A survey of non-prehensible pneumatic manipulation surfaces : principles, models and control.

International audienceMany manipulation systems using air flow have been proposed for object handling in a non-prehensile way and without solid-to-solid contact. Potential applications include high-speed transport of fragile and clean products and high-resolution positioning of thin delicate objects. This paper discusses a comprehensive survey of state-of-the-art pneumatic manipulation from the macro scale to the micro scale. The working principles and actuation methods of previously developed air-bearing surfaces, ultra-sonic bearing surfaces, air-flow manipulators, air-film manipulators, and tilted air-jet manipulators are reviewed with a particular emphasis on the modeling and the control issues. The performance of the previously developed devices are compared quantitatively and open problems in pneumatic manipulation are discussed

Particle in Cell and Hybrid Simulations of the Z Double-Post-Hole Convolute Cathode Plasma Evolution and Dynamics

The Z-accelerator at Sandia National Laboratories (SNL), is a high-current pulsed power machine used to drive a range of high energy density physics (HEDP) experiments [1]. To achieve peak currents of >20MA, in a rise time of ~100ns, the current is split over four levels of transmission line, before being added in parallel in a double-post-hole convolute (DPHC) and delivered to the load through a single inner magnetically insulated transmission line (MITL). The electric field on the cathode electrode, >107Vm-1, drives the desorption and ionisation of neutral contaminants to form a plasma from which electrons are emitted into the anode-cathode (a-k) gap. The current addition path in the DPHC forms magnetic 'null' regions, across which electrons are lost to the anode, shunting current from the inner MITL and load. In experiment, current losses of >10% have been measured within the convolute; this reduces the power delivered to the load, negatively impacting the load performance, as well as complicating the prediction of the Poynting flux used to drive detailed magneto-hydrodynamic (MHD) simulations [2, 3]. In this thesis we develop 3-dimensional (3D) Particle-in-Cell (PIC) and hybrid fluid-PIC computer models to simulate the plasma evolution in the DPHC and inner MITL. The expected experimental current loss at peak current was matched in simulations where Hydrogen plasma was injected from the cathode elec- trode at a rate of 0.0075mlns-1 (1ml=1015cm-2), with an initial temperature of 3eV. The simulated current loss was driven by plasma penetrating the downstream side of the anode posts, reducing the effective a-k gap spacing and enhancing electron losses to the anode. The current loss at early time (<10MA), was matched in simulations where space-charge-limited (SCL) electron emission was allowed directly from the cathode; to match the loss over the entire current pulse, a delay model is motivated. Here, plasma injection was delayed after the start of SCL emission, based on realistic plasma expansion velocities of ~3cmμs-1. The PIC model, which was necessary to accurately simulate the kinetic behaviour of the lower density plasma and charged particle sheaths, was computationally intensive such that the spatial resolutions achieved in the 3D simulations were relatively poor. With the aim of reducing the computational overhead, allowing finer spatial resolutions to be accessed, we investigate the applicability of hybrid techniques to simulating the cathode plasma in the convolute. Our PIC model was both implemented in the resistive MHD code, Gorgon, where part of the plasma was modelled in the single fluid approximation, and extended to include an inertial two-fluid description of the plasma. The hybrid models were applied to the DPHC simulations, the results from which are used to motivate a three component model; here, the densest part of the convolute plasma is modelled using the single fluid MHD approximation, transitioning to a fully kinetic PIC description of the lower density plasma and charged particle sheaths, linked by a two-fluid description

Magnetic instabilities and resulting energy conversion in astrophysics

textBecause the universe is primarily composed of plasma, the interaction of plasmas and magnetic fields is of great importance for astrophysics. In this dissertation, we investigate three magnetic instabilities and examine their possible effects on astrophysical objects. First, we model solar coronal structures as Double Beltrami states, which are the lowest energy equilibria of Hall magnetohydrodynamics. We find that these states can undergo a catastrophe with characteristics similar to those of a solar eruption, such as a flare or coronal mass ejection. We then investigate magnetic reconnection and particle acceleration in moderately magnetized relativistic pair plasmas with three-dimensional particle-in-cell simulations of a kinetic-scale current sheet. We find that in three dimensions the tearing instability produces a network of interconnected and interacting magnetic flux ropes. In its nonlinear evolution, the current sheet evolves toward a three-dimensional, disordered state in which the resulting flux rope segments contain magnetic substructure on kinetic scales and sites of temporally and spatially intermittent dissipation. We find that reconnection produces significant particle acceleration, primarily due to the electric field in the X-line regions between flux ropes; the resulting particle energy spectrum can extend to high Lorentz factors. We find that the highest energy particles are moderately beamed within.Astronom

Classical and Quantum Mechanical Models of Many-Particle Systems

The topic of this meeting were non-linear partial differential and integro-differential equations (in particular kinetic equations and their macroscopic/fluid-dynamical limits) modeling the dynamics of many-particle systems with applications in physics, engineering, and mathematical biology. Typical questions of interest were the derivation of macro-models from micro-models, the mathematical analysis (well-posedness, stability, asymptotic behavior of solutions), and “to a lesser extent” numerical aspects of such equations. A highlight of this meeting was a mini-course on the recent mathematical theory of Landau damping

Magnetars: the physics behind observations

Magnetars are the strongest magnets in the present universe and the combination of extreme magnetic field, gravity and density makes them unique laboratories to probe current physical theories (from quantum electrodynamics to general relativity) in the strong field limit. Magnetars are observed as peculiar, burst--active X-ray pulsars, the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma Repeaters (SGRs); the latter emitted also three "giant flares," extremely powerful events during which luminosities can reach up to 10^47 erg/s for about one second. The last five years have witnessed an explosion in magnetar research which has led, among other things, to the discovery of transient, or "outbursting," and "low-field" magnetars. Substantial progress has been made also on the theoretical side. Quite detailed models for explaining the magnetars' persistent X-ray emission, the properties of the bursts, the flux evolution in transient sources have been developed and confronted with observations. New insight on neutron star asteroseismology has been gained through improved models of magnetar oscillations. The long-debated issue of magnetic field decay in neutron stars has been addressed, and its importance recognized in relation to the evolution of magnetars and to the links among magnetars and other families of isolated neutron stars. The aim of this paper is to present a comprehensive overview in which the observational results are discussed in the light of the most up-to-date theoretical models and their implications. This addresses not only the particular case of magnetar sources, but the more fundamental issue of how physics in strong magnetic fields can be constrained by the observations of these unique sources.Comment: 81 pages, 24 figures, This is an author-created, un-copyedited version of an article submitted to Reports on Progress in Physic

SIRM 2017

This volume contains selected papers presented at the 12th International Conference on vibrations in rotating&nbsp;machines, SIRM, which took place February 15-17, 2017 at the campus of the Graz University of Technology.&nbsp;By all meaningful measures, SIRM was a great success, attracting about 120 participants (ranging from senior&nbsp;colleagues to graduate students) from 14 countries. Latest trends in theoretical research, development, design and&nbsp;machine maintenance have been discussed between machine manufacturers, machine operators and scientific&nbsp;representatives in the field of rotor dynamics.&nbsp;SIRM 2017 included thematic sessions on the following topics: Rotordynamics, Stability, Friction, Monitoring,&nbsp;Electrical Machines, Torsional Vibrations, Blade Vibrations, Balancing, Parametric Excitation, and Bearings.&nbsp;The papers struck an admirable balance between theory, analysis, computation and experiment, thus contributing&nbsp;a richly diverse set of perspectives and methods to the audience of the conference