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91.
《Journal of Analytical and Applied Pyrolysis》2009,86(1-2):163-170
Grey alder (Alnus incana (L.) Moench.) wood is often used in the Baltic countries for the production of curing smoke. Unfortunately, the smoke contains an elevated concentration of polycyclic aromatic hydrocarbons (PAH). The effect of the content of wood extractives and the wood storage time after felling on the formation of benzo(a)pyrene (B(a)P), flavouring compounds and antioxidants was studied. Storage time demonstrated a considerable effect on the overall increase of the B(a)P formation. The extraction (elimination) of extractives did not show any definite coherency with the concentration of B(a)P in smoke primary condensates, which was within the range from 1.1 to 8.7 μg/kg. Storage time and the elimination of extractives increased the yields of both 2-hydroxyacetaldehyde and 1,6-anhydro-β,D-glucopyranose (levoglucosan) from 1.8 to 10 times during the pyrolysis process and smouldering. It is interesting that the intensified formation of both substances takes place simultaneously, which commonly does not occur. Nevertheless, the prolonged storage time and the elimination of extractives do not substantially improve the quality of smoke and its condensates. 相似文献
92.
Jinzhu Tan Y.J. Chao Haifeng Wang Jianming Gong J.W. Van Zee 《Polymer Degradation and Stability》2009,94(11):2072-2078
Proton exchange membrane (PEM) fuel cell stack requires elastomeric gaskets in each cell to keep the reactant gases within their respective regions. Long-term durability of the fuel cell stacks depends heavily on the functionality of the elastomeric gasket material. Chemical and mechanical stability of the elastomeric material is of great concern to the overall performance of the fuel cell stacks. The degradation of a commercially available gasket material, ethylene-propylene-diene monomer (EPDM), was investigated in a simulated PEM fuel cell environment in this work. One solution and two temperatures, based on actual fuel cell operation, were used in this study. Optical microscopy was used to show the topographical changes on the sample surface. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the gasket material before and after exposure to the simulated PEM fuel cell environment over time. Atomic absorption spectrometry was used to identify the leachants in the soaking solution from the elastomeric material. Microindentation test and dynamic mechanical analysis (DMA) were conducted to assess the change of mechanical properties of the samples exposed to the environment. The atomic absorption spectrometer analysis shows that silicon and calcium were leached from the material into the soaking solution. The ATR-FTIR results indicate that the chemical changes were not apparent. The microindentation test and DMA results reveal that mechanical properties were not changed significantly. 相似文献
93.
Amy R. Stefan Christopher R. Dockery Brittany M. Baguley Brandi C. Vann Alexander A. Nieuwland James E. Hendrix Stephen L. Morgan 《Analytical and bioanalytical chemistry》2009,394(8):2087-2094
Designed experiments based on a simplex mixture design were employed to explore the effects of three solvent components (water,
formic acid, and aqueous acetic acid), extraction time, and extraction temperature for the automated microextraction of basic
(cationic) dyes from acrylic fibers. Extractions were conducted by an automated liquid handling system, and dye extraction
was evaluated using a UV/visible microplate reader. Highest extraction efficiency for two subclasses of basic dyes (methine
and azo) from acrylic fibers was achieved with an extraction solvent containing 88% formic acid/12% water. Cationic dyes were
analyzed by capillary electrophoresis using a 45 mM ammonium acetate buffer in acetonitrile–water at pH 4.7. The utility of
microextraction combined with capillary electrophoresis–mass spectrometry for analysis of extracts from trace fibers was demonstrated
by the detection and characterization of three basic dyes extracted from a 2-mm length of single acrylic fiber. 相似文献
94.
95.
Yong S. Chong Dr. William R. Carroll William G. Burns Mark D. Smith Ken D. Shimizu Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(36):9117-9126
An atropisomeric molecular balance was developed to study face‐to‐face arene–arene interactions. The balance has a large central 1,4,5,8‐naphthalene diimide surface that forms intramolecular arene–arene interactions with two pendent arms. The balance adopts distinct syn and anti isomers with varying numbers of intramolecular interactions. Thus, the strength of the arene–arene interaction could be quantitatively measured by NMR spectroscopy from the anti/syn ratios. The size of the arene arms was easily varied, which allowed examination of the relationship between arene size and strength of the interaction. A nonlinear size dependence was observed in solution with larger arene arms having a disproportionately stronger arene–arene interaction. The intramolecular arene–arene interactions were also characterized in the solid state by X‐ray crystallography. These studies were facilitated by the kinetic stability of the syn and anti isomers at room temperature due to the high isomerization barrier (ΔG=27.0 kcal mol?1). Thus, the anti isomer could be selectively isolated and crystallized in its folded conformation. The X‐ray structures confirmed that the anti isomers formed two strong intramolecular arene–arene interactions with face‐to‐face geometries. The solid‐state structure analysis also reveals that the rigid framework may contribute to the observed nonlinear size trend. The acetate linker is slightly too long, which selectively destabilizes the balances with smaller arene arms. The larger arene arms are able to compensate for the longer linker and form effective intramolecular arene–arene interactions. 相似文献
96.
在本文,我们研究谱半径至多为$\sqrt[r]{2+\sqrt{5}}$的超图.我们得到此种超图必须具有一个基普结构,这与Woo-Neumaier在2007年对谱半径至多为$\frac{3}{2}\sqrt{2}$的图的分类结果类似. 相似文献
97.
98.
A new polymorph of Bi2(SO4)3 was prepared by reaction of LiBiO2 with H2SO4 and its crystal structure was solved from X-ray powder diffraction. This new polymorph crystallizes in C2/c space group with lattice parameters a = 17.3383(3) Å, b = 6.77803(12) Å, c = 8.30978(13) Å, β = 101.4300(12)°. Bi2(SO4)3 presents a layered structure made of SO4 sulfate groups and signs of stereochemically active Bi3+ lone pairs. The new Bi2(SO4)3 absorbs water to form Bi2(H2O)2(SO4)2(OH)2 through an intermediate Bi2O(OH)2SO4 phase, and the transition is reversible when heated under vacuum. 相似文献
99.
Mohammad M. Khani Zaid M. Abbas Brian C. Benicewicz 《Journal of polymer science. Part A, Polymer chemistry》2017,55(9):1493-1501
The preparation of well‐defined polyisoprene‐grafted silica nanoparticles (PIP‐g‐SiO2 NPs) was investigated. Surface initiated reversible addition fragmentation chain transfer (SI‐RAFT) polymerization was used to polymerize isoprene from the surface of 15 nm silica NPs. A high temperature stable trithiocarbonate RAFT agent was anchored onto the surface of particles with controllable graft densities. The polymerization of isoprene mediated by silica anchored RAFT with different densities were investigated and compared to the polymerization mediated by free RAFT agents. The effects of different temperatures, initiators, and monomer feed ratios on the kinetics of the SI‐RAFT polymerization were also investigated. Using this technique, block copolymers of polyisoprene and polystyrene on the surface of silica particles were also prepared. The well‐defined synthesized PIP‐g‐SiO2 NPs were then mixed with a polyisoprene matrix which showed a good level of dispersion throughout the matrix. These tunable grafted particles have potential applications in the field of rubber nanocomposites. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1493–1501 相似文献
100.
In this paper we provide an elementary proof of the existence of canard solutions for a class of singularly perturbed planar systems in which there occurs a transcritical bifurcation of the quasi steady states. The proof uses the one-dimensional result proved by V.F. Butuzov, N.N. Nefedov and K.R. Schneider, and an appropriate monotonicity assumption on the vector field. The result is applied to identify all possible predator–prey models with quadratic vector fields allowing for the existence of canard solutions. 相似文献