12,907 research outputs found
Stabilization of solitons of the multidimensional nonlinear Schrodinger equation: Matter-wave breathers
We demonstrate that stabilization of solitons of the multidimensional
Schrodinger equation with a cubic nonlinearity may be achieved by a suitable
periodic control of the nonlinear term. The effect of this control is to
stabilize the unstable solitary waves which belong to the frontier between
expanding and collapsing solutions and to provide an oscillating solitonic
structure, some sort of breather-type solution. We obtain precise conditions on
the control parameters to achieve the stabilization and compare our results
with accurate numerical simulations of the nonlinear Schrodinger equation.
Because of the application of these ideas to matter waves these solutions are
some sort of matter breathers
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
Differential Astrometry over 15 degrees
We observed the pair of radio sources 1150+812 and 1803+784 in November 1993
with a VLBI array, simultaneously recording at 8.4 and 2.3 GHz. We determined
the angular separation between the two sources with submilliarcsecond accuracy
by using differential techniques. This result demonstrates the feasibility of
high precision differential astrometry for radio sources separated in the sky
by almost 15 degrees, and opens the avenue to its application to larger samples
of radio sources.Comment: 6 pages, latex2e, 2 figures, To appear in the proceedings of the
EVN/JIVE Symposium No. 4, New Astronomy Reviews (eds. Garret, M. Campbell,
R., and Gurvits, L.
Hierarchy of Floquet gaps and edge states for driven honeycomb lattices
Electromagnetic driving in a honeycomb lattice can induce gaps and
topological edge states with a structure of increasing complexity as the
frequency of the driving lowers. While the high frequency case is the most
simple to analyze we focus on the multiple photon processes allowed in the low
frequency regime to unveil the hierarchy of Floquet edge-states. In the case of
low intensities an analytical approach allows us to derive effective
Hamiltonians and address the topological character of each gap in a
constructive manner. At high intensities we obtain the net number of edge
states, given by the winding number, with a numerical calculation of the Chern
numbers of each Floquet band. Using these methods, we find a hierarchy that
resembles that of a Russian nesting doll. This hierarchy classifies the gaps
and the associated edge states in different orders according to the
electron-photon coupling strength. For large driving intensities, we rely on
the numerical calculation of the winding number, illustrated in a map of
topological phase transitions. The hierarchy unveiled with the low energy
effective Hamiltonians, alongside with the map of topological phase transitions
discloses the complexity of the Floquet band structure in the low frequency
regime. The proposed method for obtaining the effective Hamiltonian can be
easily adapted to other Dirac Hamiltonians of two dimensional materials and
even the surface of a 3D topological insulator.Comment: Phys. Rev. A 91, 04362
Multi-wavelength differential astrometry of the S5 polar cap sample
We report on the status of our S5 polar cap astrometry program. Since 1997 we
have observed all the 13 radio sources of the complete S5 polar cap sample at
the wavelengths of 3.6 cm, 2 cm and 7 mm. Images of the radio sources at 3.6
and 2 cm have already been published reporting morphological changes.
Preliminary astrometric analyses have been carried out at three frequencies
with precisions in the relative position determination ranging from 80 to 20
microarcseconds. We report also on the combination of our phase-delay global
astrometry results with the microarcsecond-precise optical astrometry that will
be provided by future space-based instruments.Comment: 2 pages. 1 figure. Proceedings of the 7th European VLBI Network
Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R.
Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico
Nacional), p. 323-324. Needs evn2004.cl
Non-perturbative laser effects on the electrical properties of graphene nanoribbons
The use of Floquet theory combined with a realistic description of the
electronic structure of illuminated graphene and graphene nanoribbons is
developed to assess the emergence of non-adiabatic and non-perturbative effects
on the electronic properties. Here, we introduce an efficient computational
scheme and illustrate its use by applying it to graphene nanoribbons in the
presence of both linear and circular polarization. The interplay between
confinement due to the finite sample size and laser-induced transitions is
shown to lead to sharp features on the average conductance and density of
states. Particular emphasis is given to the emergence of the bulk limit
response.Comment: 14 pages, 8 figures, to appear in J. Phys.: Condens. Matter, special
issue on "Ultrafast and nonlinear optics in carbon nanomaterials
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