Continuum dynamics of the intention field under weakly cohesive social interaction

We investigate the long-time dynamics of an opinion formation model inspired by a work by Borghesi, Bouchaud and Jensen. First, we derive a Fokker–Planck-type equation under the assumption that interactions between individuals produce little consensus of opinion (grazing collision approximation). Second, we study conditions under which the Fokker–Planck equation has non-trivial equilibria and derive the macroscopic limit (corresponding to the long-time dynamics and spatially localized interactions) for the evolution of the mean opinion. Finally, we compare two different types of interaction rates: the original one given in the work of Borghesi, Bouchaud and Jensen (symmetric binary interactions) and one inspired from works by Motsch and Tadmor (non-symmetric binary interactions). We show that the first case leads to a conservative model for the density of the mean opinion whereas the second case leads to a non-conservative equation. We also show that the speed at which consensus is reached asymptotically for these two rates has fairly different density dependence

Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

International audienceThis paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r. Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge

Spatiotemporally resolved imaging of streamer discharges in air generated in a wire-cylinder reactor with (sub)nanosecond voltage pulses

We use (sub)nanosecond high-voltage pulses to generate streamers in atmospheric-pressure air in a wire-cylinder reactor. We study the effect of reactor length, pulse duration, pulse amplitude, pulse polarity, and pulse rise time on the streamer development, specifically on the streamer distribution in the reactor to relate it to plasma-processing results. We use ICCD imaging with a fully automated setup that can image the streamers in the entire corona-plasma reactor. From the images, we calculate streamer lengths and velocities. We also develop a circuit simulation model of the reactor to support the analysis of the streamer development. The results show how the propagation of the high-voltage pulse through the reactor determines the streamer development. As the pulse travels through the reactor, it generates streamers and attenuates and disperses. At the end of the reactor, it reflects and adds to itself. The local voltage on the wire together with the voltage rise time determine the streamer velocities, and the pulse duration the consequent maximal streamer length

2D positive streamer modelling in NTP air under extreme pulse fronts. What about runaway electrons?

International audienc

Capillary microplasmas for ozone generation

Microplasmas inside confined cavities, pores and capillaries of dielectric materials present a great potential for various environmental applications. The paper briefly introduces the physical properties of the AC microplasmas generated by the discharges inside porous ceramics foams and focuses on their chemical effects in various mixtures of nitrogen and oxygen. Ozone formation as an example tool to evaluate the chemical potential of the microplasmas was investigated as a function of discharge power, gas mixture composition and total gas flow rate

Electron density and temperature in a diffuse nanosecond pulse discharge in air at atmospheric pressure

This work presents the first experimental results on the electron properties of a nanosecond diffuse fast ionisation wave generated in synthetic dry air at atmospheric pressure under very strong overvoltage. Both density and mean temperature of electrons are investigated by incoherent Thomson scattering. The electron density is also derived from the Stark broadening of oxygen lines resolved by optical emission spectroscopy. The extreme voltages applied question some common hypothesis of the diagnostics implemented. The solutions adopted and the remaining limitations are discussed in the paper. Each diagnostic covers a specific region of interest within the discharge and they show good agreement in conditions where they overlap. It is shown that most of the volume of the pin-to-plane discharge is quite representative of a quasi-steady state glow discharge dominated by the emission of the first and second positive systems of nitrogen. Once its propagation completed within the first two nanoseconds and until the end of the 10 ns pulse, it is characterized by rather homogeneous properties close to the axis. The electron density is of the order of 1015 cm−3 and the mean temperature is about 3 eV within the whole air gap. About 6 ns after the start of the discharge from the pin, a sub-millimetric region of strong ionization develops at the pin, which is consistent with the observation of a continuum of emission spreading from the UV to the near-IR spectral range. Within this part of the discharge, the electron density reaches values greater than 1017 cm−3 with an ionization degree higher than 1%. The radiative recombination of nitrogen ions N2+ and the three-body recombination of N+ with a large number of electrons could help to explain the continuum.</p

Insights into the peculiar field structure of a recent diffuse discharge under extreme voltage conditions by electric field induced second harmonic generation and optical emission spectroscopy

International audienceThe axial temporal evolution of the electric field of a diffuse nanosecond air discharge is measured with high resolution (<100 ps). This discharge is generated at atmospheric pressure in a pin-to-plane configuration for voltages ranging from 20 to 85 kV The electric field is derived by field induced second harmonic generation. It is shown that for peak voltages above 56 kV, the electric field behind the field front increases with voltage and exceeds the ionization threshold at 85 kV. Results are compared to recent measurements [1]

Experimental and numerical study of the propagation of a discharge in a capillary tube in air at atmospheric pressure

International audienceThis paper presents an experimental and numerical study of a pulsed air plasma discharge at atmospheric pressure propagating in a capillary glass tube. In this work, we have compared the discharge structures and the axial propagation velocities of discharges. First, we have studied a needle-to-plane configuration without tube. For applied voltages in the range 7-18 kV, we have observed in experiments and in simulations that a plasma ball starts to develop around the needle tip. Then, for applied voltages less than 14 kV, in experiments, the discharge rapidly splits into several streamer channels with a main axial streamer. In simulations, we have computed only the main axial discharge. For applied voltages higher than 14 kV, in experiments and in simulations, we have observed that the discharge propagates with a cone shape in the gap. For all studied voltages, a good experiment/modelling agreement is obtained on the axial propagation velocity of the discharge, which increases with the applied voltage. Then, we have studied the propagation of discharges inside capillary tubes with radii in the range 37.5-300 μm. In experiments and simulations, we have observed that for small tube radius, the discharge front is quite homogeneous inside the tube and becomes tubular when the tube radius increases. Experimentally, we have observed that the velocity of the discharge reaches a maximum for a tube radius slightly less than 100 μm. We have noted that for a tube radius of 100 μm, the discharge velocity is three to four times higher than the velocity obtained without tube. This clearly shows the influence of the confinement by a capillary tube on the discharge dynamics. In this work, we have only simulated discharges for tube radii in the range 100-300 μm. We have noted that both in experiments and in simulations, the velocity of the discharge in tubes increases linearly with the applied voltage. As the radius of the tube decreases, the discharge velocity derived from the simulations slightly increases but is less than the experimental one. We have noted that the discrepancy on the discharge velocity between experiments and simulations increases as the voltage increases