Nonlinear dynamics of electromagnetic turbulence in a nonuniform magnetized plasma

By using the hydrodynamic electron response with fixed (kinetic) ions along with Poisson's equation as well as Ampere's law, a system of nonlinear equations for low-frequency (in comparison with the electron gyrofrequency) long-(short-) wavelength electromagnetic waves in a nonuniform resistive magnetoplasma has been derived. The plasma contains equilibrium density gradient and sheared equilibrium plasma flows. In the linear limit, local dispersion relations are obtained and analyzed. It is found that sheared equilibrium flows can cause instability of Alfven-like electromagnetic waves even in the absence of a density gradient. Furthermore, it is shown that possible stationary solutions of the nonlinear equations without dissipation can be represented in the form of various types of vortices. On the other hand, the temporal behavior of our nonlinear dissipative systems without the equilibrium density inhomogeneity can be described by the generalized Lorenz equations which admit chaotic trajectories. The density inhomogeneity may lead to even qualitative changes in the chaotic dynamics. The results of our investigation should be useful in understanding the linear and nonlinear properties of nonthermal electromagnetic waves in space and laboratory plasmas. (C) 1998 American Institute of Physics.5361662

A class of stationary nonlinear dusty plasma equilibria

It is shown that nonparallel density and temperature gradients can produce magnetic fields in dusty plasmas. Spontaneously created magnetic fields can be maintained if there exists plasma vorticity. In order to understand this phenomena, a self-consistent dusty plasma equilibrium model is constructed by employing a kinetic description and invoking the Hamiltonian approach. Stationary nonlinear dusty plasma equilibria contain specific profiles for the plasma number density, the plasma current, and the magnetic field. The relevance of this investigation to low-temperature laboratory dusty and space plasmas is discussed. (C) 1999 American Institute of Physics. [S1070-664X(99)01407-X].672950295

Chaos in the parallel sheared plasma flow driven electromagnetic turbulence in nonuniform magnetoplasmas

By employing the two-fluid model, a system of nonlinear equations for low-frequency electromagnetic waves in nonuniform collisional magnetoplasmas has been derived. The plasma contains both the equilibrium density gradient and sheared flows. In the linear limit, a local dispersion relation has been obtained and analyzed in several interesting limiting cases. It is found that equilibrium sheared plasma flows cause instabilities of Alfven-type waves even in the absence of the density gradient. The numerical results also show a large growth rate of electromagnetic parallel velocity shear (PVS) mode compared to the electrostatic mode for some ionospheric parameters. For this case, the temporal nonlinear behavior of the relevant governing mode coupling equations is governed by six coupled equations, which are a generalization of the Lorenz-Stenflo equations and which admit chaotic trajectories. The results of this investigation should be useful for understanding the linear and nonlinear properties of electromagnetic waves that are generated by sheared plasma flows in magnetized plasmas. (C) 1999 American Institute of Physics. [S1070-664X(99)03604-6].641107111

Oligodendrocyte progenitor cells become regionally diverse and heterogeneous with age

Oligodendrocyte progenitor cells (OPCs), which differentiate into myelinating oligodendrocytes during central nervous system (CNS) development, are the main proliferative cells in the adult brain. OPCs are conventionally considered a homogeneous population, particularly with respect to their electrophysiological properties, but this has been debated. We show, by using single-cell electrophysiological recordings, that OPCs start out as a homogeneous population, but become functionally heterogeneous, varying both within and between brain regions and with age. These electrophysiological changes in OPCs correlate with the differentiation potential of OPCs; thus, they may underlie the differentiational differences in OPCs between regions and likewise differentiation failure with age.We acknowledge the support of the Wellcome - MRC Cambridge Stem Cell Institute core facility managers, in particular for this work Dr Maike Paramor and Miss Victoria Murray with RNA sequencing, and all staff members of the University Biomedical Services (UBS). This project has received funding from: the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 771411; R.T.K, K.A.E); the Wellcome Trust, a Research Career Development Fellowship (R.T.K. and K.A.E. 091543/Z/10/Z) and a Studentship (102160/Z/13/Z; Y.K); The Paul G Allen Frontiers Group, Allen Distinguished Investigator Award (12076, R.T.K., D.K.V.); The Medical Research Council, a studentship (S.O.S.); The Gates Foundation, a Gates Scholarship (S.S.), The Biotechnology and Biological Sciences Research Council, a studentship (S.A.); Homerton College Cambridge, a Junior Research Fellowship (D.K.V); The UK MS Society, a Cambridge Myelin Repair Centre grant (50; R.T.K, O.D.F.); The Fonds de recherche du Québec-Santé, a scholarship (Y.K.); The Cambridge Commonwealth European & International Trust, a scholarship (Y.K.); and the Lister Institute, a Research Prize (R.T.K., K.A.E, SOS)

A novel method for standardized application of fungal spore coatings for mosquito exposure bioassays

<p>Abstract</p> <p>Background</p> <p>Interest in the use of fungal entomopathogens against malaria vectors is growing. Fungal spores infect insects via the cuticle and can be applied directly on the insect to evaluate infectivity. For flying insects such as mosquitoes, however, application of fungal suspensions on resting surfaces is more realistic and representative of field settings. For this type of exposure, it is essential to apply specific amounts of fungal spores homogeneously over a surface for testing the effects of fungal dose and exposure time. Contemporary methods such as spraying or brushing spore suspensions onto substrates do not produce the uniformity and consistency that standardized laboratory assays require. Two novel fungus application methods using equipment developed in the paint industry are presented and compared.</p> <p>Methods</p> <p>Wired, stainless steel K-bars were tested and optimized for coating fungal spore suspensions onto paper substrates. Different solvents and substrates were evaluated. Two types of coating techniques were compared, i.e. manual and automated coating. A standardized bioassay set-up was designed for testing coated spores against malaria mosquitoes.</p> <p>Results</p> <p>K-bar coating provided consistent applications of spore layers onto paper substrates. Viscous Ondina oil formulations were not suitable and significantly reduced spore infectivity. Evaporative Shellsol T solvent dried quickly and resulted in high spore infectivity to mosquitoes. Smooth proofing papers were the most effective substrate and showed higher infectivity than cardboard substrates. Manually and mechanically applied spore coatings showed similar and reproducible effects on mosquito survival. The standardized mosquito exposure bioassay was effective and consistent in measuring effects of fungal dose and exposure time.</p> <p>Conclusions</p> <p>K-bar coating is a simple and consistent method for applying fungal spore suspensions onto paper substrates and can produce coating layers with accurate effective spore concentrations. The mosquito bioassay was suitable for evaluating fungal infectivity and virulence, allowing optimizations of spore dose and exposure time. Use of this standardized application method will help achieve reliable results that are exchangeable between different laboratories.</p