| 1. |
- Abdelsalam, UM, et al.
(författare)
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Ion-acoustic solitary waves in a dense pair-ion plasma containing degenerate electrons and positrons
- 2008
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Ingår i: Physics Letters A. - Amsterdam : Elsevier. - 0375-9601 .- 1873-2429. ; 372:22, s. 4057-4061
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Tidskriftsartikel (refereegranskat)abstract
- Fully nonlinear propagation of ion-acoustic solitary waves in a collisionless dense/quantum electron-positron-ion plasma is investigated. The electrons and positrons are assumed to follow the Thomas-Fermi density distribution and the ions are described by the hydrodynamic equations. An energy balance-like equation involving a Sagdeev-type pseudo-potential is derived. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The small-but finite-amplitude limit is also considered and an exact analytical solution is obtained. The present studies might be helpful to understand the excitation of nonlinear ion-acoustic solitary waves in a degenerate plasma such as in superdense white dwarfs.
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| 2. |
- Abdelsalam, UM, et al.
(författare)
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Localized electrostatic excitations in a Thomas-Fermi plasma containing degenerate electrons
- 2008
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Ingår i: Physics of Plasmas. - Melville : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- By using the Thomas-Fermi electron density distribution for quantum degenerate electrons, the hydrodynamic equations for ions, and the Poisson equation, planar and nonplanar ion-acoustic solitary waves in an unmagnetized collisionless plasma are investigated. The reductive perturbation method is used to derive cylindrical and spherical Korteweg-de Vries equations. Numerical solutions of the latter are presented. The present results can be useful in understanding the features of small but finite amplitude localized ion-acoustic solitary pulses in a degenerate plasma.
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| 3. |
- Ali, S, et al.
(författare)
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Wake potential with mobile positive/negative ions in multicomponent dusty plasmas
- 2008
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Ingår i: Physics Letters A. - Amsterdam : Elsevier. - 0375-9601 .- 1873-2429. ; 372:44, s. 6650-6652
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Tidskriftsartikel (refereegranskat)abstract
- We employ the test charge approach to calculate the electrostatic potential for a test charge in a multicomponent dusty plasma, whose constituents are the Boltzmann distributed electrons, mobile positive and negative ions, and immobile positive/negative charged dust particles. By using the modified dielectric constant of the dust-ion-acoustic (DIA) waves, the Debye screening and wake potentials are obtained. It is found that the presence of mobile negative ions significantly modify the DIA speed and the wake potential. The present results are relevant to polar mesosphere and microelectronic in the context of charged particle attraction and repulsion.
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| 4. |
- El-Taibany, WF, et al.
(författare)
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On the instability of electrostatic waves in a nonuniform electron-positron magnetoplasma
- 2008
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Ingår i: Physics Letters A. - Amsterdam : Elsevier. - 0375-9601 .- 1873-2429. ; 372:22, s. 4067-4075
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Tidskriftsartikel (refereegranskat)abstract
- The dispersion properties of three-dimensional electrostatic waves in a nonuniform electron-positron (EP) magnetoplasma are analyzed. A new dispersion relation is derived by use of the electron and positron density responses arising from the electron and positron continuity and Poisson equations. In the local approximation, the dispersion relation admits two wave modes with different velocities. The growth rates of various modes are illustrated both analytically and numerically. Considering the temperature gradients produces a linearly stable transverse mode. The growth rate of the slow mode instability due to the density inhomogeneity only is the highest one, though it appears at higher thermal energy. The angle of the wave propagation affects drastically on the instability features in each case. The applications of the present analysis are briefly discussed.
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| 5. |
- Mishra, A, et al.
(författare)
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Diminishing benefits of urban living for children and adolescents' growth and development
- 2023
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 615:7954, s. 874-883
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Tidskriftsartikel (refereegranskat)abstract
- Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.
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| 6. |
- Moslem, WM, et al.
(författare)
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Finite amplitude envelope surface solitons
- 2008
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Ingår i: Physics of Plasmas. - Melville : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 15:4
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Tidskriftsartikel (refereegranskat)abstract
- Known results on the nonlinear coupling of surface plasma waves with quasistationary ion density perturbations are generalized to include finite amplitude density modulations. A more rigorous analytical criterion is provided for the existence of the surface soliton, by using the pseudopotential formalism. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The present results are useful in understanding the nonlinear dynamics and the periodic oscillatory structures on plasma surfaces.
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| 7. |
- Moslem, WM, et al.
(författare)
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Solitary and blow-up electrostatic excitations in rotating magnetized electron-positron-ion plasmas
- 2009
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Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear dynamics of a rotating magnetoplasma consisting of electrons, positrons and stationary positive ions is considered. The basic set of hydrodynamic and Poisson equations are reduced to a Zakharov-Kuznetsov (ZK) equation for the electric potential. The ZK equation is solved by applying an improved modified extended tanh-function method (2008 Phys. Lett. A 372 5691) and its characteristics are investigated. A set of new solutions are derived, including localized solitary waves, periodic nonlinear waveforms and divergent (explosive) pulses. The characteristics of these nonlinear excitations are investigated in detail.
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| 8. |
- Moslem, WM, et al.
(författare)
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Solitary, explosive, and periodic solutions of the quantum Zakharov-Kuznetsov equation and its transverse instability
- 2007
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Ingår i: Physics of Plasmas. - Melville : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 14:8
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Tidskriftsartikel (refereegranskat)abstract
- By employing the quantum hydrodynamic model and the reductive perturbation technique, a quantum Zakharov-Kuznetsov (QZK) equation is derived for finite but small amplitude ion-acoustic waves in a quantum magnetoplasma. The extended Conte's truncation method is used to obtain the solitary, explosive, and periodic solutions of the QZK equation. Furthermore, the stability of the solitary wave solution of the QZK equation is investigated by using the small-k perturbation expansion method.
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| 9. |
- Moslem, WM, et al.
(författare)
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The optimum shielding around a test charge in plasmas containing two negative ions
- 2011
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Ingår i: Journal of Plasma Physics. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 77:5, s. 663-673
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on the progress in understanding the shielding around a test charge in the presence of ion-acoustic waves in multispecies plasmas, whose constituents are positive ions, two negative ions, and Boltzmann distributed electrons. By solving the linearized Vlasov equation with Poisson equation, the Debye-Huckel screening potential and wakefield (oscillatory) potential distribution around a test charge particle are derived. It is analytically found that both the Debye-Huckel potential and the wakefield potential are significantly modified due to the presence of two negative ions. The present results might be helpful to understand and to form new materials from plasmas containing two negative ions such as Xe(+) - F(-) - SF(6)(-) and Ar(+) - F(-) - SF(6)(-) plasmas, as well as to tackle extension of the test charge problem in multinegative ions' coagulation/agglomeration.
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| 10. |
- Sabry, R, et al.
(författare)
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Cylindrical and spherical ion-acoustic envelope solitons in multicomponent plasmas with positrons
- 2009
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American physical society. - 1539-3755 .- 1550-2376. ; 79:5
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear wave modulation of planar and nonplanar (cylindrical and spherical) ion-acoustic envelope solitons in a collisionless unmagnetized electron-positron-ion plasma with two-electron temperature distributions has been studied. The reductive perturbative technique is used to obtain a modified nonlinear Schrodinger equation, which includes a damping term that accounts for the geometrical effect. The critical wave number threshold K(c), which indicates where the modulational instability sets in, has been determined for various regimes. It is found that an increase in the positron concentration (alpha) leads to a decrease in the critical wave number (K(c)) until alpha approaches certain value alpha(c) (critical positron concentration), then further increase in alpha beyond alpha(c) increases the value of K(c). Also, it is found that there is a modulation instability period for the cylindrical and spherical wave modulation, which does not exist in the one-dimensional case.
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