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951.
A mixture of 9-amino-(9-deoxy)epi-dihydroquinidine and salicylic acid was able to promote the direct reaction of various cyclohexanones with dibenzoyl peroxide, thus affording the corresponding protected α-hydroxy carbonyl compounds in high yield and enantioselectivity. Interestingly the same catalytic salt was found to be active when 1-indanones derivatives were directly employed in the reaction with dibenzoyl peroxide furnishing chiral 1-oxo-2,3-dihydro-1H-inden-2-yl benzoates in high yields and enantioselectivity. Furthermore their treatment with NaBH(4) gives easy access to the corresponding enantioenriched 1,2-diols in high yields and without any loss of stereoselectivity. 相似文献
952.
953.
Michele Zappalorto Paolo Lazzarin 《International Journal of Solids and Structures》2009,46(9):1901-1910
The paper deals with nonlinear stress and strain distributions at the root of sharp and rounded notches with different opening angles under antiplane shear loading and small scale yielding. In order to make an easier comparison with the Neuber rule, the material is thought of as obeying the particular nonlinear law used in the past just by Neuber.By solving the linear differential equation resulting from the use of the hodograph transformation, a new relationship linking linear and nonlinear stress and strain concentrations is found. The relationship is written also in terms of the relevant notch stress intensity factors. In contrast with the Neuber rule, this relationship strictly depends on the notch opening angle. Even when the notch opening angle is zero, it does not match the Neuber Rule, but results in an additional factor 2 which is in agreement with Hult and McClintock’s solution when the notch tip radius tends to zero and the notch becomes a crack. 相似文献
954.
Paolo Pennacchi 《Nonlinear dynamics》2009,57(4):607-622
Electromechanical interaction in rotating machinery is an interesting nonlinear phenomenon. The methods used to analyze this
phenomenon depend on the type of the electrical machine, synchronous or asynchronous, and on its size, but they are often
related to the study of the unbalanced magnetic pull (UMP). In this paper the nonlinear behavior of generators with smooth
poles of high-speed turbogenerators is presented during and after the excitation of the magnetic field in the air-gap in order
to fully exploit the effect of the UMP. In the first part of the paper a method, which allows the simulation of the dynamical
behavior of a flexible rotor caused by the UMP, is presented. In the second part, the simulation of a magnetic field excitation
transient in a turbogenerator is presented and the nonlinear aspects in the system response and forcing are highlighted. 相似文献
955.
956.
Paolo Podio-Guidugli Tomáš Roubíček Giuseppe Tomassetti 《Archive for Rational Mechanics and Analysis》2010,198(3):1057-1094
We propose a continuum theory describing the evolution of magnetization and temperature in a rigid magnetic body. The theory
is based on a microforce balance, an energy balance, and an entropy imbalance. We advance the choice of a class of constitutive
equations, consistent with the entropy imbalance, that appear appropriate to describe the phase transition taking place in
a ferromagnet at the Curie point. By combining these constitutive equations with the balance laws, we formulate an initial-boundary
value problem for the magnetization and temperature fields, and we prove existence of weak solutions. 相似文献
957.
In this paper we redefine the well-known metric-affine Hilbert Lagrangian in terms of a spin connection and a spin-tetrad. On applying the Poincaré–Cartan method and using the geometry of gauge-natural bundles, a global gravitational superpotential is derived. On specializing to the case of the Kosmann lift, we recover the result originally found by Kijowski [Gen. Rel. Gravity 9 (1978) (10) 857] for the metric (natural) Hilbert Lagrangian. On choosing a different, suitable lift, we can also recover the Nester–Witten 2-form, which plays an important role in the energy positivity proof and in many quasi-local definitions of mass. 相似文献
958.
Signorini Raffaella Meneghetti Moreno Bozio Renato Brusatin Giovanna Innocenzi Plinio Guglielmi Massimo Negra Federico Della 《Journal of Sol-Gel Science and Technology》2001,22(3):245-253
Hybrid organic-inorganic materials are investigated as suitable materials for inclusion of fullerene derivatives and for fabrication of laser protection devices. A specific synthesis has been developed in order to optimize non-linear optical performances of fullerene derivatives. 3-glicydoxypropyltrymethoxysilane has been used as an inorganic and organic network former to obtain the host material. The sol-gel synthesis consists of the hydrolysis and condensation in acidic conditions of the inorganic network. Epoxy polymerization has been achieved by using zirconium or BF3 alkoxides precursors. Bulk and multilayer materials doped with a fullerene derivative have been fabricated. They show good optical requirements: high fullerenes concentration, high microstructural homogeneity, high laser damage threshold and high optical limiting efficiency. Optical limiting (OL) mechanisms have been investigated. The most effective in the sol-gel materials is the reverse saturable absorption (RSA) one. However, different mechanisms, like non-linear (NL) scattering and NL refraction contribute to a different extent. Open- and closed-aperture OL and z-scan measurements on sol-gel samples show the contribution of NL scattering and NL refraction at 690 nm. Laser damage threshold has been characterized as a function of the structure of the samples and of the optical configurations (f/66 and f/5). 相似文献
959.
Roberto Della Pergola Luigi Garlaschelli Mario Manassero Mirella Sansoni Donatella Strumolo 《Journal of Cluster Science》2001,12(1):23-34
The cluster [HIr5(CO)12]2- (1) was prepared by condensation of [HIr4(CO)11]- and [Ir(CO)4]- (molar ratio 1:1) in refluxing THF, with almost quantitative yields. Its solid state structure was determined by X-ray diffraction at low temperature on the salt [PPh3CH2Ph]2[HIr5(CO)12]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand was located indirectly as a bridge between apical and equatorial metal atoms. The phosphine-substituted cluster [HIr4(CO)10PPh3]- (2) was synthetized by CO displacement on [HIr4(CO)11]-, in THF at room temperature. This reaction is selective, with no traces of polysubstitution products. In the solid state, the hydride and the triphenylphosphine are axially bound on basal iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir–H distance of 1.57(9) Å. On the contrary, two isomers are present in THF solution, and they interconvert rapidly at room temperature, as shown by1H and 31P NMR spectra. 相似文献
960.
Giovanna Baron Giulio Ferrario Cristina Marinello Marina Carini Paolo Morazzoni Giancarlo Aldini 《Molecules (Basel, Switzerland)》2021,26(18)
A fully-detailed LC-MS qualitative profiling of red grape skin, extracted with a mixture of ethanol and water (70:30 v:v) has permitted the identification of 65 compounds which can be classified into the following chemical classes: organic and phenolic acids (14 compounds), stilbenoids (1 compound), flavanols (21 compounds), flavonols (15 compounds) and anthocyanins (14 compounds). The extraction yield obtained with water at different temperatures (100 °C, 70 °C, room temperature) was then evaluated and the overall polyphenol content indicates that EtOH:H2O solvent is the most efficient and selective for polyphenol extraction. However, by analyzing the recovery yield of each single polyphenol, we found that water extraction under heating conditions is effective (extraction yield similar or even better in respect to the binary solvent) for some polyphenolic classes, such as hydrophilic procyanidins, phenolic acids, flavonol glucosides and stilbenoids. However, according to their lipophilic character, a poor yield was found for the most lipophilic components, such as flavonol aglycones, and in general for anthocyanins. The radical scavenging activity was in accordance with the polyphenol content, and hence, much higher for the extract obtained with the binary solvent in respect to water extraction. All the tested extracts were found to have an anti-inflammatory activity in the R3/1 cell line with NF-kb reporter challenged with 0.01 µg/mL of IL-1α, in a 1 to 250 µg/mL concentration range. An intriguing result was that the EtOH:H2O extract was found to be superimposable with that obtained using water at 100 °C despite the lower polyphenol content. Taken together, the results show the bioactive potentialities of grape skin extracts and the possibility to exploit this rich industrial waste. Water extraction carried out by heating is an easy, low-cost and environmentally friendly extraction method for some polyphenol classes and may have great potential for extracts with anti-inflammatory activities. 相似文献