• Carbon letters
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• v.2 no.1
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• pp.55-60
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• 2001

Graphite intercalation compounds (GIC) were prepared by direct reaction of $SO_3$ gas with flake graphite. The intercalated $SO_3$ molecules were ejected by rapid heating to $950^{\circ}C$ under an oxidizing atmosphere for about 1 minute, resulting in surprisingly high expansion in the direction of c-axis. The characteristics of the micro-structure and pore size distribution were examined with a SEM and mercury intrusion porosimetry. The XRD analysis and spectroscopic analysis were used for the identification of the graphite and surface chemistry state. The pore size distribution of the exfoliated graphite (EG) was a range of $1{\sim}170{\mu}m$. The higher expanding temperature the higher expanded volume, so oil sorption capacities were 58.8 g of bunker-C oil and 34.7 g of diesel oil per 1 g of the the EG. The sorption equilibrium was achieved very rapidly within several minutes. As the treatment temperature increases, bulk density decreases.

• Carbon letters
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• v.10 no.4
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• pp.339-344
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• 2009

Henequen fiber was air-stabilized, carbonized, and steam-activated to obtain high surface area activated henequen fiber (AHF). Thermal behavior of henequen fibers has been studied by TGA. The structural morphology and characteristics were observed by SEM and BET surface area measurement. The yield of AHF from natural henequen was in the range of 20~25 wt%. Mesopores (2~2.5 nm) were developed on the AHF as the activation temperature was raised up to $700^{\circ}C$, and the band of mesopore size distribution moved to 15~30 nm when the activation were carried out at $900^{\circ}C$ for 30 min. The specific surface area and the total pore volume were about $1394\;m^2/g$ and $1.30\;cm^3/g$, respectively at this activation conditions.

• Steel and Composite Structures
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• v.28 no.3
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• pp.381-388
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• 2018

In this paper, forced vibration of micro cylindrical shell reinforced by functionally graded carbon nanotubes (FG-CNTs) is presented. The structure is subjected to transverse harmonic load and modeled by beam model. The size effects are considered based on strain gradient theory containing three small scale parameters. The mixture rule is used for obtaining the effective material properties of the structure. Based on sinusoidal shear deformation theory of beam, energy method and Hamilton's principle, the motion equations are derived. Applying differential quadrature method (DQM) and Newmark method, the frequency curves of the structure are plotted. The effect of different parameters including, CNTs volume percent and distribution type, boundary conditions, size effect and length to thickness ratio on the frequency curves of the structure is studied. Numerical results indicate that the dynamic deflection of the FGX-CNT-reinforced cylindrical is lower with respect to other type of CNT distribution.

• Journal of Korea Foundry Society
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• v.14 no.1
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• pp.62-74
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• 1994

The concentration and particle size distribution of non-metallic inclusions which suspended in the molten aluminum at $700^{\circ}C$ were measured by using LiMCA apparatus. The result revealed that the number of inclusions increased with increasing the applied current or decreasing the orifice diameter, while decreased with increasing the purity of aluminum. And also, it was found that the number of inclusions increased with increasing the amount of boron added to molten aluminum. This was found to be attributed to the formation of the inclusions of TiB and $V_3B_2$. It was investigated that the average concentration of inclusions in a constant volume of 20ml of molten aluminum was increased in the order of pure molten aluminum, molten aluminum containing 20ppm of boron and molten aluminum used repeatly in the experimental casting in this study.

• The korean journal of orthodontics
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• v.25 no.2 s.49
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• pp.201-208
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• 1995

Recently, magnetic forces are considered as a method for more efficient tooth movement. The purpose of this study was to evaluate the effects of the changes of the magnetic volume on the magnetic forces. The universal testing machine and the electronic balance were used for the exact measurement of the force with constant air gap. While the magnet was kept same on one side, the magnetic volume of the other side was increased gradually in four manners. In the first group, the thickness was increased by adding same size of the magnets one after another while the thickness was increased by changing with a thicker magnet gradually in the second group. In the third group. the width was increased by adding same size of the magnets while the width was increased by changing with a wider magnet gradually in the last group. The results were as follows : 1. With the increase of the thickness, the magnetic force increased, while the magnetic force decreased with the increase of the width. 2. The magnetic force according to the change of the magnetic volume showed the distribution of the logarithmic function. 3. An originally thick magnet showed larger force than the added magnets although both of them had same volume.

• Korean Journal of Materials Research
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• v.31 no.2
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• pp.101-107
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• 2021

Pores produced by carbonization in bulk graphite process degrade the mechanical and electrical properties of bulk graphite. Therefore, the pores of bulk graphite must be reduced and an impregnation process needs to be performed for this reason. In this study, bulk graphite is impregnated by varying the viscosity of the impregnant. The pore volume and pore size distribution, according to the viscosity of the impregnant, are analyzed using a porosimeter. The total pore volume of bulk graphite is analyzed from the cumulative amount of mercury penetrated. The volume for a specific pore size is interpreted as the amount of mercury penetrating into that pore size. This decreases the cumulative amount of mercury penetrating into the recarbonized bulk graphite after impregnation because the viscosity of the impregnant is lower. The cumulative amount of mercury penetrating into bulk graphite before impregnation and after three times of impregnation with 5.1cP are 0.144 mL/g and 0.125 mL/gm, respectively. Therefore, it is confirmed that the impregnant filled the pores of the bulk graphite well. In this study, the impregnant with 5.1 cP, which is the lowest viscosity, shows the best effect for reducing the total pore volume. In addition, it is confirmed by Raman analysis that the impregnant is filled inside the pores. It is confirmed that phenolic resin, the impregnant, exists inside the pores through micro-Raman analysis from the inside of the pore to the outside.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.3
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• pp.163-170
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• 2002

This report describes the use of a transtubular bioreactor to study the relative effects of diffusion versus perfusion of medium on antibody production by a hybridoma cell line. The study was performed with a high-density cell culture maintained in a serum-free, low-protein medium for 77 days. It was determined that the reactor possessed a macro-mixing pattern residence time distribution similar to a continuous stirred tank reactor (CSTR), However, due to the arrangement of the medium lines in the reactor, the flow patterns for nutrient distribution consist of largely independent medium path lengths ranging from short to long. When operated with cyclic, reversing, transtubular medium flow, some regions of the reactor (with short residence times) are more accessible to medium than others (with long residence times). From this standpoint, the reactor can be divided into three regions: a captive volume, which consists of medium primarily delivered via diffusion; a lapped volume, which provides nutrients through unilateral convection; and a swept volume, which operates through bilateral convection. The relative sizes of these three volumes were modified experimentally by changing the period over which the direction of medium flow was reversed from 15 min (larger captive volume) to 9 h (larger swept volume). The results suggest that antibody concentration increases as the size of the diffusion-limited (captive) volume is increased to a maximum at around 30 min with a sharp decrease thereafter. As reflected by changes in measured consumption of glucose and production of lactate, no significant difference in cellular metabolism occurred as the reactor was moved between these different states. These results indicate that the mode of operation of the transtubular bioreactor may influence antibody productivity under serum-free, low-protein conditions with minimal effects on cellular metabolism.

• KIEAE Journal
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• v.15 no.5
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• pp.5-12
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• 2015

Purpose: Retention and infiltration of small and frequently-occurring rainfall by LID facilities account for a large proportion of the annual precipitation volume. Based on 4 standard facilities such as Porous Pavement, Infiltration Trench, Cylindrical Infiltration Well, Rectangular Infiltration Well by Seoul Metropolitan Handbook of the Prior Consultation for LID. The total retention volume of each facility was calculated according to the type and size. The Purpose of this study is to find out the quantitative relationship between Percentile Rainfall Event and Design Volume of Infiltration Facilities. Methode: For the estimation of Percentile Rainfall Event, Daily Precipitation of Seoul from 2005 to 2014 was sorted ascending and the distribution of percentile was estimated by PERCENTILE spreadsheet function. The managed Rainfall Depth and Percentile of each facility was calculated at the several sizes. In response to the rainwater charge volume of 5.5mm/hr by the Category "Private large site", the 3 types of facilities were planned for example. The calculated Rainfall Depth and Percentile were 54.4mm and 90% by the use of developed Calculation-Module based on the Spreadsheet program. Result: With this Module the existing Designed Infiltration volume which was introduced from Japan was simply converted to the Percentile-Rainfall-Event used in USA.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.8
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• pp.51-59
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• 2020

The objective of this study is to enrich the literature by investigating the impact of introduction of index future trading on spot market returns and trading volume in Vietnam. Data used in this study mainly consist of daily VN30-Index and market trading volume series during the period from February 6^th, 2012 to December 31^st, 2019. Using OLS, GARCH(1,1) and EGARCH(1,1) models, the empirical findings consistently confirm that the introduction of index future trading has no impact on the spot market returns. In addition, the results of the EGARCH(1,1) model indicate that the leverage effect on the spot market volatility is existence in HOSE. Specifically, bad news has a greater effect on the market volatility than good news of the same size. Moreover, our empirical findings reveal that the introduction of index future contracts has the positive impact on the underlying market trading volume. Specifically, the trading volume of the post-index futures introduction increases by 7.5 percent compared with the pre-index futures introduction. Finally, the results obtained from the Granger causality test for the relationship between the spot market returns and the future trading activity confirm that only uni-directional causality running from the market returns to the future trading activity exists in HOSE.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.251-256
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• 2019

In the process of ZnO ceramic sintering at a temperature of 1385℃, higher than the normal sintering temperature, some grains were growth up to mm scale. When sintered at 1400℃ for 8 hours, the size of the grains that are not involved in the abnormal growth is as large as 30~40 ㎛, but the size of the abnormal grown grain reaches 1,000 ㎛, which is more than 10,000 times bigger in volume than the normal one within 8 hr growth. As a cause of rapid and abnormal grain growth, primary particle size distribution, compaction density variation within sample and doping of impurities could be considered. The primary particle size distribution could be considered main reason for abnormal grain growth but no solid evidence was obtained. Through the observation of the microstructure, it is presumed that the giant grains grow absorbing the neighbor grains through a grain rotation process.