• Carbon letters
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• 제10권4호
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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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• 제28권3호
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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.

• 한국주조공학회지
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• 제14권1호
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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.

• 대한치과교정학회지
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• 제25권2호
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• pp.201-208
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• 1995

교정치료시 보다 효과적인 치아 이동을 위한 한 방법으로 최근 자석 사용이 고려되고 있다. 영구자석의 체적 변화가 자력에 미치는 영향을 파악하고자 한 쪽에 한 개의 자석을 고정하고 반대쪽 자석의 두께나 넓이를 일정한 비율로 증가시키면서 양측 간에 나타나는 자력을 비교 연구한 결과 다음과 같은 결과를 얻었다. 1. 두께를 증가시킨 경우에는 자력이 증가하였으나 넓이를 증가시킨 경우 자력이 오히려 감소하였다. 2. 체적 증가에 따른 자력의 증감은 대수함수 분포 양상을 나타내었다. 3. 두께 증가로 체적을 변화시킨 경우, 같은 두께라도 처음부터 크게 제작한 자석이 작은 자석을 여러 개 합한 것보다 큰 자력을 보였다. 본 연구 결과 구강내에서 자력을 증가시키기 위해서는, 마주보는 자석면은 같게 유지하면서 넓이 증가보다는 두께를 증가시키는 방법이, 그리고 처음부터 두꺼운 자석을 사용하는 것이 보다 효율적임을 알 수 있었다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제7권3호
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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.

• 한국재료학회지
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• 제31권2호
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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.

• KIEAE Journal
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• 제15권5호
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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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• 제7권8호
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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.

• 한국결정성장학회지
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• 제29권6호
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• pp.251-256
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• 2019

ZnO를 통상적인 소결온도 이상의 온도 1385℃에서 소결하는 과정에서 mm 크기로 거대 성장된 입자를 갖는 세라믹스를 제조하였다. 1400℃에서 8시간 소결하는 경우 성장에 참여하지 않은 입자의 크기는 30~40 ㎛이고 거대 성장된 입자는 1,000 ㎛에 달하여 부피비 최소 10,000배 이상의 급속한 성장이 이루어졌다. 이러한 급속한 성장의 원인으로 일차 입자 크기분포, 성형압 불균일 또는 불순물의 합입등을 고려하였으며, 이들 중 일차입자 크기 분포일 것으로 추정되나 확실한 증거를 확보하지 못하였다. 미세구조 관찰을 통해 거대입자 성장은 주변의 입자를 통째로 합치는 과정을 통해 성장하는 것으로 추정된다.

• 한국염색가공학회지
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• 제34권4호
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• pp.261-271
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• 2022

Waterborne polyurethane(WPU) is greatly affected by its properties depending on the average particle size. In this study, by analyzing the characteristics of WPUs with different average particle sizes according to the DMPA content and we confirmed that the WPU-Ms have different properties from the physical properties of WPU by mixing two types of WPU with different particle sizes in the same volume. At this time, we mixed WPU at an ideal ratio of 7:3 through literature research. In the thermal characteristic analysis, it was confirmed that the thermal decomposition temperature decreased and Tg increased as the content of DMPA, which is the hard segment, increased. In addition, the average particle size of WPU decreased as DMPA increased, and physical properties and adhesive strength were improved due to increased interaction. When mixed with each other in a weight ratio of 7:3, it was observed that adhesion and mechanical properties were improved compared to only WPU.