5,935 research outputs found
Age determination of the HR8799 planetary system using asteroseismology
Discovery of the first planetary system by direct imaging around HR8799 has
made the age determination of the host star a very important task. This
determination is the key to derive accurate masses of the planets and to study
the dynamical stability of the system. The age of this star has been estimated
using different procedures. In this work we show that some of these procedures
have problems and large uncertainties, and the real age of this star is still
unknown, needing more observational constraints. Therefore, we have developed a
comprehensive modeling of HR8799, and taking advantage of its gamma
Doradus-type pulsations, we have estimated the age of the star using
asteroseismology. The accuracy in the age determination depends on the rotation
velocity of the star, and therefore an accurate value of the inclination angle
is required to solve the problem. Nevertheless, we find that the age estimate
for this star previously published in the literature ([30,160] Myr) is
unlikely, and a more accurate value might be closer to the Gyr. This
determination has deep implications on the value of the mass of the objects
orbiting HR8799. An age around 1 Gyr implies that these objects are
brown dwarfs.Comment: 5 pages, 3 figures, accepted in MNRAS Letter
Complexity-entropy analysis at different levels of organization in written language
Written language is complex. A written text can be considered an attempt to
convey a meaningful message which ends up being constrained by language rules,
context dependence and highly redundant in its use of resources. Despite all
these constraints, unpredictability is an essential element of natural
language. Here we present the use of entropic measures to assert the balance
between predictability and surprise in written text. In short, it is possible
to measure innovation and context preservation in a document. It is shown that
this can also be done at the different levels of organization of a text. The
type of analysis presented is reasonably general, and can also be used to
analyze the same balance in other complex messages such as DNA, where a
hierarchy of organizational levels are known to exist
Solution to the Landau-Zener problem via Susskind-Glogower operators
We show that, by means of a right-unitary transformation, the fully quantized
Landau-Zener Hamiltonian in the weak-coupling regime may be solved by using
known solutions from the standard Landau-Zener problem. In the strong-coupling
regime, where the rotating wave approximation is not valid, we show that the
quantized Landau-Zener Hamiltonian may be diagonalized in the atomic basis by
means of a unitary transformation; hence allowing numerical solutions for the
few photons regime via truncation.Comment: 6 pages, 5 figure
The Spectral Function for Finite Nuclei in the Local Density Approximation
The spectral function for finite nuclei is computed within the framework of
the Local Density Approximation, starting from nuclear matter spectral
functions obtained with a realistic nucleon-nucleon interaction. The spectral
function is decomposed into a single-particle part and a ''correlated'' part;
the latter is treated in the local density approximation.
As an application momentum distributions, quasi-particle strengths and
overlap functions for valence hole states, and the light-cone momentum
distribution in finite nuclei are computed.Comment: 21 pages + 9 figures available upon request, RevTex, preprint
KVI-108
Propagation and perfect transmission in three-waveguide axially varying couplers
We study a class of three-waveguide axially varying structures whose dynamics
are described by the su(3) algebra. Their analytic propagator can be found
based on the corresponding Lie group generators. In particular, we show that
the field propagator corresponding to three-waveguide structures that have
arbitrarily varying coupling coefficients and identical refractive indices is
associated with the orbital angular momentum algebra. The conditions necessary
to achieve perfect transmission from the first to the last waveguide element
are obtained and particular cases are elucidated analytically.Comment: 5 pages, 4 figure
Structural transitions in vertically and horizontally coupled parabolic channels of Wigner crystals
Structural phase transitions in two vertically or horizontally coupled
channels of strongly interacting particles are investigated. The particles are
free to move in the -direction but are confined by a parabolic potential in
the -direction. They interact with each other through a screened power-law
potential (). In vertically coupled systems the channels
are stacked above each other in the direction perpendicular to the
-plane, while in horizontally coupled systems both channels are aligned
in the confinement direction. Using Monte Carlo (MC) simulations we obtain the
ground state configurations and the structural transitions as a function of the
linear particle density and the separation between the channels. At zero
temperature the vertically coupled system exhibits a rich phase diagram with
continuous and discontinuous transitions. On the other hand the vertically
coupled system exhibits only a very limited number of phase transitions due to
its symmetry. Further we calculated the normal modes for the Wigner crystals in
both cases. From MC simulations we found that in the case of vertically coupled
systems the zigzag transition is only possible for low densities. A
Ginzburg-Landau theory for the zigzag transition is presented, which predicts
correctly the behavior of this transition from which we interpret the
structural phase transition of the Wigner crystal through the reduction of the
Brillouin zone.Comment: 9 pages, 13 figure
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