• Transactions on Electrical and Electronic Materials
• /
• 제11권5호
• /
• pp.230-233
• /
• 2010

The authors investigated the anodization mechanism of aluminum in an oxalic acid solution, and the electrochemical reaction is very unique for pore formation via the dissolution process, which is very dependent on the surface geometry in nanoporous alumina templates. The cross-sectional nanochannels showed that the geometrical curvature of the initial surface can cause the branching of nanochannels to be adjusted in volume occupancy to be direct to the electric field normal to the surface. The nanoporous alumina with the crystalline $\gamma-Al_2O_3$ phase showed hexagonal ordering at a voltage of 40 V, with a nanohole distance of 102 nm from the charge density oscillation of the oxalic acid solution.

• Bulletin of the Korean Chemical Society
• /
• 제32권7호
• /
• pp.2301-2305
• /
• 2011

The potential energy surface (PES) for the loss of HCN or HNC from the pyrazine molecular ion was determined based on quantum chemical calculations using the G3//B3LYP method. Four possible dissociation pathways to form four $C_3H_3N^{+{{\bullet}}$ isomers were examined. A Rice-Ramsperger-Kassel-Marcus quasi-equilibrium theory model calculation was performed to predict the dissociation rate constant and the product branching ratio on the basis of the obtained PES. The resultant rate constant for the HCN loss agreed with the previous experimental result. The kinetic analysis predicted that the formation of $CH=CHN{\equiv}CH^{+{\bullet}}+HCN$ was predominant, which occurred by three consecutive steps, a C-C bond cleavage to form a linear intermediate, a rearrangement to form an H-bridged intermediate, and elimination of HCN.

• 한국전기전자재료학회논문지
• /
• 제13권5호
• /
• pp.411-419
• /
• 2000

In this paper we have investigated the surface degradation by ultraviolet-irradiation in high-temperature vulcanized silicone rubber. Through the measurement of surface potential decay by corona-charging and of contact angle it is found that the change of surface electrostatic properties and the decrease of contact angle under UV-radiation. For the changes in micro-morphological and chemical structure of the UV-treated silicone rubber we utilized several analytical techniques such as SEM, ATR-FTIR,XPS. From this study it is shown that the chemical reactions(scissoring of side chain(S-$CH_3$) cross-linking and branching) occur on the surface of silicone rubber during the UV-irradiation. Also we obtained the results of the loss of low molecular weight chain by cross-linking and oxidation reaction.

• Journal of Korean Society for Atmospheric Environment
• /
• 제18권E2호
• /
• pp.107-120
• /
• 2002

Dimethyl sulfide (DMS) is the major sulfur gas released from the ocean. The atmospheric DMS released from the ocean is oxidized mainly by hydroxyl (OH) radical during the day and nitrate (NO$_3$) radical at night to form sulfur dioxide (SO$_2$) as well as other stable products. The oxidation mechanism of DMS via OH has been known to proceed by two channels; abstraction and addition channels. The major intermediate product of the addition channel has been known to be dimethylsulfoxide (DMSO) based on laboratory chamber studies and field experiments. However, a branching ratio for DMSO formation is still uncertain. The reaction of DMSO with OH ultimately produces SO$_2$and dimethylsulfone. The major product of the abstraction channel has known to be SO$_2$from laboratory chamber studies. But overall conversion efficiency for DMS to SO$_2$from DMS oxidation is still inconsistent in the literature. Based on laboratory and field studies, the conversion efficiency from the abstraction channel is likely to be greater than 0.5, while that from the addition channel is likely to be greater than 0.6. Overall conversion efficiency from DMS to SO$_2$might be greater than 0.5 based on the above two values in the remote marine boundary layer (MBL). This high efficiency in the remote MBL is supported by strong coupling between DMS and SO$_2$measurements with high temporal resolution.

• The Plant Pathology Journal
• /
• 제18권2호
• /
• pp.93-97
• /
• 2002

Aster yellows phytoplasma-infected chrysanthemums showing stunt, rosette, and excessive branching were treated with a foliar spray of 400 mg/I oxytetracycline at three-day interval for 1,2,3 and 4 months. Two months after the final treatment, new shoots from the recovered chrysanthemums showed the recurrence of the disease symptoms. However, cuttings from chrysanthemums treated with oxytetracycline did not express any photoplasma infection symptoms for more than 10 months. Also, chrysanthemums dipped in 100 mg/I oxytetracycline solution combined with a foliar spray of 400 mg/I oxytetracycline for 4 weeks showed the same results. Using an electron microscope, ultrathin sections of leaf midribs of chrysanthemum cuttings treated with oxytetracycline for 4 months did not show phytoplasma bodies 10 months after treatment. Nucleic acids from chrysanthemums, which did not express phytoplasma infection symptoms for more than 10 months, did not amplify 16S rRNA gene of phytoplasma by polymerase chain reaction. These results may have implications in the propagation of phytoplasma-free healthy stocks for a wide range of plant species.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
• /
• pp.769-772
• /
• 2002

Dendrimers are well-defined macromolecules exhibiting a tree-like structure, first derived by the cascade molecule approach. Peculiar features of the dendritic geometry are the large number of end groups as well as the shape persistence in higher generations, approaching spherical geometry. And one of the most peculiar characteristics of dendritic macromolecules is their controlled molecular structure and orientation, which means that they have a practical application in achieving a highly organized molecular arrangement. We attempted to fabricate a dendrimer LB films containing 48 pyridinepropanol functional end group. As the pyridinepropanol functional group could form a complex structure with metal ions. We investigated the surface activity of dendrimer films at air-water interface compared with pure dendrimer and its complex with $Fe^{2+}$ ions into subphase. We though that metal ions are contributed to networking or branching reaction between dendrimers. And we expected that it can result in the differences on the electrical properties. We have studied the electrical properties of the ultra thin dendrimer LB films investigated by the current-voltage characteristics of metal dendrimer LB films/metal (MIM) structure.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 추계학술발표대회 논문집
• /
• pp.60-63
• /
• 2002

Metal/intermetallic laminated composites have been manufactured by SHS reactions between Ni and Al elemental metal foils. Microstructure showed that the intermetallic volume fraction was 55%, 45%, 35% in the 1:1, 2:1, 4:1 thickness ratio(Ni:Al) specimen and the main phases of the intermetallic were transformed from $Ni_2Al_3$ to NiAl when the thickness ratio was increased. Tensile strength and elongation were increased when the volume fraction of Ni metallic phase was increased. Under assumptions of isostrain condition, the tensile strength of metal/intermetallic laminated composites didn't obey the ROM due to the thermal residual stress and this was confirmed by X-ray residual stress analysis. Fracture toughness results by the SENB test showed R-curves with upward curvature based on LSB condition. Bridging stress based on LSB condition was determined by the curve fitting analysis, In-situ observed microstructure during fracture test showed that the various bridging mechanism such as crack bridging, crack branching and ductile failure of metallic layer were occurred

• 대한세포병리학회지
• /
• 제10권1호
• /
• pp.73-78
• /
• 1999

Myxopapillary ependymoma generally arise in the conus medullaris and filum terminale of adult spinal cord. These tumors are readily recognized due to unique histopathologic features, however, their cytologic features are not well described. When only a tiny sample is obtained, cytologic examination using crush preparation may be a useful diagnostic tool to help appropriate intraoperative diagnosis. We present the crush cytologic features of myxopapillary ependymoma arising in thoracic and lumbar spinal cord of a 13-year-old boy. The patient had complained of paraparesis and back pain for 1 month. The MRI image revealed a relatively well demarcated intramedullary mass in T11-L1 levels. Crush preparation for cytology were peformed by biopsy material. Crush cytologic findings revealed high cellularity and small sized branching papillary clusters on fibrillary or mucinous background. The tumor cells had uniform round or elongated nuclei. The cytoplasmic process of tumor cells were attached to the vascular wall. Between the tumor cells and vascular walls, the perivascular collar of globoid acellular stroma with metachromatic reaction on toluidin blue stain was noted. The crush preparation of myxopapillary ependymoma is considered as a simple and highly accurate diagnostic tool for differentiation from other intramedullary neoplasms of central nervous system.

• 한국자동차공학회논문집
• /
• 제6권4호
• /
• pp.166-177
• /
• 1998

Combustion characteristics of natural gas premixed flames is studied experimently and numerically by adopting a counterflow as a flamelet model in turbulent flames. Flame speeds are measured by employing LDV, and the results show that flame speed increases linearly with strain rate, which agrees well with numerical results. Parametric dependences of extinction strain rates are studied numerically with detailed kinetic mechanism to show that the addition of ethand to a methane premixed flame makes the flame more resistant to strain rate. The effect of pressure on the extinction strain rate is that the extinction strain rate increases up to 10 atm and them decreases, which is explained by competition of chain branching H+O2=OH+O and recombination reaction H+O2+M=HO2+M. Detailed mechanism having seventy-four step is systematically reduced to a nine-step and a five-step thermal NOx chemistry is reduced to two-step. Comparison between the results of the detailed and the reduced mechanisms demonstrates that the reduced mechanism successfully describes the essential features of natural gas premixed flames including extinction strain rate and NOx production.

• 미생물학회지
• /
• 제27권4호
• /
• pp.366-372
• /
• 1989

Reichstein's substance S의 $11\beta$-hydroxylation 활성이 있는 균주를 선택하고자 21 균주를 실험한 결과 4균주에서 $11\beta$-hydroxylation의 활성이 발견되었으며, 그 중 Pellicularia fillamentosark 가장 높은 효소활성을 보였다. 이 균주의 $11\beta$-hydroxylation의 합성을 강력하게 저해하였다. $11\beta$-hydroxylation의 최적 pH 범위는 2.0-8.0으로 광범위하였다. 성장단계 중 균사체 분지시기와 완전하게 성숙한 균사체 시기에 효소합성의 유도가 가장 활발하였으며, 70시간 배양된 균사체가 가장 좋았다. 반면, 포자에는 기질에 의한 $11\beta$-hydroxylation의 유도현상이 없는 것으로 판정되었다.