Electrostatic Potential Structure Research Articles

Nonlinear electrostatic periodic waves and solitons in an inhomogeneous magnetized dusty plasma

Low frequency nonlinear electrostatic cnoidal and solitary waves are investigated in an inhomogeneous magnetized dusty plasma in the presence of shear flow. The Sagdeev potential approach is used to find the nonlinear wave solution. It is found that nonlinear electrostatic potential rarefactive (dip) structures are formed for cnoidal waves and solitons in a magnetized inhomogeneous dusty plasma instead of compressive (hump) nonlinear electrostatic wave structures formed in an inhomogeneous magnetized electron-ion plasma. The amplitude of the nonlinear electrostatic potential structure is found to be increased in the case of decreasing shear flow parameter values in comparison with the case of increasing shear flow parameter values. The D'Angelo instability in an inhomogeneous magnetized dusty plasma in the presence of shear flow is also discussed. The numerical plots are also presented for illustrations which are applicable to space dusty plasma regions containing shear flows. The Hamiltonian function of such a dynamical planar system is also discussed for its phase portrait analysis.

Non-Linear Ion-Acoustic Solitary Waves in Electron-Positron-Ion Plasma with Non-Thermal Electrons

Ion-acoustic solitary (IAS) waves in electron-positron-ion (e-p-i) plasma have been of interest to many researchers probably due to their relevance in understanding the Universe. However, the study of non-linear ion-acoustic waves in e-p-i plasma with non-thermal electrons has not been adequately studied. A theoretical investigation on non-linear IAS waves in e-p-i plasma comprising of warm inertial adiabatic fluid ions and electrons that are kappa distributed, and Boltzman distributed positron is presented here using the Sagdeev potential technique. It was found that existence domains of finite amplitude IAS waves were confined within the limits of minimum and maximum Mach numbers with varying k values. For lower values of k, the amplitude of the solitary electrostatic potential structures increased as the width decreased, while for high values, the potential amplitude decreased as the width of the solitary structure increased.

THE INVESTIGATION OF SPECTROSCOPIC AND THEORETICAL METHODS OF BISISOXAOLINE DERIVATIVE OF NORBORNADIEN

In this study, the synthesis of bisisoxaoline derivative of norbornadien from heterocyclic compounds was performed via 1,3-dipolar cycloaddition reaction, the structural properties of derivative characterized by spectroscopic analysis such as FT-IR, 1 H-NMR, 13 C-NMR, UV-Vis and the single-crystal X-ray diffraction technique. The 3,7-bis(4-(tert-butyl)phenyl)-3a,4,4a,7a,8,8a-hexahydro-4,8-methanobenzo[1,2-d:4,5-d’]diisoxazole compound was optimized using Density Functional Theory (DFT/B3LYP) method with 6-311G(d,p) basis set in the ground state and the geometric parameters compared with single-crystal X-ray diffraction technique. The compound crystallizes in the monoclinic space group C2/c with a = 20.634(4) Å, b = 11.179(2) Å, c = 11.0690(17) Å and Z = 4 unit cell parameters. Also, the spectral results were examined with calculated vibrational frequencies, 1 H-NMR, 13 C-NMR chemical shift values and absorption wavelengths, theoretically. The energetic behaviour of the compound in different solvent media was examined with TD-DFT/B3LYP method and 6-311G(d,p) basis set using the Conductor Polarizable Continuum Model (CPCM). The frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) and electronic structure parameters (dipole moment, electronegativity, chemical hardness-softness, ionization potential, electron affinity, etc.) were examined to get information about the chemical stability of the structure.

Nonlinear ion-acoustic solitons in a magnetized quantum plasma with arbitrary degeneracy of electrons.

Nonlinear ion-acoustic waves are analyzed in a nonrelativistic magnetized quantum plasma with arbitrary degeneracy of electrons. Quantum statistics is taken into account by means of the equation of state for ideal fermions at arbitrary temperature. Quantum diffraction is described by a modified Bohm potential consistent with finite-temperature quantum kinetic theory in the long-wavelength limit. The dispersion relation of the obliquely propagating electrostatic waves in magnetized quantum plasma with arbitrary degeneracy of electrons is obtained. Using the reductive perturbation method, the corresponding Zakharov-Kuznetsov equation is derived, describing obliquely propagating two-dimensional ion-acoustic solitons in a magnetized quantum plasma with degenerate electrons having an arbitrary electron temperature. It is found that in the dilute plasma case only electrostatic potential hump structures are possible, while in dense quantum plasma, in principle, both hump and dip soliton structures are obtainable, depending on the electron plasma density and its temperature. The results are validated by comparison with the quantum hydrodynamic model including electron inertia and magnetization effects. Suitable physical parameters for observations are identified.

Electrostatic fluctuations in a magnetized two-component plasma with q-nonextensive electrons and thermal ions

The effect of ion temperature on nonlinear low frequency electrostatic potential structures is studied in a two component magnetized plasma with q-nonextensive hot electrons. The standard Sagdeev pseudo-potential approach is used to investigate the existence of ion acoustic solitons and double layers and their dependence on finite ion temperature. Only solitons are found to exist, with the amplitude decreasing as the ion temperature increases. For parameters typical of the auroral plasma, our model yields a soliton electric field amplitude of 22 mV/m, which is within the range measured by satellites, and as such can be helpful in understanding the electrostatic fluctuations phenomena in space environments.

Synthesis, Z-Scan and Degenerate Four Wave Mixing characterization of certain novel thiocoumarin derivatives for third order nonlinear optical applications

The third order nonlinear optical features of certain novel thiocoumarin derivatives have been studied. Single beam Z-scan study on these compounds reveals that the compounds exhibit self defocusing effect upon irradiation with 532 nm, 7 ns pulses of Nd:YAG laser. Nonlinear absorption coefficient, nonlinear refractive index and second-order molecular hyperpolarizability values were estimated. The optical power limiting properties of the compounds are found to be attributable to both two-photon and excited state absorption. Some of the samples show nonlinear absorption coefficient (βeff) as high as 24.5 cm/GW. UV–Visible and photoluminescence outputs of these compounds reveal remarkable absorptive and emissive properties. This article also reports extraordinary growth of third order optical nonlinearity in pure coumarin upon certain donor substitutions in lieu of hydrogen. Degenerate Four Wave Mixing (DFWM) signals of the compounds were analyzed to verify the Z-scan results. Electrostatic Surface Potential (ESP) mapping and structure optimization techniques have been employed to interpret the structure-property relationship of each molecule.

Solitary waves in a self-gravitating opposite polarity dust-plasma medium

A more general and realistic dusty plasma model, namely, self-gravitating opposite polarity dust-plasma system (containing inertial positive and negative dust, and inertialess ions and electrons following Maxwellian distribution) is considered. The possibility for the formation of solitary electrostatic and self-gravitational potential structures in such a dust-plasma system is thoroughly examined. The standard reductive perturbation method, which is valid for small but finite amplitude solitary structures, is employed. The parametric regimes for the existence of solitary electrostatic and self-gravitational potential structures, and their basic properties (viz., polarity, amplitude, width, and speed) are found to be significantly modified by the combined effects of positively charged dust component and self-gravitational field. The applications of the present investigation in different space dusty plasma environments and laboratory dusty plasma devices are briefly discussed.

Imaging of built-in electric field at a p-n junction by scanning transmission electron microscopy.

Precise measurement and characterization of electrostatic potential structures and the concomitant electric fields at nanodimensions are essential to understand and control the properties of modern materials and devices. However, directly observing and measuring such local electric field information is still a major challenge in microscopy. Here, differential phase contrast imaging in scanning transmission electron microscopy with segmented type detector is used to image a p-n junction in a GaAs compound semiconductor. Differential phase contrast imaging is able to both clearly visualize and quantify the projected, built-in electric field in the p-n junction. The technique is further shown capable of sensitively detecting the electric field variations due to dopant concentration steps within both p-type and n-type regions. Through live differential phase contrast imaging, this technique can potentially be used to image the electromagnetic field structure of new materials and devices even under working conditions.

Interaction of a biased cylinder with a flowing dusty plasma

AbstractExperimental observations of supersonically flowing dusty plasmas and their interaction with an electrically biased circular cylinder are presented. Two methods for producing flowing dusty plasmas are described. The dusty plasma is produced in a DC anode glow discharge plasma. In Configuration I, a secondary dust cloud, initially formed near a biased grid, flowed away from the grid at supersonic speeds when the grid voltage was suddenly changed. In Configuration II, a pencil-like dust beam was produced using a nozzle-like (converging-diverging) electrostatic potential structure. Using Configuration I, the streaming dust encountered a biased cylinder (wire) whose axis was oriented transverse to the dust flow. The flowing dust particles were repelled by the electrostatic field of the negatively charged cylinder, and a dust void was formed around the cylinder. A detached electrohydrodynamic bow shock, akin to the Earth's magnetohydrodynamic bow shock, was formed on the upstream side of the cylinder, while an extended teardrop-shaped wake region was formed on the downstream side. Video imaging of the dust stream allowed for observations of the structure and evolution of the bow shock. Configuration II was used to produce a narrow beam of dust particles and observe how the beam was deflected around the biased cylinder. Three multimedia files (movies) of the observed phenomena are provided in the online Supplementary material.

Zakharov-Kuznetsov equation for ion acoustic waves with superthermal electrons in cylindrical geometry

The nonlinear wave structures of ion acoustic waves (IAWs) in a magnetized plasma with the combined effect of bounded cylindrical geometry and superthermal electrons and warm ions are studied. Using the standard reductive perturbation technique, the nonlinear cylindrical Zakharov-Kuznetsov (ZK) equation is derived for the propagation of ion acoustic solitary waves (IASWs). The influence of superthermal electrons and the effects caused by the cylindrical geometry on IAWs are investigated. It is shown that, in cylindrical geometry a new type of solitonlike structures appears as time goes by. It is also observed that a decrease in the superthermality of electrons (i.e., increasing κ) increases the amplitude of the solitary electrostatic potential structures. The numerical results are also presented to understand the formation of IASWs in relation with the plasma parameters in nonplanar geometry. The present investigation is of relevance in the study of propagation of IAWs in space and laboratory plasmas.

ELECTRON ACCELERATIONS AT HIGH MACH NUMBER SHOCKS: TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS IN VARIOUS PARAMETER REGIMES

Electron accelerations at high Mach number collision-less shocks are investigated by means of two-dimensional electromagnetic Particle-in-Cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron beta_e (the ratio of the thermal pressure to the magnetic pressure). We found electrons are effectively accelerated at a super-high Mach number shock (MA~30) with a mass ratio of M/m=100 and beta_e=0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with the large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely-high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

On the dynamics of vortex modes within magnetic islands

Recent work investigating the interaction of magnetic islands with micro-turbulence has uncovered the striking observation of large scale vortex modes forming within the island structure [W. A. Hornsby et al., Phys. Plasmas 17, 092301 (2010)]. These electrostatic vortices are found to be the size of the island and are oscillatory. It is this oscillatory behaviour and the presence of turbulence that leads us to believe that the dynamics are related to the geodesic acoustic mode (GAM), and it is this link that is investigated in this paper. Here, we derive an equation for the GAM in the MHD limit, in the presence of a magnetic island modified three-dimensional axisymmetric geometry. The eigenvalues and eigenfunctions are calculated numerically and then utilised to analyse the dynamics of oscillatory large-scale electrostatic potential structures seen in both linear and non-linear gyro-kinetic simulations.

Kadomtsev–Petviashvili equation for acoustic wave in quantum pair plasmas

AbstractThe Kadomtsev–Petviashvili equation is derived for two-dimensional propagations of electrostatic solitons in unmagnetized dense pair-plasmas. The reductive perturbation method is employed and two-dimensional electrostatic potential hump structures are obtained. The conditions for a stable two-dimensional solitary structure are discussed using energy consideration method. The numerical results are also presented by considering the parameters for the outer layers of white dwarfs/neutron stars.

Nonplanar ion acoustic waves with kappa-distributed electrons

Using the standard reductive perturbation technique, nonlinear cylindrical and spherical Kadomtsev-Petviashvili equations are derived for the propagation of ion acoustic solitary waves in an unmagnetized collisionless plasma with kappa distributed electrons and warm ions. The influence of kappa-distributed electrons and the effects caused by the transverse perturbation on cylindrical and spherical ion acoustic waves (IAWs) are investigated. It is observed that increase in the kappa distributed electrons (i.e., decreasing κ) decreases the amplitude of the solitary electrostatic potential structures. The numerical results are presented to understand the formation of ion acoustic solitary waves with kappa-distributed electrons in nonplanar geometry. The present investigation may have relevance in the study of propagation of IAWs in space and laboratory plasmas.

Acoustic solitons in magnetized quantum electron–positron plasmas

Nonlinear acoustic wave propagation in dense magnetized electron–positron (e–p) plasmas in the presence of ions is studied. The e–p quantum fluid is taken to be dynamic, while the ions are assumed to be stationary to neutralize the plasma background only. The quantum hydrodynamics model is employed and the reductive perturbation method is used to derive the Zakharov–Kuznetsov equation. Electrostatic potential hump structures are obtained and it is found that an increase in positron concentration decreases the wave amplitude. However, an increase in magnetic field strength reduces the width of the structure significantly. The numerical results are also shown for illustration; the parameters used are taken from the data for the outer layers of white dwarfs.

Space-charge waves in a relativistic electron beam with ion-channel guiding

AbstractSpace-charge waves in a relativistic electron beam that completely fills a cylindrical metallic waveguide and is guided by an ion channel are analyzed numerically. Equilibrium consists of a uniform and rigid rotation without betatron oscillations. Using cold fluid equations a differential equation and boundary conditions are derived that constitute an eigenvalue problem. This eigenvalue problem is solved, numerically, with the finite difference scheme using shooting method. Dispersion characteristics and electrostatic potential structures of azimuthally symmetric and nonsymmetric space-charge waves are studied. Perfect agreement with analytical results at asymptotic limit of zero axial velocity is found. It was found that relativistic effects modify the dispersion characteristics of the space-charge waves considerably and can concentrate the electric field energy of the wave into a thin and small shell around the axis.

Solution Structure of an Active Mutant of Maize Ribosome-Inactivating Protein (MOD) and Its Interaction with the Ribosomal Stalk Protein P2

Ribosome-inactivating proteins (RIPs) are N-glycosidases that depurinate a specific adenine residue in the conserved sarcin/ricin loop of ribosomal RNA. This modification renders the ribosome unable to bind the elongation factors, thereby inhibiting the protein synthesis. Maize RIP, a type III RIP, is unique compared to the other type I and type II RIPs because it is synthesized as a precursor with a 25-residue internal inactivation region, which is removed in order to activate the protein. In this study, we describe the first solution structure of this type of RIP, a 28-kDa active mutant of maize RIP (MOD). The overall protein structure of MOD is comparable to those of the other type I RIPs and the A-chain of type II RIPs but shows significant differences in specific regions, including (1) shorter β6 and αB segments, probably for accommodating easier substrate binding, and (2) an α-helix instead of an antiparallel β-sheet in the C-terminal domain, which has been reported to be involved in binding ribosomal protein P2 in some RIPs. Furthermore, NMR chemical shift perturbation experiments revealed that the P2 binding site on MOD is located at the N-terminal domain near the internal inactivation region. This relocation of the P2 binding site can be rationalized by concerted changes in the electrostatic surface potential and 3D structures on the MOD protein and provides vital clues about the underlying molecular mechanism of this unique type of RIP.

Electrostatic Korteweg–de Vries solitons in pure pair-ion and pair-ion–electron plasmas

Linear and nonlinear electrostatic waves are studied in unmagnetized pure pair-ion (PI) and pair-ion–electron (PIE) plasmas. The nonlinear electrostatic potential structures are obtained using the reductive perturbation technique. It is found that potential hump and dip structures are obtained in pure PI plasmas, when there is a slight difference of temperature between positive and negative ions. The electrostatic potential humps are formed when the temperature of the negative ions is greater than that of the positive ions, while the potential dips are obtained in the reverse temperature condition of the plasma species. The electrostatic solitons are also obtained in the presence of electrons in PI plasmas. It is found that only potential dip structures are obtained in the PIE plasma case. The numerical results are also presented for illustration.

Electrostatic solitons in unmagnetized hot electron–positron–ion plasmas

Linear and nonlinear electrostatic waves in unmagnetized electron–positron–ion (e–p–i) plasmas are studied. The electrons and positrons are assumed to be isothermal and dynamic while ions are considered to be stationary to neutralize the plasma background only. It is found that both upper (fast) and lower (slow) Langmuir waves can propagates in such a type of pair (e–p) plasma in the presence of ions. The small amplitude electrostatic Korteweg–de Vries (KdV) solitons are also obtained using reductive perturbation method. The electrostatic potential hump structures are found to exist when the temperature of the electrons is larger than the positrons, while the electrostatic potential dips are obtained in the reverse temperature conditions for electrons and positrons in e–p–i plasmas. The numerical results are also shown for illustration. The effects of different ion concentration and temperature ratios of electrons and positrons, on the formation of nonlinear electrostatic potential structures in e–p–i plasmas are also discussed.

A non-linear model for elastic dielectric crystals with mobile vacancies

A framework is developed for electromechanical behavior of dielectric crystalline solids subjected to finite deformations. The theory is formulated in the context of electrostatics; however, vacancies in the lattice may carry an electric charge, and their concentrations may be large. The material is treated as a continuous body with a continuous distribution of point vacancies, but volumes and charges of individual defects enter the description. The deformation gradient is decomposed multiplicatively into terms accounting for recoverable thermoelasticity and irreversible volume changes associated with vacancies. Thermodynamic arguments lead to constitutive relations among electromechanical quantities framed in the elastically unloaded intermediate configuration, with the Cauchy stress tensor consistently non-symmetric as a result of electrostatic effects. The requirement of non-negative dissipation imposes constraints on vacancy migration. Following postulation of a quadratic form for the free energy potential, a kinetic equation for vacancy flux is derived in the intermediate configuration, with diffusion driven by gradients of vacancy concentration, electrostatic potential, hydrostatic pressure, and crystal structure. Effects of geometric non-linearity (i.e. finite elastic strains and large vacancy concentrations) are found to affect vacancy diffusion in a body subjected to biaxial lattice strain, for example a film device with lattice mismatch at its interfaces.