Symplectic Cuts and Projection Quantization

The recently proposed projection quantization, which is a method to quantize particular subspaces of systems with known quantum theory, is shown to yield a genuine quantization in several cases. This may be inferred from exact results established within symplectic cutting.Comment: 12 pages, v2: additional examples and a new reference to related wor

Flow of magnetic repelling grains in a two-dimensional silo

During a typical silo discharge, the material flow rate is determined by the contact forces between the grains. Here, we report an original study concerning the discharge of a two-dimensional silo filled with repelling magnetic grains. This non-contact interaction leads to a different dynamics from the one observed with conventional granular materials. We found that, although the flow rate dependence on the aperture size follows roughly the power-law with an exponent $3/2$ found in non-repulsive systems, the density and velocity profiles during the discharge are totally different. New phenomena must be taken into account. Despite the absence of contacts, clogging and intermittence were also observed for apertures smaller than a critical size determined by the effective radius of the repulsive grains.Comment: 6 pages, 8 figure

New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach

We have calculated proper motions and re-evaluated the membership probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC 1807. We have obtained absolute proper motions from 25 plates in the reference system of the Tycho-2 Catalogue. The plates have a maximum epoch difference of 81 years; and they were taken with the double astrograph at Zo-Se station of Shanghai Observatory, which has an aperture of 40 cm and a plate scale of 30 arcsec/mm. The average proper motion precision is 1.55 mas/yr. These proper motions are used to determine the membership probabilities of stars in the region, based on there being only one very extended physical cluster: NGC 1817. With that aim, we have applied and compared parametric and non-parametric approaches to cluster/field segregation. We have obtained a list of 169 probable member stars.Comment: 11 pages, 8 figures, A&A in pres

Multivector Field Formulation of Hamiltonian Field Theories: Equations and Symmetries

We state the intrinsic form of the Hamiltonian equations of first-order Classical Field theories in three equivalent geometrical ways: using multivector fields, jet fields and connections. Thus, these equations are given in a form similar to that in which the Hamiltonian equations of mechanics are usually given. Then, using multivector fields, we study several aspects of these equations, such as the existence and non-uniqueness of solutions, and the integrability problem. In particular, these problems are analyzed for the case of Hamiltonian systems defined in a submanifold of the multimomentum bundle. Furthermore, the existence of first integrals of these Hamiltonian equations is considered, and the relation between {\sl Cartan-Noether symmetries} and {\sl general symmetries} of the system is discussed. Noether's theorem is also stated in this context, both the ``classical'' version and its generalization to include higher-order Cartan-Noether symmetries. Finally, the equivalence between the Lagrangian and Hamiltonian formalisms is also discussed.Comment: Some minor mistakes are corrected. Bibliography is updated. To be published in J. Phys. A: Mathematical and Genera

La cohesión y la seguridad ciudadana : un enfoque global

El artículo revisa el concepto de cohesión social y la noción de seguridad, partiendo del análisis de los profundos desequilibrios y desigualdades sociales que el modelo económico dominante a escala global desde los años 1980 crea o intensifica en América Latina. Centrado en las transformaciones que generaron la pérdida de confianza en las instituciones, en el Estado, en el mercado del trabajo, en la educación, incluso en la religión y en la familia, sobre las cuales reposaba la solidaridad orgánica en el marco de la sociedad industrial capitalista, examina cinco indicadores de la existencia de problemas de inseguridad en relación con la cohesión social. Pone de relieve que el problema de la inseguridad se asocia con la ruptura o la fragilidad de los mecanismos de integración y de mediación social y sostiene la necesidad de reconstruir la cohesión social para alcanzar la seguridad ciudadana, destacando que este proceso se funda en una profunda modificación política, económica y social enfocada en la inclusión social, de la que son co-responsables el Estado y los ciudadanos como actores de su propio desarrollo.The article reviews the concept of social cohesion and the notion of security, based on deep analysis of the imbalances and inequalities that the dominant economic model on a global scale since 1980 creates or intensifies in Latin America. Focused on the changes that generated a loss of confidence in institutions in the state, labor market, education, even religion and family, on which rested the organic solidarity within society industrial capitalism, examines five indicators of the existence of problems of insecurity in relation to social cohesion. Highlights that the problem of insecurity is associated with the break or fragility of the mechanisms of social integration and mediation and supports the need to rebuild social cohesion to achieve security, noting that this process is based on profound political change, economic and social focus on social inclusion, of which are co-responsible for the state and citizens as actors in their own development.Fil: Klein, Juan Luis. Université du Québec (Canadá)Fil: Enríquez, D.. Université du Québec (Canadá)Fil: Vega, R. V.. Université du Québec (Canadá

The extended halo of NGC 2682 (M 67) from Gaia DR2

Context: NGC 2682 is a nearby open cluster, approximately 3.5 Gyr old. Dynamically, most open clusters should dissolve on shorter timescales, of ~ 1 Gyr. Having survived until now, NGC 2682 was likely much more massive in the past, and is bound to have an interesting dynamical history. Aims: We investigate the spatial distribution of NGC 2682 stars to constrain its dynamical evolution, especially focusing on the marginally bound stars in the cluster outskirts. Methods: We use Gaia DR2 data to identify NGC 2682 members up to a distance of ~150 pc (10 degrees). Two methods (Clusterix and UPMASK) are applied to this end. We estimate distances to obtain three-dimensional stellar positions using a Bayesian approach to parallax inversion, with an appropriate prior for star clusters. We calculate the orbit of NGC 2682 using the GRAVPOT16 software. Results: The cluster extends up to 200 arcmin (50 pc) which implies that its size is at least twice as previously believed. This exceeds the cluster Hill sphere based on the Galactic potential at the distance of NGC 2682. Conclusions: The extra-tidal stars in NGC 2682 may originate from external perturbations such as disk shocking or dynamical evaporation from two-body relaxation. The former origin is plausible given the orbit of NGC 2682, which crossed the Galactic disk ~40 Myr ago.Comment: 9 pages, 5 figures, accepted for publication on A&

Structural complexity governs seagrass acclimatization to depth with relevant consequences for meadow production, macrophyte diversity and habitat carbon storage capacity

Analyses of the integrated seagrass response to depth support the previously documented low plasticity and consistent shade-adapted leaf physiology of a habitat-builder that dominates well-illuminated reef environments. Two structural responses, "canopy-opening" and "below-ground-mass-depletion", govern the photoacclimatory response and facilitate, respectively, light penetration within the canopy and functional adjustments in whole-plant carbon balances. Conversely, "canopy-closing" may also explain dense canopies formed close to the waterline, as they provide shade and photoprotection to a susceptible leaf physiology under high-light. Canopy light attenuation is primarily regulated by the leaf area index (LAI), which is governed by changes in shoot size and density. Shoot density diminishes non-linearly with depth, while shoot size increases to a maximum followed by a decline. The initial increase in shoot size, which resembles a self-thinning response, increases LAI and meadow production in shallow depths. These seagrass structural adjustments have relevant ecological implications. Canopy-thinning allows macrophyte diversity to increase with depth, while seagrass production and carbon storage diminish exponentially, and are maximal only in a shallow coastal fringe. The results support the universality of plant self-thinning, from phytoplankton to complex canopies, likely the consequence of simple physical laws related to light limitation and pigment self-shading within photosynthetic structures and communities

On the k-Symplectic, k-Cosymplectic and Multisymplectic Formalisms of Classical Field Theories

The objective of this work is twofold: First, we analyze the relation between the k-cosymplectic and the k-symplectic Hamiltonian and Lagrangian formalisms in classical field theories. In particular, we prove the equivalence between k-symplectic field theories and the so-called autonomous k-cosymplectic field theories, extending in this way the description of the symplectic formalism of autonomous systems as a particular case of the cosymplectic formalism in non-autonomous mechanics. Furthermore, we clarify some aspects of the geometric character of the solutions to the Hamilton-de Donder-Weyl and the Euler-Lagrange equations in these formalisms. Second, we study the equivalence between k-cosymplectic and a particular kind of multisymplectic Hamiltonian and Lagrangian field theories (those where the configuration bundle of the theory is trivial).Comment: 25 page

Non-standard connections in classical mechanics

In the jet-bundle description of first-order classical field theories there are some elements, such as the lagrangian energy and the construction of the hamiltonian formalism, which require the prior choice of a connection. Bearing these facts in mind, we analyze the situation in the jet-bundle description of time-dependent classical mechanics. So we prove that this connection-dependence also occurs in this case, although it is usually hidden by the use of the ``natural'' connection given by the trivial bundle structure of the phase spaces in consideration. However, we also prove that this dependence is dynamically irrelevant, except where the dynamical variation of the energy is concerned. In addition, the relationship between first integrals and connections is shown for a large enough class of lagrangians.Comment: 17 pages, Latex fil