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71.
We investigate the physical parameters controlling the low-energy screening in carbon nanotubes via electron energy loss spectroscopy and inelastic X-ray scattering. Two plasmon-like features are observed, one near 9 eV (the so-called π plasmon) and one near 20 eV (the so-called π + σ plasmon). At large nanotube diameters, the π + σ plasmon energies are found to depend on the number of walls and not on the radius or chiral vector. The observed shift with number of walls indicates a change in the strength of the screening and in the effective interaction at inter-atomic distances; thus this result suggests a mechanism for tuning the properties of nanotubes. 相似文献
72.
Iwona Kuźniarska-Biernacka Ana R. Silva Ana P. Carvalho João Pires Cristina Freire 《Catalysis Letters》2010,134(1-2):63-71
The chiral Mn(III) salen complex (C1) was immobilised onto a natural clay (BEN) and a porous clay heterostructure (PCH) functionalised with 3-aminopropyltriethoxysilane (APTES). FTIR, XPS and Mn chemical analysis confirm the C1 anchorage in both materials, but with higher efficiency in BEN_APTES clay. The catalytic activity of C1@BEN_APTES and C1@PCH_APTES, was assessed in the epoxidation of styrene (sty) and ∝-methylstyrene (∝-Mesty) using NaOCl and m-chloroperoxybenzoic acid (m-CPBA)/N-methylmorpholine-N-oxide (NMO). Both materials behave as moderate catalysts, show high epoxide selectivity but low enantiomeric excesses. In the case of sty epoxidation with m-CBPA/NMO the C1@PCH_APTES catalyst showed the highest catalytic activity, whereas in ∝-Mesty epoxidation, the C1@PCH_APTES catalyst, although leading to lower substrate conversion than the BEN analogue, presented the lowest complex leaching. In all cases, the oxidant NaOCl had some destructive effect in the hybrid catalysts, highlighting the importance of a careful choice of catalyst and oxidant system. 相似文献
73.
Boehmite/multi-wall carbon nanotube (MWCNT) composite powders were prepared by hydrothermal processing. Starting chemical of aluminum acetate powders (2Al(OH)(C2H3O2)2) and MWCNTs were mixed for the formation of stoichiometric boehmite powders in an attempt to synthesize MWCNT-reinforced boehmite nano-powders via hydrothermal synthesis at 200 °C for 2 h. Kinetically stable suspensions of MWCNT–boehmite composite powders were prepared and subsequently electrophoretic deposition (EPD) was applied to obtain complex shape products in the form of micro-gears. It is shown that the EPD technique is a powerful tool to manufacture small components in a short time. Detail TEM observations also indicated that hydrothermal processing provides an ideal environment to obtain homogeneous mixtures of MWCNT–boehmite powders due to effective surface functionalization of MWCNTs under hydrothermal conditions. 相似文献
74.
Ming-Sin Ng Yee-Shan Ku Wai-Shing Yung Sau-Shan Cheng Chun-Kuen Man Liu Yang Shikui Song Gyuhwa Chung Hon-Ming Lam 《International journal of molecular sciences》2021,22(21)
Soybeans are nutritionally important as human food and animal feed. Apart from the macronutrients such as proteins and oils, soybeans are also high in health-beneficial secondary metabolites and are uniquely enriched in isoflavones among food crops. Isoflavone biosynthesis has been relatively well characterized, but the mechanism of their transportation in soybean cells is largely unknown. Using the yeast model, we showed that GmMATE1 and GmMATE2 promoted the accumulation of isoflavones, mainly in the aglycone forms. Using the tobacco BrightYellow-2 (BY-2) cell model, GmMATE1 and GmMATE2 were found to be localized in the vacuolar membrane. Such subcellular localization supports the notion that GmMATE1 and GmMATE2 function by compartmentalizing isoflavones in the vacuole. Expression analyses showed that GmMATE1 was mainly expressed in the developing soybean pod. Soybean mutants defective in GmMATE1 had significantly reduced total seed isoflavone contents, whereas the overexpression of GmMATE1 in transgenic soybean promoted the accumulation of seed isoflavones. Our results showed that GmMATE1, and possibly also GmMATE2, are bona fide isoflavone transporters that promote the accumulation of isoflavones in soybean seeds. 相似文献
75.
Seok Ku Jeon Chan Seung Park Sang Done Kim Byung Ho Song Joseph M. Norbeck 《Korean Journal of Chemical Engineering》2008,25(6):1279-1285
Steam-methane reforming (SMR) reaction was studied using a tubular reactor packed with NiO/γ-Al2O3 catalyst to obtain synthesis gases with H2/CO ratios optimal for the production of synthetic diesel fuel from steam-hydrogasification of carbonaceous materials. Pure
CH4 and CH4-CO2 mixtures were used as reactants in the presence of steam. SMR runs were conducted at various operation parameters. Increasing
temperature from 873 to 1,023 K decreased H2/CO ratio from 20 to 12. H2/CO ratio decreased from 16 to 12 with pressure decreasing from 12.8 to 1.7 bars. H2/CO ratio also decreased from about 11 to 7 with steam/CH4 ratio of feed decreasing from 5 to 2, the lowest limit to avoid severe coking. With pure CH4 as the feed, H2/CO ratio of synthesis gas could not be lowered to the optimal range of 4–5 by adjusting the operation parameters; however,
the limitation in optimizing the H2/CO ratio for synthetic diesel fuel production could be removed by introducing CO2 to CH4 feed to make CH4-CO2 mixtures. This effect can be primarily attributed to the contributions by CO2 reforming of CH4 as well as reverse water-gas shift reaction, which led to lower H2/CO ratio for the synthesis gas. A simulation technique, ASPEN Plus, was applied to verify the consistency between experimental
data and simulation results. The model satisfactorily simulated changes of H2/CO ratio versus the operation parameters as well as the effect of CO2 addition to CH4 feed. 相似文献
76.
Tsermaa Galya Vladimír Sedlařík Ivo Kuřitka Radko Novotný Jana Sedlaříková Petr Sáha 《应用聚合物科学杂志》2008,110(5):3178-3185
The importance of antibacterial materials for biomedical applications is growing nowadays. The presented article deals with the characterization of structural, mechanical and thermal properties and of antibacterial polymeric films based on polyvinyl alcohol (PVA) and silver nitrate, which can find their applicability in wound dressing components and protective coating. The methods of transmission electron microscopy, UV–vis and XRD spectroscopy, optical microscopy, differential scanning calorimetry, stress–strain analysis, and agar diffusion test were used to characterize the polymer films prepared. The results showed strong antibacterial activity against Escherichia coli and Staphylococcus aureus already at the lowest addition level of silver nitrate. An improvement of mechanical properties (Young's modulus) was also noticed due to a modification of PVA with silver nitrate up to 1 wt. % of silver content. Furthermore, the results show a strong effect of the thermal history of the sample preparation on the degree of silver‐ion reduction and formation of nanoparticles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
77.
The stability of Fe/ZSM‐5 de‐NOx catalyst has been investigated. The samples are prepared by sublimation of iron chloride.
Substantial amount of protons are found to remain in the fresh catalyst after washing and calcination. After 10 h exposure
to wet exhaust gas at 600°C, the catalyst is severely deactivated. The presence of steam induces dealumination of the ZSM‐5 matrix, because the protons
provide the point of attack by water. In addition, highly reactive distorted tetrahedral iron species and tetrahedral species
change to less reactive octahedral iron ions or iron agglomerates upon aging treatment. With the second sublimation of iron
chloride, the iron loading is increased and thus the concentration of remaining protons is reduced. Also, the catalyst turns
out to preserve more reactive iron ions after aging treatment. In conclusion, the second sublimation is believed to bring
about a remarkable improvement in the stability of the Fe/ZSM‐5 catalyst although its de‐NOx activity is slightly decreased.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
78.
Park Ji-Woo Ku Tae-Wan Kim Jeong Kim Kwang-Ho Kang Beom-Soo 《Journal of Mechanical Science and Technology》2016,30(5):2203-2210
Journal of Mechanical Science and Technology - Flexible forming technology such as Multi-point dieless forming (MDF) has benefits for the sheet metal field because it can implement a variety of... 相似文献
79.
Dong‐Seon Won Jin‐Hyang Kim Hyo Jin No You Jin Cho Ju‐Yeon Lee Bum Ku Rhee Hee‐Dok Choi 《Polymer International》2010,59(2):162-168
Stabilization of electrically induced dipole alignment is one of the important criteria in the development of nonlinear optical (NLO) polymers for electro‐optic device applications. Polyurethanes for NLO applications have attracted attention because of their high thermal stability due to hydrogen bonding. In the work reported here, we designed and synthesized a new type of NLO polyurethane, in which the pendant NLO chromophores are part of the polymer backbone. This mid‐type NLO polymer is expected to have the merits of both main‐chain and side‐chain NLO polymers, namely stable dipole alignment and good solubility. 1‐[3,4‐Di‐(2‐hydroxyethoxy)phenyl]‐2‐(2‐thienyl)ethene was prepared and condensed with 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate to yield a polyurethane. This polyurethane was reacted with tetracyanoethylene to give a novel Y‐type polyurethane (7) containing 1‐(3,4‐dioxyphenyl)‐2‐[5‐(1,2,2‐tricyanovinyl)‐2‐thienyl]ethenes as NLO chromophores, which constitute part of the polymer backbone. Polyurethane 7 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of ca 162 °C. The second harmonic generation (SHG) coefficient (d33) of a poled polymer film of he polyurethane at 1560 nm fundamental wavelength is ca 1.11 × 10?18 C. Polymer 7 exhibits an enhanced thermal stability and no significant SHG decay is observed below 150 °C, which is acceptable for NLO device applications. Copyright © 2009 Society of Chemical Industry 相似文献