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31.
The reaction of 2,5-didodecyl-1,4-dipropynylbenzene with different molybdenum sources (Mo(CO)6, norbornadiene-Mo(CO)4, cyclooctadiene-Mo(CO)4, cycloheptatriene-Mo(CO)3, (PhCCPh)3Mo(CO), (acac)2MoO2/AlEt3) was investigated in the presence of 4-chlorophenol or 2-fluorophenol. Upon heating to 105-130 °C, the formation of didodecyl-PPE resulted. The degree of polymerization of the PPE is dependent on the used phenol and to the utilized molybdenum precursor. The most active catalyst forms from (acac)2MoO2, AlEt3 and 2-fluorophenol. This catalyst combination gives high molecular weight PPEs after 6 h at 105 °C. 相似文献
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33.
Following the variational principles for linear initial valueproblems associated with the wave and heat conduction equationsdiscussed by Gurtin and Leitmann and using time convolutionsit is shown that general variational principles exist for theseproblems with sources on the boundaries and within the regionunder consideration. 相似文献
34.
Modified Locally One Dimensional Methods for Parabolic Partial Differential Equations in Two Space Variables 总被引:1,自引:0,他引:1
In this note we consider the locally one dimensional methodas discussed in Gourlay & Mitchell (1969, 1972) and indicatehow this scheme can be used to solve accurately a parabolicpartial differential equation in two space variables. 相似文献
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37.
We use the Signorini expansion method to determine second-order Saint-Venant solution for an infinitesimally bent and stretched
bar. The bar in the unstressed reference configuration is straight, prismatic, isotropic, homogeneous and made of a second-order
elastic material. These solutions and those found earlier for a pretwisted bar give generalized Poynting effects. A bar when
bent stretches and the elongation is determined by the first and second-order elasticities, area of cross-section, torsional
rigidity, bending vector and the inertia tensor. When an infinitesimally twisted bar is deformed, there is a second-order
bending deformation even when there is no resultant bending moment applied on the end faces.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
The problem of defining and determinating the shear centre is present in the literature since the first decades of this century.
It soon interlaced with the definition of the twist centre and their ways became unextricable in the following decades. A
number of researchers dealt with this subject meeting with variable issues, yet in the authors' opinion it seems of some interest
to run through it again. In this paper a general survey of the literature is performed and the two definitions of the shear
centre (here named kinematic and energetic) are compared. It is remarked how the energetic definition for the shear centre
makes it coincide with a suitably chosen twist centre. An example is given to show that the two definitions generally fail
to provide the same place even for simple cross sections. It is shown that the two definitions provide the same place, using
standard approximate formul?, in the case of thin-walled mono-connected sections with regularly varying thickness and two-connected
sections with constant thickness. As a new result, it will be shown that the two definitions of shear centre do not provide
the same place for thin-walled sections with connection higher than two even in the trivial case of uniform thickness; an
example is given.
Received November 25, 1997 相似文献
39.
Giuseppe C. Ruta 《Journal of Elasticity》1998,52(2):99-110
The flexure of a Saint-Venant cylinder is defined from a kinematic point of view. A complete solution for the field equations
is provided and the gauge choices to define the center of shear and rotation are made consequently. This seems to eliminate
some ambiguities present in the literature.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
40.
Justė Baranauskaitė Valdas Jakštas Liudas Ivanauskas Dalia M. Kopustinskienė Gailutė Drakšienė Ruta Masteikova 《Natural product research》2016,30(6):672-674
The aim of our study was to increase the extraction efficiency of carvacrol, rosmarinic, oleanolic and ursolic acid from the different species of oregano herbs (Origanum onites L., Origanum vulgare spp. hirtum and Origanum vulgare L.). Various extraction methods (ultrasound-assisted, heat-reflux, continuous stirring, maceration, percolation) and extraction conditions (different solvent, material:solvent ratio, extraction temperature, extraction time) were used, and the active substances were determined by HPLC. The lowest content of carvacrol, rosmarinic, oleanolic and ursolic acid was obtained by percolation. During heat-reflux extraction, the content of active substances depended on the solvent used: ethanol/non-aqueous solvent (glycerol or propylene glycol) mixture was more effective compared with ethanol alone. The results showed that for each species of oregano the most optimal extraction method should be selected to maximize the content of biologically active substances in the extracts. 相似文献