13,883 research outputs found
Cylindrical plasmas generated by an annular beam of ultraviolet light
We investigate a cylindrical plasma system with ionization, by an annular beam of ultraviolet light, taking place only in the cylinderās outer region. In the steady state, both the outer and inner regions contain a plasma, with that in the inner region being uniform and field-free. At the interface between the two regions, there is an infinitesimal jump in ion density, the magnitude approaching zero in the quasi-neutral (kD ! 0) limit. The system offers the possibility of producing a uniform stationary plasma in the laboratory, hitherto obtained only with thermally produced alkali plasmas
Effect of assortative mixing in the second-order Kuramoto model
In this paper we analyze the second-order Kuramoto model presenting a
positive correlation between the heterogeneity of the connections and the
natural frequencies in scale-free networks. We numerically show that
discontinuous transitions emerge not just in disassortative but also in
assortative networks, in contrast with the first-order model. We also find that
the effect of assortativity on network synchronization can be compensated by
adjusting the phase damping. Our results show that it is possible to control
collective behavior of damped Kuramoto oscillators by tuning the network
structure or by adjusting the dissipation related to the phases movement.Comment: 7 pages, 6 figures. In press in Physical Review
Low-dimensional behavior of Kuramoto model with inertia in complex networks
Low-dimensional behavior of large systems of globally coupled oscillators has
been intensively investigated since the introduction of the Ott-Antonsen
ansatz. In this report, we generalize the Ott-Antonsen ansatz to second-order
Kuramoto models in complex networks. With an additional inertia term, we find a
low-dimensional behavior similar to the first-order Kuramoto model, derive a
self-consistent equation and seek the time-dependent derivation of the order
parameter. Numerical simulations are also conducted to verify our analytical
results.Comment: 6 figure
Spectra of random networks in the weak clustering regime
The asymptotic behaviour of dynamical processes in networks can be expressed
as a function of spectral properties of the corresponding adjacency and
Laplacian matrices. Although many theoretical results are known for the spectra
of traditional configuration models, networks generated through these models
fail to describe many topological features of real-world networks, in
particular non-null values of the clustering coefficient. Here we study effects
of cycles of order three (triangles) in network spectra. By using recent
advances in random matrix theory, we determine the spectral distribution of the
network adjacency matrix as a function of the average number of triangles
attached to each node for networks without modular structure and degree-degree
correlations. Implications to network dynamics are discussed. Our findings can
shed light in the study of how particular kinds of subgraphs influence network
dynamics
A treecode to simulate dust-plasma interactions
The interaction of a small object with surrounding plasma is an area of plasma-physics research with a multitude of applications. This paper introduces the plasma octree code pot , a microscopic simulator of a spheroidal dust grain in a plasma. pot uses the Barnes-Hut treecode algorithm to perform N -body simulations of electrons and ions in the vicinity of a chargeable spheroid, employing also the Boris particle-motion integrator and Hutchinson's reinjection algorithm from SCEPTIC; a description of the implementation of all three algorithms is provided. We present results from pot simulations of the charging of spheres in magnetized plasmas, and of spheroids in unmagnetized plasmas. The results call into question the validity of using the Boltzmann relation in hybrid PIC codes
Cooperative behavior between oscillatory and excitable units: the peculiar role of positive coupling-frequency correlations
We study the collective dynamics of noise-driven excitable elements,
so-called active rotators. Crucially here, the natural frequencies and the
individual coupling strengths are drawn from some joint probability
distribution. Combining a mean-field treatment with a Gaussian approximation
allows us to find examples where the infinite-dimensional system is reduced to
a few ordinary differential equations. Our focus lies in the cooperative
behavior in a population consisting of two parts, where one is composed of
excitable elements, while the other one contains only self-oscillatory units.
Surprisingly, excitable behavior in the whole system sets in only if the
excitable elements have a smaller coupling strength than the self-oscillating
units. In this way positive local correlations between natural frequencies and
couplings shape the global behavior of mixed populations of excitable and
oscillatory elements.Comment: 10 pages, 6 figures, published in Eur. Phys. J.
The CCD and readout electronics for the OMC instrument on Integral
The Optical Monitoring Camera (OMC) on ESA's Integral gamma-ray astronomy satellite is devoted to optical wavelength observations simultaneously covering the same field-of-view as the gamma-ray and X-ray instruments. The OMC consists of a refracting telescope with a CCD as the imaging device in the focal plane. Here we describe the CCD and its associated readout electronics, in particular pointing out features of interest to users of the OMC instrument and its data
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