of Provil $novo^{(R)}$ and Imprint 3. When abutment material is tooth, the number of voids on the surface of master cast was smallest compared with that of other abutment materials. The number of voids increased in order of casting metal, amalgam and composite resin 4. The number of voids on the surface of the dental stone master cast was smallest when Spannex $II^{(R)}$ was used, followed by $Cohere^{(R)}$ treated group and non-treated group. These results suggest that the difference in wettability caused by the types of rubber base impression materials as well as abutment materials can affect the number of voids. And the use of topical surfactant for rubber base impression materials can improve the wettability of the materials and enhance the accurate master cast which has fewer surface voids.

• Journal of the Korean Wood Science and Technology
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• v.36 no.6
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• pp.13-22
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• 2008

Internal voids affecting the mechanical properties of wood composite were classified into two catagories and characteristics of voids were examined according to density variation of strandboard. The void distribution and content of strandboard according to board density were measured by X-ray computed tomography system and analized using image processing software. Prior to investigation, the densities of strandboard were measured by densitometer and the results were showed high correlation with conventional oven drying method. Based on the image analysis conducted on captured images by X-ray tomography, low resolution can be used to capture the macro-voids (between strand) but not the micro-voids (within strands). Intermediate resolution can be used to capture both the macro and the micro-voids and high resolution can be successfully used to capture the majority of the micro-voids. The content of macro-void was measured and content of micro-void was computed by corresponding related equation. The macro-void distribution can be successfully understood and void content can be correctly estimated through the results.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.397-399
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• 2015

Recently, cosmic voids have been recognized as a powerful cosmological probe. A number of studies have focused on the effects of the gravitational lensing by voids on the temperature (and in some cases polarization) anisotropy of the Cosmic Microwave Background (CMB) background at relatively large to medium scales, l ~ 1000. Many of these studies attempt to explain the unusually large cold spot in CMB temperature maps and dynamical evidence of dark energy via detections of late-time integrated Sachs Wolfe (ISW) effect. Here, the effects of lensing by voids on the CMB temperature anisotropy at small scales, up to l = 3000, will be investigated. This work is carried out in the light of the benefits of adding large catalogues of cosmic voids, to be identified by future large galaxy surveys such as EUCLID and LSST, to the analysis of CMB data such as those from Planck mission. Our numerical simulation utilizes two methods, namely, the small-de ectionangle approximation and full ray-tracing analysis. Using the fitted void density profiles and radius (RV ) distribution available in the literature from N-body simulations, we simulated the secondary temperature anisotropy (lensing) of CMB photons induced by voids along a line of sight from redshift 0 to 2. Each line of sight contains approximately 1000 voids of effective radius $RV_{,eff}=35h^{-1}Mpc$ with randomly distributed radial and projected positions. Both methods are used to generate temperature maps. The two methods will be compared for their accuracy and effciency in the implementation of theoretical modeling.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.221-227
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• 2005

The presence of voids behind tunnel linings is very likely to result in settlement or structural collapse. One proposed method of detecting such voids by non-destructive method is radar. More than effectively judging the existence of voids behind tunnel linings, this study aims to develop the analysis algorithm of radar capable of estimation of the shape of specific voids. To acquire directional information and estimate the shape of three-dimensional voids, the radar of three-dipole antenna type is used. As a foundation to this ongoing research, an investigation of microwave polarization methods using three-dipole antenna carried out with various void orientations and void geometries. As a result, it is clarified that the response of four microwave polarization modes depends on void geometry and thus there is a possibility of identifying the geometry and orientation (the shape) of specific voids using radar of three-dipole antenna type.

• Korean Journal of Materials Research
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• v.24 no.9
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• pp.458-464
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• 2014

Light scattering enhancement is widely used to enhance the optical absorption efficiency of dye-sensitized solar cells. In this work, we systematically analyzed the effects of spherical voids distributed as light-scattering centers in photoanode films made of an assembly of zinc oxide nanoparticles. Spherical voids in electrode films were formed using a sacrificial template of polystyrene (PS) spheres. The diameter and volume concentration of these spheres was varied to optimize the efficiency of dye-sensitized solar cells. The effects of film thickness on this efficiency was also examined. Electrochemical impedance spectroscopy was performed to study electron transport in the electrodes. The highest power conversion efficiency of 4.07 % was observed with $12{\mu}m$ film thickness. This relatively low optimum thickness of the electrode film is due to the enhanced light absorption caused by the light scattering centers of voids distributed in the film.

• Structural Engineering and Mechanics
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• v.49 no.5
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• pp.597-618
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• 2014

For the structures containing multiple discontinuities (voids, inclusions, and cracks), the simulation technologies in the framework of extended finite element method (XFEM) are discussed in details. The level set method is used for representing the location of inner discontinuous interfaces so that the mesh does not need to align with these discontinuities. Several illustrations have been given to verify that the implemented XFEM program is effective. Then, the implemented XFEM program is used to investigate the effects of the voids, inclusions, and minor cracks on the path of major crack propagation. For a plate containing cracks and voids, two possibly crack path can be observed: i) the crack propagates into the void; ii) the crack initially curves towards the void, then, the crack reorients itself and propagates along its original orientation. For a plate with a soft inclusion, the final predicted crack paths tend to close with the inclusion, and an evident difference of crack paths can be observed with different inclusion material properties. However, for a plate with a hard inclusion, the paths tend to away from the inclusion, and a slightly difference of crack paths can only be seen with different inclusion material properties. For a plate with several minor cracks, the trend of crack paths can still be described as that the crack initially curves towards these minor cracks, and then, the crack reorients itself and propagates almost horizontally along its original orientation.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.2
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• pp.106-114
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• 2017

This paper presents an automated subsurface micro void detection technique based on pulsed infrared thermography for inspecting epoxy molding compounds (EMC) used in electronic device packaging. Subsurface micro voids are first detected and visualized by extracting a lock-in amplitude image from raw thermal images. Binary imaging follows to achieve better visualization of subsurface micro voids. A median filter is then applied for removing sparse noise components. The performance of the proposed technique is tested using 36 EMC samples, which have subsurface (below $150{\mu}m{\sim}300{\mu}m$ from the inspection surface) micro voids ($150{\mu}m{\sim}300{\mu}m$ in diameter). The experimental results show that the subsurface micro voids can be successfully detected without causing any damage to the EMC samples, making it suitable for automated online inspection.