Generation of auroral kilometric radiation by a finite-size source in a dipole magnetic field. Part II

Propagation and amplification of extraordinary electromagnetic waves in a dipole magnetic field in a narrow 3D plasma cavity in which a weakly relativistic electron beam propagates along the magnetic field in the direction of the gradient of the magnetic field strength is investigated. The domain of wave vectors at the starting point for which the wave amplification factors at the output of the density cavity reach their maximum values is found, and the amplification factor as a function of the wave frequency is determined. It is shown that the longitudinal velocity of fast electrons, which enables generation of waves in a broader frequency range, plays an important role in the formation of the spectrum of the auroral kilometric radiation (AKR). In this case, waves with the largest amplification factors at the output of the cavity have frequencies exceeding the cutoff frequency of the background plasma at the wave generation altitude. The global inhomogeneity of the magnetic field and plasma density, which governs the residence time of the waves in the amplification region, plays a key role in the formation of the AKR spectrum. It is shown that this time is the main factor determining the energy of the waves emerging from the source.     

Boundary of the adiabatic motion of a charged particle in a dipole magnetic field

The motion of a charged particle in a dipole magnetic field is considered using a quasi-adiabatic model in which the particle guiding center trajectory is approximated by the central trajectory, i.e., a trajectory that passes through the center of the dipole. A study is made of the breakdown of adiabaticity in the particle motion as the adiabaticity parameter χ (the ratio of the Larmor radius to the radius of the magnetic field line curvature in the equatorial plane) increases. Initially, for χ?0.01, the magnetic moment μ of a charged particle undergoes reversible fluctuations, which can be eliminated by subtracting the particle drift velocity. For χ?0.1, the magnetic moment μ undergoes irreversible fluctuations, which grow exponentially with χ. Numerical integration of the equations of motion shows that, during the motion of a particle from the equatorial plane to the mirror point and back to the equator in a coordinate system related to the central trajectory, the analogue of the magnetic moment μ is conserved. In the equatorial plane, this analogue undergoes a jump. The long-term particle dynamics is described in a discrete manner, by approximating the Poincaré mapping. The existence of the regions of steady and stochastic particle motion is established, and the boundary between these regions is determined. The position of this boundary depends not only on the adiabaticity parameter χ but also on the pitch angle. The calculated boundary is found to agree well with that obtained previously by using the model of a resonant interaction between particle oscillations associated with different degrees of freedom.     

Generation of low-frequency radiation by a nonequilibrium plasma of an RF discharge in a linear mirror magnetic confinement system

The generation of ion-cyclotron radiation in a plasma resonator formed by an RF discharge in a linear mirror magnetic confinement system is revealed and investigated. It is shown that the experimental setup makes it possible to study the composition of a multicomponent discharge plasma and to detect multiply charged ions. Collisional losses in such a resonator are estimated, and the pressure range within which the growth rate of the ion-cyclotron instability substantially exceeds the collisional damping rate is determined.     

Radiation from a pulsed dipole source in a moving magnetized plasma

The problem of radiation from a pulsed dipole source in a moving magnetized plasma described by a diagonal permittivity tensor is considered. An exact solution describing the spatiotemporal behavior of the excited electromagnetic field is obtained. The shape of an electromagnetic pulse that is generated by the source and propagates at different angles to both the direction of the external magnetic field and the direction of plasma motion is investigated. It is found that even nonrelativistic motion of the plasma medium can substantially influence the parameters of radiation from prescribed unsteady sources.     

Effect of a constant magnetic field and gamma radiation on the hereditary structure of somatic cells. Effect of the combination of a constant magnetic field and ionizing radiation on human lymphocytes in vitro

Samples of human whole blood were exposed in CMF (field induction, 0.3 T) for 15, 30, 45, 60, 75, 90, 120, 150, 180, 240, 300 or 360 min. 15 min following exposure, the samples were gamma-irradiated in a dose of 0.0516 C/kg (137Cs) at a dose rate of 1.95 A/kg. The following chromosome aberrations were scored: deletions dicentrics, rings, and symmetrical exchanges. Exposure of the blood in CMF for 15 to 360 min decreased radiation damage to cells as compared with unexposed irradiated samples. The extention of time from 15 to 180 min increases the effect the smallest amount of chromosome damages being scored at 150-180 min. A 2.8 - fold, 3 - fold and 3.5 - fold decrease was registered in the number of aberrant cells, deletions and dicentrics, respectively. With increasing time of exposure (240 min), the radiomodifying effect started decreasing, and with 300-360 min exposure it was the same as that observed at 15-45 min.     

Pumping action on blood by a magnetic field

We report here an analysis of pumping of blood by means of a non-invasive circulatory-assist device using the principle of Magnetohydrodynamics. This study shows that such a pump would require the application of a slowly moving axial magnetic field of strength of about 10⁸ amp turns/m (approximately 10⁶ oersteds). The results indicate that the temperature rise on account of induced currents is within permissible range.     

Ion sepation by a curved magnetic field in a multicomponent plasma

It is shown that a curved magnetic field can be used to separate ions in a multicomponent plasma. Without selective ion preheating, the separation over one cycle is inefficient: the separated ion fractions will only be enriched with ions of the corresponding isotopes. Selective ion cyclotron resonance heating makes it possible to achieve essentially a complete separation of the ions.     

Self-consistent model of an inductive RF plasma source in an external magnetic field

A theory is developed that makes it possible to calculate RF power absorption in an inductive plasma source. Conditions are determined under which most of the power is deposited in the plasma. It is shown that these conditions correspond to the excitation of spatial waves (an oblique Langmuir wave and a helicon wave). A simple self-consistent model of a plasma source is proposed that describes all of the experimentally observed distinctive properties of plasma sources well.     

Orientation of lipid tubules by a magnetic field.

Lipid tubules, which are straight hollow cylinders consisting of lipid bilayers, are shown to orient in strong magnetic fields. Birefringence measurements were made of dilute samples of tubules of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC23PC) in magnetic fields of up to 4 T. The tubules were found to orient with their long axes parallel to the field direction, with saturated orientation [P2 (cos theta] approximately greater than 0.95) found at approximately 2 T. From known distributions of lengths and the number of bilayers in the walls, a value delta chi = (-7 +/- 1) X 10(-9) erg cm-3 G-2 was calculated for the tubules, which compares well with some previously reported values for phosphatidylcholines. Magnetic alignment will permit more sophisticated structural studies of monomeric and polymeric tubules, and provide a method of orienting macromolecules in the tubule walls or interior.     

Inhibition of pentylenetetrazole-induced seizure in mice by using a 4 Hz magnetic field: a comparative study with a 60 Hz magnetic field

We investigated the comparative effects of 4 and 60 Hz magnetic fields on pentylenetetrazole (PTZ)-induced seizure in mice. For this study, we measured the latent time to seizure, seizure duration, and lethality induced by PTZ in mice exposed to 4 and 60 Hz magnetic fields (MF) for 30 min. Compared to sham-exposed controls, the latent time to tail twitching and seizure in the 4 Hz MF group was significantly decreased while the latent time to seizure in the 60 Hz MF group was significantly increased. The seizure duration in the 4 Hz MF group was significantly decreased while that in the 60 Hz MF group was significantly increased. More importantly, while the mice exposed to a 60 Hz MF experienced significantly increased lethality after seizure convulsion, those exposed to a 4 Hz MF showed no lethality, with a shortening of the duration of seizure. This beneficial effect of a 4 Hz MF on seizure has the same implication as the anti-oxidative effects of a 4 Hz MF observed in our previous work. The results of our current and previous works indicate that a 4 Hz MF may be used as a therapeutic physical agent for the treatment of oxidative stress-induced diseases, including seizure, with or without chemical drugs.     

Solvent density and long-range dipole field around a DNA-binding protein studied by molecular dynamics

The distribution and orientation of solvent around a DNA-binding protein, 434 Cro, were investigated by molecular dynamics simulations with a periodic-boundary condition. The protein was treated in two states: charged and neutral. The computed high-density sites of the solvent around the protein correlated well with the experimentally determined crystal-water sites, in both the charged and neutral states. A local density map, introduced to investigate the solvent density around the highly mobile regions of the protein, showed a hydration shell around hydrophobic sidechains and hydrogen-bondable sites around hydrophilic sidechains, and also showed that the solvent density is sensitive to the slight concaves of the sidechain surface. The long-range solvent-dipole field was observed around the protein, where the pattern of the dipole ordering was considerably different between the charged and neutral states. A local solvent-dipole field was introduced, and the pattern of the dipole ordering was different between the hydrophobic and hydrophilic sidechains. The dipole field from the charged state provided a higher correlation to the electrostatic field obtained from the Poisson-Boltzmann's equation than that from the neutral state, although the correlation become weak quickly for the both states with increasing the protein-solvent distance.     

Static magnetic field treatment enhanced photosynthetic performance in soybean under supplemental ultraviolet-B radiation

Photosynthesis Research - The study was performed to analyze the impact of seed pretreatment by static magnetic field (SMF) of 200 mT for 1 h on photosynthetic performance of soybean...     

Generation of terahertz radiation from a low-density plasma slab irradiated by a laser pulse

The generation of terahertz electromagnetic radiation when a laser pulse propagates through a low-density plasma slab is considered. It is shown that terahertz waves are excited because of the growth of a weakly damped, antisymmetric leaking mode of the plasma slab. The spectral, angular, and energy parameters of the terahertz radiation are investigated, as well as the spatiotemporal structure of the emitted waves. It is demonstrated that terahertz electromagnetic wave fields are generated most efficiently when the pulse length is comparable to the slab thickness.     

Electromagnetic beam-plasma interactions in a magnetic field

The excitation of plasma oscillations in a thin-walled annular plasma by an annular electron beam in a cylindrical waveguide is considered in the linear approximation. The instability growth rates and spatial amplification coefficients in the beam-plasma system under the conditions of the Cherenkov and anomalous Doppler resonances are obtained and compared with those in a transversely homogeneous system. The contributions from different instability mechanisms are analyzed.     

Plasma heating in a variable magnetic field

The problem of particle acceleration in a periodically variable magnetic field that either takes a zero value or passes through zero is considered. It is shown that, each time the field [0]passes through zero, the particle energy increases abruptly. This process can be regarded as heating in the course of which plasma particles acquire significant energy within one field period. This mechanism of plasma heating takes place in the absence of collisions between plasma particles and is analogous to the mechanism of magnetic pumping in collisional plasma considered by Alfvén.     

Implementation of magnetic field force in molecular dynamics algorithm: NAMD source code version 2.12

The mechanism of C-H bond activation of ethane was catalyzed by palladium halide cations (PdX+ (X = F, Cl, Br, H, and CH3)), which was investigated using density functional theory (DFT) at B3LYP level. The reaction mechanism was taken into account in triplet and singlet spin state potential energy surfaces. For PdF+, PdCl+, and PdBr+, the high spin states were the ground states, whereas the ground states were the low spin states in PdH+ and PdCH3+. The reaction of PdF+, PdCl+, and PdBr+ with ethane occurred via a typical “two-state reactivity” mechanism. In contrast, for PdH+ and PdCH3+, the overall reaction performed on the ground state PESs in a spin-conserving manner. The crossing points between two potential energy surfaces were observed and effectively decreased the activation barrier in PdX+/C2H6 (X = F, Cl, and Br). The minimum energy crossing points (MECP) were obtained used the algorithm in Harvey method. The natural valence electron configuration calculations were analyzed by natural bond orbital. The distribution and contribution of the front molecular orbital of the initial complexes could be further understand by the density of states. The feature of the bonding evolution in the main pathways was studied using topological analysis including localized orbital locator and atoms in molecules.     

Helicon plasma in a nonuniform magnetic field

The distributions of the electron density in a plasma produced by helicon waves and the correspond-ing wave amplitudes and phases are studied experimentally. The measurements were carried out in an argon plasma at a pressure of 3 mtorr and at an input RF power of up to 600 W. The magnetic field was caried in the range from 0 to 200 G. The efficiency of plasma production in both uniform and nonuniform fields is investigated. It is shown that, in a nonuniform magnetic field, the electron density can be substantially increased (up to 5×10¹² cm^?3) by placing an antenna in the region in which the magnetic field is weaker than in the main plasma.     

Generation of strong magnetic fields by counterpropagating moderate-intensity laser pulses in a low-density plasma

A study is made of the generation of strong quasistatic magnetic fields by counterpropagating moderate-intensity laser pulses of different frequencies in a low-density plasma. Strong magnetic fields are generated by small-scale large-amplitude plasma waves excited at different frequencies by ponderomotive forces in the interaction region of laser pulses. It is shown that magnetic fields are generated most efficiently under resonance conditions such that the frequency difference between laser pulses coincides with the plasma frequency. The spatial distribution of quasistatic magnetic fields is investigated, and the pattern of the contour lines of the electric current is calculated.     

Dynamics of a magnetic field in dusty plasma

The problem of the expansion of a magnetic field in a complex (e.g., dusty) plasma is considered, with a focus on the effects produced by the independent transport of charged components that does not break plasma quasineutrality. Solutions to a set of nonlinear equations are obtained for different initial and boundary conditions. In particular, it is shown that the field rapidly penetrates into the plasma when the dust is charged negatively and does not penetrate at all when the dust charge is positive.