30,053 research outputs found
Fractional Euler-Lagrange differential equations via Caputo derivatives
We review some recent results of the fractional variational calculus.
Necessary optimality conditions of Euler-Lagrange type for functionals with a
Lagrangian containing left and right Caputo derivatives are given. Several
problems are considered: with fixed or free boundary conditions, and in
presence of integral constraints that also depend on Caputo derivatives.Comment: This is a preprint of a paper whose final and definite form will
appear as Chapter 9 of the book Fractional Dynamics and Control, D. Baleanu
et al. (eds.), Springer New York, 2012, DOI:10.1007/978-1-4614-0457-6_9, in
pres
Microlensing path parametrization for Earth-like Exoplanet detection around solar mass stars
We propose a new parametrization of the impact parameter u0 and impact angle
{\alpha} for microlensing systems composed by an Earth-like Exoplanet around a
Solar mass Star at 1 AU. We present the caustic topology of such system, as
well as the related light curves generated by using such a new parametrization.
Based on the same density of points and accuracy of regular methods, we obtain
results 5 times faster for discovering Earth-like exoplanet. In this big data
revolution of photometric astronomy, our method will impact future missions
like WFIRST (NASA) and Euclid (ESA) and they data pipelines, providing a rapid
and deep detection of exoplanets for this specific class of microlensing event
that might otherwise be lost.Comment: 8 pages, 7 figures, accepted to be published in The Astronomical
Journa
The dust masses of powerful radio galaxies: clues to the triggering of their activity
We use deep Herschel Space Observatory observations of a 90% complete sample
of 32 intermediate-redshift 2Jy radio galaxies (0.05 < z < 0.7) to estimate the
dust masses of their host galaxies and thereby investigate the triggering
mechanisms for their quasar-like AGN. The dust masses derived for the radio
galaxies (7.2x10^5 < M_d < 2.6x10^8 M_sun) are intermediate between those of
quiescent elliptical galaxies on the one hand, and ultra luminous infrared
galaxies (ULIRGs) on the other. Consistent with simple models for the
co-evolution of supermassive black holes and their host galaxies, these results
suggest that most of the radio galaxies represent the late time re-triggering
of AGN activity via mergers between the host giant elliptical galaxies and
companion galaxies with relatively low gas masses. However, a minority of the
radio galaxies in our sample (~20%) have high, ULIRG-like dust masses, along
with evidence for prodigious star formation activity. The latter objects are
more likely to have been triggered in major, gas-rich mergers that represent a
rapid growth phase for both their host galaxies and their supermassive black
holes.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
DMRG study of the Bond Alternating \textbf{S}=1/2 Heisenberg ladder with Ferro-Antiferromagnetic couplings
We obtain the phase diagram in the parameter space and an
accurate estimate of the critical line separating the different phases. We show
several measuments of the magnetization, dimerization, nearest neighbours
correlation, and density of energy in the different zones of the phase diagram,
as well as a measurement of the string order parameter proposed as the non
vanishing phase order parameter characterizing Haldane phases. All these
results will be compared in the limit with the behaviour of the
Bond Alternated Heisenberg Chain (BAHC). The analysis of our
data supports the existence of a dimer phase separated by a critical line from
a Haldane one, which has exactly the same nature as the Haldane phase in the
BAHC.Comment: Version 4. 8 pages, 15 figures (12 figures in document
The radiation of a uniformly accelerated charge is beyond the horizon: a simple derivation
We show, by exploring some elementary consequences of the covariance of
Maxwell's equations under general coordinate transformations, that, despite
inertial observers can indeed detect electromagnetic radiation emitted from a
uniformly accelerated charge, comoving observers will see only a static
electric field. This simple analysis can help understanding one of the most
celebrated paradoxes of last century.Comment: Revtex, 6 pages, 2 figures. v2: Some small corrections. v3: Citation
of a earlier paper included. v4: Some stylistic changes. v5: Final version to
appear in AJ
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