Alfvén resonance heating in Uragan-2M torsatron

Uragan-2M is a medium-size torsatron with reduced helical ripples. This machine has the major plasma radius R = 1.7 m, the average minor plasma radius r _p ≤ 0.24 m and the toroidal magnetic field B ₀ ≤ 2.4 T. The Alfvén resonance heating in a high k _‖ regime is advantageous for small size machines since it can be realized at smaller plasma densities than the minority and second harmonic heating. The Alfvén resonance heating is examined numerically in the approximation of radially non-uniform plasma cylinder with identical ends. The numerical model for wave excitation and propagation accounts for the longitudinal electron thermal motion and the finite ion gyroradius which allow the model to treat correctly the propagation and damping of the kinetic Alfvén wave in hot plasma. A compact antenna consisting of four loop elements is chosen to provide operation in a high k _‖ regime. The major drawback of such an approach is the presence of plasma peripher y heating owing to unavoidable excitation of low k _‖ Alfvén resonances. Calculations show that, with the proper choice of heating regime, the periphery heating has an acceptable level and the major part of the power is deposited inside plasma column.     

Effect of the periodic ripple in an axial confining magnetic field on the Alfvén heating of a cylindrical plasma

In a uniform axial magnetic field, the structure of local Alfvén resonance and the resonant absorption of RF power are governed by collisions, finite ion Larmor radius effects, and electron inertia. It is shown that, in a cylindrical plasma in a constant, periodically rippled, axial magnetic field, the structure of Alfvén resonance and the absorption of RF power can strongly depend on the ripple amplitude. The conditions under which the effect in question is dominant are intrinsic, e.g., to the modular Wendelstein stellarators.     

On the possibility of reflection of Alfvén waves in a curvilinear magnetic field

The propagation of Alfvén waves in a plasma immersed in a curvilinear magnetic field is investigated by using a 2D model. The waves are described by a 1D equation that formally coincides with the equation for the case of a quasi-uniform straight magnetic field with a modified Alfvén velocity that takes into account the longitudinal dependence of the Lame coefficients. It is shown that toroidal and poloidal Alfvén modes depend differently on the magnetic-field geometry. In the case of a 2D plane-parallel configuration of the magnetic field, poloidal modes are efficiently reflected from regions where the magnetic field lines sharply converge or diverge. This effect can result in the formation of open-field-line Alfvén quasi-resonators.     

Nonlinear nonstationary Alfvén resonance in a finite-pressure plasma

A nonlinear equation for a resonant Alfvén disturbance in a finite-pressure plasma is derived and matching conditions for a fast magnetosonic wave are obtained. The evolution of the resonant disturbance and the rate of resonant energy absorption are calculated for two cases: when the source is switched-on exponentially and instantaneously. It is shown that the evolution to a nonlinear regime is accompanied by the stratification of the resonant disturbance and the average plasma parameters at a progressively decreasing spatial scale. Essential properties of the nonlinear resonant disturbance are the nonlinear saturation of its amplitude, the displacement of the resonance layer, and the disappearance of resonant energy absorption.     

Kelvin-Helmholtz instability on the magnetopause, magnetohydrodynamic waveguide in the outer magnetosphere, and Alfvén resonance deep in the magnetosphere

Oscillations of the “magnetosphere-solar wind” system are studied analytically in the framework of a plane-stratified model of the medium. The properties of oscillations are determined by three phenomena: Kelvin-Helmholtz instability on the tangential discontinuity (magnetopause) separating the magnetosphere and the solar wind, the presence of a waveguide for fast magnetosonic waves in the magnetosphere, and the Alfvén resonance—a sharp increase in the amplitude of oscillations having the properties of Alfvén waves—in the inner magnetosphere. The oscillations of the system form a discrete spectrum of eigenmodes. Analytical expressions are obtained for the frequency and growth rate of instability of each mode, as well as for the functions describing the spatial structure of these modes. All these characteristics of the eigenmodes are shown to depend on the velocity of the solar wind as a parameter. The dependences of the main mode characteristics (such as the instability thresholds, the points of the maximum and minimum growth rate, and the spatial distributions of the oscillation energy) on this parameter are determined for each eigenmode.     

Toroidal Alfvén Modes in the Plasma of the Globus-M Spherical Tokamak

Plasma Physics Reports - Results of experimental studies of toroidal Alfvén eigenmodes (TAEs) in the Globus-M spherical tokamak (R = 36 cm, a = 24 cm) are reported. The experiments were...     

Viscous damping of Alfvén surface waves in the solar atmosphere

The dispersion relation for the propagation of viscous Alfvén surface waves along viscous plasmaplasma interface has been derived. Two modes of Alfvén surface waves are found to propagate with their characteristics depend on the interface parameters like magnetic field, density ratio, viscosity, etc. The viscous damping of Alfvén surface waves has been studied in the astrophysical point of view. The damping length of Alfvén surface waves due to viscosity in the solar atmosphere has been estimated.     

Experimental study of toroidal Alfvén modes in the Globus-M spherical tokamak

In the experiments carried out on the Globus-M tokamak in regimes with injection of 26-keV neutral beams with a power of 0.75–0.85 MW, two branches of instabilities excited by fast ions were observed in the early stage of a discharge: a low-frequency energetic particle mode (EPM) in the frequency range of 5–30 kHz and a high-frequency mode in the range of 50–200 kHz, identified as a toroidal Alfvén eigenmode (TAE). The TAE developed in the initial phase of the discharge at q(0) > 1 and terminated when sawtooth oscillations were excited at q(0) < 1. The spectrum and spatial localization of the mode agree with predictions of the linear theory. The modes observed in the Globus-M tokamak possess both properties common to other tokamaks and their own specific features.     

Generation of zonal flows by kinetic Alfvén waves

The generation of zonal flows by kinetic Alfvén waves is analyzed. It is noted that the basic approach underlying the existing theory of this phenomenon is too simplified because it attributes the generation of zonal flows to instabilities of an individual monochromatic wave packet of kinetic Alfvén waves. It is shown that, when a monochromatic wave packet is stable, it is necessary to analyze a more complicated situation with a double-peak packet (or, in the simplest case, with two pump waves). It is found that, for a double-peak packet of kinetic Alfvén waves, there is a new class of instabilities of zonal flows and that these instabilities are analogous to two-stream instabilities in linear theory. The main types of such instabilities are investigated.     

The influence of ion concentrations on the dynamic behavior of the Hodgkin–Huxley model-based cortical network

Action potentials (APs) in the form of very short pulses arise when the cell is excited by any internal or external stimulus exceeding the critical threshold of the membrane. During AP generation, the membrane potential completes its natural cycle through typical phases that can be formatted by ion channels, gates and ion concentrations, as well as the synaptic excitation rate. On the basis of the Hodgkin–Huxley cell model, a cortical network consistent with the real anatomic structure is realized with randomly interrelated small population of neurons to simulate a cerebral cortex segment. Using this model, we investigated the effects of Na⁺ and K⁺ ion concentrations on the outcome of this network in terms of regularity, phase locking, and synchronization. The results suggested that Na⁺ concentration does slightly affect the amplitude but not considerably affects the other parameters specified by depolarization and repolarization. K⁺ concentration significantly influences the form, regularity, and synchrony of the network-generated APs. No previous study dealing directly with the effects of both Na⁺ and K⁺ ion concentrations on regularity and synchronization of the simulated cortical network-generated APs, allowing for the comparison of results obtained using our methods, was encountered in the literature. The results, however, were consistent with those obtained through studies concerning resonance and synchronization from another perspective and with the information revealed through physiological and pharmacological experiments concerning changing ion concentrations or blocking ion channels. Our results demonstrated that the regularity and reliability of brain functions have a strong relationship with cellular ion concentrations, and suggested the management of the dynamic behavior of the cellular network with ion concentrations.     

Measuring the influence of unmanned aerial vehicles on Adélie penguins

Unmanned aerial vehicles (UAVs) have become a useful tool in polar research. While their performance is already proven, little is known about their impact on wildlife. To assess the disturbance caused on the penguins, flights with a UAV were conducted over an Adélie penguin (Pygoscelis adeliae) colony. Vertical and horizontal flights were performed between 10 and 50 m in altitude. Penguins’ reactions were video-recorded, and the behavioural response was used to indicate the level of disturbance. During any flight mode, disturbance increased immediately after takeoff and remained elevated at all altitudes between 20 and 50 m. When the UAV descended below 20 m, the disturbance increased further with almost all individuals being vigilant. Only at these low altitudes, vertical flights caused an even higher level of disturbance than horizontal ones. Repetitions of horizontal overflights showed no short-term habituation occurring. Since the results are only valid for the specific UAV model used, we recommend a more extensive approach with different UAV specifications. As the highest flight altitudes already caused detectable but not subjectively visible responses, we also recommend to regard subjective impressions of disturbance with caution.     

Small-scale Alfvén waves localized near an extremum in the finite-amplitude perturbation of the radial plasma density profile

A study is made of electromagnetic waves localized in the region where the radial plasma density profile has an extremum between two local Alfvén resonances. Analytic expressions for the eigenfrequencies and eigenmodes are obtained. It is shown that kinetic and inertial Alfvén waves can propagate in the vicinity of a maximum and a minimum in the density profile, respectively. Passage to the limiting case in which the plasma density is nonuniform and has a parabolic profile is considered.     

Generation of Alfvén waves by a plasma inhomogeneity moving in the Earth’s magnetosphere

The generation of an Alfvén wave by an azimuthally drifting cloud of high-energy particles injected in the Earth’s magnetosphere is studied analytically. In contrast to the previous studies where the generation mechanisms associated with the resonant wave-particle interaction were considered, a nonresonant mechanism is investigated in which the wave is excited by the alternating current produced by drifting particles. It is shown that, at a point with a given azimuthal coordinate, a poloidally polarized wave, in which the magnetic field lines oscillate predominantly in the radial direction, is excited immediately after the passage of the particle cloud through this point. As the cloud moves away from that point, the wave polarization becomes toroidal (the magnetic field lines oscillate predominantly in the azimuthal direction). The azimuthal wavenumber m is defined as the ratio of the wave eigenfrequency to the angular velocity of the cloud (the drift velocity of the particles). It is shown that the amplitudes of the waves so generated are close to those obtained under realistic assumptions about the density and energy of the particles.     

On the influence of prenatal hypoxia on formation of the orexinergic system and sleep–wake cycle in early ontogenesis of rats

The role of orexin in the organization of the sleep–wake cycle (SWC) is well known. The aim of this study was to examine the timing of the orexinergic system formation in rat postnatal ontogenesis and to assess the role of orexin A in the SWC organization under normal conditions and after prenatal hypoxia undergone on days 14 and 19 of embryogenesis. The SWC was investigated in 30-day-old rats with electrodes implanted into the somatosensory and occipital cortex. Immunoreactivity within the orexigenic structures of the lateral hypothalamus was analyzed. It was shown that in control 14-day-old animals the orexinergic structures were in their formative stage, whereas in 30-day-old rats they were already as formed as in adults. In 14-day-old rats, prenatal hypoxia evoked retarded formation of the orexinergic system. In 30-day-old animals, hypoxia undergone in the prenatal period increased the activity of the orexinergic system, which was higher in animals exposed to hypoxia on day 19 than on day 14 of gestation. In 30-day-old rats, these changes were reflected in the SWC formation in the form of shorter slow-wave sleep, more fitful sleep and increased number of transitions from slow- to fast-wave sleep. The results obtained are discussed in the light of the adaptive-compensatory role of the orexigenic system in postnatal ontogenesis after prenatal damage to the central nervous system.     

Alfvén eigenmode evolution computed with the VENUS and KINX codes for the ITER baseline scenario

A new application of the VENUS code is described, which computes alpha particle orbits in the perturbed electromagnetic fields and its resonant interaction with the toroidal Alfvén eigenmodes (TAEs) for the ITER device. The ITER baseline scenario with Q = 10 and the plasma toroidal current of 15 МА is considered as the most important and relevant for the International Tokamak Physics Activity group on energetic particles (ITPA-EP). For this scenario, typical unstable ТАЕ-modes with the toroidal index n = 20 have been predicted that are localized in the plasma core near the surface with safety factor q = 1. The spatial structure of ballooning and antiballooning modes has been computed with the ideal MHD code KINX. The linear growth rates and the saturation levels taking into account the damping effects and the different mode frequencies have been calculated with the VENUS code for both ballooning and antiballooning TAE-modes.     

Studies on the Fluorescence of Saké

By spectrofluorophotometric investigation on various kinds of Saké it was found that they have at least two kinds of fluorescent colors, the one is blue, the other yellowish green. The former is always more dominant than the latter, but is unstable although the intensities of both color decrease remarkably by treatment of active charcoal. Ferulic acid and harman as the blue fluorescent components are isolated, the former from Saké in young, the latter from Saké kept for a long time under direct sun light.     

The influence of structural variations in the F- and FG-helix of the β-subunit modified oxyHb-NES on the heme structure detected by resonance Raman spectroscopy

The dispersion of the depolarization ratio of two prominent Raman lines (1,375 cm^–1 and 1,638 cm^–1) of oxyhemoglobin-N-ethyl succinimide have been examined for pH values between pH=6.0 and 8.5. Both exhibit a significant pH dependence. Calculation of the Raman tensor in terms of a fifth-order time dependent theory provides information about the pH-dependence of parameters reflecting symmetry classified distortions of the prosthetic heme group. To correlate these distortions with the functional properties of the molecule the following protocol was used: 1) An allosteric model suggested by Herzfeld and Stanley (1974) has been applied to O₂-binding curves measured at different pH values between 6.5 and 9.0. From this calculation one obtains both, the energy differences between different molecular conformations and the equilibrium constants of oxygen and proton binding. 2) A titration model was formulated relating each conformation of a molecule to a distinct set of distortion parameters of the heme group. 3) The distortion parameters resulting from the analysis of our Raman data were assigned as an effective value due to incoherent superposition of the distortion parameters related to the different titration states. The application of this procedure yields an excellent reproduction of the pH-dependent effective distortion parameters of both Raman lines investigated. It is shown that the protonation of two tertiary effector groups located in the -subunits affect the symmetry of the heme in a contrary manner: the protonation of a His-residue (pK=8.2, probably His(FG4)) causes a symmetric position of the proximal imidazole thus lowering the perturbations of the heme core. Further it influences the interaction between amino acid residues of the heme cavity and pyrrole side chains (probably Val (FG5)-vinyl (pyrrole 3) thus causing a decrease of the distortions related to the peripheral part of the heme. In contrast, the protonation of Lys (EF6) causes a tilt position of the proximal imidazole and an increase of asymmetric perturbations of the heme core, whereas the interaction between the pyrrole side chains and the heme cavity is weakened. Our results are consistent with stereochemical predictions of Moffat (1971) concerning the existence of an H-bond between His(FG4) and Cys(F9).Abbreviations DPR depolarization ratio - EP excitation profile - HbA human hemoglobin - oxyHb oxyhemoglobin - NEM N-ethyl-maleimide - NES N-ethyl-succimide - BME Bis (N-maleimidodimethyl)ether     

Exact solutions for oblique solitary Alfvén waves in plasma

The properties of solitary Alfvén waves are studied for different ratios between the thermal plasma pressure and the magnetic pressure. It is shown that the wave propagation is accompanied by the generation of a nonlinear ion current along the magnetic field, the contribution of which to the Sagdeev potential was previously ignored. An expression for the quasi-potential of Alfvén waves with allowance for this effect is derived. It is found that Alfvén waves are compression waves in the inertial limit, whereas kinetic Alfvén waves are rarefaction waves. In a high-pressure plasma, a solitary wave has the form of either a well or a hump in the plasma density, depending on the relations between the Mach number, angle between the wave propagation direction and the magnetic field, and the value of the plasma beta.     

Lecithin influence on the effectiveness of the antioxidant effect of flavonoids and α-tocopherol

Influence of the widely used food additive lecithin on the effectiveness of the inhibiting effect of the natural antioxidants (quercetin, dihydroquercetin, and α-tocopherol) has been studied in dependence on the rate of free radicals generation in the model oxidation reactions. It has been found that during the initiated and autoxidation of methyl oleat, lecithin decreased the antioxidant effectiveness of flavonoids. The effect value increased with the lecithin concentration increase. Under similar conditions while oxidation inhibiting by α-tocopherol and lecithin mixtures, the latter did not influence the tocopherol antioxidant effectiveness (additivity) or led to the increase of the inhibition effectiveness (synergism).     

Conversion of fast magnetosonic waves into Alfvén waves in a longitudinally inhomogeneous gyrotropic plasma

A model is considered of the conversion of running fast magnetosonic waves into Alfvén waves in a longitudinally inhomogeneous gyrotropic plasma in a magnetic field with open field lines. The set of equations for the amplitudes of the interacting modes is obtained and investigated in the Wentzel-Kramers-Brillouin approximation. In the synchronization region, where the wave vectors of the two modes approach one another, most of the energy of fast magnetosonic waves is converted into the Alfvén wave energy. The phases of the waves are matched in such a way that the phase difference is most favorable for wave conversion. The fact that the conversion is resonant in nature may help to explain the onset of quasi-monochromatic signals in the Earth’s magnetosphere and in the magnetospheres of the giant planets.