107 research outputs found
Fluid theory of coherent magnetic vortices in high-beta space plasmas
In-situ observations in the Earth's and Saturn's magnetosheaths and in the
solar wind reveal the presence of Alfv\'en vortices as intermittent structures
in the range of scales from fluid lengths down to few ion lengths. The density
and the magnetic field associated with them appear to be compressible for
higher plasma betas. Until now, only incompressible Alfv\'en vortices have been
known. Motivated by space plasma observations we develop a new model of
magnetic vortices in high-beta plasmas with anisotropic temperature, possessing
compressible density and magnetic field, whose typical size ranges from fluid
to ion scales. At magneto-fluid scales we find novel non-propagating
field-aligned cylindrical monopoles and inclined propagating dipoles. Their
transverse magnetic and velocity fluctuations are aligned, but not identical,
{and they exhibit density and compressible magnetic field fluctuations and localized inside the vortex core. In the presence of
thermal anisotropy and acoustic effects, they may be correlated or
anti-correlated ;
fluctuations whose velocity along the magnetic field is below the ion thermal
speed are always correlated.} At ion or kinetic scales (with the smallest radii
) {and in the absence of acoustic
perturbations}, only dipolar Alfv\'en vortices survive with similar properties
as those at fluid scales, except for their that reaches the
level of . At kinetic scales we find also pressure balanced
dipolar structures, possessing finite parallel electric field and
purely compressional magnetic field perturbation
Propagation of ultrastrong femtosecond laser pulses in PLASMON-X
The derivation is presented of the nonlinear equations that describe the
propagation of ultrashort laser pulses in a plasma, in the Plasmon-X device. It
is shown that the Plasmon-X scheme used for the electron acceleration uses a
sufficiently broad beam () that justifies the use
of the standard stationary 1-D approximation in the electron hydrodynamic
equations, since the pulse width is sufficiently bigger than the pulse length
(). Furthermore, with the laser power of TW
and the spot size, the dimensionless laser vector potential
is sufficiently small , the nonlinearity is sufficiently weak to allow the power
expansion in the nonlinear Poissons's equation. Such approximation yields a
nonlinear Schr\" odinger equation with a reactive nonlocal nonlinear term. The
nonlocality contains a cosine function under the integral, indicating the
oscillating wake. For a smaller spot size that is used for the Thomson
scattering, m, the length and the width of the pulse are
comparable, and it is not possible to use the 1-D approximation in the
hydrodynamic equations. With such small spot size, the laser intensity is very
large, and most likely some sort of chanelling in the plasma would take place
(the plasma gets locally depleted so much that the electromagnetic wave
practically propagates in vacuum).Comment: Oral contribution O3.205 delivered at the 38th EPS Conference on
Plasma Physics, Strasbourg, France, 26 June - 1 July, 201
Self consistent thermal wave model description of the transverse dynamics for relativistic charged particle beams in magnetoactive plasmas
Thermal Wave Model is used to study the strong self-consistent Plasma Wake
Field interaction (transverse effects) between a strongly magnetized plasma and
a relativistic electron/positron beam travelling along the external magnetic
field, in the long beam limit, in terms of a nonlocal NLS equation and the
virial equation. In the linear regime, vortices predicted in terms of
Laguerre-Gauss beams characterized by non-zero orbital angular momentum (vortex
charge). In the nonlinear regime, criteria for collapse and stable oscillations
is established and the thin plasma lens mechanism is investigated, for beam
size much greater than the plasma wavelength. The beam squeezing and the
self-pinching equilibrium is predicted, for beam size much smaller than the
plasma wavelength, taking the aberrationless solution of the nonlocal Nonlinear
Schroeding equation.Comment: Poster presentation P5.006 at the 38th EPS Conference on Plasma
Physics, Strasbourg, France, 26 June - 1 July, 201
Soliton solutions of 3D Gross-Pitaevskii equation by a potential control method
We present a class of three-dimensional solitary waves solutions of the
Gross-Pitaevskii (GP) equation, which governs the dynamics of Bose-Einstein
condensates (BECs). By imposing an external controlling potential, a desired
time-dependent shape of the localized BEC excitation is obtained. The stability
of some obtained localized solutions is checked by solving the time-dependent
GP equation numerically with analytic solutions as initial conditions. The
analytic solutions can be used to design external potentials to control the
localized BECs in experiment.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Quantumlike description of the nonlinear and collective effects on relativistic electron beams in strongly magnetized plasmas
A numerical analysis of the self-interaction induced by a relativistic
electron/positron beam in the presence of an intense external longitudinal
magnetic field in plasmas is carried out. Within the context of the Plasma Wake
Field theory in the overdense regime, the transverse beam-plasma dynamics is
described by a quantumlike Zakharov system of equations in the long beam limit
provided by the Thermal Wave Model. In the limiting case of beam spot size much
larger than the plasma wavelength, the Zakharov system is reduced to a 2D
Gross-Pitaevskii-type equation, where the trap potential well is due to the
external magnetic field. Vortices, "beam halos" and nonlinear coherent states
(2D solitons) are predicted.Comment: Poster presentation P5.021 at the 38th EPS Conference on Plasma
Physics, Strasbourg, France, 26 June - 1 July, 201
Titanium dioxide nanoparticles enhance mortality of fish exposed to bacterial pathogens
Nano-TiO2 is immunotoxic to fish and reduces the bactericidal function of fish neutrophils. Here, fathead minnows (Pimephales promelas) were exposed to low and high environmentally relevant concentration of nano-TiO2 (2 ng g−1 and 10 μg g−1 body weight, respectively), and were challenged with common fish bacterial pathogens, Aeromonas hydrophila or Edwardsiella ictaluri. Pre-exposure to nano-TiO2 significantly increased fish mortality during bacterial challenge. Nano-TiO2 concentrated in the kidney and spleen. Phagocytosis assay demonstrated that nano-TiO2 has the ability to diminish neutrophil phagocytosis of A. hydrophila. Fish injected with TiO2 nanoparticles displayed significant histopathology when compared to control fish. The interplay between nanoparticle exposure, immune system, histopathology, and infectious disease pathogenesis in any animal model has not been described before. By modulating fish immune responses and interfering with resistance to bacterial pathogens, manufactured nano-TiO2 has the potential to affect fish survival in a disease outbreak
Stressing Issue of a Piezoceramic Cantilever with Electrode Coatings and Transversal Polarization
This paper presents a general case of stressing a rectangular piezoceramic cantilever with transversal polarization which is loaded at the free end by a concentrated force. Two mutually opposite surfaces of the rectangular cantilever are with electrode coatings on which an excitation electric voltage is applied to. By applying the reverse method for solving the problems of electroelasticity theory, componential displacements, electric potential, specific strains, electric fields and piezoelectric displacements are determined for the rectangular piezoceramic cantilever made from PZT4 piezoceramic material
WIRELESS SYSTEM FOR MEASUREMENT OF NATURAL BACKGROUND GAMMA RADIATION
In this paper a solution of wireless system for measurement of natural background gamma radiation using a commercial portable instrument GAMMA-SCOUT is presented. Since the GAMMA-SCOUT does not have factory built-in wireless communication it is necessary to upgrade its functionality by implementing an additional hardware module. Prototype of the module is based on a microcontroller Microchip PIC16F887 and RF transceiver Telit LE70-868. Structure and functionality of this hardware module are also presented in this paper in detail, as well as the experimental results obtained by the realized system
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