267 research outputs found
A cocycle on the group of symplectic diffeomorphisms
We define a cocycle on the group of symplectic diffeomorphisms of a
symplectic manifold and investigate its properties. The main applications are
concerned with symplectic actions of discrete groups. For example, we give an
alternative proof of the Polterovich theorem about the distortion of cyclic
subgroups in finitely generated groups of Hamiltonian diffeomorphisms.Comment: 19 pages, no figures, corrected versio
Types de familles, conditions de vie, fonctionnement du système familial et inadaptation sociale au cours de la latence et de l’adolescence dans les milieux défavorisés
Les données manquent concernant l'impact de certains types de familles, et les résultats sont souvent discordants concernant l'inadaptation. Après avoir décrit les variations de l'activité délictueuse et des troubles de comportement selon les types de familles, nous analysons les difficultés de fonctionnement du système familial. Six types de familles sont comparés pour 763 garçons de 10 ans, 319 adolescentes et 426 adolescents de 14 et 15 ans: les familles intactes, les familles monoparentales patricentriques et matricentriques, les familles recomposées patricentriques et matricentriques et les familles substituts. Les données présentées montrent qu'en cette fin des années 1980, près de 40 % des enfants et des adolescents des quartiers à faible statut socio-économique de Montréal vivent dans des familles désunies. Les données confirment en outre une observation classique: les familles désunies, en comparaison aux familles intactes, sont défavorisées sur le plan des conditions de vie, déficientes sur le plan du fonctionnement psychosocial et propices aux troubles de comportement et à l'activité délictueuse. Par ailleurs, il est établi que certains types de familles désunies constituent un facteur de risque considérable. L'effet dommageable de la structure de la famille s'accroît dans l'ordre suivant: familles intactes, familles monoparentales matricentriques, familles recomposées matricentriques, familles substituts, familles recomposées patricentriques et familles monoparentales patricentriques. Pour terminer, quelques pistes d'intervention pour la prévention des difficultés comportementales et familiales sont proposées.Available data on the impact of certain types of families is lacking, and the results are often misleading with respect to maladjustment. Following a description of variations in delinquent activity and behaviour problems according to family type, the authors analyse the difficulties in the operation of family systems. Comparisons of six family types apply to data from 763 boys aged 10, 319 female and 426 male adolescents, aged 14 and 15: intact families, father-based and mother-based single- parent families, father-based and mother-based reconstituted families and substitute families. The article's data show that in the late eighties, nearly 40 per cent of children and adolescents living in low-income districts in Montreal belonged to disunited families. In addition, the data confirm a classic observation: in comparison with intact families, disunited families are underprivileged in relation to living conditions, deficient in relation to psychosocial functioning, and propitious to behaviour problems and delinquent activity. In addition, it has been established that certain disunited family types represent a considerable risk factor. The damaging effect of family structure increases in the following order: intact families, mother-based single-parent families, mother-based reconstituted families, substitute families, father-based reconstituted families and father-based single-parent families. Finally, certain intervention methods are suggested to help prevent behaviour and family problems
Symplectic geometry on moduli spaces of J-holomorphic curves
Let (M,\omega) be a symplectic manifold, and Sigma a compact Riemann surface.
We define a 2-form on the space of immersed symplectic surfaces in M, and show
that the form is closed and non-degenerate, up to reparametrizations. Then we
give conditions on a compatible almost complex structure J on (M,\omega) that
ensure that the restriction of the form to the moduli space of simple immersed
J-holomorphic Sigma-curves in a homology class A in H_2(M,\Z) is a symplectic
form, and show applications and examples. In particular, we deduce sufficient
conditions for the existence of J-holomorphic Sigma-curves in a given homology
class for a generic J.Comment: 16 page
Global symplectic coordinates on gradient Kaehler-Ricci solitons
A classical result of D. McDuff asserts that a simply-connected complete
Kaehler manifold with non positive sectional curvature admits
global symplectic coordinates through a symplectomorphism (where is the complex dimension of ), satisfying the following
property (proved by E. Ciriza): the image of any complex totally
geodesic submanifold through the point such that ,
is a complex linear subspace of . The aim of this paper is
to exhibit, for all positive integers , examples of -dimensional complete
Kaehler manifolds with non-negative sectional curvature globally
symplectomorphic to through a symplectomorphism satisfying Ciriza's
property.Comment: 8 page
Inequivalent contact structures on Boothby-Wang 5-manifolds
We consider contact structures on simply-connected 5-manifolds which arise as
circle bundles over simply-connected symplectic 4-manifolds and show that
invariants from contact homology are related to the divisibility of the
canonical class of the symplectic structure. As an application we find new
examples of inequivalent contact structures in the same equivalence class of
almost contact structures with non-zero first Chern class.Comment: 27 pages; to appear in Math. Zeitschrif
Seidel elements and mirror transformations
The goal of this article is to give a precise relation between the mirror
symmetry transformation of Givental and the Seidel elements for a smooth
projective toric variety with nef. We show that the Seidel elements
entirely determine the mirror transformation and mirror coordinates.Comment: 36 pages. We corrected several issues as pointed out by the refere
Discontinuous symplectic capacities
We show that the spherical capacity is discontinuous on a smooth family of
ellipsoidal shells. Moreover, we prove that the shell capacity is discontinuous
on a family of open sets with smooth connected boundaries.Comment: We include generalizations to higher dimensions due to the unknown
referee and Janko Latschev. We add examples of open sets with connected
boundary on which the shell capacity is not continuous. 3rd and 4th version:
minor changes, to appear in J. Fixed Point Theory App
Birational cobordism invariance of uniruled symplectic manifolds
A symplectic manifold is called {\em (symplectically) uniruled}
if there is a nonzero genus zero GW invariant involving a point constraint. We
prove that symplectic uniruledness is invariant under symplectic blow-up and
blow-down. This theorem follows from a general Relative/Absolute correspondence
for a symplectic manifold together with a symplectic submanifold. A direct
consequence is that symplectic uniruledness is a symplectic birational
invariant. Here we use Guillemin and Sternberg's notion of cobordism as the
symplectic analogue of the birational equivalence.Comment: To appear in Invent. Mat
Massey products in symplectic manifolds
The paper is devoted to study of Massey products in symplectic manifolds.
Theory of generalized and classical Massey products and a general construction
of symplectic manifolds with nontrivial Massey products of arbitrary large
order are exposed. The construction uses the symplectic blow-up and is based on
the author results, which describe conditions under which the blow-up of a
symplectic manifold X along its submanifold Y inherits nontrivial Massey
products from X ot Y. This gives a general construction of nonformal symplectic
manifolds.Comment: LaTeX, 48 pages, 2 figure
Gauged vortices in a background
We discuss the statistical mechanics of a gas of gauged vortices in the
canonical formalism. At critical self-coupling, and for low temperatures, it
has been argued that the configuration space for vortex dynamics in each
topological class of the abelian Higgs model approximately truncates to a
finite-dimensional moduli space with a Kaehler structure. For the case where
the vortices live on a 2-sphere, we explain how localisation formulas on the
moduli spaces can be used to compute explicitly the partition function of the
vortex gas interacting with a background potential. The coefficients of this
analytic function provide geometrical data about the Kaehler structures, the
simplest of which being their symplectic volume (computed previously by Manton
using an alternative argument). We use the partition function to deduce simple
results on the thermodynamics of the vortex system; in particular, the average
height on the sphere is computed and provides an interesting effective picture
of the ground state.Comment: Final version: 22 pages, LaTeX, 1 eps figur
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