• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.322-323
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• 2002

Partial volume averaging effect of PET data influences on the accuracy of quantitative measurements of regional brain metabolism because spatial resolution of PET is limited. The purpose of this study was to evaluate the accuracy of partial volume correction carried out on $^{18}$ F-PET images using Hoffman brain phantom. $^{18}$ F-PET Hoffman phantom images were co-registered to MR slices of the same phantom. All the MR slices of the phantom were then segmented to be binary images. Each of these binary images was convolved in 2 dimensions with the spatial resolution of the PET. The original PET images were then divided by the smoothed binary images in slice-by-slice, voxel-by-voxel basis resulting in larger PET image volume in size. This enlarged partial volume corrected PET image volume was multiplied by original binary image volume to exclude extracortical region. The evaluation of partial volume corrected PET image volume was performed by region of interests (ROI) analysis applying ROIs, which were drawn on cortical regions of the original MR image slices, to corrected and original PET image volume. From the ROI analysis, range of regional mean values increases of partial volume corrected PET images was 4 to 14%, and average increase for all the ROIs was about 10% in this phantom study. Hoffman brain phantom study was useful for the objective evaluation of the partial volume correction method. This MR-based correction method would be applicable to patients in the. quantitative analysis of FDG-PET studies.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.4
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• pp.10-17
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• 2000

This work presents an investigation of aerodynamic characteristics of fuel spray injected from a high pressure hollow cone swirl injector into a constant volume chamber. Laser tomography visualization was used to interrogate the fuel and air mixing characteristics and the effect of chamber pressure and temperature increase was analyzed, Preliminary results on spray development showed that mixing effect tends to increase with the increase of injection pressure and chamber gas pressure yielding a decrease of spray penetration and an attenuation of well-defined vortex structure. Topological analysis of the spray structure has been performed to initiate the understanding of mixing and vaporization process. For the present experimental conditions fuel injection pressure and chamber gas pressure appear as the dominant factors which govern the transient mixing characteristics. Moreover spray atmixation characteristics are improved by increasing chamber gas temperature.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.21-25
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• 2002

Effect of abnormal grain growth and heat treatment time on the electrical properties of donor-doped semiconductive BaTiO$_3$ceramics was examined. La-doped BaTiO$_3$ceramics was sintered at 134$0^{\circ}C$ for different times from 10 to 600 min in order to change the volume fraction of the abnormal grains in samples. As a result, samples with different volume fraction of abnormal grain growth from 22 to 100% were prepared. The samples were annealed at 120$0^{\circ}C$ for various times. The resistivity of the sam-ples at room and above Curie temperature was examined. The complex impedance measurement as functions of the volume fraction of abnormal grains and annealing time was conducted. Separation of complex impedance semicircle was observed in a sample in which abnormal and fine grains coexist. The results are discussed from a viewpoint of microstructure-property relationship.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.256-261
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• 2004

To evaluate the effect of spring shape on the fretting wear of nuclear fuel rod, sliding wear tests were performed using three kinds of space grid springs in room temperature air and water. With increasing slip amplitude, wear volume of each spring gradually increased. It is apparently shown that spring with convex shape had a relatively high wear resistance compared with concave shape springs. It is suggested that the ratio of the wear volume to the worn area can be suggested as an efficient and valid parameter to evaluate the wear resistibility of a fuel grid spring.

• The Korean Journal of Food And Nutrition
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• v.14 no.4
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• pp.317-321
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• 2001

Sweet dough bread is made by using sponge & dough method with the sweet dough formula which consists of wheat gluten and baking powder. The effect of wheat gluten and baking powder to the bread has been studied after the dough frozen, stored, thawed, fermented. and baked. The bread quality has been evaluated by measuring the product volute and also by the sensory evaluation after baking. When 4% of wheat gluten and 4% of baking powder were added into the dough. the bread has a larger volume than that of 2% wheat gluten and 2% baking powder in volume. However. wheat gluten shows better result than baking powder in terms of volume. In sensory evaluation, the bread has higher score when 2% of wheat gluten and 2% of baking powder were added into the dough than that of 4% wheat gluten and 4% baking powder. Consequently, breads show better result when 2% wheat gluten and 2% baking powder were added into the dough than that of 4% wheat gluten and 4% baking powder.

• Journal of Ocean Engineering and Technology
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• v.5 no.2
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• pp.58-66
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• 1991

Not only difference of fatigue crack growth and propagation behavior resulted from the grain size, the hardness ratio and volume fraction in M.E.F. dual phase steel composed of martensite in hard phase and ferrite in soft phase, but also the effects of the plastic constraint were investigated by fracture mechanics and microstructural method. The main results obtained are as follows: 1) The fatigue endurance of M.E.F. steel increases with decreasing the grain size, increasing the ratio of hardness and volume fraction. 2) The initiation of slip and crack occures faster as the stress level goes higher. These phenomena result from the plastic constraint effect of the second phase. 3) The crack propagation rate in the constant stress level is faster as the grain size gets larger, the ratio of hardness lower and volume fraction smaller.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.1
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• pp.78-84
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• 2005

The main goal of this work is to study the effects of temperature and volume fraction of fiber on the Charpy impact test with GF/PP composites. The critical fracture energy and failure mechanisms of GF/PP composites are investigated in the temperature range of 60^{\circ}C$ to -50^{\circ}C$ by impact test. The critical fracture energy increased as the fiber volume fraction ratio increased. The critical fracture energy shows a maximum at ambient temperature and it tends to decreases as temperature goes up or goes down. Major failure mechanisms can be classified such as fiber matrix debonding, fiber pull-out and/or delamination and matrix deformation.

• Journal of Powder Materials
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• v.10 no.1
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• pp.51-56
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• 2003

To investigate the effect of the parameters of the plasma arc discharge process on the particle formation and particle characteristics of the iron nano powder, the chamber pressure, input current and the hydrogen volume fraction in the powder synthesis atmosphere were changed. The particle size and phase structure of the synthesized iron powder were studied using the FE-SEM, FE-TEM and XRD. The synthesized iron powder particle had a core-shell structure composed of the crystalline $\alpha$-Fe in the core and the crystalline $Fe_3O_4$ in the shell. The powder generation rate and particle size mainly depended on the hydrogen volume fraction in the powder synthesis atmosphere. The particle size increased simultaneously with increasing the hydrogen volume fraction from 10% to 50%, and it ranged from about 45nm to 130 nm.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.537-538
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• 2009

To estimate the effect of fiber volume fraction on first cracking strength and flexural tensile strength of UHPC, flexrual tensile tests were carried out within 5 vol.% fiber reinforcement. The test results informed that both first cracking strength and flexural tensile strength improved linearly as fiber volume fraction increased.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.231-235
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• 2002

A theoretical and experimental study on the combustion process in a constant volume micro combustor is described. Unlike in a macro scale constant volume combustor, the heat loss to the wall plays a major role in flame propagation in a micro micro combustor. In order to analyze the effect of heat loss on combustion phenomena, pressure transition from ignition was measured. A number of cylindrical micro combustors with different diameter and depth were used for experiment to study the effect of length scales and shape factor. The diameter of combustor ranged from 7.5mm to 22.5 mm and the height of cylinder was from 1mm to 4mm. Initial pressure was also varied for the experiment. The diagnostic methods were severely limited due to the size of the apparatus and uncertainties of certain quantities to be measured in a small-scale environment. An analytical method to derive physical quantities that are essential for performance prediction from the pressure measurements is described.