Effect of Space Fractional Parameter on Nonlinear Ion Acoustic Shock Wave Excitation in an Unmagnetized Relativistic Plasma

In this work, the model equation with space fractional-order (FO) is used to investigate the nonlinear ion acoustic shock wave excitations (NIASWEs) in an unmagnetized collisionless weakly relativistic plasma having inertial relativistic ions fluid with viscous effects, inertial-less non-thermal electrons and inertial-less Boltzmann positrons. To do it, the Korteweg-de Vries Burgers equation (KdVBE) is derived from the considered fluid model equations by implementing the standard reductive perturbation method. Accordingly, such equation is converted to space fractional KdVBE via Agrawal’s variational principle with the help of the beta fractional derivative and its properties. The exact analytical solutions of KdVBE with space FO are determined via the modified Kudryashov method. The influence of space fractional and other related plasma parameters on NIASWEs are investigated. The outcomes would be useful to understand the nature of shocks with the presence of non-local or local space in many astrophysical and space environments (especially in the relativistic wind of pulsar magnetosphere, polar regions of neutron stars, etc.) and further laboratory verification.

Readout for simple and precise analog acoustic impact initialization

An economic concept of acoustic shock wave sensing readout system for simple computer processing is introduced in this work. Its application can be found in precise initialization of the stopwatch from the starter sound, handclap or gun in competitive sport races but also in many other places. The proposed device consists of several low-cost commercially available components and it is powered by a 9 V battery. The proposed device reliably reacts on incoming acoustic shock wave by generation of explicit impulse having controllable duration. It significantly overcomes basic implementations using only a microphone and amplifier (generating parasitic burst instead of defined and distinct impulse) or systems allowing a limited number of adjustable features (gain and/or threshold of the comparator—our concept offers the adjustment of gain, cut-off frequency, threshold level and time duration of active state). In comparison with standard methods, the proposed approach simplifies and makes sensing device less expensive and universal for any powder-based starting gun (without necessity to adapt starting gun). The proposed device, among others, has the following features: impulse duration can be controlled from hundreds of μs up to 2.3 s, the gain range of linear part of processing from 6 to 40 dB and open-collector output compatible with 5 V TTL or 3.3 V CMOS logic. The initialization has been tested in the range from tens of centimeters up to four meters. In order to highlight the important spectral components, the spectral character of the signal can be optimally reduced by a low-pass filter. The quiescent power consumption of the designed simple analog circuit reaches 90 mW. Several use cases, response of the designed system on gunshot signature, talking, hand-clapping and hit on the sensing microphone, are studied and compared to each other. Simulation and experimental results confirm functionality of the realized system.

Acoustic/shock wave heating in the gravitationally stratified partially ionized plasmas: the two-fluid effects

<p> The chromospheric heating problem is a long-standing intriguing topic of solar physics, and the acoustic wave/shock wave heating in the chromospheric plasma has been investigated in the last several decades. It has been confirmed that acoustic waves, and the shock waves induced by the steepening acoustic waves in the gravitationally stratified chromospheric plasma, are able to transport energy to the chromosphere, but the energy supplied in this way is not necessarily sufficient for heating the chromosphere. Here, we further investigate the acoustic/shock wave heating process while taking into account the two-fluid effects.</p><p> As the plasma in the chromosphere is weakly or partially ionized,  neutrals play an important role in wave propagation in this region. Therefore,  a two-fluid computational model treating neutrals and charged particles (electrons and ions) as two separate fluids is used for modelling the acoustic/shock wave propagation in idealised partially ionized plasmas, while taking into account the ion-neutral collisions, ionization and recombination. We have thus investigated  the collisional and reactive interactions between separated ions and neutrals, as well as the resulting effects in the acoustic/shock wave propagation and damping. In the numerical simulations, both the initial hydrostatic equilibrium and chemical equilibrium are taken into account to provide different density profiles for comparison.</p><p>We have found that the shock heating in the partially ionized plasmas strongly depends on the ionization fraction. In particular, the relatively smaller ionization fraction resulting from the initial chemical equilibrium significantly enhances the shock wave heating, which dominates the overall heating effect according to an approximated quantitative comparison. Moreover, the decoupling between ions and neutrals is also enhanced while considering ionization and recombination, resulting in stronger collisional heating.</p>