• Steel and Composite Structures
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• 제27권5호
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

• Asian Pacific Journal of Cancer Prevention
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• 제15권23호
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• pp.10281-10287
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• 2015

Background: Development of a nanosized polymeric delivery system for erlotinib was the main objective of this research. Materials and Methods: Poly caprolactone-polyethylene glycol-polycaprolactone (PCEC) copolymers with different compositions were synthesized via ring opening polymerization. Formation of triblock copolymers was confirmed by HNMR as well as FT-IR. Erlotinib loaded nanoparticles were prepared by means of synthesized copolymers with solvent displacement method. Results: Physicochemical properties of obtained polymeric nanoparticles were dependent on composition of used copolymers. Size of particles was decreased with decreasing the PCL/PEG molar ratio in used copolymers. Encapsulation efficiency of prepared formulations was declined by decreasing their particle size. Drug release behavior from the prepared nanoparticles exhibited a sustained pattern without a burst release. From the release profiles, it can be found that erlotinib release rate from polymeric nanoparticles is decreased by increase of CL/PEG molar ratio of prepared block copolymers. Based on MTT assay results, cell growth inhibition of erlotinib has a dose and time dependent pattern. After 72 hours of exposure, the 50% inhibitory concentration (IC50) of erlotinib hydrochloride was appeared to be $14.8{\mu}M$. Conclusions: From the obtained results, it can be concluded that the prepared PCEC nanoparticles in this study might have the potential to be considered as delivery system for erlotinib.

• Journal of Pharmaceutical Investigation
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• 제41권2호
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• pp.95-102
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• 2011

An amphiphilic cationic branched methoxy poly (ethylene glycol)-branched polyethylenimine - poly(L-phenylalanine) (mPEG-bPEI-pPhe) block copolymer was successfully synthesized by ring-opening polymerization (ROP) of N-carboxyanhydride of L-phenylalanine (Phe-NCA) with mPEG-bPEI for the preparation of more stable polyelectrolyte complex (PEC) included a hydrophobic interaction. mPEG-bPEI was firstly prepared by the coupling of mPEG and bPEI using hexamethylene diisocyanate (HMDI). The structural properties of mPEG-bPEI-pPhe copolymers were confirmed by $^1H$ NMR. The copolymers exhibited a self-assemble behavior in water above critical aggregate concentration (CAC) in the range of 0.01-0.14 g/L. The CAC of copolymers obviously depended on the hydrophobic block content in the copolymers (the value decreased with the increase of the pPhe block content). The cationic copolymers have the ability to form multi-interaction complex (MIC) with bovine serum albumin (BSA) and plasmid DNA through multi-interaction (electrostatic and hydrophobic interaction). The physicochemical characterization of the complex was carried out by the measurement of zeta potential and particle size. Their zeta-potentials were positive (approximately +10 mV) and their sizes decreased with increasing pPhe contents in the copolymers (PPF/BSA wt% ratio = 2). The complex showed good stability at high ionic strength. Therefore, mPEG-bPEI-pPhe block copolymer was considered as a potential material to enhance the stability of complex including biotherapuetic drugs.

• Journal of Microbiology and Biotechnology
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• 제21권10호
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• pp.1001-1011
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• 2011

To explore bacterial diversity for elucidating genetic variability in acylhomoserine lactone (AHL) lactonase structure, we screened 800 bacterial strains. It revealed the presence of a quorum quenching (QQ) AHL-lactonase gene (aiiA) in 42 strains. These 42 strains were identified using rrs (16S rDNA) sequencing as Bacillus strains, predominantly B. cereus. An in silico restriction endonuclease (RE) digestion of 22 AHL lactonase gene (aiiA) sequences (from NCBI database) belonging to 9 different genera, along with 42 aiiA gene sequences from different Bacillus spp. (isolated here) with 14 type II REs, revealed distinct patterns of fragments (nucleotide length and order) with four REs; AluI, DpnII, RsaI, and Tru9I. Our study reflects on the biodiversity of aiiA among Bacillus species. Bacillus sp. strain MBG11 with polymorphism (115Alanine > Valine) may confer increased stability to AHL lactonase, and can be a potential candidate for heterologous expression and mass production. Microbes with ability to produce AHL-lactonases degrade quorum sensing signals such as AHL by opening of the lactone ring. The naturally occurring diversity of QQ molecules provides opportunities to use them for preventing bacterial infections, spoilage of food, and bioremediation.

• 폴리머
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• 제24권2호
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• pp.141-148
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• 2000

Polycaprolactone (PCL)을 base로 하는 효과적인 compost 필름을 만들기 위하여 옥수수전분을 블렌딩한 뒤 기계적 특성과 미생물에 의한 생분해도를 조사하였다. 비상용성을 보이는 옥수수전분/PCL 블렌드에 대한 상용화제로는 2-hydroxyethylmethacrylate (HEMA)-PCL macromer를 옥수수전분에 그래프팅시킨 공중합체를 사용하였는데 옥수수전분에 대한 HEMA의 그래프팅율이 가장 높은 것과 가장 낮은 것을 선택하여 일정한 조성의 $\varepsilon$-caprolactone에 그래프팅시킨 상용화제들의 상용화 효과를 비교하였다. 상용화제를 함유한 옥수수전분/PCL (50/50) 블렌드의 신장율이 상당히 증가하였으며 SEM 관찰 결과 이는 상용화제로 인해 옥수수전분 알갱이와 PCL 기질간의 계면 접착력이 증가하였기 때문으로 판단된다. 그러나 모듈러스와 인장강도는 상용화치 사용에도 불구하고 별다른 변화가 없었다.

• Macromolecular Research
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• 제15권4호
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• pp.337-342
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• 2007

The n-butyllithium-initiated ring-opening polymerization of ethylene oxide, in a mixture of benzene and dimethylsulfoxide (DMSO), between $25-45^{\circ}C$, with potassium tert-butoxide, is a useful and powerful method to control the molecular weight as well as achieve a quantitative chain-end functionalization yield of the resulting polymeric alkoxide via a one pot synthesis. The molecular weight of the product could be controlled by adjusting the ratio of grams of monomer to moles of initiators, such as n-butyllithium ([n-BuLi]) and potassium t-butoxide ([t-BuOK]). The yields for the macromonomer and ${\omega}-brominated$ poly(ethylene oxide) (PEO) were quantitative in relation to the chain-end functionalizations of the polymeric alkoxide formed. The resulting products were characterized by a combination of $^1H-NMR$ spectroscopic and size exclusion chromatographic analyses.

• 폴리머
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• 제36권3호
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• pp.262-267
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• 2012

할로겐화알킬($PhCH_2Br$, $PhCH_2Cl$, MeI)과 설폰산에스테르(MeOTf)를 개시제로 사용하여 $100^{\circ}C$, 24시간의 반응조건으로 2-(1,3,3-trimethyl-6-azabicyclo[3,2,1]-oct-6-yl)-4,5-dihydro-1,3-oxazoline(TAO)의 중합을 실시, 개시제에 의한 폴리머구조의 영향을 관찰한 결과, 양쪽 개시제 모두 거의 동일한 연쇄이동에서 나타나는 경향과 비슷한 결과를 얻었다. 그러나 개시제에 의한 폴리머의 구조는 설폰산에스테르계 개시제에서는 거의 100% pendant type 폴리머가 생성되는 반면, 할로겐화알킬계 개시제를 사용한 TAO중합은 pendant type 단위와 main chain type의 단위가 소량 생성됨이 확인되어 이것은 구핵성이 높은 할로겐 음이온에 의한 이중이성화중합이 부분적으로 진행되었음을 확인하였으며, 개시제로 Merrifield수지를 사용한 TAO와의 공중합에서는 다량의 단일중합체가 부생되는 그래프트 공중합체가 생성되었다.

• 한국중재학회지:중재연구
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• 제26권1호
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• pp.89-105
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• 2016

2008 began with the American financial crisis which gave way to the liquidity crisis (Fannie Mae and Freddie Mac) situation in which 'the withdrawal of investment initiated from the insufficiency of the U.S. subprime mortgage loan companies', 'the large size loss situation of the financial company (Bear Stearns) due to the American structured bond insufficiency' and the second half opening part national debt mortgage company. Within the American financial crisis was propagated the crisis of international derivatives. Due to this, the withdrawal of foreign investment progressed in the interior of a country with the considerable. By the end of 2007, the exchange rate fluctuation was absorbed in the domestic financial circle on the belief the potentiality of the domestic financial market had been growing drastically through the expansion of the foreign currency debt according to this and it came to the defence but while the exchange rate jumped up to the dollar shortage according to the international crisis, the small and medium companies making the banks and exchange rate-related derivatives contract were going bankrupt due to the derivatives loss. The small and medium factories establish the bank exchange rate-related derivatives has nose (KIKO), pivot (PIVOT), and snowball (Snowball) etc. at that time and the damage which it is the KIKO grasped at 6 end of the months in 2008 caused by reaches to 1 thousand billion 4 thousand hundred million dollars. Small and medium companies in which the dollar which it has to denounce among small and medium companies bearing the KIKO contract in fact with the Knock-In generation city bank exceeds the amount of sales were known to be 68 enterprises among 480 enterprises. This paper departs in this awareness of a problem and tries to look into the risk factor of the derivatives, including nose and study the essential ring risk management plan of small and medium manufacturer.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.401-408
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• 2005

Recently shield TBM tunnellings are being applied to subway construction in Korean cities. Generally these kinds of tunnellings have the problems in the stability of ground such as subsidence because urban subway is constructed in the shallow depth. A sinkhole occurred on the road just above the tunnel during tunneling in Kwangju, so a survey for upper layer of the tunnel was needed. But conventional Ground Probing Radar can't be applicable due to the presence of steel-mesh screen in the shield segment, so no existent geophysical method is applicable in this site. Because the outer surface of each shield segment is electrically insulated, dipole-dipole resistivity method which is popular in engineering site investigation, was tried to this survey for the first time. Specially manufactured flexible ring-type electrodes were installed into the grouting holes at an interval of 2.4 m on the ceiling. The K-Ohm II system which has been developed by KIGAM and tested successfully in many sites, was used in this site. The system consists of 1000Volt-1Ampere constant-current transmitter, optically isolated 24 bit sigma-delta A/D conversion receiver - maximum 12 channel simultaneous measurements, and graphical automatic acquisition software for easy data quality check in real time. Borehole camera logging with circular white LED lighting was also done to investigate the state of the layer. Measured resistivity data lack of some stations due to failing opening lids of holes, shows general high-low trend well. The dipole-dipole resistivity inversion results discriminate (1) one approximately 4 meter diameter cavity (grouted but incompletely hardened, so low resistivity - less than $30{\Omega}m$), (2) weak zone (100-200${\Omega}m$), and (3) hard zone (high resistivity - more than 1000${\Omega}m$) very well for the distance of 320 meters. The 2-D inversion neglects slight absolute 3-D effect, but we can get satisfactory and useful information. Acquired resistivity section and video tapes by borehole camera logging will be reserved and reused if some problem occurs in this site in the future.

• 공업화학
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• 제18권2호
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• pp.116-120
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• 2007

양이온 개환중합형 광고분자 시스템용 단량체의 합성에 핵심적인 중간체로 사용되는 1-[2-(3-{7-oxabicyclo[4.1.0] heptyl}1,1,3,3-tetramethyldisiloxane (Mono)의 합성방법의 최적화에 관하여 연구하였다. Speier 촉매의 존재 하에서, 4-vinyl-1-cyclohexene 1,2-epoxide (VCHO)를 과량의 1,1,3,3- tetramethyldisiloxane (TMDS)과 수소규소화 반응시켜 TMDS의 한쪽 실리콘 하이드라이드를 미반응 상태로 유지하고 나머지 한쪽만이 VCHO와 반응한 형태의 Mono를 합성할 수 있었으며, 생성된 Mono의 구조 및 순도는 FT-IR, $^1H-NMR$ 및 $^{29}Si-NMR$을 통하여 확인할 수 있었다. VCHO와 TMDS의 몰비를 1 : 4로 고정하고 촉매 함량 및 반응 온도를 변화시킨 결과, Speier 촉매 함량 5 ppm, 반응온도 $55^{\circ}C$가 Mono의 선택적 합성에 가장 최적인 반응조건으로 판단되었다.