1,617 research outputs found
Connection between type B (or C) and F factorizations and construction of algebras
In a recent paper (Del Sol Mesa A and Quesne C 2000 J. Phys. A: Math. Gen. 33
4059), we started a systematic study of the connections among different
factorization types, suggested by Infeld and Hull, and of their consequences
for the construction of algebras. We devised a general procedure for
constructing satellite algebras for all the Hamiltonians admitting a type E
factorization by using the relationship between type A and E factorizations.
Here we complete our analysis by showing that for Hamiltonians admitting a type
F factorization, a similar method, starting from either type B or type C ones,
leads to other types of algebras. We therefore conclude that the existence of
satellite algebras is a characteristic property of type E factorizable
Hamiltonians. Our results are illustrated with the detailed discussion of the
Coulomb problem.Comment: minor changes, 1 additional reference, final form to be published in
JP
Stability Properties of Strongly Magnetized Spine Sheath Relativistic Jets
The linearized relativistic magnetohydrodynamic (RMHD) equations describing a
uniform axially magnetized cylindrical relativistic jet spine embedded in a
uniform axially magnetized relativistically moving sheath are derived. The
displacement current is retained in the equations so that effects associated
with Alfven wave propagation near light speed can be studied. A dispersion
relation for the normal modes is obtained. Analytical solutions for the normal
modes in the low and high frequency limits are found and a general stability
condition is determined. A trans-Alfvenic and even a super-Alfvenic
relativistic jet spine can be stable to velocity shear driven Kelvin-Helmholtz
modes. The resonance condition for maximum growth of the normal modes is
obtained in the kinetically and magnetically dominated regimes. Numerical
solution of the dispersion relation verifies the analytical solutions and is
used to study the regime of high sound and Alfven speeds.Comment: 42 pages includes 7 figures, to appear in Ap
Particle acceleration in electron-ion jets
Weibel instability created in collisionless shocks is responsible for
particle (electron, positron, and ion) acceleration. Using a 3-D relativistic
electromagnetic particle (REMP) code, we have investigated particle
acceleration associated with a relativistic electron-ion jet fronts propagating
into an ambient plasma without initial magnetic fields with a longer simulation
system in order to investigate nonlinear stage of the Weibel instability and
its acceleration mechanism. The current channels generated by the Weibel
instability induce the radial electric fields. The z component of the Poynting
vector (E x B) become positive in the large region along the jet propagation
direction. This leads to the acceleration of jet electrons along the jet. In
particular the E x B drift with the large scale current channel generated by
the ion Weibel instability accelerate electrons effectively in both parallel
and perpendicular directions.Comment: 2 pages, 1 figure, Proceedings for Astrophysical Sources of High
Energy Particles and Radiation, AIP proceeding Series, eds . T. Bulik, G.
Madejski and B. Ruda
Catecismo de oratoria sagrada. Obra póstuma del Rmo. P. Gregorio Domínguez, preposito general del órden de clerigos menores y predicador de S.M.
Copia digital : Diputación de Málaga. Biblioteca Canovas del Castillo, 201
Validation of a globally-applicable method to measure urban tolerance of birds using citizen science data
Understanding species-specific responses to urbanization is essential to mitigate and preserve biodiversity in the face of increasing urbanization, but a major challenge is how to estimate urban tolerances for a wide array of species applicable over disparate regions. A promising approach is to assess urban tolerance by integrating geo-referenced information on species detections from citizen science data with estimations of urbanization intensity based on remotely-sensed night-time lights. While such citizen science urbanness scores (CSUS) are cost-effective, intuitive, and easily-repeatable anywhere in the world, whether the scores accurately describe urban tolerance still awaits empirical verification. By analysing >900 bird species worldwide, we find that CSUS correlates well with a standard measure of urban tolerance based on changes in abundance between urbanized and non-urbanized nearby habitats. Our analyses show that there is substantial variability in the relationship between these two metrics, but nevertheless highlights the potential for the CSUS approach in the future. Future improvements to the index, including incorporating rare species, and understanding the influence of intra-specific variability in response to urbanization, will be necessary to maximize the broad utility of the approach
Radiation from relativistic jets
Nonthermal radiation observed from astrophysical systems containing
relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic
nuclei (AGNs), and Galactic microquasar systems usually have power-law emission
spectra. Recent PIC simulations of relativistic electron-ion
(electron-positron) jets injected into a stationary medium show that particle
acceleration occurs within the downstream jet. In the presence of relativistic
jets, instabilities such as the Buneman instability, other two-streaming
instability, and the Weibel (filamentation) instability create collisionless
shocks, which are responsible for particle (electron, positron, and ion)
acceleration. The simulation results show that the Weibel instability is
responsible for generating and amplifying highly nonuniform, small-scale
magnetic fields. These magnetic fields contribute to the electron's transverse
deflection behind the jet head. The ``jitter'' radiation from deflected
electrons in small-scale magnetic fields has different properties than
synchrotron radiation which is calculated in a uniform magnetic field. This
jitter radiation, a case of diffusive synchrotron radiation, may be important
to understand the complex time evolution and/or spectral structure in gamma-ray
bursts, relativistic jets, and supernova remnants.Comment: 8 pages,3 figures, accepted for the Proceedings of Science of the
Workshop on Blazar Variability across the Electromagnetic Spectrum, April 22
to 25, 200
Vida del V. siervo de Dios Antonio Bermejo ...
Traducción de la obra de José Agustín Monge Solórzano y BarrientosCopia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201
Magnetic Field Generation in Core-Sheath Jets via the Kinetic Kelvin-Helmholtz Instability
We have investigated magnetic field generation in velocity shears via the
kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet
core and stationary plasma sheath. Our three-dimensional particle-in-cell
simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15
for both electron-proton and electron-positron plasmas. For electron-proton
plasmas we find generation of strong large-scale DC currents and magnetic
fields which extend over the entire shear-surface and reach thicknesses of a
few tens of electron skin depths. For electron-positron plasmas we find
generation of alternating currents and magnetic fields. Jet and sheath plasmas
are accelerated across the shear surface in the strong magnetic fields
generated by the kKHI. The mixing of jet and sheath plasmas generates
transverse structure similar to that produced by the Weibel instability.Comment: 28 pages, 12 figures, in press, ApJ, September 10, 201
Grafica y Accion Directa. Cinco horizontes de circulación en la producción del Taller 4 Rojo
In the research “Rojo y más Rojo. Taller 4 Rojo; producción gráfica y acción directa” (2009-2012), which led to a curatorship and a homonyms publication (2015), we paid special attention to broadly outline the visual production developed by the Group Taller 4 Rojo during the 1970s, which have been partially addressed and described by different studies in the field of art history in Colombia; we set out to identify sources and creative practices that characterized the production of this platform of collective creation as well to discuss their circulation. This article is a partial result of this research, from which we tried to point out five creative practices and fields of circulation that demonstrate the horizon of political action that Group Taller 4 Rojo proposed for itself, and was sustained by a combination of subjects, creative processes and practices.En la investigación “Rojo y más Rojo. Taller 4 Rojo; producción gráfica y acción directa” (2009-2012), de la que derivó una curaduría y una publicación homónimas (2015), prestamos especial atención a conformar un espectro amplio sobre la producción visual desarrollada por el Grupo Taller 4 Rojo durante la década de 1970, parcialmente abordada y descrita por diferentes trabajos del campo de la Historia del arte en Colombia; nos propusimos identificar fuentes y prácticas creativas que caracterizaron la producción de esta plataforma de creación colectiva así como sus horizontes de circulación. Este artículo es una lectura parcial sobre dicha investigación con la que esperamos señalar cinco prácticas creativas y campos de circulación que con mayor claridad manifiestan el horizonte de acción política que el Grupo Taller 4 Rojo se propuso, donde la combinación de temas, procesos creativos y prácticas de circulación sustentaron tales intereses
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