56 research outputs found
Transverse quasilinear relaxation in inhomogeneous magnetic field
Transverse quasilinear relaxation of the cyclotron-Cherenkov instability in
the inhomogeneous magnetic field of pulsar magnetospheres is considered. We
find quasilinear states in which the kinetic cyclotron-Cherenkov instability of
a beam propagating through strongly magnetized pair plasma is saturated by the
force arising in the inhomogeneous field due to the conservation of the
adiabatic invariant. The resulting wave intensities generally have nonpower law
frequency dependence, but in a broad frequency range can be well approximated
by the power law with the spectral index -2. The emergent spectra and fluxes
are consistent with the one observed from pulsars.Comment: 14 Pages, 4 Figure
Quasi-linear diffusion driving the synchrotron emission in active galactic nuclei
We study the role of the quasi-linear diffusion (QLD) in producing X-ray
emission by means of ultra-relativistic electrons in AGN magnetospheric flows.
We examined two regions: (a) an area close to the black hole and (b) the outer
magnetosphere. The synchrotron emission has been studied for ultra-relativistic
electrons and was shown that the QLD generates the soft and hard X-rays, close
to the black hole and on the light cylinder scales respectively. By considering
the cyclotron instability, we show that despite the short synchrotron cooling
timescales, the cyclotron modes excite transverse and longitudinal-transversal
waves. On the other hand, it is demonstrated that the synchrotron reaction
force and a force responsible for the conservation of the adiabatic invariant
tend to decrease the pitch angles, whereas the diffusion, that pushes back on
electrons by means of the aforementioned waves, tends to increase the pitch
angles. By examining the quasi-stationary state, we investigate a regime in
which these two processes are balanced and a non-vanishing value of pitch
angles is created.Comment: 4 pages, 3 figure
Weak turbulence theory of the non-linear evolution of the ion ring distribution
The nonlinear evolution of an ion ring instability in a low-beta
magnetospheric plasma is considered. The evolution of the two-dimensional ring
distribution is essentially quasilinear. Ignoring nonlinear processes the
time-scale for the quasilinear evolution is the same as for the linear
instability 1/t_ql gamma_l. However, when nonlinear processes become important,
a new time scale becomes relevant to the wave saturation mechanism. Induced
nonlinear scattering of the lower-hybrid waves by plasma electrons is the
dominant nonlinearity relevant for plasmas in the inner magnetosphere and
typically occurs on the timescale 1/t_ql w(M/m)W/nT, where W is the wave energy
density, nT is the thermal energy density of the background plasma, and M/m is
the ion to electron mass ratio, which has the consequence that the wave
amplitude saturates at a low level, and the timescale for quasilinear
relaxation is extended by orders of magnitude
Close range photogrammetry in the survey of the coastal area geoecological conditions (on the example of Portugal)
Close range digital photogrammetry, which involves the application of unmanned aerial vehicle (UAV), has been used in a growing number of diverse applications across different scientific disciplines. Our objective was to use the mentioned method in the survey of the contemporary geoecological conditions of the coastal area on the example of Portuguese northwest coastal zone. The coastal zone can be subdivided into two geomorphological sectors: Sector 1, between the Minho River and the town of Espinho, where the coastal segments consist of estuaries, sandy and shingle beaches with rocky outcrops, and Holocene dune systems. The estuaries and the foredunes in particular are very degraded by human activities; and Sector 2, between Espinho and the Mondego Cape, where coastal lagoons and Holocene dune systems occur. We chose two beaches for surveying – Aguçadoura and Ramalha to which the drone swinglet CAM took the photos. We used the ground control software eMotion 2 to plan the flights over the study area and controlled the drone’s trajectory during flight. After processing the obtained images in the program of AgisoftPhotoscanPro, we generated the 2D orthophotos and 3D digital elevation models (DEM) of the research sections. At this stage of study we derived the above product without using the ground control points, or we used only the camera GPS data. Based on these models the compilation of the large-scale maps of high resolution (1cm-5cm) will be possible in the GISs for monitoring and management of the geoecological state of the mentioned beaches in case to precise the x, y and z values of the models with the geodetic device of Differential GPSs in the selected ground control points (GCP).We are grateful to the European Commission ERASMUS-MUNDUS Action-2 ELECTRA program and the Earth Sciences Centre of the University of Minho (Braga, Portugal) in supporting us to conduct the field works and research.info:eu-repo/semantics/publishedVersio
The generation of connected high and very high energy -rays and radio emission in active galactic nuclei
We consider relativistic electrons in magnetospheric flows close to a
supermassive black hole and study the mechanism of quasi-linear diffusion (QLD)
to investigate the correlation between -ray and radio emission in
active galactic nuclei. Moving in the nonuniform magnetic field the particles
experience a force that is responsible for the conservation of the adiabatic
invariant. This force, together with the radiation reaction force, tends to
decrease the pitch angles. Contrary to this, the QLD attempts to increase the
pitch angle, and this maintains the synchrotron emission regime. To examine the
balance between the QLD and the aforementioned dissipative factors we
investigate the quasi-stationary state by applying the kinetic equation.
Considering the magnetospheric plasma close to the supermassive black hole, we
examined the efficiency of the QLD for different parameters. By examining the
cyclotron instability, we show that despite the efficient dissipative factors,
the cyclotron modes excite transverse and longitudinal-transversal waves which
leads to the QLD. We find that the QLD provides a connection of emission in the
-ray and radio domains. We show that under favourable conditions the
radio emission from 22 MHz to 9 GHz on the mpc scale is associated with
-ray emission from 900 GeV down to 9 GeV on the same scale.Comment: 5 pages, 5 figure
Linear coupling and over-reflection phenomena of magnetohydrodynamic waves in smooth shear flows
Special features of magnetohydrodynamic waves linear dynamics in smooth shear
flows are studied. Quantitative asymptotic and numerical analysis are performed
for wide range of system parameters when basic flow has constant shear of
velocity and uniform magnetic field is parallel to the basic flow. The special
features consist of magnetohydrodynamic wave mutual transformation and
over-reflection phenomena. The transformation takes place for arbitrary shear
rates and involves all magnetohydrodynamic wave modes. While the
over-reflection occurs only for slow magnetosonic and Alfv\'en waves at high
shear rates. Studied phenomena should be decisive in the elaboration of the
self-sustaining model of magnetohydrodynamic turbulence in the shear flows
Joining S100 proteins and migration:for better or for worse, in sickness and in health
The vast diversity of S100 proteins has demonstrated a multitude of biological correlations with cell growth, cell differentiation and cell survival in numerous physiological and pathological conditions in all cells of the body. This review summarises some of the reported regulatory functions of S100 proteins (namely S100A1, S100A2, S100A4, S100A6, S100A7, S100A8/S100A9, S100A10, S100A11, S100A12, S100B and S100P) on cellular migration and invasion, established in both culture and animal model systems and the possible mechanisms that have been proposed to be responsible. These mechanisms involve intracellular events and components of the cytoskeletal organisation (actin/myosin filaments, intermediate filaments and microtubules) as well as extracellular signalling at different cell surface receptors (RAGE and integrins). Finally, we shall attempt to demonstrate how aberrant expression of the S100 proteins may lead to pathological events and human disorders and furthermore provide a rationale to possibly explain why the expression of some of the S100 proteins (mainly S100A4 and S100P) has led to conflicting results on motility, depending on the cells used. © 2013 Springer Basel
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