41,268 research outputs found
Nonlinear Interaction of Transversal Modes in a CO2 Laser
We show the possibility of achieving experimentally a Takens-Bogdanov
bifurcation for the nonlinear interaction of two transverse modes ()
in a laser. The system has a basic O(2) symmetry which is perturbed by
some symmetry-breaking effects that still preserve the symmetry. The
pattern dynamics near this codimension two bifurcation under such symmetries is
described. This dynamics changes drastically when the laser properties are
modified.Comment: 16 pages, 0 figure
Competing mechanisms of stress-assisted diffusivity and stretch-activated currents in cardiac electromechanics
We numerically investigate the role of mechanical stress in modifying the
conductivity properties of the cardiac tissue and its impact in computational
models for cardiac electromechanics. We follow a theoretical framework recently
proposed in [Cherubini, Filippi, Gizzi, Ruiz-Baier, JTB 2017], in the context
of general reaction-diffusion-mechanics systems using multiphysics continuum
mechanics and finite elasticity. In the present study, the adapted models are
compared against preliminary experimental data of pig right ventricle
fluorescence optical mapping. These data contribute to the characterization of
the observed inhomogeneity and anisotropy properties that result from
mechanical deformation. Our novel approach simultaneously incorporates two
mechanisms for mechano-electric feedback (MEF): stretch-activated currents
(SAC) and stress-assisted diffusion (SAD); and we also identify their influence
into the nonlinear spatiotemporal dynamics. It is found that i) only specific
combinations of the two MEF effects allow proper conduction velocity
measurement; ii) expected heterogeneities and anisotropies are obtained via the
novel stress-assisted diffusion mechanisms; iii) spiral wave meandering and
drifting is highly mediated by the applied mechanical loading. We provide an
analysis of the intrinsic structure of the nonlinear coupling using
computational tests, conducted using a finite element method. In particular, we
compare static and dynamic deformation regimes in the onset of cardiac
arrhythmias and address other potential biomedical applications
Redescripción de Hemibrycon orcesi Böhlke, 1958 y H. polyodon (Günther, 1864) (Pisces, Characidae), incluye clave para las especies de Hemibrycon en Ecuador
Hemibrycon orcesi is readily distinguished from its congeners by its 13 to 16 teeth on maxilla, base of caudal fin scaled, 34 to 36 scales on lateral line with pores and 17 to 18 branched anal fin rays. H. polyodon is distinguished from its congeners by simple and branched dorsal fin rays of equal length and shape of humeral spot.
Key words: Characidae, Fishes, Taxonomy, Hemibrycon orcesi, Hemibrycon polyodon.Hemibrycon orcesi se distingue de las demás especies del género por presentar 13 a 16 dientes en el maxilar, por la base de la aleta caudal escamada, por 34 a 36 escamas con poros de la línea lateral, por 17 a 18 radios ramificados en la aleta anal. Mientras H. polyodon se distingue de sus congeneres por presentar la aleta dorsal con radios simples y ramificados de igual longitud y la forma de la mancha humeral.
Palabras claves: Peces, Characidae, Taxonomia, Hemibrycon orcesi, Hemibrycon polyodon
Aspectos taxonómicos de Cetopsorhamdia boquillae y C. nasus (Pisces, Heptapteridae), con anotaciones sobre su ecología en la cuenca alta de los ríos Magdalena y Cauca, Colombia
A taxonomic analysis of Cetopsorhamdia boquillae and Cetopsorhamdia nasus from the Magdalena and Cauca river basin in Colombia is reported here based on fresh topotypical materials. Cetopsorhamdia boquillae can be differentiated from its congener by the color pattern, mainly concerning three dark lines: one on the supraoccipital bone, another at the dorsal fin base and a third at the caudal fin base. The pterygiophore of the dorsal fin first ray is inserted anterior to the ninth vertebra. C. nasus is readily distinguished from its congener by its lack of supraneural spines, fewer than 60 premaxilla teeth, the posterior edge of mesethmoid, and orbitonasal lamina joined by a cartilage band, and the shape of the frontal canal. Cetopsorhamdia boquillae can be distinguished from C. nasus by the length of the adipose-dorsal fin base(statistically significant) (F = 21, P = 0.05), the number of
principal unbranched anal rays (5–6 in C. boquillae, 4 in C. nasus), and fewer vertebrae (36 in C. boquillae,
39 in C. nasus). Chemical, physical and ecological data are included to characterize the species habitats.Se efectuó un análisis taxonómico de Cetopsorhamdia boquillae y Cetopsorhamdia nasus de la cuenca alta de los ríos Magdalena y Cauca, basado en material fresco y topotípico. Cetopsorhamdia boquillae se distingue de las demás especies conocidas por la coloración (principalmente en presentar una banda vertical oscura a nivel de la base de la aleta caudal, otra banda oscura a nivel del supraoccipital que cubre todo el dorso, otra a nivel del origen de la aleta dorsal). El pterigióforo del primer radio de la aleta dorsal insertado anterior a la novena vértebra. C. nasus se distingue de sus congeneres por la ausencia de supraneurales, menos de 60 dientes en el premaxilar, por el borde posterior
del mesetmóides, la lámina orbitonasal unidos al frontal por una banda de cartílago, y la forma de la fontanela
craneal. Cetopsorhamdia boquillae se distingue de C. nasus por la distancia aleta adiposa–aleta dorsal y es
estadísticamente significativa (F = 21, P = 0,05), por el número de radios simples principales de la aleta anal (5–
6 en C. boquillae, 4 en C. nasus), y por el número menor de vértebras (36 en C. boquillae, 39 en C. nasus). Se incluyen datos ecológicos, físicos y químicos sobre las características de hábitat de las dos especies válidas
Features of the Extension of a Statistical Measure of Complexity to Continuous Systems
We discuss some aspects of the extension to continuous systems of a
statistical measure of complexity introduced by Lopez-Ruiz, Mancini and Calbet
(LMC) [Phys. Lett. A 209 (1995) 321]. In general, the extension of a magnitude
from the discrete to the continuous case is not a trivial process and requires
some choice. In the present study, several possibilities appear available. One
of them is examined in detail. Some interesting properties desirable for any
magnitude of complexity are discovered on this particular extension.Comment: 22 pages, 0 figure
Opaque or transparent? A link between neutrino optical depths and the characteristic duration of short gamma-ray bursts
Cosmological gamma ray bursts (GRBs) are thought to occur from violent
hypercritical accretion onto stellar mass black holes, either following core
collapse in massive stars or compact binary mergers. This dichotomy may be
reflected in the two classes of bursts having different durations. Dynamical
calculations of the evolution of these systems are essential if one is to
establish characteristic, relevant timescales. We show here for the first time
the result of dynamical simulations, lasting approximately one second, of
post--merger accretion disks around black holes, using a realistic equation of
state and considering neutrino emission processes. We find that the inclusion
of neutrino optical depth effects produces important qualitative temporal and
spatial transitions in the evolution and structure of the disk, which may
directly reflect upon the duration and variability of short GRBs.Comment: Accepted for publication in ApJ Letter
Can rigidly rotating polytropes be sources of the Kerr metric?
We use a recent result by Cabezas et al. to build up an approximate solution
to the gravitational field created by a rigidly rotating polytrope. We solve
the linearized Einstein equations inside and outside the surface of zero
pressure including second-order corrections due to rotational motion to get an
asymptotically flat metric in a global harmonic coordinate system. We prove
that if the metric and their first derivatives are continuous on the matching
surface up to this order of approximation, the multipole moments of this metric
cannot be fitted to those of the Kerr metric.Comment: LaTeX, 17 pages, submitted to CQ
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
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