arXiv subjects

A. A. Mamun

Publications and source records attributed to A. A. Mamun.

At least 55 records · Page 3Linked to original sources

arXiv2018

Self-gravitating envelope solitons in a degenerate quantum plasma system

The existence and the basic features of ion-acoustic (IA) envelope solitons in a self-gravitating degenerate quantum plasma system (SG-DQPS), containing inertial non-relativistically degenerate light and heavy ion species as well as inertialess non-relativistically degenerate positron and electron species, have been theoretically investigated by deriving the nonlinear Schrödinger (NLS) equation. The NLS equation, which governs the dynamics of the IA waves, has disclosed the modulationally stable and unstable regions for the IA waves. The unstable region allows to generate bright envelope solitons which are modulationaly stable. It is found that the stability and the growth rate dependent on the plasma parameters (like, mass and number density of the plasma species). The implications of our results in astronomical compact object (viz. white dwarfs, neutron stars, and black holes, etc.) are briefly discussed.

physics.plasm-ph↗

arXiv2018

Self-gravitating envelope solitons in astrophysical compact objects

The propagation of ion-acoustic waves (IAWs) in a collisionless unmagnetized self-gravitating degenerate quantum plasma system (SG-DQPS) has been studied theoretically for the first time. A nonlinear Schrödinger equation is derived by using the reductive perturbation method to study the nonlinear dynamics of the IAWs in the SG-DQPS. It is found that for $k_c > k$ ($k_c < k$) (where $k_c$ is critical value of the propagation constant $k$ which determines the stable and unstable region of IAWs) the IAWs are modulationally unstable (stable), and that $k_c$ depends only on the ratio of the electron number density to light ion number density. It is also observed that the self-gravitating bright envelope solitons are modulationally stable. The results obtained from our present investigation are useful for understanding the nonlinear propagation of the IAWs in astrophysical compact objects like white dwarfs and neutron stars.

physics.plasm-ph↗

arXiv2018

Modulated dust-acoustic wave packets in an opposite polarity dusty plasma system

The nonlinear propagation of the dust-acoustic bright and dark envelope solitons in an opposite polarity dusty plasma system (composed of non-extensive $q$-distributed electrons, isothermal ions, and positively as well as negatively charged warm dust) have been theoretically investigated. The reductive perturbation method (which is valid for a small, but finite amplitude limit) is employed to derive the nonlinear Schrödinger equation. Two types of modes (namely, fast and slow dust-acoustic (DA) modes) have been observed. The conditions for the modulational instability (MI) and its growth rate in the unstable regime of the DA waves are significantly modified by the effects of non-extensive electrons, dust mass, temperatures of different plasma species, etc. The implications of the obtained results from our current investigation in space (viz. Jupiters magnetosphere, upper mesosphere, and comets tails) and laboratory (e.g. direct current and radio-frequency discharges, plasma processing reactors, fusion plasma devices, and solid-fuel combustion products, etc.) dusty plasmas are briefly discussed.

physics.plasm-ph↗

arXiv2017

Dust-acoustic rogue waves in an opposite polarity dusty plasma featuring non-extensive statistics

Modulational instability (MI) of dust acoustic waves (DAWs), which propagates in an opposite polarity dusty plasma system, containing inertial warm negatively and positively charged dust particles as well as non-extensive q-distributed elec- trons and ions, has been theoretically investigated. The nonlinear Schrodinger (NLS) equation is derived by employing the reductive perturbation method. The NLS equation leads to the MI of DAWs as well as to the formation of DAW rogue waves (DARWs), which are formed due to the effects of nonlinearity in the propagation of DAWs. Both stable and unstable regions are revealed from the analysis of the NLS equation. It is observed that the basic features of the DAWs (viz. stability of the wave profile, MI growth rate, amplitude, and width of DARWs) are significantly modified by the various plasma parameters such as non-extensive parameter, electron number density, and electron temperature. The existence of the non-extensive electron/ion distribution creates an influence on the MI of the waves. It is observed that non-extensive distributed ions have more effect on the MI of the DAWs than electrons.

physics.plasm-ph↗

arXiv2017

Pairing properties from random distributions of single-particle energy levels

Exploiting the similarity between the bunched single-particle energy levels of nuclei and of random distributions around the Fermi surface, pairing properties of the latter are calculated to establish statistically-based bounds on the basic characteristics of the pairing phenomenon. When the most probable values for the pairing gaps germane to the BCS formalism are used to calculate thermodynamic quantities, we find that while the ratio of the critical temperature Tc to the zero-temperature pairing gap is close to its BCS Fermi gas value, the ratio of the superfluid to the normal phase specific heats at Tc differs significantly from its Fermi gas counterpart. The largest deviations occur when a few levels lie closely on either side of the Fermi energy but other levels are far away from it. The influence of thermal fluctuations, expected to be large for systems of finite number of particles, were also investigated using a semiclassical treatment of fluctuations. When the average pairing gaps along with those differing by one standard deviations are used, the characteristic discontinuity of the specific heat at Tc in the BCS formalism was transformed to a shoulder-like structure indicating the suppression of a second order phase transition as experimentally observed in nano-particles and several nuclei. Contrasting semiclassical and quantum treatments of fluctuations for the random spacing model is currently underway.

nucl-th↗

arXiv2017

Oblique propagation of electrostatic waves in a magnetized EPI plasma

A theoretical investigation is carried out to understand the basic features of nonlinear propagation of heavy ion-acoustic (HIA) waves subjected to an external magnetic field in an electron-positron-ion (EPI) plasma which consists of cold magnetized positively charged heavy ion fluids, and superthermal distributed electrons and positrons. In the nonlinear regime, the Korteweg-de Vries (K-dV) and modified K-dV(MK-dV) equations describing the propagation of HIA waves are derived. The latter admits a solitary wave solution with both positive and negative potentials (for K-dV equation) and only positive potential (for mK-dV equation) in the weak amplitude limit. It is observed that the effects of external magnetic field (obliqueness), superthermal electrons and positrons, different plasma species concentration, heavy ion dynamics and temperature ratio significantly modify the basic features of solitary waves (SWs). The application of the results in a magnetized EPI plasma, which occurs in many astrophysical objects (e.g., pulsars, cluster explosions, and active galactic nuclei) is briefly discussed.

physics.plasm-ph↗

arXiv2017

Nucleus-acoustic solitons in self-gravitating magnetized quantum plasmas

The basic properties of the nucleus-acoustic (NA) solitary waves (SWs) are investigated in a super-dense self-gravitating magnetized quantum plasma (SDSGMQP) system in the presence of an external magnetic field, whose constituents are the non-degenerate light (heavy) nuclei, and non/ultra-relativistically degenerate electrons. The Korteweg-de Vries (KdV) equation has been derived by employing the reductive perturbation method. The NA SWs are formed with negative (positive) electrostatic (self-gravitational) potential. It is also observed that the effects of non/ultra-relativistically degenerate electron pressure, and the obliqueness of the external magnetic field significantly change the basic properties (e.g. amplitude, width, and speed) of NA SWs. The findings of our present analysis can be very helpful to explain the physics behind the formation of the NA SWs in astrophysical compact objects, specially neutron stars, which are briefly discussed.

physics.plasm-ph↗

arXiv2017

Nucleus-acoustic solitary waves and double layers in a magnetized degenerate quantum plasma

The properties of nucleus-acoustic (NA) solitary waves (SWs) and double layers (DLs) in a four-component magnetized degenerate quantum plasma system (containing non-degenerate inertial light nuclei, both non-relativistically and ultra-relativistically degenerate electrons and positrons, and immobile heavy nuclei) are theoretically investigated by the reductive perturbation method. The Korteweg-de Vries (K-dV), the modified K-dV (MK-dV), and the Gardner equations are derived to examine the basic features (viz. amplitude, speed, and width) of NA SWs and DLs. It is found that the effects of the ultra-relativistically degenerate electrons and positrons, stationary heavy nuclei, external magnetic field (obliqueness), etc. significantly modify the basic features of the NA SWs and DLs. The basic features and the underlying physics of NA SWs and DLs, which are relevant to some astrophysical compact objects including white dwarfs and neutron stars, are pinpointed.

physics.plasm-ph↗

arXiv2017

Solitary waves and double layers in an adiabatic multi-component space plasma

The formation and propagation of small amplitude Heavy-ion-acoustic (HIA) solitary waves and double layers in an unmagnetized collisionless multi-component plasma system consisting of superthermal electrons, Boltzmann distributed light ions, and adiabatic positively charged inertial heavy ions are theoretically investigated. The reductive perturbation technique is employed to derive the modified Korteweg-de Vries (mK-dV) and standard Gardner (SG) equations. The solitary wave (SW) solution of mK-dV and SG equations as well as Double Layers (DLs) solution of SG equation is studied for analysis of higher-order nonlinearity. It is found that the plasma system under consideration supports positive and negative potential Gardner solitons but only positive potential mK-dV solitons. In addition, it is shown that, the basic properties of HIA mK-dV and Gardner solitons and DLs (viz. polarity, amplitude, width, and phase speed) are incomparably influenced by the adiabaticity effect of heavy ions and the superthermality effect of electrons. The relevance of the present findings to the system of space plasmas as well as to the system of researchers interest is specified.

physics.plasm-ph↗

arXiv2017

Ion-acoustic solitary pulses in a dense plasma

The propagation of ion-acoustic solitary waves (IASWs) in a magnetized, collisionless degenerate plasma system for describing collective plasma oscillations in dense quantum plasmas with relativistically degenerate electrons, oppositely charged inertial ions, and positively charged immobile heavy elements is investigated theoretically. The perturbations of the magnetized quantum plasma are studied employing the reductive perturbation technique to derive the Korteweg-de Vries (K-dV) and the modified K-dV (mK-dV) equations that admits solitary wave solutions. Chandrasekhar limits are used to investigate the degeneracy effects of interstellar compact objects through equation of state for degenerate electrons in case of non-relativistic and ultra-relativistic cases. The basic properties of small but finite-amplitude IASWs are modified significantly by the combined effects of the degenerate electron number density, pair ion number density, static heavy element number density and magnetic field. It is found that the obliqueness affects both the amplitude and width of the solitary waves, whereas the other parameters mainly influence the width of the solitons. The results presented in this paper can be useful for future investigations of astrophysical multi-ion plasmas.

physics.plasm-ph↗

arXiv2017

Solitary potentials in a three component space plasma

The heavy ion acoustic solitary waves (HIASWs) in a magnetized, collisionless, three component space plasma system in the presence of dynamical heavy particles and bi-kappa distributed two distinct temperature of electrons has been carried out. The Korteweg-de Vries (K-dV), the modified K-dV (mK-dV), and the further mK-dV (fmK-dV) equations are derived by employing the well known reductive perturbation method. The basic features of HIASWs (speed, amplitude, width etc.) are found to be significantly modified by the effects of number density of plasma species, superthermal electrons with two distinct temperatures and the magnetic field (obliqueness). The K-dV and fm-KdV solitons exhibit both compressive and rarefactive structures, whereas the mK-dV solitons support only compressive structures. In order to trace the vicinity of the critical heavy ion density, neither the magnetized KdV nor magnetized mKdV equation is suitable for describing the HIASWs. Therefore, we have considered a higher order nonlinearity to describe the solitary profiles by deriving fmK-dV equation. The implication of our results in some space and laboratory plasma situations are concisely discussed.

physics.plasm-ph↗

arXiv2017

Rogue waves in space dusty plasmas

The modulational instability of dust-acoustic (DA) waves (DAWs), and corresponding DA rogue waves (DARWs) in a realistic space dusty plasma system (containing inertial warm positively and negatively charged dust, isothermal ions, and nonthermal kappa distributed electrons) has been theoretically investigated. The nonlinear Schrödinger (NLS) equation is derived by using reductive perturbation method for this investigation. It is observed that the dusty plasma system under consideration supports two modes, namely fast and slow modes, and that both of these two modes can be stable or unstable depending the sign of ratio of the dispersive and nonlinear coefficients. The numerical analysis have shown that the basic features (viz. stability/instabilit, growth rate, amplitude, etc.) of the DAWs associated with the fast mode are significantly modified by superthermal parameter ($κ$) and other various plasma parameters. The results of our present investigation should be useful for understanding DARWs in space plasma systems, viz. mesosphere and ionospehre.

physics.plasm-ph↗

arXiv2017

Modulational Instability and Generation of Envelope Solitons in Four Component Space Plasmas

A four component space plasma system (consisting of immobile positive ions, inertial cold positrons as well as hot electrons and positrons following Cairns' nonthermal distribution function is considered. The nonlinear propagation of the positron-acoustic (PA) waves, in which the inertia (restoring force) is provided by the cold positron species (nonthermal pressure of both hot electron and positron species) has been theoretically investigated by deriving the nonlinear Schrödinger (NLS) equation. It is found from the numerical analysis of this NLS equation that the space plasma system under consideration supports the existence of both dark and bright envelope solitons associated with PA waves, and that the dark (bright) envelope solitons are modulationally stable (unstable). It is also observed that the basic properties (viz. stable regime and unstable regime with growth rate) of the PA envelope solitions are significantly modified by related plasma parameters (viz. number densities and temperature of plasma species), which correspond to different realistic space plasma situations.

physics.plasm-ph↗

arXiv2017

Self-gravito-acoustic shock signals in astrophysical compact objects

The existence of self-gravito-acoustic (SGA) shock signals (SSs) associated with negative self-gravitational potential in the perturbed state of the astrophysical compact objects (ACOs) (viz. white dwarfs, neutron stars, black holes, etc.) is predicted for the first time. A modified Burgers equation (MB), which is valid for both planar and non-planar spherical geometries, by the reductive perturbation method. It is shown that the longitudinal viscous force acting in the medium of any ACO is the source of dissipation, and is responsible for the formation of these SGA SSs. The time evolution of these SGA SSs is also shown for different values (viz. $0.5$, $1$, and $2$ ) of the ratio of nonlinear coefficient to dissipative coefficient in the MB equation. The theory presented here is so general that it can be applied in any ACO of planar or non-planar spherical shape.

physics.plasm-ph↗

arXiv2017

Nucleus-acoustic envelope solitons and their modulational instability in a degenerate quantum plasma system

The basic features of nucleus-acoustic (NA) envelope bright and dark solitons, which exist in degenerate quantum plasmas, have been theoretically investigated by deriving the nonlinear Schrödinger (NLS) equation. The reductive perturbation method, which is valid for a small but finite amplitude limit, is employed. It is found that the bright envelope solitons are modulationally unstable, whereas the dark ones are stable. It is also observed that the fundamental properties (viz. Modulational instability (MI) growth rate, width and energy concentration of NA waves, etc.) of NA unstable bright envelope solitons are significantly modified by constituent particles number density. The implications of our results obtained from our present investigation in astrophysical compact objects like white dwarfs and neutron stars are briefly discussed.

physics.plasm-ph↗

arXiv2017

Modulational instability and ion-acoustic envelope solitons in four component plasmas

Modulational instability (MI) of ion-acoustic waves (IAWs) has been theoretically investigated in a plasma system which is composed of inertial warm adiabatic ions, isothermal positrons, and two temperature superthermal electrons. A nonlinear Schrödinger (NLS) equation is derived by using reductive perturbation method that governs the MI of the IAWs. The numerical analysis of the solution of NLS equation shows the existence of both stable (dark envelope solitons exist) and unstable (bright envelope solitons exist) regimes of IAWs. It is observed that the basic features (viz. stability of the wave profile and MI growth rate) of the IAWs are significantly modified by the superthermal parameter ($κ$) and related plasma parameters. The results of our present investigation should be useful for understanding different nonlinear phenomena in both space and laboratory plasmas.

physics.plasm-ph↗

arXiv2017

Heavy ion-acoustic rogue waves in electron-positron multi-ion plasmas

The nonlinear propagation of heavy-ion-acoustic (HIA) waves (HIAWs) in a four component multi-ion plasma (containing inertial heavy negative ions and light positive ions, as well as inertialess nonextensive electrons and positrons) has been theoretically investigated. The nonlinear Schrödinger (NLS) equation is derived by employing the reductive perturbation method. It is found that the NLS equation leads to the modulational instability (MI) of HIAWs, and to the formation of HIA rogue waves (HIARWs), which are due to the effects of nonlinearity and dispersion in the propagation of HIAWs. The conditions for MI of HIAWs, and the basic properties of the generated HIARWs are identified. It is observed that the striking features (viz. instability criteria, growth rate of MI, amplitude and width of HIARWs, etc.) of the HIAWs are significantly modified by effects of nonextensivity of electrons and positrons, ratio of light positive ion mass to heavy negative ion mass, ratio of electron number density to light positive ion number density, and ratio of electron temperature to positron temperature, etc. The relevancy of our present investigation to the observations in the space (viz. cometary comae and earth's ionosphere) and laboratory (laser plasma interaction experimental devices) plasmas is pointed out.

physics.plasm-ph↗

arXiv2017

Self-gravitational solitary waves in astrophysical compact objects

The condition for the existence of self-gravitational solitary waves (SGSWs), and their polarity in any astrophysical compact object are theoretically found for the first time. The pseudo-potential approach, which is valid for arbitrary amplitude SGSWs, is emplyed. The general analytical results are applied in white dwarfs and neutron stars to identify the basic features (polarity, amplitude, and width) of the SGSWs formed in them. It found for the first time that the SGSWs exist with negative self-gravitational potential in perturbed states of white dwarfs and neutron stars. It is also estimated that for their typical degenerate plasma parmeters, the amplitude and the width of the SGSWs (moving with the speed 2 cm/s) in white dwarfs are $\sim -1.5$ ergs/gm and $\sim 50$ cm, respectively, and those of the SGSWs (moving with the speed $\sim 27$ m/s) in neutron stars are $\sim -7.76\times 10^4$ Joules/kg, and $5.5$ km, respectively.

physics.plasm-ph↗