• Polymer(Korea)
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• v.32 no.6
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• pp.516-522
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• 2008

Biodegradable polymers have been used extensively as scaffolding materials to regenerate new tissues and the ingrowth of tissue have been reported to be dependent directly of the porosity, pore diameter, pore shape, and porous structure of the scaffold. In this study, porous poly (L-lactide-co-glycolide) (PLGA) scaffolds with five different pore sizes were fabricated to investigate the effect of pore sizes for AF tissue regeneration. Cellular viability and proliferation were assayed by MTT test. Hydroxyproline/DNA content of AF cells on each scaffold was measured. sGAG analyses were performed at each time point of 2 and 6 weeks. Scaffold seeded AF cells were implanted into the back of athymic nude mouse to observe the difference of formation of disc-like tissue depending on pore size in vivo. We confirmed that scaffold with $180{\sim}250{\mu}m$ pores displayed high cell viability in vitro and produced higher ECM than scaffold with other pore sizes in vivo.

• Membrane Journal
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• v.15 no.1
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• pp.52-61
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• 2005

Permeate flux decline in a microfiltration was analyzed by measuring the permeability of bentonite colloidal solution through polyethylene capillary membranes. The flux decline with time was due to the growth of cake layer on the membrane surface and to the pore blocking by particles. As the time approaches to steady state, the permeate flux is almost controlled by the cake filtration model. Faster flux decline at high trans-membrane pressure was attributed to the formation of denser packed cake layer and pore blocking. The ratio of permeate flux to the initial permeate flux, J/J₁, decreased with increasing the trans-membrane pressure, from 45% for 0.5 kg/sub f//㎠ to 38% for 2.0 kg/sub f//㎠. In comparing the ratio of each fouling component to the total fouling for the 0.5 kg/sub f//㎠ TMP condition, complete blocking was 23.4%, standard blocking was about 14.6% and cake filtration was 62.0%, respectively. Permeate flux through the membrane increases with cross flow velocity, and the effect of the variation of velocity is more significant at 1.0 kg/sub f//㎠ rather than at 2.0 kg/sub f//㎠ of the operation pressure. Permeate flux for the membrane having the average pore diameter of 0.34 ㎛ was higher than that for the membrane of 0.24 ㎛ pore size, with the higher flux with the low concentration of feed. On the operation using the membrane of 0.34 ㎛ pore, the pore blocking in the low concentration of 200 ppm is negligible relative to the pore blocking in the 1000 ppm feed.

• Journal of the Korean Geotechnical Society
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• v.31 no.6
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• pp.45-58
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• 2015

The aim of this study is to suggest a semi-empirical equation for estimating the hydraulic conductivity of sands using geoelectrical measurements technique. The suggested formula is based on the original Kozeny-Carman equation; therefore varying factors affecting the Kozeny-Carman equation were selected as the testing variables, and six different sands with varying particle sizes and particle shapes were used as the testing materials in this study. To measure both hydraulic and electrical conductivities, a series of constant head permeameter tests equipped with the four electrodes conductivity probe was conducted. Test results reveal that the effects of both pore water conductivity and flow rate in relation between hydraulic conductivity and formation factor (=pore water conductivity / measused conductivity of soil) of tested materials are negligible. However, because the variations of hydraulic conductivity of the tested sands according to particle sizes are significant, the estimated hydraulic conductivity using the formation factor varies with particle sizes. The overall comparison between the measured hydraulic conductivity and the estimated hydraulic conductivity using the suggested formula shows a good agreement, and the variation of hydraulic conductivity with varying Archie's m exponents is smaller compared with varying porosities.

• Journal of Korea Foundry Society
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• v.3 no.3
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• pp.181-187
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• 1983

Effects of retained compression strength on the collapsibility of $CO_2$ mold sand using sodium silicate were studied. The results obtained from the experiment are summurized as follows; 1) The sand mixtures increased their compression strength and retained compression strength when content of sodium silicate is high or mole ratio of sodium silicate is high. 2) Increase of retained strength has a maximum value at temperatures about $200^{\circ}C$. When the sample reached $800^{\circ}C$, the binder bridge are homogeneous. The retained strength is increased. 3) Decrease of retained strength at temperatures over $200^{\circ}C$ is caused by pore formation and additives of seacoal markedly accelerated pore formations.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1465-1469
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• 2012

For given electrolytes, different behaviors of anodic aluminum oxide (AAO) and anodic titanium oxide (ATO) during electrochemical thinning are explained by ionic and electronic current modes. Branched structures are unavoidably created in AAO since the switch of ionic to electronic current is slow, whereas the barrier oxide in ATO is thinned without formation of the branched structures. In addition, pore opening can be possible in ATO if chemical etching is performed after the thinning process. The thinning was optimized for complete pore opening in ATO and potential-current behavior is interpreted in terms of ionic current-electronic current switching.

• Geomechanics and Engineering
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• v.10 no.4
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• pp.437-454
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• 2016

Wellbore instability problem is one of the main problems that met frequently during drilling, particularly in high temperature, high pressure (HPHT) formations. There are large amount of researches about wellbore stability in HPHT formations, which based on the thermo-poroelastic theory and some achievements were obtained; however, few studies have investigated on the fully coupled thermo-poroelastoplasticity analysis of wellbore stability, especially the analysis of wellbore stability while the filter cake formed. Therefore, it is very necessary to do some work. In this paper, the three-dimensional wellbore stability model which overall considering the effects of fully coupled thermo-poroelastoplasticity and filter cake is established based on the finite element method and Drucker-Prager failure criterion. The distribution of pore pressure, wellbore stress and plastic deformation under the conditions of different mud pressures, times and temperatures have been discussed. The results obtained in this paper can offer a great help on understanding the distribution of pore pressure and wellbore stress of wellbore in the HPHT formation for drilling engineers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.45-45
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• 2009

This paper describes the formation of porous 3C-SiC by anodization. 3C-SiC thin films were deposited on p-type Si(100) substrates by APCVD using HMDS (Hexamethyildisilane: $Si_2(CH_3)_6$). UV-LED(380 nm) was used as a light source. The surface morphology was observed by SEM and the pore size was increased with increase of current density. Pore diameter of 70 ~ 90 nm was achieved at 7.1 $mA/cm^2$ current density and 90 sec anodization time. FT-IR was conducted for chemical bonding of thin film and porous 3C-SiC. The Si-H bonding was observed in porous 3C-SiC around wavenumber 2100 $cm^{-1}$. PL shows the band gap enegry of thin film (2.5 eV) and porous 3C-SiC (2.7 eV).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.429-429
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• 2009

Nanoporous anodic alumina membranes (NAAM) with high-density through-hole pores fabricated by hard anodization of aluminum in 0.3 M oxalic acid under the applied voltage of 40 (mild anodization), 80, 100, 120 and 140 V were investigated. The current-time responses monitored using a PC-controlled anodization cell and the corresponding pore structures attainable from field-enhanced scanning electron microscopy (FE-SEM) were analyzed in order to establish the optimum fabrication process. The nanoporous structure can be produced for all the voltage conditions, while the stabilized through-hole pore formation seems to occur at 40, 80 and 140 V. The growth rate under 140 V hard anodization was over 30 times higher than under 40 V mild anodization (1.5 um/hr).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.830-833
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• 2002

최근 나노 구조 (nano structure)를 만들기 위한 시도 중 하나로서 스스로 조직화(self organization)하여 나노 구조를 형성하는 물질을 나노 소자 제작을 위한 형틀 (template)로 이용하려는 시도가 활발히 진행되고 있다. 이러한 물질로서 주목을 받고있는 것 중 하나가 전해질 용액에서 알루미늄을 양극산화(anodization) 시켰을 때 형성되는 다공성 알루미나 박막이다. 본 연구에서는 고 순도 알루미늄을 기계적으로 연마(mechanical polishing)하고 공기 분위기에서 어닐링 (annealing)하여 알루미늄을 재결정화(recrystallization) 시키고 인가 전압이 40 V인 정 전압하에서 0.3 M의 수산(oxalic acid)을 전해질로 사용하면서 양극산화를 수행하여 평균 직경이 65 nm인 고도로 배열된 육방밀집구조의 나노 다공성 박막을 제작하였다. 또한 같은 방향의 육방밀집 배열은 크기가 수 ${\mu}m$인 영역(grain)을 형성하고 있었으며, 평균적인 pore의 밀도는 $1.1{\times}10^{10}/cm^2$였다.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.608-617
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• 1999

The powder mixture which has a bimodal size distribution, with a large mode corresponding to AUC-UO$_2$ powder and a small one corresponding to ADU-UO$_2$ powder, was prepared, pressed into compacts, and sintered at 1680t for 4 hours in hydrogen gas. The compact density of the powder mixture increases with increasing ADU-UO$_2$content within a content of 20 wt %, since small ADU-UO$_2$ particles can fill interstices between large AUC-UO$_2$particles. The UO$_2$ pellet made using the powder mixture has a lower open porosity than that made using AUC-UO$_2$ powder alone. The mechanism for the formation of a flake-like pore is proposed, and the decrease in open porosity may be ascribed to the decrease in the number of flake-like pores.