다공질 Si의 열적 안정성 연구

권영해,조훈영,홍치유 동국대학교 자연과학연구원 1995 자연과학연구 논문집 Vol.15 No.-

The oxidation and pressure effects of electrochemically etched porous Si have been investigated by photoluminescence(PL) and Raman spectroscopy. The porous Si sample was etched with a current density of 50mA/㎠ for 20 min, and shows a PL signal at 710 nm and a Raman peak at 517 cm. Rapid-thermal-annealing of the as-etched sample at 400℃ shows a rapid drop in the PL intensity. On the other hand, the intensity of the rapid-thermal-oxidized sample remains constant in the temperature range from 600℃ to 800℃. The Raman signal of the oxidized sample also showed thermal stability. The reverse leakage current of the oxidized porous Si was reduced to 100 times in comparision to that of as-grown porous Si. The PL peak position of the oxidized porous Si shows the shifts to 705 nm and the Raman peak shifts to a higher energy, closer that of the bulk polycrystalline Si. This can be explained in terms of the stress on the Si columnar structure. The initial tensile stress induced by the etching process is reduced by the compressive stres caused by the formation of oxides (SiO₂) in the gaps. It is supposed that this can cause the blue shift in the PL spectrum and the recovery of the Raman peak position.

전류밀도 향상을 위한 금속 산화물 피막 제조에 관한 연구

채경선,유국현 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-

구조물의 부식을 저감시키기 위한 재료로 사용되려면 전기 전도성이 좋아야 하며, 여러 산업환경에 적용될 수 있도록 내식성이 뛰어나야한다. 이리 듐-루테늄 산화물 피막은 이러한 성질을 만족시키는 물질로, 이들 산화물 피막 의 성질은 대개 양극 제조 공정에 의해 크게 좌우되므로 본 연구에서는 전류 밀도 향상을 위한 제조 공정을 최적화하고자 하였다. Dip-coating법으로 전도성 코팅층인 이리듐-루테늄 산화물 피막을 기지금속인 티타늄 위에 피복 시키는데, 이 코팅층의 내식성 향상을 위해서 다구치 방법을 도입하여 최적 공정 조건을 구하였다. 이때 사용된 변수는 전처리 방법, 열처리 온도, 열처리시 주입 가스량, 열처리 시간으로 이들 변수를 3가지로 변화시켜 실험하였다. 실험결과 이리듐-루테늄 산화물 피막 제조시 기판위에 티타늄산화물 중간층을 plasma spray법으로 제조하고, 열처리 온도 450℃, 주입가스량 3sccm, 열처리시간을 120분으로 하였을 때 방식전류밀도가 가장 우수한 코팅층(활성화 코팅층)을 얻었다.

Synthesis and Characterization of the Temperature/pH-Sensitive Polymers for Drug Delivery Systems

Yoo, Mi-Kyong,Sung, Yong-Kiel 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-

The stimuli-sensitive polymers were synthesized by copolymerizing varying ratios of N-isopropyl acrylamide(NIPAAm) and acrylic acid(AAc). The influence of polyelectrolytes on the lower critical solution temperatures(LCSTs) of these temperature/pH sensitive polymers was investigated in the pH range of 2∼12. The polyelectrolyte complexes were prepared by mixing poly(NIPAAm-co-AAc) as anionic polyelectrolyte with poly(allyl amine)(PAA) or poly(L-lysine)(PLL) as cationic polyelectrolytes, respectively. The effect of polyelectrolyte complex formation on the conformation of PLL was studied as a function of temperature by means of circular dichroism(CD). Swelling ratio of poly(NIPAAm-co-AAc) hydrogels as a function of pH at various temperature was obtained by measuring the weight of the hydrogels in buffer solutions. The LCSTs of the poly(NIPAAm-co-AAc) were strongly affected by pH, polyelectrolyte solutes, AAc content, and charge density. The influence of more hydrophobic PLL as a polyelectrolyte on the cloud point of PNIPAAm/water in the copolymer was stronger than that of poly(allyl amine)(PAA). Indomethacin was loaded into these hydrogels and their drug release characteristics were determined under various temperature and pH conditions using UV/Vis spectrophotometer.

Uniqueness of Steady-state Solutions for Electrophoretic Model of Three Reacting Species in R²

Kim, Euhee 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-

In this paper we extend the result of [4] to the reactive case for the powers of non-linearity in the reaction term without the electro-neutrality condition and prove uniqueness of steady-state solutions for a system of diffusion-migration-reaction equations arising from an electrophoretic model in a bounded domain of R²

Upper Semicontinuous Regularizations of Quasi-Plurisubharmonic Functions

Bang, Hyun-Soo 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-

We discuss about upper semicontinuous regularization of a function which is locally bounded above, and has the following properties; for each real number α, {χ∈Ω:u(x)<α} is analytic, and for every χ∈Ω, and for every pluri-Jensen measure at χ, inequality (1,1) holds. It turns out that this regularization is plurisubharmonic and coincide with the original function outside pluripolar set.

Alkaline Earth Ions Promote the Self-splicing of Phage T4 Thymidylate Synthase Intron RNA

LIM, EUN-HEE,PARK, IN-KOOK 동국대학교 자연과학연구원 1998 자연과학연구 논문집 Vol.3 No.-

Effects of alkaline earth ions such as Ba2+ and Sr2+ on in vitro RNA self-splicing of phage T4 thymidylate synthase intron were investigated. Ba2+ and Sr2+ tested didnt initiate the splicing of T4 td intron by themselves. Activation of the splicing was observed when these ions were added to the splicing reaction containing 2 or 3 mM Mg2+. It appears that Ba2+ and Sr2+ by themselves could not catalyze self-splicing reaction but strengthened the role of Mg2+ in promoting the proper folding of td intron for self-splicing. The results suggest that Ba2+ and Sr2+ somehow reinforces the catalytic activity of Mg2+ in self-splicing reaction of phage T4 td intron.

인공산란숙주에 대한 무늬수중다리좀벌의 산란행동

Lee, Jang-Hoon,Lee, Hai-Poong 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-

Artificial pupa with paraffin coating was developed for inducing an oviposition of Brachymeria lasus (Walker)(Hymenoptera: Braconidae). The parasitoid needed the external kairomone for host location and antennal searching, and the internal kairomone for oviposition. Female parasitoid displayed host acceptance behavior toward the artificial pupae treated with external kairomone, the Ethyl alcohol extract of fall webworm pupae when supernatant of homogenate of the host pupae was inside, whereas they did not complete the host acceptance when physiological saline was inside. When the homogenate was diluted to low concentration of < 25%, the parasitoid did not show an oviposition.

Convenient Routine Production and Quality Control of ??mIBG

YANG, SEUNG-DAE,SUH, YUNG-SUP,YU, KOOK-HYUN 동국대학교 자연과학연구원 1998 자연과학연구 논문집 Vol.3 No.-

In this paper radiolabelling of radioiodinated m-iodobenzylguanidine ([123I]mlBG) was studied by a Cu(I) assisted nucleophilic exchange reaction in aqueous solution. At 100℃ with 2.0mg cold-mlBG the radiochemical purity reached over 98% at 30 min. The procedure has been utilized with up to 1.0ml 123I(in 0.01N NaOH) or about 100mCi 123I. This method could be used labelling of[123I]mlBG for routine production.

Antimutagenic Activity of Chitosan Oligosaccharides

Shon, Yun-Hee,Ha, Young-Min,Nam, Kyung-Soo 동국대학교 자연과학연구원 2000 자연과학연구 논문집 Vol.5 No.-

The antimutagenic effects of chitosan oligosaccharide I and chitosan oligosaccharide Ⅱ were examined using the Ames/Salmonella test. No antimutagenic activity was found against the directly-acting mutagens, 4-nitro-o-phenylenediamine(NPD) using the tester strain TA 98 and sodium azide (NaN3) using the tester strain TA 100 in the absence of S9 mix. In contrast, chitosan oligosaccharide showed inhibitory effect on the mutagenicities of the indirectly-acting mutagens, 2-aminofluorene (2-AF) and 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline(MeIQx) using the tester strain TA 98 and benzo[a]pyrene (B[a]P) using the tester strain TA 100 in the presence of S9. These results suggested that chitosan oligosaccharide had antimutagenic properties and may play a role in the prevention of cancer.

Cytotoxic effects of Scutellaria barbata and cisplatin on mammalian cells

Jun, Hyun-Ik,Goo, Sun Young,Sung, Jung Suk 동국대학교 자연과학 연구원 2008 자연과학연구 논문집 Vol.9 No.-

Scutellaria barbata is a perennial herb which has been applied to treat cancer, inflammation, and urinary disease throughout Asia, but the reaction mechanisms of antitumor components of S. barbata are still unclear. Cisplatin is known for the most active cytotoxic anti-cancer drugs applied currently in anti-tumor therapy. Here, we show that genotoxic mechanisms of S. barbata are obviously different from DNA damage responses induced by cisplatin. Co-treatment of S. barbata and cisplatin effectively induced apoptosis of HeLa cells compared to the treatment of S. barbata or cisplatin alone. In addition, mouse embryonic fibroblast pol ? knock-out cells appeared to be more hypersensitive to the treatment of S. barbata than wild-type cells. Our results implied that co-treatment of S. barbata and cisplatin can be developed as an effective anti-cancer therapy.