Nonlinear Dynamic Responses of a Honeycomb Sandwich Plate Subject to Transverse Excitations

Nonlinear dynamic behaviors of a simply supported honeycomb sandwich plate subjected to the transverse excitations are investigated in this paper. Based on the classical thin plate theory and Von Karman large deformation theory, the governing equation of motion for the honeycomb sandwich plate is established by using the Hamilton principle. The nonlinear governing partial differential equation is discretized to the ordinary differential equations by differential quadrature method and then solved by Runge-Kutta-Fehlberg method. Based on the numerical simulations, combined with nonlinear dynamic theory, the influences of the frequency and amplitude of the transverse excitation are investigated respectively by using the bifurcation diagrams, Poincare maps and phase portraits. The results exhibit the existence of the period-1, period-2 and chaotic responses with the variation of the excitations, which demonstrate that those motions appear alternately

Dynamic Response of Nano Spherical Shell Subjected to Termo-Mechanical Shock Using Nonlocal Elasticity Theory

In this paper, we present an analytical method for analysis of nano-scale spherical shell subjected to thermo-mechanical shocks based on nonlocal elasticity theory. Thermo-mechanical properties of nano shpere is assumed to be temperature dependent. Governing partial differential equation of motion is solved analytically by using Laplace transform for time domain and power series for spacial domain. The results in Laplace domain is transferred to time domain by employing the fast inverse Laplace transform (FLIT) method. Accuracy of present approach is assessed by comparing the the numerical results with the results of published work in literature. Furtheremore, the effects of non-local parameter and wall thickness on the dynamic characteristics of the nano-sphere are studied

The Effect of Flipped Classroom on Iranian EFL Learners\' Speech Act Production: Does Flip Type Make a Difference?

This study investigated the effect of two types of flipped classroom on the Iranian upper-intermediate EFL learners' appropriate use of refusals, apologies and requests. The participants of the study included 60 upper-intermediate EFL learners from a language institute in Tehran, Iran. The participants were selected based on convenience sampling in the form of three intact classes. Then, the three classes were randomly assigned to three groups namely, traditional flipping group, debate-oriented flipping group and non-flipping group. The three groups were exposed to 14 treatment sessions. Speech act instruction was offered to the flipping groups through explicit flipped instruction and to the non-flipping group through explicit non-flipped instruction. Moreover, a Multiple Choice Discourse Completion Test (WDCT) was administered to the participants to measure their speech act production ability at the pre-treatment and post-treatment, phases of the study. The results revealed that both types of flipped instruction had a significantly positive effect on the EFL learners' use of the speech acts (F=10.622, p<.0.05; F=19.358, p<.0.05; F=18.785, p<.0.05). Accordingly, EFL teachers are recommended to use flipping methods in an attempt to enhance EFL learners' appropriate use of speech acts