4,123 research outputs found
A Secular Relativistic Model For Solar System's Numerical Simulations
Using Gauss' averaged equations, we compute the secular relativistic effects
generated by the Sun on the argument of the perihelion and the mean anomaly of
an orbit. Then we test different alternative simpler models that have been
proposed to reproduce the secular relativistic effects in the orbital elements.
Generally, models introduce artificial perturbations that are
velocity-independent but that depend on the heliocentric distance. If these
perturbations are set as an impulse in a constant timestep integrator, when the
particle approaches perihelion the generated impulse could be very strong and
badly sampled, originating a spurious orbital evolution. In order to overcome
this setback, we propose two new models based on a constant,
distance-independent, perturbation. With these models we obtain the correct
secular drift in the argument of perihelion and the expected secular orbital
evolution is reproduced. We also discuss with some detail the secular effect
generated on the mean anomaly by different models.Comment: This work is an expanded version of Venturini and Gallardo (2010
Stellar laboratories. V. The Xe VI ultraviolet spectrum and the xenon abundance in the hot DO-type white dwarf RE0503-289
For the spectral analysis of spectra of hot stars with a high resolution and
high signal-to-noise ratio (S/N), advanced non-local thermodynamic equilibrium
(NLTE) model atmospheres are mandatory. These are strongly dependent on the
reliability of the atomic data that are used for their calculation.
Reliable Xe VI oscillator strengths are used to identify Xe lines in the
ultraviolet spectrum of the DO-type white dwarf RE0503-289 and to determine its
photospheric Xe abundance.
We publish newly calculated oscillator strengths that are based on a recently
measured Xe VI laboratory line spectrum. These strengths were used to consider
their radiative and collisional bound-bound transitions in detail in our NLTE
stellar-atmosphere models to analyze Xe VI lines exhibited in high-resolution
and high S/N UV observations of RE0503-289.
We identify three hitherto unknown Xe VI lines in the ultraviolet spectrum of
RE0503-289 and confirm the previously measured photospheric Xe abundance of
this white dwarf (log Xe = -4.2 +/- 0.6).
Reliable measurements and calculations of atomic data are prerequisite for
stellar-atmosphere modeling. Observed Xe VI line profiles in the ultraviolet
spectrum of the white dwarf RE0503-289 were well reproduced with the newly
calculated Xe VI oscillator strengths.Comment: 3 pages, 4 figure
The mass-radius relationship from solar-type stars to terrestrial planets: a review
In this review, we summarize our present knowledge of the behaviour of the
mass-radius relationship from solar-type stars down to terrestrial planets,
across the regime of substellar objects, brown dwarfs and giant planets.
Particular attention is paid to the identification of the main physical
properties or mechanisms responsible for this behaviour. Indeed, understanding
the mechanical structure of an object provides valuable information about its
internal structure, composition and heat content as well as its formation
history. Although the general description of these properties is reasonably
well mastered, disagreement between theory and observation in certain cases
points to some missing physics in our present modelling of at least some of
these objects. The mass-radius relationship in the overlaping domain between
giant planets and low-mass brown dwarfs is shown to represent a powerful
diagnostic to distinguish between these two different populations and shows
once again that the present IAU distinction between these two populations at a
given mass has no valid foundation.Comment: Cool Stars, Stellar Systems and the Sun 15, invited revie
Time boundary terms and Dirac constraints
Time boundary terms usually added to action principles are systematically
handled in the framework of Dirac's canonical analysis. The procedure begins
with the introduction of the boundary term into the integral Hamiltonian action
and then the resulting action is interpreted as a Lagrangian one to which
Dirac's method is applied. Once the general theory is developed, the current
procedure is implemented and illustrated in various examples which are
originally endowed with different types of constraints.Comment: 12 page
Range extension of Sanopus reticulatus (Teleostei: Batrachoididae) in the Yucatán Peninsula
AbstractThe geographic range of Sanopus reticulatus Collette, 1983 in the Yucatán Peninsula is extended about 75km southwest to Celestún and about 200km to Las Coloradas. During the periods of algal blooms in Telchac and Las Coloradas and specific sampling in Celestún, Yucatán, on August 14 and September 26 and 27, 2015, 10 specimens were collected, proving that this species has a distribution all along the Yucatán state coast
Some applications of quasi-velocities in optimal control
In this paper we study optimal control problems for nonholonomic systems
defined on Lie algebroids by using quasi-velocities. We consider both
kinematic, i.e. systems whose cost functional depends only on position and
velocities, and dynamic optimal control problems, i.e. systems whose cost
functional depends also on accelerations. The formulation of the problem
directly at the level of Lie algebroids turns out to be the correct framework
to explain in detail similar results appeared recently (Maruskin and Bloch,
2007). We also provide several examples to illustrate our construction.Comment: Revtex 4.1, 20 pages. To appear in Int. J. Geom. Meth. Modern Physic
Magnetization in AIIIBV semiconductor heterostructures with the depletion layer of manganese
The magnetic moment and magnetization in GaAs/GaInAs/GaAs
heterostructures with Mn deluted in GaAs cover layers and with atomically
controlled Mn -layer thicknesses near GaInAs-quantum well (3 nm)
in temperature range T=(1.8-300)K in magnetic field up to 50 kOe have been
investigated. The mass magnetization all of the samples of
GaAs/GaInAs/GaAs with Mn increases with the increasing of the
magnetic field that pointed out on the presence of low-dimensional
ferromagnetism in the manganese depletion layer of GaAs based structures. It
has been estimated the manganese content threshold at which the ferromagnetic
ordering was found.Comment: 8 pages, 3 figure
Crystal Structures of [Fe]-Hydrogenase from Methanolacinia paynteri Suggest a Path of the FeGP-Cofactor Incorporation Process
[Fe]-hydrogenase (Hmd) catalyzes the reversible heterolytic cleavage of H-2, and hydride transfer to methenyl-tetrahydromethanopterin (methenyl-H4MPT+). The iron-guanylylpyridinol (FeGP) cofactor, the prosthetic group of Hmd, can be extracted from the holoenzyme and inserted back into the protein. Here, we report the crystal structure of an asymmetric homodimer of Hmd fromMethanolacinia paynteri(pHmd), which was composed of one monomer in the open conformation with the FeGP cofactor (holo-form) and a second monomer in the closed conformation without the cofactor (apo-form). In addition, we report the symmetric pHmd-homodimer structure in complex with guanosine monophosphate (GMP) or guanylylpyridinol (GP), in which each ligand was bound to the protein, where the GMP moiety of the FeGP-cofactor is bound in the holo-form. Binding of GMP and GP modified the local protein structure but did not induce the open conformation. The amino-group of the Lys150 appears to interact with the 2-hydroxy group of pyridinol ring in the pHmd-GP complex, which is not the case in the structure of the pHmd-FeGP complex. Lys150Ala mutation decreased the reconstitution rate of the active enzyme with the FeGP cofactor at the physiological pH. These results suggest that Lys150 might be involved in the FeGP-cofactor incorporation into the Hmd protein in vivo
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