Precursors of backflow events and their relationship with the near-wall self-sustaining process

This study examines the precursors and consequences of rare backflow events at the wall using direct numerical simulation of turbulent pipe flow with a high spatiotemporal resolution. The results obtained from conditionally averaged fields reveal that the precursor of a backflow event is the asymmetric collision between a high- and a low-speed streak (LSS) associated with the sinuous mode of the streaks. As the collision occurs, a lifted shear layer with high local azimuthal enstrophy is formed at the trailing end of the LSS. Subsequently, a spanwise or an oblique vortex spontaneously arises. The dominant nonlinear mechanism by which this vortex is engendered is enstrophy intensification due to direct stretching of the lifted vorticity lines in the azimuthal direction. As time progresses, this vortex tilts and orientates towards the streamwise direction and, as its enstrophy increases, it induces the breakdown of the LSS located below it. Subsequently, this vortical structure advects as a quasi-streamwise vortex, as it tilts and stretches with time. As a result, it is shown that reverse flow events at the wall are the signature of the nonlinear mechanism of the self-sustaining process occurring at the near-wall region. Additionally, each backflow event has been tracked in space and time, showing that approximately 50 % of these events are followed by at least one additional vortex generation that gives rise to new backflow events. It is also found that up to a maximum of seven regenerations occur after a backflow event has appeared for the first time.

Does Foreign Direct Investment Impact Energy Intensity? Evidence from Developing Countries

The paper presents the results of a study that attempts to investigate the impact of foreign direct investment (FDI) on energy intensity by constructing panel regression model and panel smooth transition regression (PSTR) model. Based on panel data from 1990 to 2014, this study contributes to conduct the impact of FDI on energy intensity from the perspective of emerging country, including BRICS and non-BRICS countries, and investigates the channels of influence of FDI on energy intensity. Besides that, we intend to employ the PSTR model to reveal the nonlinear mechanism of FDI on energy intensity. Our findings reveal several key conclusions: first, FDI exerts insignificant impact on energy intensity in the emerging countries. Second, the impact of FDI on energy intensity is heterogeneous between BRICS and non-BRICS countries. Third, innovation capacity plays various moderating effects on the relationship of FDI and energy intensity among different types of emerging countries. Furthermore, the nonlinear mechanism of FDI on energy intensity is realized with industrial structure as the transition variable, which plays a different effect on the impact of FDI on energy intensity between different samples.

The Effects of Cracks and Fluids on Post-Seismic Healing

<p>It is now well established that large seismic events change the surrounding velocities, and that these velocities slowly recover over time.  Precisely which mechanisms control the recovery process are less well understood.  We present the results of laboratory experiments to better characterise what properties of the underlying material control the recovery process.  We do this by mixing two waves, one which perturbs the velocity of the sample (as an earthquake does in field data) and one which senses the change in velocity (as in changing noise correlations).  This is an inherently nonlinear experiment as we mix two waves and measure the effects of this wave mixing.  Within our experiments, we vary the properties of the samples to understand which are most important in controlling the nonlinear response.  We focus on two mechanisms.  The first is fractures and how changes in fracture properties change the nonlinear response.  The second is fluids, in particular the effect of low saturations on the nonlinear response.  By changing the fluids and fractures we can turn on and off the nonlinear mechanism, helping us to move toward a better understanding of the underlying mechanisms of these wave-wave interactions.</p>

Regular and Irregular Vegetation Pattern Formation in Semiarid Regions: A Study on Discrete Klausmeier Model

The research on regular and irregular vegetation pattern formation in semiarid regions is an important field in ecology. Applying the framework of coupled map lattice, a novel nonlinear space- and time-discrete model is developed based on discretizing the classical Klausmeier model and the vegetation pattern formation in semiarid regions is restudied in this research. Through analysis of Turing-type instability for the discrete model, the conditions for vegetation pattern formation are determined. The discrete model is verified by Klausmeier’s results with the same parametric data, and shows advantages in quantitatively describing diverse vegetation patterns in semiarid regions, such as the patterns of regular mosaicirregular patches, stripes, fractured stripesspots, and stripes-spots, in comparing with former theoretical models. Moreover, the discrete model predicts variations of rainfall and vegetation types can cause transitions of vegetation patterns. This research demonstrates that the nonlinear mechanism of the discrete model better captures the diversity and complexity of vegetation pattern formation in semiarid regions.

Накопление повреждений при статическом деформировании твердого тела регулярного строения: микротрещины, неотрелаксированные напряжения

Using the methods of acoustic emission in the variant of linear location and internal friction, it is shown that when an initially equilibrium composition of the CFRP type is stretched, unrelaxed stresses accumulate in the places of intense microcrack formation. This is due to the incomplete completeness of the relaxation redistribution of the accumulated energy / elastic deformation by a nonlinear mechanism. The increasing level of unrelaxed stresses inevitably transforms the heterogeneous solid into a metastable state. As a result, the dissipative capacity of the system as a whole is reduced and the probability of a nonequilibrium crack appears.