One-step synthesis of nano-porous monolithic polyimide aerogel

Kim, Jinyoung,Kwon, Jinuk,Kim, Seung-Ik,Kim, Myeongsoo,Lee, Daero,Lee, Sangrae,Kim, Gunhwi,Lee, Juheon,Han, Haksoo Elsevier 2016 Microporous and mesoporous materials Vol.234 No.-

<P><B>Abstract</B></P> <P>A facile one-step method for synthesis of a porous monolithic polyimide aerogel was successfully developed. The specific thermal curing, slow desiccating process and swelling method were used in synthesizing monolithic polyimide aerogel without any additional chemical reaction to create a connected structure among the polyimide-based spherical aerogel microparticles. Using this method, the monolithic polyimide aerogel can be easily fabricated whilst using no additional chemicals for crosslinking. This type of polyimide aerogel was produced homogeneously by the polyimidization of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA). The synthesized porous monolithic polyimide aerogel has many good properties which could be used in various industries, as it maintained a high thermal decomposition temperature (10% weight decomposition temperature: T<SUB>d10%</SUB>) of approximately 577 °C and a glass transition temperature (T<SUB>g</SUB>) of 432 °C, with bulk density of 490.7 kg/m<SUP>3</SUP>, porosity of approximately 45% and average pore size of 4 nm (by nitrogen adsorption test) of polymer and 157 nm (by mercury intrusion method) of space observed in FE-SEM image. Also, the monolithic polyimide aerogel had an excellent oil-adsorbing capacity of 150%, and the adsorbed oil could be separated easily using a simple drying process. The dried monolithic polyimide aerogel showed significant recoverability and reusability of adsorbed oil. In addition, the monolithic polyimide aerogel exhibited high mechanical resistance such that the structure can withstand a high pressure greater than 122.3 kPa, under which the monolithic polyimide aerogel (MPA) was compressed but did not break. This type of MPA shows excellent thermal, mechanical properties and great processability, and could be the new candidate for high performance materials in various industries, especially catalyst field.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Unlike other aerogel synthesis, in this study, the polyimide aerogel monolith is created without adding any other chemicals. </LI> <LI> The polyimide aerogel monolith has excellent thermal, mechanical properties and great processability for application in various industries. </LI> <LI> The polyimide aerogel monolith synthesized with homogeneity fully maintained in very convenient and easy method. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The effects of hydroxyl groups on the thermal and optical properties of poly(amide-imide)s with high adhesion for transparent films

Kim, Kwangin,Yoo, Taewon,Lee, Juheon,Kim, Myeongsoo,Lee, Sangrae,Kim, Gunhwi,Kim, Jinyoung,Han, Patrick,Han, Haksoo Elsevier Sequoia 2017 Progress in organic coatings Vol.112 No.-

<P><B>Abstract</B></P> <P>In this study, transparent thin films for coating material are synthesized by adding bulky CF<SUB>3</SUB> and hydroxyl groups intro into poly(amide-imide)s. As expected, these poly(amide-imide)s show higher shear adhesion and higher glass transition temperatures than the neat poly(amide-imide) due to hydrogen bonding of the hydroxyl groups. In addition, the modification to the poly(amide-imide) structure leads to only slight decreases in transmittance and yellow index.</P> <P>Consequently, the successful synthesis of poly(amide-imide)s with wide applications as transparent coating materials due to their optical properties and high adhesion is demonstrated. Transparent flexible display and coating products can be manufactured with poly(amide-imide)s having high reliability and a low chance of cracking due to their favorable thermal properties.</P>

단일 엔코더 및 디코더를 이용하는 다시점 비디오 시스템

김학수(Haksoo Kim),김윤(Yoon Kim),김만배(Manbae Kim) 한국방송·미디어공학회 2006 방송공학회논문지 Vol.11 No.1

Marques formelles pour une analyse automatique des langues naturelles

Haksoo KIM 경기대학교 인문학연구소 1997 시민인문학 Vol.5 No.-

Parametric Fragility Analysis of Steel Highway Bridges with Multi-Column Bents

Haksoo Kim,Eunsoo Choi,Il-Yoon Choi 대한토목학회 2004 KSCE journal of civil engineering Vol.8 No.1

Preliminary Dosimetric Study of Proton Minibeam Radiation Therapy for the Treatment of Choroidal Melanoma

Kim Myeongsoo,Kim Sang Soo,Kim Haksoo,Moon Sung Ho,Lim Young Kyung,Hwang Ui-Jung,Choi Sang Hyoun 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.5

This study aimed to evaluate dosimetrically the feasibility of saving both the lens and the ciliary body in the treatment of a choroidal melanoma by using spatially fractionated proton minibeams. A multi-slit brass collimator was designed by using Monte Carlo simulation data and was fabricated with a 0.4-mm beam opening and a 1.1-mm center-to-center distance. A phantom was also fabricated for proton beam dosimetry, involving five polymethylmethacrylate (PMMA) plates of 2 mm and 8 mm thicknesses, respectively. The peak-to-valley dose ratio (PVDR) of the proton minibeams was used to validate the feasibility of lens and ciliary body sparing. The typical single-scattered proton beam for treating a patient with a choroidal melanoma was delivered to Gafchromic EBT3 films in the phantom after having passed through the multi-slit: the energy of proton beam was 60 MeV, and its depth dose profile was a full spread-out Bragg peak (SOBP). The average dose at mid-depth of the SOBP was approximately 3 CGE with ±3% of ripple. Dosimetric evaluation showed the PVDR depended on the air gap strongly. It varied from 3.4 to 1.1 in the air gap range from 2 mm to 62 mm. The PVDR values at PMMA depths of 2, 12, 22, and 32 mm were 2.0, 1.5, 1.1, and 1.06, respectively. This result shows that a spatially fractionated proton beam might save the lens and ciliary body seated at a shallow depth in the eye ball when a choroidal melanoma is treated using proton minibeam radiotherapy.

An Efficient Algorithm for Zero-Forcing Coordinated Beamforming

Haksoo Kim,Heejung Yu,Youngchul Sung,Lee, Y. H. IEEE 2012 IEEE COMMUNICATIONS LETTERS Vol.16 No.7

<P>The problem of beam tracking for zero-forcing coordinated beamforming in multiple-cell time-varying multiple-input multiple-output channels is considered. Based on null-space perturbation theory, an efficient update algorithm for block-diagonalization-based zero-forcing coordinated beam design is proposed and its performance is analyzed. In slowly-varying channels, the proposed algorithm well tracks the zero-forcing beam solution and significantly reduces computational complexity by simply updating beamforming matrices instead of redesigning them with new channel state information at each time step.</P>

New continuous process developed for synthesizing sponge-type polyimide membrane and its pore size control method via non-solvent induced phase separation (NIPS)

Kim, Myeongsoo,Kim, Gunhwi,Kim, Jinyoung,Lee, Daero,Lee, Sangrae,Kwon, Jinuk,Han, Haksoo Elsevier 2017 Microporous and mesoporous materials Vol.242 No.-

<P><B>Abstract</B></P> <P>In this study, the improvement of synthesizing method of sponge-type polyimide (PI) membrane and its newly developed pore size control techniques are mainly described. The sponge-type polyimide membrane with large pore size (0.1–10 µm) and high permeability was successfully synthesized by using non-solvent phase separation method (NIPS) in continuous process and its full polyimidization is confirmed via Fourier-transform infrared technique. The theoretical approach in this research induced by Jurin's law which describes the height of a liquid within a thin capillary tube. In this theory, the pore size of membrane is highly influenced by the interactive tension between the polymer and solvents during synthesizing process of polymer membrane. There are two ways of controlling pore size established from Jurin's law. The validity of the application of Jurin's law was proven via comparison with theoretical and experimental data. Its inner structure of membrane and pore size are identified by field emission-scanning electron microscopy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of sponge-type polyimide membrane for continuous system using non-solvent phase separation (NIPS) method. </LI> <LI> Two ways of controlling pore size established from Jurin's law. </LI> <LI> Comparison of pore size with theoretical and experimental data. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Limited Feedback for Multicell Zero-Forcing Coordinated Beamforming in Time-Varying Channels

Haksoo Kim,Heejung Yu,Lee, Yong H. IEEE 2015 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.64 No.6

<P>We consider limited feedback for zero-forcing-based coordinated beamforming over time-varying channels. Most previous work on limited feedback focuses on the feedback rate of the channel state information (CSI), while assuming that feedback occurs for every channel use. This feedback update policy, however, may not be optimal for time-varying channels. To take channel variations into account, we propose a scheme that adjusts both the feedback rate and the feedback update period, depending on channel statistics. We derive an upper bound of the expected rate loss caused by the limited feedback. Based on this bound, we formulate an optimization problem minimizing the residual interference power and derive closed-form solutions for the feedback rate and the feedback update period while fixing one of the parameters and optimizing the other. Using the closed-form expressions, we propose an algorithm that iteratively updates the parameters. Simulation results demonstrate that the proposed limited feedback scheme can outperform the conventional scheme, which feeds back the CSI at every channel use.</P>

Effect of LiCoO₂-Coated Cathode on Performance of Molten Carbonate Fuel Cell

Kim, Dohyeong,Kim, Hyung Tae,Song, Shin Ae,Kim, Kiyoung,Lim, Sung Nam,Woo, Ju Young,Han, Haksoo The Korean Electrochemical Society 2022 Journal of electrochemical science and technology Vol.13 No.1

Molten carbonate fuel cells (MCFCs) are environmentally friendly, large-capacity power generation devices operated at approximately 650℃. If MCFCs are to be commercialized by improving their competitiveness, their cell life should be increased by operating them at lower temperatures. However, a decrease in the operating temperature causes a reduction in the cell performance because of the reduction in the electrochemical reaction rate. The cell performance can be improved by introducing a coating on the cathode of the cell. A coating with a high surface area expands the triple phase boundaries (TPBs) where the gas and electrolyte meet on the electrode surface. And the expansion of TPBs enhances the oxygen reduction reaction of the cathode. Therefore, the cell performance can be improved by increasing the reaction area, which can be achieved by coating nanosized LiCoO₂ particles on the cathode. However, although a coating improves the cell performance, a thick coating makes gas difficult to diffuse into the pore of the coating and thus reduces the cell performance. In addition, LiCoO₂-coated cathode cell exhibits stable cell performance because the coating layer maintains a uniform thickness under MCFC operating conditions. Therefore, the performance and stability of MCFCs can be improved by applying a LiCoO₂ coating with an appropriate thickness on the cathode.