Effect of dust charge fluctuations on dust acoustic structures in magnetized dusty plasma containing nonextensive electrons and two-temperature isothermal ions

Effect of dust electrical charge fluctuations on the nature of dust acoustic solitary waves (DASWs) in a four-species magnetized dusty plasma containing nonextensive electrons and two-temperature isothermal ions has been investigated. In this model, the negative dust electric charge is considered to be proportional to the plasma space potential. The nonlinear Zakharov–Kuznetsov (ZK) and modified Zakharov–Kuznetsov (mZK) equations are derived for DASWs by using the standard reductive perturbation method. The combined effects of electron nonextensivity and dust charge fluctuations on the DASW profile are analyzed. The different ranges of the nonextensive q-parameter are considered. The results show that solitary waves the amplitude and width of which depend sensitively on the nonextensive q-parameter can exist. Due to the electron nonextensivity and dust charge fluctuation rate, our dusty plasma model can admit both positive and negative potential solitons. The results show that the amplitude of the soliton increases with increasing electron nonextensivity, but its width decreases. Increasing the electrical charge fluctuations leads to a decrease in both the amplitude and width of DASWs.     

Evolutionary sheath structure in magnetized collisionless plasma with electron inertia

A classical hydrodynamic model is methodologically formulated to see the equilibrium properties of a planar plasma sheath in two-component magnetized bounded plasma. It incorporates the weak but finite electron inertia instead of asymptotically inertialess electrons. The effects of the externally applied oblique (relative to the bulk plasma flow) magnetic field are judiciously accented. It is, for the sake of simplicity, assumed that the relevant physical parameters (plasma density, electrostatic potential, and flow velocity) vary only in a direction normal to the confining wall boundary. It is noticed for the first time that the derived Bohm condition for sheath formation is modified conjointly by the electron inertia, magnetic field, and field orientation. It is manifested that the electron inertia in the presence of plasma gyrokinetic effects slightly enhances the ion Mach threshold value (typically, M _i0 ≥ 1.139) toward the sheath entrance. This flow supercriticality is in contrast with the heuristic formalism (M _i0 ≥ 1) for the zero-inertia electrons. A numerical illustrative scheme on the parametric sheath features on diverse nontrivial apposite arguments is constructed alongside ameliorative scope.     

Rogue Waves in Multi-Ion Cometary Plasmas

The effect of pair ions on the formation of rogue waves in a six-component plasma composed of two hot and one colder electron component, hot ions, and pair ions is studied. The kappa distribution, which provides an unambiguous replacement for a Maxwellian distribution in space plasmas, is connected with nonextensive statistical mechanics and provides a continuous energy spectrum. Hence, the colder and one component of the hotter electrons is modeled by kappa distributions and the other hot electron component, by a q-nonextensive distribution. It is found that the rogue wave amplitude is different for various pair-ion components. The magnitude, however, increases with increasing spectral index and nonextensive parameter q. These results may be useful in understanding the basic characteristics of rogue waves in cometary plasmas.     

Nonlinear propagation of ion-acoustic waves through the Burgers equation in weakly relativistic plasmas

The Burgers equation is obtained to study the characteristics of nonlinear propagation of ionacoustic shock, singular kink, and periodic waves in weakly relativistic plasmas containing relativistic thermal ions, nonextensive distributed electrons, Boltzmann distributed positrons, and kinematic viscosity of ions using the well-known reductive perturbation technique. This equation is solved by employing the (G'/G)-expansion method taking unperturbed positron-to-electron concentration ratio, electron-to-positron temperature ratio, strength of electrons nonextensivity, ion kinematic viscosity, and weakly relativistic streaming factor. The influences of plasma parameters on nonlinear propagation of ion-acoustic shock, periodic, and singular kink waves are displayed graphically and the relevant physical explanations are described. It is found that these parameters extensively modify the shock structures excitation. The obtained results may be useful in understanding the features of small but finite amplitude localized relativistic ion-acoustic shock waves in an unmagnetized plasma system for some astrophysical compact objects and space plasmas.     

Small-amplitude shock waves and double layers in dusty plasmas with opposite polarity charged dust grains

Theoretical investigation is carried out for understanding the properties of nonlinear dust-acoustic (DA) waves in an unmagnetized dusty plasma whose constituents are massive, micron-sized, positive and negatively charged inertial dust grains along with q (nonextensive) distributed electrons and ions. The reductive perturbation method is employed in order to derive two types of nonlinear dynamical equations, namely, Burgers equation and modified Gardner equation (Gardner equation with dissipative term). They are also numerically analyzed to investigate the basic features (viz., polarity, amplitude, width, etc.) of shock waves and double layers. It has been observed that the effects of nonextensivity, opposite polarity charged dust grains, and different dusty plasma parameters have significantly modified the fundamental properties of shock waves and double layers. The results of this investigation may be used for researches of the nonlinear wave propagation in laboratory and space plasmas.     

Solitary waves in dusty plasmas with weak relativistic effects in electrons and ions

Two distinct classes of dust ion acoustic (DIA) solitary waves based on relativistic ions and electrons, dust charge Z _d and ion-to-dust mass ratio Q’ = m _i /m _d are established in this model of multicomponent plasmas. At the increase of mass ratio Q’ due to increase of relativistic ion mass and accumulation of more negative dust charges into the plasma causing decrease of dust mass, relativistic DIA solitons of negative potentials are abundantly observed. Of course, relativistic compressive DIA solitons are also found to exist simultaneously. Further, the decrease of temperature inherent in the speed of light c causes the nonlinear term to be more active that increases the amplitude of the rarefactive solitons and dampens the growth of compressive solitons for relatively low and high mass ratio Q’, respectively. The impact of higher initial streaming of the massive ions is observed to identify the point of maximum dust density N _d to yield rarefactive relativistic solitons of maximum amplitude.     

Transport processes in plasma with an admixture of several heavy impurities

A two-temperature magnetohydrodynamic model of an ideal, fully ionized magnetized plasma consisting of electrons and several types of ions is developed for the case in which the mass of ions of the first type is much lower than that of jth-type ions, where j = 2,3,…, m ₁ ? m _j, while the densities of heavy ions are so low that collisions between them can be neglected. The ion component is assigned a common velocity, common temperature, and common density, while its composition can vary in time and space.     

Nonlinear dust-acoustic structures in space plasmas with superthermal electrons,positrons, and ions

Some features of nonlinear dust-acoustic (DA) structures are investigated in a space plasma consisting of superthermal electrons, positrons, and positive ions in the presence of negatively charged dust grains with finite-temperature by employing a pseudo-potential technique in a hydrodynamic model. For this purpose, it is assumed that the electrons, positrons, and ions obey a kappa-like (κ) distribution in the background of adiabatic dust population. In the linear analysis, it is found that the dispersion relation yield two positive DA branches, i.e., the slow and fast DA waves. The upper branch (fast DA waves) corresponds to the case in which both (negatively charged) dust particles and (positively charged) ion species oscillate in phase with electrons and positrons. On the other hand, the lower branch (slow DA waves) corresponds to the case in which only dust particles oscillate in phase with electrons and positrons, while ion species are in antiphase with them. On the other hand, the fully nonlinear analysis shows that the existence domain of solitons and their characteristics depend strongly on the dust charge, ion charge, dust temperature, and the spectral index κ. It is found that the minimum/maximum Mach number increases as the spectral index κ increases. Also, it is found that only solitons with negative polarity can propagate and that their amplitudes increase as the parameter κ increases. Furthermore, the domain of Mach number shifts to the lower values, when the value of the dust charge Z _d increases. Moreover, it is found that the Mach number increases with an increase in the dust temperature. Our analysis confirms that, in space plasmas with highly charged dusts, the presence of superthermal particles (electrons, positrons, and ions) may facilitate the formation of DA solitary waves. Particularly, in two cases of hydrogen ions H⁺ (Z _i = 1) and doubly ionized Helium atoms He²⁺ (Z _i = 2), the mentioned results are the same. Additionally, the mentioned dusty plasma does not support DA solitons with positive polarity (compressive solitons). Furthermore, our analysis confirms that DA double layers cannot exist in such a system. Moreover, the positron density has not a considerable effect on the behavior of DA solitons in our model.     

Turbulent dynamics of helical perturbations in the edge plasma of the T-10 tokamak

Turbulent dynamics of the edge plasma in the T-10 tokamak is simulated numerically by solving nonlinear MHD equations in the framework of the four-field {?, n, p _e , p _i } reduced two-fluid Braginskii hydro-dynamics. It is shown that the transition from ohmic to electron-cyclotron heating is accompanied by a decrease in the amplitudes of turbulent fluctuations in plasma. This is caused by the enhancement of longitudinal dissipation due to the increase in the electron temperature. However, phase relations between potential fluctuations of different modes change in such a way that the Reynolds turbulent force increases, which leads to an increase in the poloidal velocity in the direction of ion diamagnetic drift. Since the poloidal and ion diamagnetic drift velocities enter into the equation of the radial force balance for ions with different signs, the radial electric field decreases. The simulation results agree qualitatively with the results of experiments in the T-10 tokamak. The dependence of the radial electric field on the plasma density, ion pressure, and neutral density is also calculated.     

Theoretical investigation of the bistability effect in non-self-sustained discharges in Kr and Ar

The electron energy distribution function and the related plasma parameters in non-self-sustained discharges in Kr and Ar are studied theoretically. The investigations are carried out by numerically solving the corresponding Boltzmann equation for the electron energy distribution function with allowance for electron-electron collisions. The electron energy distribution and electron density are calculated self-consistently as functions of the intensity q of the source of secondary electrons and the magnitude of the reduced electric field E/N. The main goal of the investigations was to determine the conditions under which the plasma exhibits bistable parameters. Calculations show that, for discharges in Kr, there is a certain range of q and E/N values in which the Boltzmann equation has two different stable solutions. For an Ar plasma, such a bistability effect was not found: over the parameter range under consideration, the Boltzmann equation has a unique solution. Various plasma parameters (such as the effective electron temperature, electron drift velocity, and electron current density) are calculated for different discharge conditions, including those corresponding to the bistability effect.     

Analysis of ionization and recombination processes under the coronal equilibrium conditions by using a statistical atomic model

Ionization and recombination processes accompanying collisions of free electrons with plasma ions are considered using a statistical atomic model in which ionization and recombination are regarded as the processes of pair electron collisions in the electron gas of an atom. An expression for the ionization rate as a function of the ionization energy I and temperature T is derived. According to this expression, the ionization rate at I ? T is proportional to exp(?I/T). The statistical atomic model provides an estimate of the recombination rate for an ion with an arbitrary nuclear charge number Z, whereas more exact calculations of the recombination rate can be performed only for large Z. The model explains relatively low values of I/T (as compared to those given by the Saha equation) under the coronal equilibrium conditions and predicts a reduction in I/T with increasing Z. The values of I/T and the average ion charge number obtained from the balance equation for multielectron ions with the use of one fitting coefficient agree with the tabulated data calculated in the multilevel coronal model.     

Electronic fine structure calculation of metal complexes with three-open-shell <Emphasis Type="Italic">s</Emphasis>, <Emphasis Type="Italic">d,and p</Emphasis> configurations

The ligand field density functional theory (LFDFT) algorithm is extended to treat the electronic structure and properties of systems with three-open-shell electron configurations, exemplified in this work by the calculation of the core and semi-core 1s, 2s, and 3s one-electron excitations in compounds containing transition metal ions. The work presents a model to non-empirically resolve the multiplet energy levels arising from the three-open-shell systems of non-equivalent ns, 3d, and 4p electrons and to calculate the oscillator strengths corresponding to the electric-dipole 3d ^m  → ns ¹3d ^m 4p ¹ transitions, with n = 1, 2, 3 and m = 0, 1, 2, …, 10 involved in the s electron excitation process. Using the concept of ligand field, the Slater-Condon integrals, the spin-orbit coupling constants, and the parameters of the ligand field potential are determined from density functional theory (DFT). Therefore, a theoretical procedure using LFDFT is established illustrating the spectroscopic details at the atomic scale that can be valuable in the analysis and characterization of the electronic spectra obtained from X-ray absorption fine structure or electron energy loss spectroscopies.     

Ion temperature profiles along a hydrogen diagnostic beam in a TORE SUPRA tokamak plasma

The active particle diagnostic technique is used to study the ion temperature at five spatial points along the path of a hydrogen diagnostic beam. The temperature of the main ion plasma component (deuterium ions) measured by this diagnostic technique along the beam path is compared with the temperature of carbon ions (C⁺⁵). A study is made of the following characteristic features of the behavior of the ion temperature profiles T_i in various TORE SUPRA operating modes: the formation of flat and even hollow T_i profiles in ohmic discharges with q ～3 at the plasma edge, the change in T_i profiles in ergodic divertor discharges, and the difference between the temperature of the bulk ions measured by the active particle diagnostic technique and the temperature of C⁺⁵ ions in the plasma region r/a>0.5. The features revealed are explained at a qualitative level.     

Relaxation of plasma rotation in toroidal magnetic confinement systems

A study is made of the relaxation of plasma rotation in nonaxisymmetric toroidal magnetic confinement systems, such as stellarators and rippled tokamaks. In this way, a solution to the drift kinetic equation is obtained that explicitly takes into account the time dependence of the distribution function, and expressions for the diffusive particle fluxes and longitudinal viscosity are derived that make it possible to write a closed set of equations describing the time evolution of the ambipolar electric field E and the longitudinal (with respect to the magnetic field) plasma velocity U₀. Solutions found to the set of evolutionary equations imply that the relaxation of these two parameters to their steady-state values occurs in the form of damped oscillations whose frequency is about 2v_T/R (where v_T is the ion thermal velocity and R is the major plasma radius) and whose damping rate depends on the ion-ion collision frequency and on the magnetic field parameters. In particular, it is shown that, for tokamaks with a slightly rippled longitudinal magnetic field, the frequency of oscillations in the range q>2 (where q is the safety factor) is, as a rule, much higher than the damping rate. For stellarators, this turns out to be true only of the central plasma region, where the helical ripple amplitude ? of the magnetic field is much smaller than the toroidal ripple amplitude δ=r/R.     

Xylem anatomy and calculated hydraulic conductance of four <Emphasis Type="Italic">Nothofagus</Emphasis> species with contrasting distribution in South-Central Chile

Nothofagus obliqua, N. dombeyi, N. alpina and N. antarctica are characteristic tree species of the temperate forests on the western slopes of the Andes with centres of distribution that differ in their temperature and moisture regimes. We tested branch wood from co-occurring specimens of these species for the inherent differences in xylem anatomy and theoretical hydraulic conductance to evaluate their resistance to drought or frost. The hydraulic conductivity of the xylem was calculated using a modified Hagen–Poiseuille equation and related to wood density. Conduit dimensions were used to predict the water potential that would cause 50 % loss of hydraulic conductivity (Ψ ₅₀). Nothofagus alpina, which mainly grows at sites with low frost frequency, exhibited the largest conduits and the highest mean values for conduit area, fraction of conduit area in the cross-section and hydraulic conductivity, but the lowest wood density. Opposite relationships were found in the plastic N. antarctica, whose xylem seems to be least vulnerable to freezing-induced, but also to drought-induced embolism. Calculated Ψ ₅₀ was highest (least negative) in N. alpina, indicating a relatively high susceptibility to cavitation. The xylem of the thermophilic N. obliqua and of N. dombeyi, which mainly occurs under oceanic climate, but can also survive at sporadically dry and warm sites, is not particularly adapted to periods of drought stress. Across all species, wood density was negatively correlated with the calculated hydraulic conductance. The xylem traits of N. alpina might contribute to its relatively high growth rate and facilitate its spread into forest gaps.     

Colony formation of highly dispersed <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> by controlling extracellular polysaccharides and calcium ion concentrations in aquatic solution

This study isolated extracellular polysaccharides (EPS) as a powder material from cyanobacterial blooms and the powdered EPS was used to trigger colony formation of dispersed unicellular M. aeruginosa by controlling EPS concentration in culture medium. The effect of Ca²⁺ ions on the colony formation of M. aeruginosa was also investigated, then the interaction between EPS and Ca²⁺ ions on colony formation was discussed. The results showed that the addition of the powdered EPS into the medium did not cause morphological changes of M. aeruginosa, suggesting that EPS alone would not induce the colony formation of M. aeruginosa. On the other hand, a high concentration of calcium ions (1000 mg/l) caused colony formation. When EPS and Ca²⁺ ions in the culture medium were adjusted to 200 and 1000 mg/l, respectively, the colony density, the average cell number per colony and the particle size of M. aeruginosa showed ca. 1.7–2.0 times greater values than those in the Ca²⁺ added medium. Calcium ion contributed to the aggregation of M. aeruginosa via crosslinked reaction with negatively charged M. aeruginosa cells, and the addition of EPS possessing negatively charged functional groups such as carboxy groups could enhance the reaction, promoting the crosslinked reaction between EPS and Ca²⁺ ions.     

Effects of nonextensivity and nonthermality on dust-acoustic Gardner solitons in dusty plasmas with distinct ion temperatures

The effects of nonextensivity and nonthermality of ions of two distinct temperatures on dustacoustic Gardner solitons (DAGSs) in an unmagnetized dusty plasma system are investigated theoretically. The constituents of the dusty plasma under consideration are negatively charged mobile dust fluid, Boltzmann-distributed electrons, and ions of two distinct temperatures following nonextensive (q) and nonthermal distributions, respectively. The Korteweg-de Vries (KdV), modified KdV, and Gardner equations are derived by using the reductive perturbation technique, and thereby their characteristic features are compared. It is observed that both the nonextensive and nonthermal ions significantly modify the basic properties and polarities of dust-acoustic solitary waves. The present investigation may be of relevance to space and laboratory dusty plasma systems.     

Nonquasineutral relativistic current filaments and their X-ray emission

Nonquasineutral electron current filaments with the azimuthal magnetic field are considered that arise due to the generation of electron vorticity in the initial (dissipative) stage of evolution of a current-carrying plasma, when the Hall number is small (σB/en _e c ? 1) because of the low values of the plasma conductivity and magnetic field strength. Equilibrium filamentary structures with both zero and nonzero net currents are considered. Structures with a zero net current type form on time scales of t < t _sk = (r ₀ω _pe /c)² t _st, where t _sk is the skin time, t _st is the typical time of electron-ion collisions, and r ₀ is the radius of the filament. It is shown that, in nonquasineutral filaments in which the current is carried by electrons drifting in the crossed electric (E _r ) and magnetic (B _θ) fields, ultrarelativistic electron beams on the typical charge-separation scale r _B = B/(4πen _e ) (the so-called magnetic Debye radius) can be generated. It is found that, for comparable electron currents, the characteristic electron energy in filaments with a nonzero net current is significantly lower than that in zero-net-current filaments that form on typical time scales of t < t _sk. This is because, in the latter type of filaments, the oppositely directed electron currents repel one another; as a result, both the density and velocity of electrons increase near the filament axis, where the velocities of relativistic electrons are maximum. Filaments with a zero net current can emit X rays with photon energies ? ω up to 10 MeV. The electron velocity distributions in filaments, the X-ray emission spectra, and the total X-ray yield per unit filament length are calculated as functions of the current and the electron number density in the filament. Analytical estimates of the characteristic lifetime of a radiating filament and the typical size of the radiating region as functions of the plasma density are obtained. The results of calculations are compared with the available experimental data.     

Assemblage-level effects of the introduced peacock hind (<Emphasis Type="Italic">Cephalopholis argus</Emphasis>) on Hawaiian reef fishes

The peacock hind Cephalopholis argus (family Serranidae), locally known as ‘roi’, was introduced from French Polynesia to Hawaii in the mid-twentieth century as a food fish. However, because of its association with ciguatera fish poisoning, it is rarely fished for food. Previous research indicates that roi could have a negative impact on native reef fish assemblages because of their high densities and prey consumption rates. However, it is unclear whether roi add to the cumulative mortality of prey (predation hypothesis), or whether predation is instead compensatory (doomed surplus hypothesis). This study experimentally assessed the effects of roi on reef fish populations through a long-term (5.5 year) predator removal experiment. A Before-After-Control-Impact study design was used to assess changes in fish assemblages following the removal of roi on 1.3 ha of patch reef. Increases in the density of prey-sized fish (<15 cm TL) were observed 18 months after roi removal. However, those effects did not translate into sustained increases in prey. While increases in potential competitors, wrasses (family Labridae), particularly the piscivorous ringtail wrasse Oxycheilinus unifasciatus, were observed on roi-free reefs, the fish assemblage did not diverge substantially in composition. Native reef fish appeared to resist the potential negative impacts of predation by roi, possibly through a refuge in size for some fish families. Management to protect intact fish assemblage size-structure could serve to bolster native resistance to invading species. In considering the threats facing coral reefs, and the possible solutions, roi removal alone will not likely replenish native fishery resources.