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排序方式: 共有346条查询结果,搜索用时 31 毫秒
111.
Laura Castañar Eduard Sistaré Albert Virgili R. Thomas Williamson Teodor Parella 《Magnetic resonance in chemistry : MRC》2015,53(2):115-119
The amplitude and the phase of cross peaks in conventional 2D HSQC experiments are modulated by both proton–proton, J(HH), and proton–carbon, 1J(CH), coupling constants. It is shown by spectral simulation and experimentally that J(HH) interferences are suppressed in a novel perfect‐HSQC pulse scheme that incorporates perfect‐echo INEPT periods. The improved 2D spectra afford pure in‐phase cross peaks with respect to 1J(CH) and J(HH), irrespective of the experiment delay optimization. In addition, peak volumes are not attenuated by the influence of J(HH), rendering practical issues such as phase correction, multiplet analysis, and signal integration more appropriate. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
112.
Teodor M. Atanackovic Stevan Pilipovic Dusan Zorica 《Continuum Mechanics and Thermodynamics》2011,23(4):305-318
We study waves in a rod of finite length with a viscoelastic constitutive equation of distributed fractional order type for
the special choice of weight functions. Prescribing boundary conditions on displacement and stress, we obtain, as special
solutions, cases corresponding to creep and forced oscillations. In solving system of differential and integro-differential
equations, we use the Laplace transformation in the time domain. 相似文献
113.
114.
Miguel Moyers-Gonzalez Teodor I. Burghelea Julian Mak 《ournal of non Newtonian Fluid Mechanics》2011,166(9-10):515-531
We study the linear stability of Plane Poiseuille flow of an elastoviscoplastic fluid using a revised version of the model proposed by Putz and Burghelea (A.M.V. Putz, T.I. Burghelea, Rheol. Acta 48 (2009) 673–689). The evolution of the microstructure upon a gradual increase of the external forcing is governed by a structural variable (the concentration of solid material elements) which decays smoothly from unity to zero as the stresses are gradually increased beyond the yield point. Stability results are in close conformity with the ones of a pseudo-plastic fluid. Destabilizing effects are related to the presence of an intermediate transition zone where elastic solid elements coexist with fluid elements. This region brings an elastic contribution which does modify the stability of the flow. 相似文献
115.
Teodor I. Burghelea Zdeněk Starý Helmut Münstedt 《ournal of non Newtonian Fluid Mechanics》2011,166(19-20):1198-1209
An experimental investigation of the viscosity overshoot phenomenon observed during uniaxial extension of a low density polyethylene is presented. For this purpose, traditional integral viscosity measurements on a Münstedt-type extensional rheometer are combined with local measurements based on the in-situ visualization of the sample under extension. For elongational experiments at constant strain rates within a wide range of Weissenberg numbers (Wi), three distinct deformation regimes are identified. Corresponding to low values of Wi (regime I), the tensile stress displays a broad maximum, but such maximum is observed with various polymeric materials deformed at low rates and it should not be confused with the “viscosity overshoot” phenomenon. Corresponding to intermediate values of Wi (regime II), a local maximum of the integral extensional viscosity is systematically observed. Moreover, within this regime, a strong discrepancy between integral measurements and the space average of the local elongational viscosity is observed which indicates large deviations from an ideal uniaxial deformation process. Images of samples within this regime reinforce this finding by showing that, corresponding to the maximum of the integral viscosity, secondary necks develop along the sample. The emergence of a maximum of the integral elongational viscosity is, thus, related to the distinct inhomogeneity of deformation states and most probably not to the rheological properties of the material. In the fast stretching limit (high Wi, regime III), the overall geometric uniformity of the sample is well preserved, no secondary necks are observed and both the integral and the space averaged transient elongational viscosity show no maximum. A detailed but yet incomplete comparison of the experimental findings with results from the literature is presented and several open questions are stated. 相似文献
116.
117.
Teodor M. Atanackovic 《Comptes Rendus Mecanique》2003,331(10):687-692
We study a viscoelastic body, in a linear stress state with fractional derivative type of dissipation. The model was formulated so that it takes into account, with a weighting factor, all derivatives of stress and strain between zero and one. We derive restrictions on the model that follow from Clausius–Duhem inequality. Several known constitutive equations are derived as special cases of the model proposed here. Two examples are discussed. To cite this article: T.M. Atanackovic, C. R. Mecanique 331 (2003). 相似文献
118.
By using Pontryagin's maximum principle we determine the shape of the lightest compressed rotating rod, stable against buckling. It is shown that the cross-sectional area function is determined from the solution of a nonlinear boundary value problem. A variational principle for this boundary value problem is formulated and a first integral is constructed. The optimal shape of a rod is determined by numerical integration. 相似文献
119.
The object of this article is to investigate inclusion, radius, and other various properties of subclasses of multivalent analytic functions, which are defined by using an extended version of the Owa-Srivastava fractional differintegral operator Ω(λ,p). 相似文献
120.
Rémi Plamont Dr. Yoshihiro Kikkawa Mayuko Takahashi Dr. Masatoshi Kanesato Dr. Michel Giorgi Anita Chan Kam Shun Prof. Dr. Christian Roussel Prof. Dr. Teodor Silviu Balaban 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11293-11300
We have developed a high‐yielding synthesis of meso‐tetraalkylporphyrins, which previously have been obtained only in lower yields. By employing Montmorrilonite K10 as the acid catalyst and 3 Å molecular sieves as the dehydrating agent, yields that reached 70 % could be achieved with some aliphatic aldehydes. The free‐base porphyrins with decyl ( C10 ) or longer chains were imaged at the single‐molecule level at the solvent/surface interface. Highly oriented pyrolytic graphite (HOPG) was used as a π‐stacking surface, whereas 1‐phenyloctane and 1‐phenylnonane were used as solvents. An odd–even effect was observed from C13 to C16 . For C13 a single‐crystal X‐ray structure allowed an unprecedented insight into how packing from two dimensions is expanded into a three‐dimensional crystal lattice. 相似文献