1,419 research outputs found
On the number of limit cycles of the Lienard equation
In this paper, we study a Lienard system of the form dot{x}=y-F(x),
dot{y}=-x, where F(x) is an odd polynomial. We introduce a method that gives a
sequence of algebraic approximations to the equation of each limit cycle of the
system. This sequence seems to converge to the exact equation of each limit
cycle. We obtain also a sequence of polynomials R_n(x) whose roots of odd
multiplicity are related to the number and location of the limit cycles of the
system.Comment: 10 pages, 5 figures. Submitted to Physical Review
Binding characteristics of Hoechst 33258 with calf thymus DNA, poly[d(A-T)] and d(CCGGAATTCCGG): Multiple stoichiometries and determination of tight binding with a wide spectrum of site affinities
Gravitomagnetic Jets
We present a family of dynamic rotating cylindrically symmetric Ricci-flat
gravitational fields whose geodesic motions have the structure of
gravitomagnetic jets. These correspond to helical motions of free test
particles up and down parallel to the axis of cylindrical symmetry and are
reminiscent of the motion of test charges in a magnetic field. The speed of a
test particle in a gravitomagnetic jet asymptotically approaches the speed of
light. Moreover, numerical evidence suggests that jets are attractors. The
possible implications of our results for the role of gravitomagnetism in the
formation of astrophysical jets are briefly discussed.Comment: 47 pages, 8 figures; v2: minor improvements; v3: paragraph added at
the end of Sec. V and other minor improvements; v4: reference added, typos
corrected, sentence added on p. 24; v5: a few minor improvement
Some results on homoclinic and heteroclinic connections in planar systems
Consider a family of planar systems depending on two parameters and
having at most one limit cycle. Assume that the limit cycle disappears at some
homoclinic (or heteroclinic) connection when We present a method
that allows to obtain a sequence of explicit algebraic lower and upper bounds
for the bifurcation set The method is applied to two quadratic
families, one of them is the well-known Bogdanov-Takens system. One of the
results that we obtain for this system is the bifurcation curve for small
values of , given by . We obtain
the new three terms from purely algebraic calculations, without evaluating
Melnikov functions
Natuurrapport 2003: toestand van de natuur in Vlaanderen: cijfers voor het beleid: samenvatting / English summary
Gène Cou nu, performances de ponte et efficacité alimentaire selon la température chez la poule
Orbital solutions derived from radial velocities and time delays for four {\it Kepler} systems with A/F-type (candidate) hybrid pulsators
The presence of A/F-type {\it Kepler} hybrid stars extending across the
entire Sct- Dor instability strips and beyond remains largely
unexplained. In order to better understand these particular stars, we performed
a multi-epoch spectroscopic study of 49 candidate A/F-type hybrid stars and one
cool(er) hybrid object detected by the {\it Kepler} mission. We determined a
lower limit of 27 % for the multiplicity fraction. For six spectroscopic
systems, we also reported long-term variations of the time delays. For four
systems, the time delay variations are fully coherent with those of the radial
velocities and can be attributed to orbital motion. We aim to improve the
orbital solutions for those systems with long orbital periods (order of 4-6
years) among the {\it Kepler} hybrid stars. The orbits are computed based on a
simultaneous modelling of the RVs obtained with high-resolution spectrographs
and the photometric time delays derived from time-dependent frequency analyses
of the {\it Kepler} light curves. We refined the orbital solutions of four
spectroscopic systems with A/F-type {\it Kepler} hybrid component stars: KIC
4480321, 5219533, 8975515 and KIC 9775454. Simultaneous modelling of both data
types analysed together enabled us to improve the orbital solutions, obtain
more robust and accurate information on the mass ratio, and identify the
component with the short-period Sct-type pulsations. In several cases,
we were also able to derive new constraints for the minimum component masses.
From a search for regular frequency patterns in the high-frequency regime of
the Fourier transforms of each system, we found no evidence of tidal splitting
among the triple systems with close (inner) companions. However, some systems
exhibit frequency spacings which can be explained by the mechanism of
rotational splitting.Comment: 11 pages, 15 figures and 5 tables. Accepted for publication in A&
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