Noble P Abraham | Mar Thoma College, Tiruvalla (original) (raw)

Papers by Noble P Abraham

Dust ion acoustic solitons is studied in a plasma composed of pair-ions (positively and negativel... more Dust ion acoustic solitons is studied in a plasma composed of pair-ions (positively and negatively charged hydrogen ions), dust (positively and negatively charged) and electrons (cold and super thermal). The non-linear studies are done by using the reductive perturbation method. The K-dV equation and its solution, thus obtained, are numerically analyzed by using the parameters observed at comet Halley by the Vega spacecraft. The results show that only rarefactive solitons can exist in such a plasma environment. The characteristics of the soliton is sensitive to the densities of positive ion and positive dust and its charge number than the concentrations of negative ions and negative dust. The soliton amplitude increases with an increase in spectral index (κ) of the hot electrons.

Advances in Space Research, 2015

ABSTRACT The two potential theory of Hasegawa has been used to derive the dispersion relation for... more ABSTRACT The two potential theory of Hasegawa has been used to derive the dispersion relation for the kinetic Alfven wave (KAW) in a plasma composed of hydrogen, oxygen and electrons. All three components have been modeled by ring distributions (obtained by subtracting two Maxwellian distributions with different temperatures) with the hydrogen and electrons drifting, respectively, with velocities VdH and Vde. For the most general case, the dispersion relation is a polynomial equation of order five; it reduces to a relation which supports only one mode when VdH = 0. For typical parameters at comet Halley, we find that both VdH and Vde can drive the wave unstable; the KAW is thus driven unstable in a current-less plasma. Such an instability was found for the ion acoustic wave by Vranjes et al. (2009).

V and dH V + , respectively, along the ambient magnetic field and positively and negatively charg... more V and dH V + , respectively, along the ambient magnetic field and positively and negatively charged oxygen ions constitute the plasma under consideration. This composition very well approximates the plasma environment around a comet. Analytical expressions for the frequency and growth / damping rate of the EIC waves around the higher harmonics of hydrogen ion gyrofrequency have been derived. The EIC waves propagate at frequencies around the harmonics of the hydrogen ion gyrofrequency and the wave growth decreases rapidly for higher harmonics. We find that, the wave can be driven unstable by the hydrogen ion drift velocity dH V + alone, at small k⊥ρLH+ as well as electron drift velocity de V at large LH k ρ ⊥ + . Also, the growth rate is dependent on the densities and temperature anisotropies of the various constituent ions.

Abstr act: The ion-acoustic (IA) wave is a mode that is easily excited when the electron streamin... more Abstr act: The ion-acoustic (IA) wave is a mode that is easily excited when the electron streaming velocity exceeds the ion-acoustic phase speed. We study the stability of this wave when streaming quasi-neutral electron-ion plasma passes through another quasineutral pair-ion electron target plasma. Such a situation occurs when the solar wind (the streaming component consisting of hydrogen (H+) and solar wind electrons (`se' )) flows past a comet. The cometary pair-ion electron plasma is composed of positively charged oxygen ions (O+), negatively charged oxygen ions (O-) and cometary electrons (`ce' ). All five constituents have been modeled by kappa distribution functions. We find that the growth rate of the IA wave, which occurs under zero-current conditions, decreases with increasing spectral indices of the kappa distributions. The growth rate which increases with increasing O+ and O- densities and electron flow speeds, decreases with increasing hydrogen densities.

Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory pl... more Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of Alfven waves in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species has been modeled by drifting distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution is simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies * cH w w + < (* w and + cH w being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the peak growth rate increases with increasing negatively charged oxygen ion densities. On the other hand, for frequencies * , cO cO w w w + -< (cO w being the oxygen ion gyro-frequencies) the region of...

Abstract: We investigate the existence of solitary waves in a five component dusty plasma. Positi... more Abstract: We investigate the existence of solitary waves in a five component dusty plasma. Positively and negatively charged dust, kappa function described photo-electrons, hot electrons and ions form the five components. The Kd-V equation is derived and the solutions plotted for different physical parameters. It is seen that different physical parameters affect the amplitude of the solitary structures differently. As the temperature of negative dust increases, the amplitude of the solitary structure increases. With the increase of positve dust number densities, the amplitude of the solitary structure decreases whereas its amplitude increases with an increase of hydrogen ion densities.

OALib, 2014

We study the stability of the ion-acoustic (IA) wave in a collisional plasma composed of hydrogen... more We study the stability of the ion-acoustic (IA) wave in a collisional plasma composed of hydrogen, positively and negatively charged oxygen ions, electrons and neutral atoms. This composition approximates very well the plasma environment around a comet. A solution of the dispersion relation yields a frequency for the IA wave at around the hydrogen plasma frequency. The growth/ damping rate is sensitively dependent on the ring parameters s u ⊥ (the ring speed) and ts v (the thermal spread). The growth rate of the wave, which decreases with increasing collisional frequencies, is larger when s ts u v ⊥ < . In the presence of negatively charged oxygen ions, the phase and group velocities of the IA wave behave in a contrasting manner when s ts u v ⊥ < (and viceversa). We propose that this behaviour be exploited as a diagnostic tool for the detection of these ions and also their thermalization.

Proc. 25th meeting of ASI (2007), …, 2008

Analysis of the density power spectra of molecular clouds seem to indicate similarity with that o... more Analysis of the density power spectra of molecular clouds seem to indicate similarity with that of super-Alfv'enic turbulence with index approx -2.7 for the column density power spectrum. Using a set of various realizations of a set of density fields having various values for the power ...

Proc. 25th meeting of ASI ( …, 2008

ABSTRACT Effect of cosmological fermionic fields in cosmology with and without Gauss-Bonnet term ... more ABSTRACT Effect of cosmological fermionic fields in cosmology with and without Gauss-Bonnet term is studied. We find inflationary scenarios with multiple inflationary eras and late time acceleration.

Journal of Astrophysics, 2013

We have, in this paper, studied the stability of the ion-acoustic wave in a plasma composed of hy... more We have, in this paper, studied the stability of the ion-acoustic wave in a plasma composed of hydrogen, positively and negatively charged oxygen ions, and electrons, which approximates very well the plasma environment around a comet. Modelling each cometary component (H + , O + , and O − ) by a ring distribution, we find that ion-acoustic waves can be generated at frequencies comparable to the hydrogen ion plasma frequency. The dispersion relation has been solved both analytically and numerically. We find that the ratio of the ring speed ( ⊥ ) to the thermal spread (V ts ) modifies the dispersion characteristics of the ion-acoustic wave. The contrasting behaviour of the phase velocity of the ion-acoustic wave in the presence of O − ions for ⊥ > V ts (and vice versa) can be used to detect the presence of negatively charged oxygen ions and also their thermalization.

Astrophysics and Space Science, 2014

ABSTRACT A popular model of a cometary plasma is hydrogen (H+) with positively charged oxygen (O+... more ABSTRACT A popular model of a cometary plasma is hydrogen (H+) with positively charged oxygen (O+) as a heavier ion component. However, the discovery of negatively charged oxygen (O−) ions enables one to model a cometary plasma as a pair-ion plasma (of O+ and O−) with hydrogen as a third ion constituent. We have, therefore, studied the stability of the ion-acoustic wave in such a pair-ion plasma with hydrogen and electrons streaming with velocities VdH+ and V de , respectively, relative to the oxygen ions. We find the calculated frequency of the ion-acoustic wave with this model to be in good agreement with the observed frequencies. The ion-acoustic wave can also be driven unstable by the streaming velocity of the hydrogen ions. The growth rate increases with increasing hydrogen density nH+ , and streaming velocities VdH+ and V de . It, however, decreases with increasing oxygen ion densities nO+ and nO− .

Earth, Moon, and Planets, 2014

ABSTRACT We have studied the stability of the electrostatic electron cyclotron wave in a plasma c... more ABSTRACT We have studied the stability of the electrostatic electron cyclotron wave in a plasma composed of hydrogen, oxygen and electrons. To conform to satellite observations in the low latitude boundary layer we model both the ionic components as drifting perpendicular to the magnetic field. Expressions for the frequency and the growth rate of the wave have been derived. We find that the plasma can support electron cyclotron waves with a frequency slightly greater than the electron cyclotron frequency ω_ce ; these waves can be driven unstable when the drift velocities of both the ions are greater than the phase velocity of the wave. We thus introduce another source of instability for these waves namely multiple ion beams drifting perpendicular to the magnetic field.

International Journal of Modern Physics A, 2010

In this work, a cosmological model inspired by string theory with Gauss-Bonnet term coupled to th... more In this work, a cosmological model inspired by string theory with Gauss-Bonnet term coupled to the fermionic field is taken into consideration. The self-interaction potential is considered as a combination of the scalar and pseudo-scalar invariants. Here the cosmological contribution of the coupling of Gauss-Bonnet term with a non-Dirac fermionic field--characterized by an \textit{interaction term}$L_{DG} ^2$-- is investigated. It is observed that the new type of coupling plays a significant role in the accelerating behavior of the universe. Specifically, in addition to the late time acceleration for the universe, LDG2L_{DG} ^2LDG2 produces an early decelerating behavior. The behavior of the equation-of-state parameter (w)(w)(w) is such that it guarantees the stability of the theory.