The Bohm sheath criterion in a collisional plasma sheath under finite ion temperature is examined with a two fluid model. It is shown that by considering the neutral-ion collision in the sheath, there will be an upper as well as lower limit for the sheath velocity criterion, but the finite ion temperature only affects the lower limit.

When an intense laser beam propagates in plasma, due to relativistic electrons resulting from the laser electric field, the plasma refractive index alters. Subsequently, the plasma behaves initially similar to a positive lens that decreases the laser spot size. In this article, the propagation of the laser beam in collisional quantum plasmas is investigated with considering a ramped density profile. Using WKB and paraxial approximations through parabolic equation, a mathematical formulation for the beam width parameter is obtained from the wave equation. Acquired equations are numerically solved by employing the fourth-order Runge-Kutta method. In the collisionless plasma, by increasing the ramp slope, the beam width focuses with less oscillation amplitude, smaller laser spot size and more oscillations. In the collisional quantum plasma, due to energy absorption, the oscillation amplitude enhances by passing through the plasma and the laser beam defocuses at a few lengths. For the greater values of the slope and the collision frequency, the laser spot size oscillates with the higher amplitude and defocuses in a shallower plasma depth. Also, greater plasma density results in smaller laser spot size and bigger oscillation frequency. Then, this effect is compared in the strong and weak quantum and classical plasmas. Decreasing the plasma temperature improves the magnetization due to the ponderomotive force related to the time variation, the beam-width oscillates with greater frequency and deeper penetration in the strong quantum plasma in comparison with the weak quantum or the classical cases.

Sheath formation and its characteristics are studied in collisional magnetized plasma consisting of nonextensive electrons and thermal ions. Using two-fluid model, the Bohm criterion for ion velocity is deduced as a function of plasma parameters and shown that ion-neutral collisions impose an upper limit for the Bohm criterion. It is also found that deviation from the standard Maxwellian distribution significantly affects the sheath characteristics. Sheath potential and ion density are considered under the effects of magnetic field, ion temperature, nonextensivity and ion-neutral collision frequency. The results indicate that by applying an external magnetic field, it is possible to control the sheath thickness

In this article, non-linear Landau damping and generation of BGK mode in non-magnetized plasma are studied by using particle simulation. As plasma environment consists of electrons and ions, it is simulated by particle method and it is supposed that ions are considered as a motionless background. On the other hand, electron’s dynamic is obtained from solving Newton’s equation and the electrons are supposed as particles. In the non-linear region, trapping of particles in potential well is investigated. These trapped particles account for stopping linear landau damping and entering to the non-linear region, and as a result of this process, the amplitude of electrostatic wave oscillates around an approximately constant magnitude. The effect of collision between particles has been studied with the help of a simple model for the collision term in the simulation code and the result of the simulation code with the theoretical result is compatible. For this purpose, it is expected that the exponential damping of electrostatic waves is due to the collision, and the ratio of this damping is in proportion with collision frequency.

In this paper, the growth of transverse-longitudinal coupled electromagnetic modes in the interaction of high-intensity lasers with dense plasma is investigated. Using kinetic theory and solving the scattering relationship for the Vlasov-Maxwell system, the collision effects on the growth of the electromagnetic mode are studied. The anisotropic distribution function considers the effects of body stress due to laser ponderomotive force and plasma density gradient. The results show that a 99% reduction in frequency in the beam path in dense plasma leads to an 88\% increase in the growth rate of unstable modes. Increasing the density prevents immediate cessation and enhances the growth of unstable modes. Increasing the density gradient by 99\%, the instability rate maximum will increase by 88\%. Overall, this paper provides insights into the effects of collision and anisotropic distribution function on the growth of transverse-longitudinal coupled electromagnetic modes in dense plasma. Overall, this paper provides insights into the interplay between various phenomena such as body stress, collision, and electromagnetic modes in dense plasma.

Short and intense laser pulses in laser-plasma interaction stimulate various local structures like solitary waves in the plasma. Relative salitons should be given special attention because the amplitude of the electromagnetic field is intense enough to set plasma electrons in relativistic motions. In the interaction of intense laser with plasma, collisions can play an important role in the physical phenomena. In this paper, the effect of the collision on the emission of solitons is investigated by considering the interaction of an intense laser with plasma. Then, the NLS equation is numerically solved and the different results are compared with each other. Also, the stability conditions of individual waves and the effect of the collision on these waves are investigated.

Plasma-material interaction has been a subject of interest for the past several decades due to its importance in various fields of research such as film deposition, surface nitriding, plasma etching, plasma reactors at low-pressure conditions etc. During this interaction, the presence of negative ions further plays a vital role to ease defect-free analysis of soft substrates. The response of plasma through the sheath formation, when a metallic plate or probe is inserted into it, depends on the plasma characteristics / parameters and the bias voltage used on the plate or probe. The Bohm’, s criterion decides such kind of interaction. The present work theoretically demonstrates a modified Bohm’, s criterion in an electronegative plasma which is collisional and has two-temperature non-extensive electrons (hot and cold electrons). The behaviour of positive ions is considered through their fluid equations, whereas the negative ions are taken to follow Boltzmann distribution. While writing the basic equations, ion source term and ionization rate are retained and Sagdeev’, s potential approach is employed to evaluate the Bohm’, s criterion which reveals a band for the positive ion velocity, means maximum and minimum values for the ion velocity. This modified Bohm’, s criterion is studied under the effects of various plasma parameters.

The fluid description is employed to investigate the instability of Newtonian viscous shear dusty plasma system in hydrodynamic regime, taking into account both viscosity and collision effects. Describing the equilibrium configuration in the presence of the binary collision terms between dust grains and neutral particles and using the local approximation method, the dispersion relation is obtained by applying the generalized hydrodynamic equation to find the spatial dependence of the initial velocity in equilibrium state. Analyzing the obtained dispersion relation shows that the main factor of free energy source to arise the instability of the system is due to the viscous force. While the collision effect plays a stabilizing role for the system by reducing the growth rate of the instability of the Newtonian strongly coupled dusty plasma system in the hydrodynamic regime.

In this paper, the collisional filamentation instability of an electron beam-weakly magnetized and ionized plasma has been investigated in the presence of background plasma, using the fluid description. By describing the equilibrium configuration in the presence of binary collision terms between charged and neutral particles and using the local approximation method, the dispersion relation (DR) of instable mode (filamentation instability) has been obtained and the effect of collision and magnetic field driven-destabilization and current-driven stabilization on the growth rate of instability has been studied. The results show the cut-off wave number and the magnetic threshold for the filamentation instability in the collisional magnetized plasma in which the instability will disappear for the larger wave number and larger magnetic fields. Studies show that the value of cut-off wave number and magnetic threshold are raised by increasing the electron beam current density.

Introduction: This study aimed, effect of platelet-rich plasma (PRP) on soft tissue healing after mandibular third molar surgery. Materials & Methods: In this semi-blinded clinical trial study, 30 selected patients requiring surgical extraction of soft tissue impacted mandibular third molar participated from cases referred to the Department of Surgery, Faculty of Dentistry, Isfahan Azad University 2017. Patients divided into both test and control groups. PRP was placed in the extracted socket of the test group, whereas the control group had no PRP. Arzhangian standard kit utilized for preparation of PRP. The outcome variables in this study were pain, swelling, inter incisal mouth opening, wound dehiscence, dry socket, bleeding, and tissue color. The collected data analyzed using statistical tests followed independent T-test, Mann-Whitney, and fisher (p value < 0. 05). Results: The mean postoperative pain score (Visual Analog Scale) lowered for the test group after several wound dehiscence on the third and seventh days after surgery which was statistically significant (p value < 0. 001). Although the mean bleeding time on the third day after surgery decreased in the test group, this difference was not statistically significant (p value = 0. 59). There were no statistically significant between both groups for The dry socket incidence on the seventh day and the mean of inter incisal mouth opening in the third and seventh days after surgery as well. Conclusion: The usage of topical PRP has beneficial advantages on soft tissue healing after mandibular third molar surgery. Unlike the control group, The PRP group provided reduced pain and better soft tissue healing.