Nonlinear structures: soliton, shocklike and explosive waves in quantum semiconductor plasma

The properties and conditions for the appearance of some nonlinear waves in a three-dimensional semiconductor plasma are discussed, by studying the described plasma fluid system with quantum gradient forces and degraded pressures. Our analytical procedure is built on the reductive perturbation theory to obtain the Kadomtsev-Petvashvili equation for the fluid model and solving it using the direct integration method and the Bäcklund transform. Through different solution methods we got different nonlinear solutions describing different pulse profiles such as soliton, kink and explosive pulses. This model can be used to identify the potential disturbances in a semiconductor plasma.

Force balance in rapidly rotating Rayleigh–Bénard convection

The force balance of rotating Rayleigh–Bénard convection regimes is investigated using direct numerical simulation on a laterally periodic domain, vertically bounded by no-slip walls. We provide a comprehensive view of the interplay between governing forces both in the bulk and near the walls. We observe, as in other prior studies, regimes of cells, convective Taylor columns, plumes, large-scale vortices (LSVs) and rotation-affected convection. Regimes of rapidly rotating convection are dominated by geostrophy, the balance between Coriolis and pressure-gradient forces. The higher-order interplay between inertial, viscous and buoyancy forces defines a subdominant balance that distinguishes the geostrophic states. It consists of viscous and buoyancy forces for cells and columns, inertial, viscous and buoyancy forces for plumes, and inertial forces for LSVs. In rotation-affected convection, inertial and pressure-gradient forces constitute the dominant balance; Coriolis, viscous and buoyancy forces form the subdominant balance. Near the walls, in geostrophic regimes, force magnitudes are larger than in the bulk; buoyancy contributes little to the subdominant balance of cells, columns and plumes. Increased force magnitudes denote increased ageostrophy near the walls. Nonetheless, the flow is geostrophic as the bulk. Inertia becomes increasingly more important compared with the bulk, and enters the subdominant balance of columns. As the bulk, the near-wall flow loses rotational constraint in rotation-affected convection. Consequently, kinetic boundary layers deviate from the expected behaviour from linear Ekman boundary layer theory. Our findings elucidate the dynamical balances of rotating thermal convection under realistic top/bottom boundary conditions, relevant to laboratory settings and large-scale natural flows.

Insight on micro bubbling mechanism in a 2D fluidized bed with Group D particles

By CFD-DEM simulations, the present work is aimed to investigate the transient gas-solid bubbling mechanisms along a whole bubble lifecycle in a 2D fluidized bed from a micro perspective. Systemic comparisons with CCD measurements confirm the validity of current simulations. Afterward, the manner of particle motion and its driving mechanisms at various stages are investigated. In order to do that, external forces are analyzed at an individual particle level, including the drag, pressure gradient force, and their resultant acceleration together with gravity. Many interesting findings have been achieved. For example, a switch in directions of drag and pressure gradient forces at the root of an initial bubble enables its detachment. And, regarding their contributions to the burst of a bubble, the drag force is several times of the pressure gradient forces. Present efforts help to offer a novel view of particle dynamics during the bubbling fluidization.

Nanoscale Continuous Directional Motion Driven by a Cyclic Thermal Field

Directional motion plays a crucial role in various mechanical systems. Although mechanisms for nanoscale directional motion have been widely used in many aspects of nanotechnology, it remains a great challenge to generate continuous and controllable motion at the nanoscale. Herein we propose a nanoscale continuous directional motion in cyclic thermal fields by using a double-walled system which consists of an outer BN/C heterojunction nanotube and a concentric inner carbon nanotube (CNT). By manipulating the heating region of the outer BN/C heterojunction tube, the continuous motion of the inner CNT can be realized with ease. The inner CNT demonstrates three distinct movements due to the joint actions of the asymmetric thermal gradient forces and interlayer attraction forces caused by the presence of the outer BN/C heterojunction nanotube. The mechanism revealed in the present study may be useful in designing novel devices for energy conversion and directional transportation.

Intensification of Loop Current Frontal Eddies and their Interactions with the Loop Current and Surrounding Flow

Loop Current Frontal Eddies (LCFEs) are cold-core vortices located in the vicinity of the Loop Current (LC) and are known to intensify and play an essential role in the LC shedding. The amplification of the LCFEs also affects the local circulation. During the 2010 Deepwater Horizon oil spill, part of the oil was entrained around and inside an intensified LCFE. The goal of this research is to characterize the LCFE intensification and understand its effects on the LC and surrounding flow. Firstly, the LC-LCFE interaction was investigated using altimetry and a mooring array. The intensification of the observed LCFEs shows similar characteristics over time, independent of their location: a steep increase in kinetic energy, a corresponding decrease in SSH, and an increase in size. LCFE intensification is dependent on the distance from the LC front. As the LCFE grows, the flow at the interface with the LC becomes stronger and deeper, and the horizontal density gradient between the features increases. Further intensification of the LC front and the LCFEs is suggested to be driven by the advection (nonlinear) term and the pressure-gradient (linear) term in the momentum budget. Secondly, the ageostrophy of the LC meanders during LCFE intensification is assessed using HYCOM velocity and geostrophic velocity from altimetry. The results indicate that during strong meandering, especially before and during LC shedding and in the presence of frontal eddies, the centrifugal force becomes as important as the Coriolis and the pressure-gradient forces, i.e., the LC meanders are in gradient-wind balance. Finally, the ability of LCFEs to transport particles without exchange with the exterior (i.e., material coherence) is investigated. The results show that the frontal eddies can remain coherent for up to 20 days at the surface and up to 25 days at deeper layers. Particles inside the frontal eddies were tracked backward in time and showed that the material coherence of the eddies builds up from Gulf water and can drive cross-shelf exchange of particles, water properties, and nutrients.

A Formula for the Maximum Vertical Velocity in Supercell Updrafts

In supercell environments, previous authors have shown strong connections between the vertical wind shear magnitude, updraft width, and entrainment. Based on these results, it is hypothesized that the influences of entrainment-driven dilution on buoyancy and maximum updraft vertical velocity w in supercell environments are a predictable function of the vertical wind shear profile. It is also hypothesized that the influences of pressure perturbation forces on maximum updraft w are small because of a nearly complete offset between upward dynamic pressure forces and downward buoyant pressure forces. To address these hypotheses, we derive a formula for the maximum updraft w that incorporates the effects of entrainment-driven dilution on buoyancy but neglects pressure gradient forces. Solutions to this formula are compared with output from previous numerical simulations. This formula substantially improves predictions of maximum updraft w over past CAPE-derived formulas for maximum updraft w, which supports the first hypothesis. Furthermore, integrated vertical accelerations along trajectories show substantial offsets between dynamic and buoyant pressure forces, supporting the second hypothesis. It is argued that the new formula should be used in addition to CAPE-derived measures for w in forecast and research applications when accurate diagnosis of updraft speed is required.