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41.
AbstractThe present article provides a review on the nonlinear mechanical behavior of polymer matrix composites (PMCs). Initially, essential mechanisms driving the nonlinear response of PMCs under different loading conditions are discussed. Rate-dependence, tension-compression asymmetry, viscous behavior, unloading characteristics, interaction between stress components and effects of environmental factors on mechanical properties are briefly reviewed. This is followed by a review of major approaches and constitutive models for predicting stress–strain behavior of PMCs. Following an increasing degree of complexity, models are categorized into four major classes: nonlinear elasticity models, elastic-plastic models, elastic-plastic-viscous models and Damage-Plasticity models. The vast number of existing models is mainly due to the anisotropy and inhomogeneity of PMCs. In brief, this review focuses on informing the reader of major frameworks, rather than addressing all the models in detail. 相似文献
42.
Biqun Chen Karthikeyan Rajagopal Fatemeh Parastesh Hamed Azarnoush Sajad Jafari Iqtadar Hussain 《理论物理通讯》2020,72(10):105003-28
The economic and financial systems consist of many nonlinear factors that make them behave as the complex systems. Recently many chaotic finance systems have been proposed to study the complex dynamics of finance as a noticeable problem in economics. In fact, the intricate structure between financial institutions can be obtained by using a network of financial systems. Therefore, in this paper, we consider a ring network of coupled symmetric chaotic finance systems, and investigate its behavior by varying the coupling parameters. The results show that the coupling strength and range have significant effects on the behavior of the coupled systems, and various patterns such as the chimera and multi-chimera states are observed. Furthermore, changing the parameters' values, remarkably influences on the oscillators attractors. When several synchronous clusters are formed, the attractors of the synchronized oscillators are symmetric, but different from the single oscillator attractor. 相似文献
43.
In this paper,the nonlinear dynamic behavior of a string-beam coupled system subjected to external,parametric and tuned excitations is presented.The governing equations of motion are obtained for the nonlinear transverse vibrations of the string-beam coupled system which are described by a set of ordinary differential equations with two degrees of freedom.The case of 1:1 internal resonance between the modes of the beam and string,and the primary and combined resonance for the beam is considered.The method of multiple scales is utilized to analyze the nonlinear responses of the string-beam coupled system and obtain approximate solutions up to and including the second-order approximations.All resonance cases are extracted and investigated.Stability of the system is studied using frequency response equations and the phase-plane method.Numerical solutions are carried out and the results are presented graphically and discussed.The effects of the different parameters on both response and stability of the system are investigated.The reported results are compared to the available published work. 相似文献
44.
K. H. Hamed 《The European physical journal. Special topics》2009,174(1):65-79
Although persistence in natural data is generally admitted, its effect on the significance of various statistical tests has
not been extensively studied and is sometimes overlooked or simply ignored in practice. In particular, modified tests that
are robust in the presence of persistence are still lacking. In many situations, need may arise to test the significance of
correlation between two observed natural time series. Although the estimation of the classical product-moment correlation
coefficient is a straightforward task, classical significance testing depends on two major assumptions. The first assumption
is that the data are Gaussian, which is violated by many natural time series. In this case, a distribution-free measure of
correlation, such as Kendall’s tau should be used. The second, and often overlooked assumption, is that the observations in
each time series are not autocorrelated, which is also violated by most natural time series. Similar to the case of trend
testing (e.g. Mann-Kendall trend test), which has received some attention recently, the existence of persistence increases
the chance of falsely detecting significant correlation when the two series are actually uncorrelated. In this paper, the
effect of both short- and long-term persistence (STP and LTP) on the distribution of Kendall’s tau as a distribution-free
measure of correlation between two time series is investigated, and an exact expression for its variance under persistence
is derived. The implications of these results for the analysis of natural data are illustrated through the study of spurious
correlation between a 133-year Nile flow time series from A.D. 1871 to A.D. 2003 and independent segments of a reconstruction
of the North Hemisphere temperature time series from A.D. 1000 to A.D. 1980, both of which exhibit LTP. It is shown that spurious
significant correlation between completely unrelated segments of the two time series is on average three times as common as
in random series of the same length at the 10% significance level, which is consistent with the theoretical results. It is
also shown that accounting for LTP by using the correct variance of the test statistic effectively reduces the probability
of false identification to near its expected nominal value of 10%. Similar results were obtained at other significance levels. 相似文献
45.
A nonlinear finite element model is provided to predict the static aero-thermal deflection and the vibration behavior of geometrically imperfect shape memory alloy hybrid composite panels under the combined effect of thermal and aerodynamic loads. The nonlinear governing equations are obtained using Marguerre curved plate theory and the principle of virtual work taking into account the temperature-dependence of material properties. The effect of large deflection is included in the formulation through the von Karman nonlinear strain-displacement relations. The thermal load is assumed to be a steady-state constant-temperature distribution, whereas the aerodynamic pressure is modeled using the quasi-steady first-order piston theory. The Newton-Raphson iteration method is employed to obtain the nonlinear aero-thermal deflections, while an eigenvalue problem is solved at each temperature step and static aerodynamic load to predict the free vibration frequencies about the deflected equilibrium position. Finally, the nonlinear deflection and free vibration characteristics of a composite panel are presented, illustrating the effects of geometric imperfection, temperature rise, aerodynamic pressure, boundary conditions and shape memory alloy fiber embeddings on the panel response. 相似文献
46.
47.
The complexes formed between IE11 and Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) were identified and confirmed by IR, UV and pH-metric titration. The uptake behavior of porous silica modified with N-propylsalicylaldimine (IE11) and these metal ions were studied. Log k(d) was found to be within the range 2.19-5.16 depending on pH and time of stirring. IE11 was used in the separation and preconcentration of Cd(II), Cr(III, VI), Cu(II), Mn(II, VII) and Pb(II) from some natural water samples. Data were compared with those obtained by the solvent extraction method APDC/MIBK. The proposed methodology allows to verify an improvement in the water quality of Nile River probably attributed to high to moderate floods in the last few years. The method was found to be accurate and not subject to random error, i.e. precise. 相似文献
48.
49.
The pattern of freezing of two varieties of grapevine during spring bud burst was characterised using infrared thermography. All plants studied showed endogenous freezing of the stems and subsequent rapid ice spread (0.47 cm/s) analogous to ice spread in bulk water suggesting ice travel in the xylem. Barriers to ice spread were observed between stembranches and more importantly between the stem and buds. Buds froze after the stem and freezing appeared to be initiated from the stem. The lack of a fully functional xylem system is proposed as the barrier to ice spread. All buds which froze suffered complete frost kill whilst frozen stem recovered unharmed. Only 58% of the buds froze and those that did not freeze survived completely. 相似文献
50.
R. H. Abu-Eittah M. M. Hamed M. M. Abdou 《International journal of quantum chemistry》1987,31(6):855-869
The electronic absorption spectra of some phenylethylamine drugs, namely, d-pseudoepherine, l-pseudoephedrine, l-ephedrine, dl-ephedrine dl-norephedrine, phenylethylamine, methoxyphenamine, and l-noradrenaline were investigated in polar and nonpolar solvents. The observed transitions were interpreted, and the role of σ-π interaction was explored. Molecular orbital calculations were performed on representatives of the above group of compounds, namely, d-pseudoephedrine, l-ephedrine, and l-noradrenaline using the INDO procedures and adopting the best conformer of the molecule. The transition energy, band intensity, and dipole moments were calculated and corresponded satisfactorily with the experimental values. 相似文献