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排序方式: 共有519条查询结果,搜索用时 93 毫秒
1.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
2.
Statistical Analysis of the Effect of Mineral Admixtures on the Strength of the Interfacial Transition Zone 总被引:1,自引:0,他引:1
Microscopic evidence indicates that the thickness of the interfacial transition zone (ITZ) between the aggregate and the cement paste is modified when mineral admixtures partially replace portland cement. Unfortunately, there is limited information on the significance of these microscopic modifications to the mechanical properties of the ITZ. This research reports experimental results on the shear and tensile strength of the ITZ as affected by the addition of the following mineral admixtures: silica fume, fly ash, and natural pozzolan. Statistical analysis was used to identify the significant parameters affecting the tensile and shear strength of the ITZ. Experimental results indicate that not only does the incorporation of silica fume and fly ash increase the strength of the ITZ, these mineral admixtures have a greater influence on the strength increase of the ITZ than in the strength increase of the cement paste. 相似文献
3.
4.
Novel mixed valence states have been obtained by the treatment of cobaltous ferrocyanides (Co+2FeII) and ferricyanides (Co+2FeIII) in an ozone flow. The CN stretching bands occur at 2085 cm–1 for Co+2FeII and at 2160 cm–1 for Co+2FeIII. After the ozonization process of Co+2FeII, an intense band approximately at 2125 cm–1 is detected. This intermediate band must correspond to a mixed valence state of the type: FeII–CN–Co2+–NC–FeIII Mössbauer spectra recorded in situ during the ozonization of Co+2FeII show the presence of two components: a doublet with isomer shift and quadrupole splitting values close to the cobalti ferricyanide and a very broad line for the mixed valence state. From the Mössbauer and infrared spectra of the aged samples of the Co+2FeII after ozonization, a relaxation process to the initial state of the samples is observed but the mixed valence state is stable. 相似文献
5.
6.
The surface modification of tire rubber after treatment with saturated NaOH aqueous solution was investigated by HATR infrared analysis, potentiometric titration, and contact angle measurements. Infrared analysis of the powdered treated rubber showed a decrease in absorption at 1540, 1450, and 1395 cm(-1). This decrease is attributed to the removal of zinc stearate, an additive present in tire formulations that often migrates and diffuses to the surface, resulting in poor adhesion between the rubber and other materials. The potentiometric titration of the suspension of powdered rubber in 0.1 M NaCl showed that more hydrochloric acid was consumed by the untreated rubber, most likely a result of the hyrdrolysis of the zinc stearate to the organic acid. Contact angles of flat tire pieces showed an homogeneity enhancement of the treated rubber surface. The decrease of the zinc stearate on the treated rubber surface explains the improvement in the adhesion of this material to the cement matrix, observed in a previous research. The promising results of this study are a starting point for future research on incorporating rubber particles into cementitious materials as a means of successfully utilizing the vast amounts of tire waste currently in landfills. 相似文献
7.
8.
A. L. M. Nasser L. P. Mazzolin C. A. Hiruma-Lima L. S. Santos M. N. Eberlin A. R. Monteiro de Souza Brito W. Vilegas 《Chromatographia》2006,64(11-12):695-699
The methanolic extract of the bark of the medicinal plant Qualea parviflora (Vochysiaceae) contains new nor-seco-triterpene and pentacyclic triterpenoids. They were separated in a preparative scale using droplet counter-current chromatography. The optimum solvent used was composed of a mixture of CHCl3/MeOH/H2O (43:37:20, v/v) in the descending mode and led to a successful separation of the new compound 28-nor-17, 22-seco-2α, 3β, 19, 22, 23-pentahydroxy-Δ12-oleanane, besides the known triterpenoids bellericagenin B, bellericaside B and arjunglucoside I . Identification was performed by ESI-MS, 1H NMR and 13C NMR analyses. 相似文献
9.
M. D. P. Monteiro Marques A. Ornelas 《Journal of Optimization Theory and Applications》1995,86(2):421-431
This paper is concerned with the existence of a minimum in a Sobolev space for the functional $$F_g (x): = \int_0^T {g(x(t)){\text{ }}dt + \int_0^T {h(x'(t)){\text{ }}dt,{\text{ }}x(0) = a,{\text{ }}x(T) = b,} }$$ wherea,b are real numbers,g is a continuous map, andh is lower semicontinuous, satisfying adequate growth conditions. As shown by Cellina and Mariconda, there exists a dense subset of the space of continuous functions bounded below such that, forg in this subset, the above functional attains its minimum no matter whichh is used. This subset contains in particular the monotone maps, as shown by Marcellini, and the concave maps, as shown by Cellina and Colombo. Our aim is twofold: first to show that this subset, although dense, is meager in the sense of the Baire category; and second to show that it contains a class of functions which we call concave-monotone, because it generalizes both the classes of concave and of monotone functions. 相似文献
10.
This paper is concerned with BV periodic solutions for multivalued perturbations of an evolution equation governed by the sweeping process (or Moreau's process). The perturbed equation has the form –DuN
C
(t)(u(t))+F(t,u(t)), whereC is a closed convex valued continuousT-periodic multifunction from [0,T] to
d
,N
C
(t)(u(t)) is the normal cone ofC(t) atu(t),F: [0,T]×
d
d
is a compact convex valued multifunction and Du is the differential measure of the periodic BV solutionu. Several existence results for this differential inclusion are stated under various assumptions on the perturbationF. 相似文献