1,554 research outputs found
Emergence of chaotic attractor and anti-synchronization for two coupled monostable neurons
The dynamics of two coupled piece-wise linear one-dimensional monostable maps
is investigated. The single map is associated with Poincare section of the
FitzHugh-Nagumo neuron model. It is found that a diffusive coupling leads to
the appearance of chaotic attractor. The attractor exists in an invariant
region of phase space bounded by the manifolds of the saddle fixed point and
the saddle periodic point. The oscillations from the chaotic attractor have a
spike-burst shape with anti-phase synchronized spiking.Comment: To be published in CHAO
Self-similar turbulent dynamo
The amplification of magnetic fields in a highly conducting fluid is studied
numerically. During growth, the magnetic field is spatially intermittent: it
does not uniformly fill the volume, but is concentrated in long thin folded
structures. Contrary to a commonly held view, intermittency of the folded field
does not increase indefinitely throughout the growth stage if diffusion is
present. Instead, as we show, the probability-density function (PDF) of the
field strength becomes self-similar. The normalized moments increase with
magnetic Prandtl number in a powerlike fashion. We argue that the
self-similarity is to be expected with a finite flow scale and system size. In
the nonlinear saturated state, intermittency is reduced and the PDF is
exponential. Parallels are noted with self-similar behavior recently observed
for passive-scalar mixing and for map dynamos.Comment: revtex, 4 pages, 5 figures; minor changes to match published versio
Magnetic Field Amplification by Small-Scale Dynamo Action: Dependence on Turbulence Models and Reynolds and Prandtl Numbers
The small-scale dynamo is a process by which turbulent kinetic energy is
converted into magnetic energy, and thus is expected to depend crucially on the
nature of turbulence. In this work, we present a model for the small-scale
dynamo that takes into account the slope of the turbulent velocity spectrum
v(l) ~ l^theta, where l and v(l) are the size of a turbulent fluctuation and
the typical velocity on that scale. The time evolution of the fluctuation
component of the magnetic field, i.e., the small-scale field, is described by
the Kazantsev equation. We solve this linear differential equation for its
eigenvalues with the quantum-mechanical WKB-approximation. The validity of this
method is estimated as a function of the magnetic Prandtl number Pm. We
calculate the minimal magnetic Reynolds number for dynamo action, Rm_crit,
using our model of the turbulent velocity correlation function. For Kolmogorov
turbulence (theta=1/3), we find that the critical magnetic Reynolds number is
approximately 110 and for Burgers turbulence (theta=1/2) approximately 2700.
Furthermore, we derive that the growth rate of the small-scale magnetic field
for a general type of turbulence is Gamma ~ Re^((1-theta)/(1+theta)) in the
limit of infinite magnetic Prandtl numbers. For decreasing magnetic Prandtl
number (down to Pm approximately larger than 10), the growth rate of the
small-scale dynamo decreases. The details of this drop depend on the
WKB-approximation, which becomes invalid for a magnetic Prandtl number of about
unity.Comment: 13 pages, 8 figures; published in Phys. Rev. E 201
Professional readiness of the teacher of physical culture to work in conditions of inclusive education
Analyzes the effectiveness of implementation in the educational system, inclusive approach. Shows the problems and the importance of preparation of qualified pedagogical staff, including in the field of physical culture and sports. Considered professional readiness pedagog for physical cultureАнализируется эффективность внедрения в образовательную систему инклюзивного подхода. Показаны проблемы и значимость подготовки квалифицированных педагогических кадров, в том числе в области физической культуры и спорта. Рассматривается профессиональная готовность педагога по физической культур
Turbulent Origin of the Galactic-Center Magnetic Field: Nonthermal Radio Filaments
A great deal of study has been carried out over the last twenty years on the
origin of the magnetic activity in the Galactic center. One of the most popular
hypotheses assumes milli-Gauss magnetic field with poloidal geometry, pervading
the inner few hundred parsecs of the Galactic-center region. However, there is
a growing observational evidence for the large-scale distribution of a much
weaker field of B \lesssim 10 micro G in this region. Here, we propose that the
Galactic-center magnetic field originates from turbulent activity that is known
to be extreme in the central hundred parsecs. In this picture the spatial
distribution of the magnetic field energy is highly intermittent, and the
regions of strong field have filamentary structures. We propose that the
observed nonthermal radio filaments appear in (or, possibly, may be identified
with) such strongly magnetized regions. At the same time, the large-scale
diffuse magnetic field is weak. Both results of our model can explain the
magnetic field measurements of the the Galactic-center region. In addition, we
discuss the role of ionized outflow from stellar clusters in producing the long
magnetized filaments perpendicular to the Galactic plane.Comment: 11 pages, accepted to ApJ Letter
Simple model of complex dynamics of activity patterns in developing networks of neuronal cultures
Living neuronal networks in dissociated neuronal cultures are widely known
for their ability to generate highly robust spatiotemporal activity patterns in
various experimental conditions. These include neuronal avalanches satisfying
the power scaling law and thereby exemplifying self-organized criticality in
living systems. A crucial question is how these patterns can be explained and
modeled in a way that is biologically meaningful, mathematically tractable and
yet broad enough to account for neuronal heterogeneity and complexity. Here we
propose a simple model which may offer an answer to this question. Our
derivations are based on just few phenomenological observations concerning
input-output behavior of an isolated neuron. A distinctive feature of the model
is that at the simplest level of description it comprises of only two
variables, a network activity variable and an exogenous variable corresponding
to energy needed to sustain the activity and modulate the efficacy of signal
transmission. Strikingly, this simple model is already capable of explaining
emergence of network spikes and bursts in developing neuronal cultures. The
model behavior and predictions are supported by empirical observations and
published experimental evidence on cultured neurons behavior exposed to oxygen
and energy deprivation. At the larger, network scale, introduction of the
energy-dependent regulatory mechanism enables the network to balance on the
edge of the network percolation transition. Network activity in this state
shows population bursts satisfying the scaling avalanche conditions. This
network state is self-sustainable and represents a balance between global
network-wide processes and spontaneous activity of individual elements
Resonant Diffraction Radiation from an Ultrarelativistic Particle Moving Close to a Tilted Grating
A simple model for calculating the diffraction radiation characteristics from
an ultrarelativistic charged particle moving close to a tilted ideally
conducting strip is developed. Resonant diffraction radiation (RDR) is treated
as a superposition of the radiation fields for periodically spaced strips. The
RDR characteristics have been calculated as a function of the number of grating
elements, tilted angle, and initial particle energy. An analogy with both the
resonant transition radiation in absorbing medium and the parametric X-ray
radiation is noted.Comment: 17 pages, 12 figures, RevTe
Thomson Scattering of Coherent Diffraction Radiation by an Electron Bunch
The paper considers the process of Thomson scattering of coherent diffraction
radiation (CDR) produced by the preceding bunch of the accelerator on one of
the following bunches. It is shown that the yield of scattered hard photons is
proportional to N, where N is the number of electrons per bunch. A
geometry is chosen for the CDR generation and an expression is obtained for the
scattered photon spectrum with regard to the geometry used, that depends in an
explicit form on the bunch size. A technique is proposed for measuring the
bunch length using scattered radiation characteristics.Comment: 14 pages, LATEX, 6 ps.gz figures, submitted to Phys.Rev.
Synthesis of substituted tetrahydro-1,3-oxazines
A number of mono-, di-, tri-, and tetrasubstituted tetrahydro-1,3-oxazines were synthesized by the reaction of 3-amino- and 3-methylamino-1-propanols with aldehydes. © 1975 Consultants Bureau
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