Sweta Srivastava

Growth of embryonic dust particles in a complex plasma

A model describing the growth of embryonic dust grains on account of accretion of neutral atoms and positively charged ionic species in a complex plasma has been developed. In deference to the recent emphasis on the character of the openness in complex plasma, the investigation is based on the balance of the number density and energy of electrons, ions, and neutral particles as well as the energy balance of the dust particles and the charge neutrality condition. To discuss the kinetics of the growth of the size of dust the processes of accretion of electrons, ions, and neutral species on the dust particles, the ionization of neutral atoms, and recombination of electrons and ions, and the elastic collisions between the constituent species of the dusty plasma have been considered; the energy exchange associated with these processes has also been taken into account. The dependence of the growth of dust particles and other relevant parameters on number density of embryonic dust grains has, in particular, been explored.

Fluctuation of Charge on Dust Particles in a Complex Plasma

This paper presents an analytical model for the evaluation of the fluctuation of the charge on the dust particles in a complex plasma. In contrast to earlier analyses, which ignored the effect of dust particles on density and temperature of electrons and ions, the present model takes into account the number and energy balance of electrons and ions. Three cases, viz., (i) no emission, (ii) thermionic emission, and (iii) photoelectric emission of electrons from the dust particles, have been considered. The results have been graphically illustrated for typical parameters. It is seen that the plasma parameters, and hence the fluctuations, are considerably affected by the consideration of number and energy balance of electrons and ions. A comparison of the results of the present analysis with those of earlier works has also been made.

Hysteresis in photoelectric charging of dust particles in a complex plasma

Starting with the basic equations of number and energy balance along with charge neutrality it is shown that the charge on the particle versus irradiance of incident radiation plot in a complex plasma, illuminated by radiation with periodic irradiance displays hysteresis.

Charge distribution of particles in an irradiated dust cloud

This communication is a discussion on the charge distribution of the dust particles in an illuminated dust cloud in near space when the photoelectric emission is the dominant mechanism for electron generation. An analytical model has been developed on the basis of charge neutrality condition and balance of number density and energy of electrons; the approach of statistical mechanics has been followed. Computations correspond to a metallic dust cloud in near space environment, where Lyman-α spectral line radiation is the dominant one for photoelectric emission. A comparison of results from the present statistical theory of charge distribution with the uniform charge theory has been presented. As an interesting conclusion, the theory predicts negative charging of a few dust particles for a certain range of parameters leading to the formation of bigger particles on account of electrostatic attraction between oppositely charged particles.

Photoelectric field emission of electrons: Photon assisted tunneling

This note is a discussion of the enhancement in electric field emission of electrons from a plane metallic surface on irradiation by light. The enhancement in the tunneling coefficient of an electron by absorption of a photon and the consequent increase in the field emission current has been evaluated. A discussion of the results and possible applications concludes the presentation. In particular it is suggested that this phenomenon may be an explanation for the observed increase in photoelectric current with increasing magnitude of negative potential of lunar dust grain simulants.

Effect of a novel nonlinearity, viz., electron temperature dependence of electron-ion recombination on electromagnetic wave. Plasma interaction: Nonlinear propagation in the E-layer

In this paper, we consider the nonlinearity in the propagation of electromagnetic (e.m.) waves in a plasma caused by the electron temperature dependence of the coefficient of recombination of electrons with ions; specifically, the ionospheric E layer has been investigated. The enhancement in electron temperature by an intense electromagnetic wave causes reduction of the electron-ion recombination coefficient and thereby enhancement of electron density, the electron collision frequency also gets enhanced. The equations for number and energy balance of electrons and the wave equation have been used to predict the dependence of electron density/collision frequency and the nonlinear refractive index and absorption coefficient on αE02 (proportional to wave irradiance). The dependence of the propagation parameters on αE02 has been used to investigate the nonlinear electromagnetic wave propagation in the ionosphere. The study concludes that the electron temperature dependence of the recombination coefficient sho...

Modification of ionospheric electron density by dust suspension

On the basis of a dynamic analysis the effectiveness of dust suspension for the reduction and enhancement of electron density in the E-layer of the ionosphere has been investigated in this paper. The analysis is based on the modelling of the E-layer as the Chapman α layer (validated earlier); the electron/ion production function, arrived at by Chapman and effective electron temperature-dependent electron–ion recombination coefficients in agreement with observations have been used. The balance of the charge on the particles and the number/energy balance of the constituents have been taken into account. The following is the physics of the change in electron density in the ionosphere by the suspension of dust. First, the dust provides a source (emission) and sink (accretion) of electrons. Second, the dust emits photoelectrons with energies much higher than those of ambient electrons, which enhances the electron temperature, leading to a reduced electron–ion recombination coefficient, and thus to a higher electron density. An interplay of these processes and the natural processes of electron production/annihilation determines the electron density and temperature in the dust suspension in the ionosphere. The numerical results, corresponding to suspension of dust of silicate (high work function) and Cs coated bronze (low work function) in the E-layer at are presented and discussed.

Nonequillibrium Effective Conductivity of a Seeded Noble Gas Flowing in a Magnetic Field

A method to compute the effective conductivity of argon, seeded with K (flowing in a magnetic field has been worked out with segmented electrodes) as a function of pressure and temperature of the gas and the induced electric field (KVB); the duct is assumed to have segmented electrodes. It is seen that for a given (KVB), the dependence of the effective conductivity on pressure and temperature of the gas is empirically given by a close fitting power law. Such a relation will considerably simplify the analysis of the flow of a seeded gas in a magnetic field. In contrast to earlier analyses, based on the phenomenological theory, this paper is based on the expressions, obtained from the solution of Boltzmann’s transfer equation. The computations correspond to the optimum seeding ratio of 0.02 for maximum conductivity.

Thermionic and photoelectric emission of electrons from positively charged particles in a plasma with Debye shielding

By utilizing the recent concept [G. Delzanno et al., Phys. Plasmas 12, 062102 (2005) and G. Delzanno and X. Tang, Phys. Rev. Lett. 113, 035002 (2014)] that the radial potential, experienced by an electron in the vicinity of a positively charged spherical particle depends on the transverse momentum of the electron, we have evaluated the rate of thermionic and photoelectron emission from a positively charged spherical particle and the corresponding average electron energy in a plasma, with Debye Screening. The effect of screening is manifested in the magnitude of a maximum in the radial potential energy versus r curve and is characterized by a parameter β which depends solely on (r0/λ). Simple expressions for the change in the rates of emission and corresponding electron energy due to inclusion of the mechanism (mentioned above) in the analysis have been derived. The results of numerical computations have been presented and discussed. Simple expressions for the rates of electron emission from positively cha...

Computational Characterization of Proteins Involved in Banana (Musa acuminata) Ripening

In fact, Banana contains a high level of easily digestible natural sugars in both their fresh and dried forms, which it releases quickly in the blood stream. It has an immense nutritional value and medicinal properties apart from be- ing an effective face pack. Any edible part of the plant, be it fruit, flower or stem, provides energy, vitamins and minerals. Cholesterol and fat content is minimal. Banana has the ability to correct acidity, gastritis and peptic ulcer. It is claimed that banana stimulates mucus production by stomach lining. Research shows that bananas contain certain enzyme inhibi- tors which are reported to be effective in controlling blood pressure in hypertensive people. Bananas are harvested when still green in order to better withstand transportation and to slow down the natural ripening process because of several weeks travel from the production areas to the end markets. There are a number of enzymes involved in the ripening proc- ess. The present work is principally aimed to computational study of these enzymes in view of understanding the ripening mechanism. The domains (conserved, 3- dimension region) of the specific enzymes, are identified using a computational tool, CDART (Conserved Domain Architecture Retrieval Tool). As a consequence, Aspartate aminotransferase (AAT_Like), Glycosyl hydrolase (Glyco_Hydr) and oxoglutarate (20G_Fe) were found to be the most conserved followed by Ethylene insensitive (EIN3), GT1, DPBB & Pollen in banana ripening proteins. The data, thus, obtained provide new insights in order to understand the stage specific role of the enzyme-proteins in the ripening process.