4,263 research outputs found
Rigid motions: action-angles, relative cohomology and polynomials with roots on the unit circle
Revisiting canonical integration of the classical solid near a uniform
rotation, canonical action angle coordinates, hyperbolic and elliptic, are
constructed in terms of various power series with coefficients which are
polynomials in a variable depending on the inertia moments. Normal forms
are derived via the analysis of a relative cohomology problem and shown to be
obtainable without the use of ellitptic integrals (unlike the derivation of the
action-angles). Results and conjectures also emerge about the properties of the
above polynomials and the location of their roots. In particular a class of
polynomials with all roots on the unit circle arises.Comment: 26 pages, 1 figur
Local stability of a gravitating filament: a dispersion relation
Filamentary structures are ubiquitous in astrophysics and are observed at
various scales. On a cosmological scale, matter is usually distributed along
filaments, and filaments are also typical features of the interstellar medium.
Within a cosmic filament, matter can contract and form galaxies, whereas an
interstellar gas filament can clump into a series of bead-like structures which
can then turn into stars. To investigate the growth of such instabilities, we
derive a local dispersion relation for an idealized self-gravitating filament,
and study some of its properties. Our idealized picture consists of an infinite
self-gravitating and rotating cylinder with pressure and density related by a
polytropic equation of state. We assume no specific density distribution, treat
matter as a fluid, and use hydrodynamics to derive the linearized equations
that govern the local perturbations. We obtain a dispersion relation for
axisymmetric perturbations and study its properties in the (k_R, k_z) phase
space, where k_R and k_z are respectively the radial and longitudinal
wavenumbers. While the boundary between the stable and unstable regimes is
symmetrical in k_R and k_z and analogous to the Jeans criterion, the most
unstable mode displays an asymmetry that could constrain the shape of the
structures that form within the filament. Here the results are applied to a
fiducial interstellar filament, but could be extended for more astrophysical
systems such as cosmological filaments and tidal tails.Comment: 8 pages, 1 figure, published in A&
Algebraic Linearization of Dynamics of Calogero Type for any Coxeter Group
Calogero-Moser systems can be generalized for any root system (including the
non-crystallographic cases). The algebraic linearization of the generalized
Calogero-Moser systems and of their quadratic (resp. quartic) perturbations are
discussed.Comment: LaTeX2e, 13 pages, no figure
Quadratic Algebra associated with Rational Calogero-Moser Models
Classical Calogero-Moser models with rational potential are known to be
superintegrable. That is, on top of the r involutive conserved quantities
necessary for the integrability of a system with r degrees of freedom, they
possess an additional set of r-1 algebraically and functionally independent
globally defined conserved quantities. At the quantum level, Kuznetsov
uncovered the existence of a quadratic algebra structure as an underlying key
for superintegrability for the models based on A type root systems. Here we
demonstrate in a universal way the quadratic algebra structure for quantum
rational Calogero-Moser models based on any root systems.Comment: 19 pages, LaTeX2e, no figure
The relationship between international humanitarian law and human rights law from the perspective of a human rights treaty body
The debate about the simultaneous applicability of international humanitarian law and human rights law also affects human rights treaty bodies. The article first considers the difficulty for a human rights body in determining whether international humanitarian law is applicable; second, it examines the problems in practice in applying the lex specialis doctrine and the question of derogation in this particular context. The author finally outlines the impact of the debate as to the extent of extraterritorial applicability of human rights law
Short-pulse photoassociation in rubidium below the D line
Photoassociation of two ultracold rubidium atoms and the subsequent formation
of stable molecules in the singlet ground and lowest triplet states is
investigated theoretically. The method employs laser pulses inducing
transitions via excited states correlated to the asymptote.
Weakly bound molecules in the singlet ground or lowest triplet state can be
created by a single pulse while the formation of more deeply bound molecules
requires a two-color pump-dump scenario. More deeply bound molecules in the
singlet ground or lowest triplet state can be produced only if efficient
mechanisms for both pump and dump steps exist. While long-range
-potentials allow for efficient photoassociation, stabilization is
facilitated by the resonant spin-orbit coupling of the states.
Molecules in the singlet ground state bound by a few wavenumbers can thus be
formed. This provides a promising first step toward ground state molecules
which are ultracold in both translational and vibrational degrees of freedom
The first derivative of the period function of a plane vector field
The algorithm of the successive derivatives introduced in \cite{5} was implemented in \cite{7}, \cite{8}. This algorithm is based on the existence of a decomposition of 1-forms associated to the relative cohomology of the Hamiltonian function which is perturbed. We explain here how the first step of this algorithm gives also the first derivative of the period function. This includes, for instance, new presentations of formulas obtained by Carmen Chicone and Marc Jacobs in \cite{3}
Nonstandard Work Arrangements in France and the United States: Institutional Contexts, Labor Market Conditions, and Patterns of Use
Allied Health Professions in the Health-sector Job Structure
This article reviews the characteristics of allied health professions in the U.S., Massachusetts, and Boston health sectors. These occupations are considered in the broader context of the multitiered job structure of the health sector and their gender and ethnic composition. The discussion includes surveys of vacancy rates and wage levels for selected allied health professions in Massachusetts hospitals. The article concludes with a more detailed, albeit national, picture of these occupations in the hospital sector per se, their demographic composition, and earnings level
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