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991.
M.G.?CarvalhoEmail author J.M.R.C.A.?Santos A.A.?Martins M.M.?Figueiredo 《Cellulose (London, England)》2005,12(4):371-383
In this work attention has been focused on the effects of papermaking beating, web forming and sizing operations on the physical/chemical
surface properties of bleached Eucalyptus globulus kraft fibres. Inverse gas chromatography (IGC) was used to determine the dispersive component of surface tension (γsd) as well as the acidic/basic character (according to the Lewis concept) of the solid surfaces (pulp fibres and pulp handsheets).
The results have shown that the main effect of beating is to increase the fibre's Lewis acidic character. Web forming caused
a strong decrease in γsd and significant increments in the adhesion works of both acidic and basic probes, lowering the ratio between the two. Nevertheless,
the surface of handsheets still exhibited a dominant acidic character. The sizing operation did not change the dispersive
component of the surface tension significantly but decreased the difference between the adhesion works of the acidic and basic
probes, rendering the handsheet surface less Lewis acidic and more Lewis basic. Thus, although internal sizing is expected
to strongly influence liquid spreading at the paper surface and liquid penetration of the fibre's network, it is concluded
that beating and web forming lead to important changes in the surface energetic properties of the Eucalyptus globulus kraft fibres. 相似文献
992.
Many types of corrosion phenomena are controlled by the ionic composition of a small volume of solution at the surface. Localized corrosion and atmospheric corrosion are two examples in which < 1 μl of solution can cause dramatic damage. Ion chromatographic (IC) techniques have been used to analyze these solutions in order to gain a better understanding of the mechanisms which govern them. Two examples are presented. The presence of minor alloying elements at localized corrosion sites in two aluminum alloys has been demonstrated, indicating non-stoichiometric dissolution of the alloy during localized corrosion. In addition, IC analysis allowed the determination of the species responsible for the atmospheric corrosion failure of electrical connectors, including their likely origin. 相似文献
993.
R M Riggin C J Shaar G K Dorulla D S Lefeber D J Miner 《Journal of chromatography. A》1988,435(2):307-318
A new high-performance size-exclusion chromatography method has been developed for the determination of potency of human growth hormone products. This method has been extensively validated and shown to correlate well with the hypophysectomized rat bioassay which has been used traditionally. The method is much more precise than the traditional bioassay and thus provides more reliable means of producing consistent biosynthetic human growth hormone batches. 相似文献
994.
The total synthesis of rac-sceletium alkaloid A41a and of its 3'-demethoxy analogue 1b via the annulation of endocyclic enamines 4a–b is presented. The Michael acceptor 5a is a useful synthon for the two-step synthesis of 2,3-disubstituted pyridines from Δ2-pyrrolines. 相似文献
995.
D. Charalambidis B. H. Feng C. Fotakis 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,14(3):223-227
Photoelectron angular distributions have been measured for the three-photon resonant one-photon ionization, (3+1), of Xe via the 7s[1 1/2]0 1 and 8s[1 1/2]0 1 states. The results are in good agreement with the theoretical predictions of Tang and Lambropoulos [13] for the 8s[1 1/2]0 1, but not for the 7s[1 1/2]0 1 state. Furthermore, the results are compared to those which have been obtained by Blazewicz et al. [1] for the three-photon resonant two-photon ionization, (3+2), of Xe via the 6s[1 1/2]0 1 state. 相似文献
996.
Resonances in a modulated light beam have been observed on five transitions in the visible band system of I2. Landé factors gJ and chemical shifts g1 have been measured for levels very close to the dissociation limit of the B state. 相似文献
997.
Oxidation of cysteine, glutathione and ascorbate by photoexcited proteins from normal and cataractous lenses was investigated using electron paramagnetic resonance in combination with spin trapping. We report that illumination of these proteins in pH 7 buffer with light > 300 nm in the presence of thiols (RSH) and a spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), afforded DMPO/S-cysteine and DMPO/SG adducts, suggesting the formation of the corresponding thiyl radicals. In a nonbuffered aqueous solution, illumination of the proteins and glutathione also produced superoxide detected as a DMPO/O2H adduct. Irradiation of these proteins in the presence of ascorbate generated ascorbate radical. We conclude that chromophores present in the natural normal and cataractous lenses are capable of initiating photooxidative processes involving endogenous thiols and ascorbic acid. This observation may be pertinent to UV-induced development of cataract. 相似文献
998.
C. FRESNEAU B. ARRIO B. LECUYER A. DUPAIX N. LESCURE P. VOLFIN 《Photochemistry and photobiology》1984,39(2):255-261
Abstract— The fluorescence of scaleworms has been attributed by Harvey (1952) to a product of the bioluminescent reaction confined in the scales of these worms. We have purified this fluorescent molecule by gel filtration. This compound has an apparent low molecular weight as shown by polyacrylamide gel clectrophoresis in the presence of SDS. The yield of the fluorescent product, after gel filtration, varies with the stimulation of the bioluminescence, triggered either chemically or enzymatically. The fluorescence spectrum of the purified product is similar to the one observed in vivo , with a maximum centered at 520 nm. Consequently, the fluorescent compound isolated is likely the reaction product of the bioluminescent reaction. 相似文献
999.
α,ω-Difluoropolydimethylsiloxanes F[(CH3)2SiO]n(CH3)2SiF have been prepared by reaction of (CH3)2SiF2 with cyclic dimethylsiloxanes [(CH3)2SiO]n (n = 3 or 4). An equilibrium is reached in the redistribution of fluorine vs. oxygen atoms after ca. 24 h at 200°C or 15 days at 150°C when catalysed by AlCl3. 16 equilibrated samples of varied (R = F/Si) overall compositions have been analysed by 1H and 19F NMR and by VPC. The presence of rings has been established for the lower values of R. The molecular constitution of the equilibrated samples is described by a set of constants. The abundance of the end units is slightly larger than expected from random distribution. The good resolution of the spectra permits the distinguishing of the 9th order of environment of the end units and the 5th order for the middle units and the verification that there is no preferential association among the building units, and thus the proportion of chains of various lengths obeys Flory's random distribution mode. The equilibrium molecular constitution of these α,ω-difluorosiloxanes is close to that of their dichloro analogs; the substitution of chlorine by fluorine atoms at the end of the chains thus appears to cause little perturbation. On the other hand, the kinetic evolution of the reaction appears to be different, since the first species which forms is always the pyro moleculeinstead of long chains and large rings as in the case of the chloro analogs. 相似文献
1000.
We have compared the experimental results of study of the preferential solvation of polyvinylpyrrolidone in halogenated solvent/proton-donor solvent mixtures, obtained by light scattering and i.r. spectroscopy and described in the two preceding papers. The preferential adsorption of the proton-donor solvent is explained by the formation of a hydrogen-bond complex of polymer with proton-donor solvent, on which other proton-donor molecules are bound by induced autoassociation. This complexing occurs even in mixtures where the “inert” solvent (1,2-dichloroethane) is preferentially adsorbed; this is experimental proof of a differing solvation of the chains in their close neighbourhood and within short range of them. 相似文献