• Title/Summary/Keyword: branching reaction.

Search Result 43, Processing Time 0.021 seconds

Electric Field Effect on Nanochannel Formation in Electrochemical Porous Structures of Alumina

  • Kim, Keun-Joo;Choi, Jae-Ho;Lee, Jung-Tack
    • Transactions on Electrical and Electronic Materials
    • /
    • v.11 no.5
    • /
    • 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.

Loss of HCN from the Pyrazine Molecular Ion: A Theoretical Study

  • Jung, Sun-Hwa;Yim, Min-Kyoung;Choe, Joong-Chul
    • Bulletin of the Korean Chemical Society
    • /
    • v.32 no.7
    • /
    • 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.

Analysis of the Surface Degradation in UV-irradiated High-Temperature Vulcanized Silicone Rubber (자외선 조사된 HTV 실리콘 고무의 표면열화 분석)

  • 연복희;이태호;허창수;이종한
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
    • /
    • v.13 no.5
    • /
    • 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.

  • PDF

Overall Conversion Efficiency for Dimethylsulfide to Sulfur Dioxide in the Marine Boundary Layer-An Overview

  • Shon, Zang-Ho
    • Journal of Korean Society for Atmospheric Environment
    • /
    • v.18 no.E2
    • /
    • 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.

Elimination of Aster Yellows Phytoplasma from Dendranthema grandiflorum by Application of Oxytetracycline as a Foliar Spray

  • Chung, Bong-Nam;Park, Gug-Seoun
    • The Plant Pathology Journal
    • /
    • v.18 no.2
    • /
    • 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.

Electrical Properties of G4-48PyP Dendrimer LB Films complex with Metal Ions (금속이온 착체에 의한 G4-48PyP 덴드리머 LB막의 전기적 특성)

  • Jung, S.B.;Yoo, S.Y.;Park, J.C.;Kwon, Y.S.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
    • /
    • 2002.07b
    • /
    • 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.

  • PDF

Mechanical Properties of Intermetallic/Metal Laminated Composite by SHS Reaction (자전고온반응에 의한 금속간화합물/금속 적층복합재료의 기계적 특성)

  • ;;Manabu Enoki
    • Proceedings of the Korean Society For Composite Materials Conference
    • /
    • 2002.10a
    • /
    • 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

  • PDF

Crush Cytologic Findings of Myxopapillary Ependymoma in Spinal Cord - A Case Report - (점액 유두상 상의세포종의 압착도말 세포학적 소견 - 1예 보고 -)

  • Jung, Soo-Jin;Yang, Young-Il
    • The Korean Journal of Cytopathology
    • /
    • v.10 no.1
    • /
    • 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.

  • PDF

Studies on Combustion Characteristics and Reduced Kinetic Mechanisms of Natural Gas Premixed Flames (천연가스 예혼합화염의 연소특성 및 축소반응메커니즘에 관한 연구)

  • 이수룡;김홍집;정석호
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.6 no.4
    • /
    • 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.

  • PDF

Induction of Steroid 11 $\beta$-hydroxylase in Pellicularia fillamentosa (Pellicularia fillamentosa로부터 Steroid 11$\beta$-hydroxylase의 유도)

  • 김말남;김영숙
    • Korean Journal of Microbiology
    • /
    • v.27 no.4
    • /
    • pp.366-372
    • /
    • 1989
  • Twenty-one strains were tested for 11$\beta$-hydroxylation of Reichstein's substance S. Four fungi exhibited ability for the reaction, among which Pellicularia fillamentosa showed the highest activity. The 11$\beta$-hydroxylase of this fungus was proved to be induced by the substrate, cycloheximide reducing significantly the activity of the enzyme. Range of optimum pH for the 11$\beta$-hydroxylation was broad and found to be 2.0-8.0. Test of the enzyme activity at different growing stages, from spore to mycelia, showed that the branching stage of hyphae and the mature mycelial stage were the most effective for the Reichstein's substance S transformation. However, 11$\beta$-hydroxylase in the intact spore was turned out to be uninducible with the substrate.

  • PDF