Progress in theory of instabilities in a rotating plasma

A review is given of the basic results of modern theory of instabilities in a rotating plasma. Both axisymmetric and nonaxisymmetric perturbations are considered. Main attention is given to the magnetorotational instability (MRI), discovered earlier by Velikhov, and the rotational-convective instability (RCI) discussed in a number of papers of astrophysical trend. For qualitative explanation of the results, a local approach is used which, with equilibrium plasma pressure gradient and/or nonsymmetry of perturbations, requires operation with nonlocal azimuthal perturbed magnetic field. The gravity and effects of pressure anisotropy are taken into account. In addition to hydrodynamic, the electrodynamic approach is formulated. The drift effects are considered. Analyzed are the ideal instabilities and those depending on the dissipative effects: viscosity and heat conductivity. The MRI is considered at presence of the charged dust particles. Besides the local approach, the nonlocal approach is formulated for the plasma model with a steplike profile of angular rotation frequency. Alongside with perturbations which frequencies are small compared to the ion cyclotron frequency, the perturbations are analyzed with frequencies larger than the ion cyclotron frequency. The latter corresponds to the Hall regime and subregime of nonmagnetized plasma.     

Low-frequency instabilities of collisionless plasma and the 16-moment approximation

Using the 16-moment equations that take into account heat fluxes in anisotropic collisionless plasma, the properties of magnetohydrodynamic (MHD) instabilities are investigated. For all instabilities occurring in the MHD approach (the normal incompressible firehose instability, the second compressible almost longitudinal firehose instability, and the almost transverse mirror instability of slow magnetosonic modes, as well as thermal instability caused by the heat flux directed along the magnetic field), their kinetic analogs are considered. The kinetic dispersion relation in the low-frequency range in the vicinity of the ion thermal velocity is analyzed. The flow of plasma ions along the magnetic field is taken into account. The thresholds and instability growth rates obtained in the MHD and kinetic approaches are found to be in good agreement. This indicates that the 16-moment MHD equations adequately describe the dynamics of collisionless plasma.     

Effects of finite heat conductivity on instabilities in a rotating plasma

Analytical theory of magnetorotational and convective instabilities in a rotating cylindrical plasma with finite heat conductivity is developed and discussed. The heat conductivity is incorporated into the standardized equations of the regular magnetohydrodynamic approach to studying these instabilities. A case of high-β plasma (β is the ratio of plasma pressure to the magnetic field pressure) and the modes with parallel phase velocity much smaller than the sound velocity is particularly emphasized and considered in the quasi-incompressible approximation. It is shown that this approximation is more adequate than the Boussinesq approximation. Both these approximations lead to the same results for aperiodical instabilities of the axisymmetric modes which are hybrids of the magnetorotational and convective instabilities. On the other hand, the Boussinesq approximation overlooks the heat-conductivity-induced instabilities predicted by the quasi-incompressible approximation describing the dissipative excitation of the slow magnetoacoustic and Alfvén waves. Non-axisymmetric aperiodical instabilities are considered. It is shown that, for such modes, the role of convective instabilities is greater than for the magnetorotational instability.     

Low-frequency electromagnetic fields induce a stress effect upon higher plants,as evident by the universal stress signal,alanine

15N NMR analysis reveals alanine production in Duckweed plants exposed to low intensity sinusoidally varying magnetic fields (SVMF) at 60 and 100Hz, and fed by 15N-labeled ammonium chloride. Alanine does not accumulate in the absence of SVMF. Addition of vitamin C, a radical scavenger, reduced alanine production by 82%, indicating the roll of free radicals in the process. Alanine accumulation in plants and animals in response to exposure to a variety of stress conditions, including SVMF, is a general phenomenon. It is proposed that alanine is a universal first stress signal expressed by cells.     

Perturbations of plant leaflet rhythms caused by electromagnetic radio-frequency radiation

The minute-range up and down rhythms of the lateral leaflets of Desmodium gyrans has been studied when exposed to electromagnetic radiation in the radio-frequency (RF) range. The RF radiation was applied as homogeneous 27.12 MHz fields in specially-designed exposure cells(and in some cases as non-homogeneous radiation of 27 MHz. amplitude modulated by 50 Hz, in front of commercial diathermy equipment). All fields were applied as pulses. We report effects in the leaflet rhythms such as temporary changes in the amplitude, period, and phase. The radiation could also cause temporary or complete cessations of the rhythms. The lowest dose (8 W/cm²) used was still effective. © 1993 Wiley-Liss. Inc.     

Low-frequency resonances of the refractive index in weakly ionized plasma with an admixture of dust

The propagation of low-frequency electromagnetic waves along the magnetic field in weakly ionized plasma with an admixture of dust is studied in the framework of the Hall magnetohydrodynamics. Explicit expressions for the coefficients of magnetic field diffusion in plasma are derived. The resonance of the refractive index is found to occur for either right- or left-hand polarized waves. A quantitative criterion is obtained that allows one to determine the polarization of waves that experience resonance at given plasma parameters. The physical mechanism of the resonance is discussed, and the obtained results are compared with the available literature data.     

Degranulation of skin mast cells caused by high frequency electromagnetic irradiation of low intensity]

It was shown by light and electron microscopy that local exposure of the projection of the MC-8 lao-gun acupuncture point in rat pad to low-intensity (0.05 mW/cm2) extremely high-frequency (42.0 GHz) electromagnetic radiation caused a degranulation of derma mast cells. It was suggested that the response of skin mast cells is an important amplifying mechanism in the chain of events leading to a systemic response of the organism to low-intensity electromagnetic radiation.     

Temperature oscillations in liquid media caused by continuous (nonmodulated) millimeter wavelength electromagnetic irradiation

Convection in liquids caused by 53–78 GHz millimeter wave irradiation with incident power density that ranged from 10 μW/cm² to 1 W/cm² was studied. Infrared thermography was used as an artifact-free method for recording surface-temperature dynamics during irradiation. It was found that continuous (nonmodulated) waves can produce a relaxation-type temperature oscillation in liquids with a relatively high stability of the period between temperature spikes. The temperature oscillation is due to the repetitive formation and dissipation of a torroidal type of convection vortex. When the vortex became stable during irradiation, we observed a temperature decrease following the initial temperature-rise phase, even though the irradiation was constantly maintained. This result constitutes a new process that can play a significant role in producing microwave bioeffects, including some so-called “nonthermal” effects and some effects that are inversely related to heating. Also, it can be considered as a newly discovered potential artifact in microwave bioeffects studies. © 1996 Wiley-Liss, Inc.     

Osmotic flow caused by chondroitin sulfate proteoglycan across well-defined nuclepore membranes

Osmotic flows generated by solutions of Swarm rat chondrosarcoma proteoglycan subunit have been analysed using Nuclepore membranes of well-defined straight-through cylindrical pores of known radius rp. Membranes with rp in the range of 27-500 nm were studied. For semipermeable membranes, which are impermeable to the proteoglycan, the flows were consistently related to r2p and not to r4p (Poiseuille's Law) which demonstrates that the flow is a diffusion-controlled process as described previously (R.P.W. Williams and W.D. Comper, J. Phys. Chem. 91 (1987) 3443). We have also identified a characteristic distance, approx. 50% of the average interparticle spacing, out from the pore surface of the membrane over which the proteoglycan has to move to generate flow. The proteoglycan generates similar osmotic permeability coefficients with membranes up to 125 nm in pore diameter which is significantly larger than the average intermolecular distance. These results have been interpreted in terms of the membrane pore recognising dynamic transient aggregates in the proteoglycan solution.     

Direction finding by hornets in a vertically rotating centrifuge

In a vertically rotating centrifuge, the direction of the resultant gravitational and centrifugal forces is constantly changing. Hornets placed in such a centrifuge will build their combs in the direction of the resultant only if the centrifuge is stopped every day and left in the same position for at least half an hour, because during the cessation of motion, they presumably “learn” some geometrical cues which enable them to determine the preferred angle of building. Hornets can detect and respond to a centrifugal force as small as 0·18% of the earth's gravitational force. At a rotational rate of 1/8 of a revolution per minute there was no comb construction whatsoever and hornet mortality rate was 100% within three days.     

Asymmetric gene flow and constraints on adaptation caused by sex ratio distorters

Asymmetric gene flow is generally believed to oppose natural selection and potentially impede adaptation. Whilst the cause of asymmetric gene flow has been seen largely in terms of variation in population density over space, asymmetric gene flow can also result from varying sex ratios across subpopulations with similar population sizes. We model the process of adaptation in a scenario in which two adjacent subpopulations have different sex ratios, associated with different levels of infection with maternally inherited endosymbionts that selectively kill male hosts. Two models are analyzed in detail. First, we consider one host locus with two alleles, each of which possesses a selective advantage in one of the subpopulations. We found that local adaptation can strongly be impeded in the subpopulation with the more female biased population sex ratio. Second, we analyze host alleles that provide resistance against the male-killing (MK) endosymbionts and show that asymmetric gene flow can prevent the spread of such alleles under certain conditions. These results might have important implications for the coevolution of MK bacteria and their hosts.     

Two-dimensional model of biofilm detachment caused by internal stress from liquid flow

A two-dimensional model for biofilm growth and detachment was used to evaluate the effect of detachment on biofilm structures. The detachment process is considered to be due to internal stress created by moving liquid past the biofilm. This model generated a variety of realistic biofilm-formation patterns. It was possible to model in a unified way two different biofilm detachment processes, erosion (small-particle loss), and sloughing (large-biomass-particle removal). The distribution of the fraction from total biomass detached as a function of detached particle mass, gives indications about which of the two mechanisms is dominant. Model simulations indicate that erosion makes the biofilm surface smoother. Sloughing, in contrast, leads to an increased biofilm-surface roughness. Faster growing biofilms have a faster detachment rate than slow-growing biofilms, under similar hydrodynamic conditions and biofilm strength. This is in perfect accordance with the experimental evidence showing that detachment is dependent on both shear- and microbial-growth rates. High growth rates trigger instability in biofilm accumulation and abrupt biomass loss (sloughing). Massive sloughing can be avoided by high liquid shear, combined with low biomass growth rates. As the modeling results show, the causes for sloughing must be sought not only in the biofilm strength, but also in its shape. Several "mushroom-like" biofilm structures like those repeatedly reported in the literature occurred, due to a combined effect of nutrient depletion and breaking at the colony base. A rough carrier surface promotes biofilm development in hydrodynamic conditions in which the biofilm on a flat surface would not form. Although biofilm patches filled completely the cavity in which they started to grow, they were unable to spill over the carrier peaks and to fully colonize the substratum.     

Effect of flow rate on heavy metal accumulation by rotating biological contactor (RBC) biofilms

Immobilized biofilms are effective in heavy metal removal. The current studies investigated the use of rotating biological contactor (RBC) biofilms in treatment of a wastewater containing cadmium, copper and zinc, each at a concentration of 100 mg L⁻¹. In particular, the influence of hydraulic retention time (HRT) on metal accumulation was studied. Longer HRTs (>12 h) were associated with greater metal removal than short HRTs, particularly with regard to cadmium and zinc. The system was also shown to operate successfully over an extended period of time, at an HRT of 24 h, with removal efficiencies of approximately 34%, 85% and 57% for Cd²⁺, Cu²⁺ and Zn²⁺ respectively after 5–8 weeks contact. Journal of Industrial Microbiology & Biotechnology (2000) 24, 244–250. Received 28 July 1999/ Accepted in revised form 21 December 1999     

Genetic instabilities of triplet repeat sequences by recombination

The expansion of triplet repeat sequences is an initial step in the disease etiology of a number of hereditary neurological disorders in humans. Diseases such as myotonic dystrophy, Huntington's, several spinocerebellar ataxias, fragile X syndrome, and Friedreich's ataxia are caused by the expansions of CTG.CAG, CGG.CCG, or GAA.TTC repeats. The mechanisms of the expansion process have been investigated intensely in E. coli, yeast, transgenic mice, mammalian cell culture, and in human clinical cases. Whereas studies from 1994-1999 have implicated DNA replication and repair at the paused synthesis sites due to the unusual conformations of the triplet repeat sequences, recent work has shown that homologous recombination (gene conversion) is a powerful mechanism for generating massive expansions, in addition to, or in concert with, replication and repair.     

Denitrification by Alcaligenes denitrificans in a closed rotating biological contactor

Biological denitrification using a pure culture of Alcaligenes denitrificans was investigated in a closed rotating biological contactor, which operated with a hydraulic retention time of 2 h, a carbon/nitrogen ratio of 2:1, with a dissolved O₂ concentration below 6 mg l^–1 and under three different phosphate concentrations. Alcaligenes denitrificans was not repressed by O₂ limitation and the removal of nitrate was about 30% more efficient at the intermediate phosphate concentration (20 mg P l^–1).     

Low-frequency vibrations of a Mg pyropheophorbide-histidine complex]

The spectrum of vibrations and normal model for the Mg piropheophorbide-histidine complex was calculated using the MNDO-PM3 (MOPAC) semiempirical quantum chemical method. The delocalization index and the distribution function were introduced to describe the shape of normal vibrations. The greatest part (approximately 65%) of the low-frequency vibrations (1-400 cm-1) was shown to delocalize over both the His and Mg piropheophorbide molecules. Leu, Met, and Asp were also studied as the fifth ligand to the Mg piropheophorbide molecule. It is concluded that the fifth amino acid ligand to porphyrin molecules causes marked geometrical distortions in porphyrin, and induces a new, compared to four coordinated pigment, spectrum of normal modes.     

Photosynthetic changes and oxidative stress caused by iron ore dust deposition in the tropical CAM tree Clusia hilariana

The effect of iron solid particulate matter (SPM_Fe) deposited onto soil and leaves on photosynthesis and oxidative stress was evaluated in Clusia hilariana, a CAM tropical tree of high occurrence in Brazilian restingas. Significant increases in iron content were found in plants exposed to SPM_Fe applied onto leaf and soil surfaces. However, only the application of SPM_Fe on leaves of C. hilariana caused significant reductions in some evaluated characteristics such as photosynthetic rate, stomatal conductance, transpiration, organic acid accumulation, potential quantum yield of PSII, and changes in daily CAM photosynthesis pattern. Increase in relative membrane permeability and reduction in catalase and superoxide dismutase activities in the leaves of plants exposed to SPM_Fe also were observed; however, lipid peroxidation did not change. These responses seem to be due to the combination of physical effects such as increase of leaf temperature, reduction in light absorption, obstruction of stomatal pores, and biochemical effects triggered by oxidative stress.