58 research outputs found
Generic Nekhoroshev theory without small divisors
In this article, we present a new approach of Nekhoroshev theory for a
generic unperturbed Hamiltonian which completely avoids small divisors
problems. The proof is an extension of a method introduced by P. Lochak which
combines averaging along periodic orbits with simultaneous Diophantine
approximation and uses geometric arguments designed by the second author to
handle generic integrable Hamiltonians. This method allows to deal with generic
non-analytic Hamiltonians and to obtain new results of generic stability around
linearly stable tori
Rigorous treatment of the averaging process for co-orbital motions in the planetary problem
We develop a rigorous analytical Hamiltonian formalism adapted to the study
of the motion of two planets in co-orbital resonance. By constructing a complex
domain of holomorphy for the planetary Hamilto-nian, we estimate the size of
the transformation that maps this Hamil-tonian to its first order averaged over
one of the fast angles. After having derived an integrable approximation of the
averaged problem, we bound the distance between this integrable approximation
and the averaged Hamiltonian. This finally allows to prove rigorous theorems on
the behavior of co-orbital motions over a finite but large timescale
Generic Nekhoroshev theory without small divisors
In this article, we present a new approach of Nekhoroshev theory for a generic unperturbed Hamiltonian which completely avoids small divisors problems. The proof is an extension of a method introduced by P. Lochak which combines averaging along periodic orbits with simultaneous Diophantine approximation and uses geometric arguments designed by the second author to handle generic integrable Hamiltonians. This method allows to deal with generic non-analytic Hamiltonians and to obtain new results of generic stability around linearly stable tori
On the nodal distance between two Keplerian trajectories with a common focus
We study the possible values of the nodal distance between
two non-coplanar Keplerian trajectories with a common
focus. In particular, given and assuming it is bounded, we compute
optimal lower and upper bounds for as functions of a
selected pair of orbital elements of , when the other elements vary.
This work arises in the attempt to extend to the elliptic case the optimal
estimates for the orbit distance given in (Gronchi and Valsecchi 2013) in case
of a circular trajectory . These estimates are relevant to
understand the observability of celestial bodies moving (approximately) along
when the observer trajectory is (close to) .Comment: 34 pages, 34 figure
Generic Nekhoroshev theory without small divisors
In this article, we present a new approach of Nekhoroshev theory for a generic unperturbed Hamiltonian which completely avoids small divisors problems. The proof is an extension of a method introduced by P. Lochak which combines averaging along periodic orbits with simultaneous Diophantine approximation and uses geometric arguments designed by the second author to handle generic integrable Hamiltonians. This method allows to deal with generic non-analytic Hamiltonians and to obtain new results of generic stability around linearly stable tori
Double exponential stability of quasi-periodic motion in Hamiltonian systems
We prove that generically, both in a topological and measure-theoretical
sense, an invariant Lagrangian Diophantine torus of a Hamiltonian system is
doubly exponentially stable in the sense that nearby solutions remain close to
the torus for an interval of time which is doubly exponentially large with
respect to the inverse of the distance to the torus. We also prove that for an
arbitrary small perturbation of a generic integrable Hamiltonian system, there
is a set of almost full positive Lebesgue measure of KAM tori which are doubly
exponentially stable. Our results hold true for real-analytic but more
generally for Gevrey smooth systems
Antibody Evasion by a Gammaherpesvirus O-Glycan Shield
All gammaherpesviruses encode a major glycoprotein homologous to the Epstein-Barr virus gp350. These glycoproteins are often involved in cell binding, and some provide neutralization targets. However, the capacity of gammaherpesviruses for long-term transmission from immune hosts implies that in vivo neutralization is incomplete. In this study, we used Bovine Herpesvirus 4 (BoHV-4) to determine how its gp350 homolog - gp180 - contributes to virus replication and neutralization. A lack of gp180 had no impact on the establishment and maintenance of BoHV-4 latency, but markedly sensitized virions to neutralization by immune sera. Antibody had greater access to gB, gH and gL on gp180-deficient virions, including neutralization epitopes. Gp180 appears to be highly O-glycosylated, and removing O-linked glycans from virions also sensitized them to neutralization. It therefore appeared that gp180 provides part of a glycan shield for otherwise vulnerable viral epitopes. Interestingly, this O-glycan shield could be exploited for neutralization by lectins and carbohydrate-specific antibody. The conservation of O-glycosylation sites in all gp350 homologs suggests that this is a general evasion mechanism that may also provide a therapeutic target
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