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The present work is devoted to the comparison between numerical and experimental determination of the velocity profile of an ionizing front (primary streamer) in a DC positive point-to-plane corona discharge in dry air at atmospheric pressure. The inception and propagation of the ionizing front is simulated by a one-dimensional model, using finite differences in a flux-corrected transport numerical scheme, including gamma -effects, and using experimental results concerning the swarm parameters. This model provides the spatio-temporal local field and charge density variations as well as the ionization front velocity. An optical measurement of the velocity is performed with the same discharge parameters, using a photomultiplier and a single-slit device. The technique is based on the experimental fact that, for a 1 cm gap in the 7-9 kV voltage range, the successive primary streamers corresponding to a given gap voltage display identical velocity profiles. As a result of the comparison, it appears that a precise coupling between simulation and experiment is possible. There is a voltage range (8-9 kV) within which good agreement is observed. The front velocity in most of the gap is about 2*107 cm s-1 and the profile presents an increase when the streamer leaves the point electrode and when it reaches the cathode. The possible mechanisms of these accelerations are discussed. The model may be applied to a large variation range for various parameters such as the nature of the gas, pressure, inter-electrode gap and curvature radius of the active electrode.

A numerical simulation including kinetics, transport phenomena and temperature gradient is presented to describe axial and radial distribution of ozone in an oxygen-fed ozonizer with cylindrical symmetry. The interdependence of three types of modelling (kinetics, hydrodynamics and electronic injection due to electrical corona discharge) is emphasized and comparisons are made with previous simpler models. The simulation is performed in the case of an industrial cylinder-to-cylinder device for which the temperature gradient is negligible, and in the case of a laboratory wire-to-cylinder ozonizer where an important radial temperature gradient is experimentally observed. Two values of pressure are considered: 760 Torr, where chemical kinetics dominates over diffusion effects, and 10 Torr where diffusion is dominant.

In nitrogen, for pressures below 200 Torr, the anodic glow is characterized by current oscillations, superimposed on a dc component. These oscillations may be attributed to fluctuations of the space charge, structured as a double sign sheath (double layer). The transition from a dark to a glow discharge can occur either directly from the oscillating state or, in the 20-200 Torr pressure range, through the appearance of a particular regime characterized by recurrent impulses. Both cases are considered here in the case of pure nitrogen, and the influence of pressure and gap length on the current and light waveforms is studied. An analysis of the light emitted by the discharge shows that a luminous structure, formed in the anode region, propagates towards the cathode, and travels a few millimetres before being absorbed by the sheath structure. This may be interpreted as the beginning of an ionizing front, which cannot propagate and is choked by the double layer. For higher applied voltages, the double layer cannot be maintained, and the current limiting effect seems to be suppressed during the time for charge evacuation; the current and light impulses corresponding to this latter case are then integrated into the much larger ones which characterize the glow discharge.

The response of shear thickening fluids (STFs) under ballistic impact has received considerable attention due to its field-responsive nature. While efforts have primarily focused on traditional ballistic fabrics impregnated with these fluids, the response of pure STFs to penetration has received limited attention. In the present study, the ballistic response of particle-based STFs is investigated and the effects of fluid density and particle strength on ballistic performance are isolated. It is shown that the loss of ballistic resistance in the STFs at higher impact velocities is governed by the material strength of the particles in suspension. The results illustrate the range of velocities over which these STFs may provide effective armor solutions.The integration of shear thickening fluids (STFs) in armor systems, a concept reported as early as Gates, 1 has received considerable interest with the recent efforts to embed STFs within ballistic fabrics, 2-5 which has been shown to increase their ballistic performance; however, experimental evidence also suggests performance limitations of these hybrid armour systems. This loss of performance is evident when considering steelcore projectiles 1,5 particularly when multiple layers and higher impact velocities are considered. 3 Park et al. 5 discussed preliminary experimental results in which a loss of effectiveness was seen against steel projectiles (FSPs) above an impact velocity of 300 m/s, the same velocity range investigated by Tan et al. 3 The coupled nature of the fluid-fabric interactions make it difficult to ascertain whether this behavior is due to a loss of performance within the STF itself or a transition in the dominant failure mode within the fibers, rendering the presence of the STF inconsequential to the ballistic response. In the present study, we investigate the ballistic penetration of several STFs, particularly focusing on the role of particle strength in determining the ballistic response of STFs through variations of the particle material and volume fraction in the suspensions.STFs are field-responsive fluids which can undergo a sudden fluid-solid transition under certain stimuli. STFs have been extensively characterized using low-stress dynamic techniques, 6-8 in which liquids are considered incompressible. These conditions are not directly relevant to the dynamic high-stress environment of a ballistic impact, where compressibility effects dominate material responses. 9 Lee and Kim 14 estimated the stagnation pressure at the nose of a steel projectile impacting a STF-impregnated fabric to be on the order of several gigapascals, stresses at which compressibility effects must be considered. Under ballistic conditions, in addition to traditional shear thickening mechanisms, a compressioninduced clustering of particles should be expected as the a) oren.petel@mail.mcgill.ca liquid density and particle volume fraction increase under high pressures, 10-13 resulting in extensive particle force chains forming around the projectile (Fig. 1a and 1b) as the...