Special Symplectic Connections

By a special symplectic connection we mean a torsion free connection which is either the Levi-Civita connection of a Bochner-K\"ahler metric of arbitrary signature, a Bochner-bi-Lagrangian connection, a connection of Ricci type or a connection with special symplectic holonomy. A manifold or orbifold with such a connection is called special symplectic. We show that the symplectic reduction of (an open cell of) a parabolic contact manifold by a symmetry vector field is special symplectic in a canonical way. Moreover, we show that any special symplectic manifold or orbifold is locally equivalent to one of these symplectic reductions. As a consequence, we are able to prove a number of global properties, including a classification in the compact simply connected case.Comment: 35 pages, no figures. Exposition improved, some minor errors corrected. Version to be published by Jour.Diff.Geo

Construction of Ricci-type connections by reduction and induction

Given the Euclidean space $\R^{2n+2}$ endowed with a constant symplectic structure and the standard flat connection, and given a polynomial of degree 2 on that space, Baguis and Cahen have defined a reduction procedure which yields a symplectic manifold endowed with a Ricci-type connection. We observe that any symplectic manifold of dimension greater than 2 endowed with a symplectic connection of Ricci-type is locally given by a local version of such a reduction. We also consider the reverse of this reduction procedure, an induction procedure: we construct globally on a symplectic manifold endowed with a connection of Ricci-type $(M,\omega,\nabla)$ a circle or a line bundle which embeds in a flat symplectic manifold $(P,\mu ,\nabla^1)$ as the zero set of a function whose third covariant derivative vanishes, in such a way that $(M,\omega,\nabla)$ is obtained by reduction from $(P,\mu ,\nabla^1)$. We further develop the particular case of symmetric symplectic manifolds with Ricci-type connections

Lusotopie joins Brill

Lusotopie was founded in 1992 (the association) and 1994 (the annual journal) by an anthropologist, Christian Geffray, a sociologist, Christine Messiant, and a historian, Michel Cahen, all three of whom wished to develop political analysis of contemporary spaces stemming from Portuguese history and colonisation. This initial trio was soon joined by a number of specialists in social sciences of thirty or so different nationalities, whose working languages were Portuguese, French and English. W..

Nebraska Blueprint – Spring/Summer 2012

Table of Contents: From the Editor Engi-Briefs UCARE Experience – Interview with senior Computer Engineering major Dongpu Jin about his involvement with the Undergraduate Creative Activities and Research Experiences (UCARE) program History of E-Week E-Week 2012 Events and Results [photographs] E-Week Keynote Speaker: Pete Ludovice The Museum in Nebraska Hall – The research branch of the University of Nebraska State Museum Nebraska Hall\u27s 80th Birthday – A history of the building at 16th and W Streets Do You Remember . . . The Day Reunion Died – A brief history and photographs of the demolition of the Reunion building across the street from Nebraska Hal

Extrinsic symplectic symmetric spaces

We define the notion of extrinsic symplectic symmetric spaces and exhibit some of their properties. We construct large families of examples and show how they fit in the perspective of a complete classification of these manifolds. We also build a natural star-quantization on a class of examples

Linear Stochastic Fluid Networks: Rare-Event Simulation and Markov Modulation

We consider a linear stochastic fluid network under Markov modulation, with a focus on the probability that the joint storage level attains a value in a rare set at a given point in time. The main objective is to develop efficient importance sampling algorithms with provable performance guarantees. For linear stochastic fluid networks without modulation, we prove that the number of runs needed (so as to obtain an estimate with a given precision) increases polynomially (whereas the probability under consideration decays essentially exponentially); for networks operating in the slow modulation regime, our algorithm is asymptotically efficient. Our techniques are in the tradition of the rare-event simulation procedures that were developed for the sample-mean of i.i.d. one-dimensional light-tailed random variables, and intensively use the idea of exponential twisting. In passing, we also point out how to set up a recursion to evaluate the (transient and stationary) moments of the joint storage level in Markov-modulated linear stochastic fluid networks

Mozambique is suffering a military expression of a political problem. An interview with historian Michel Cahen for the Rosa Luxemburg Foundation Southern Africa

Document en accès libre sur le site de la Fondation Rosa Luxembourg et sur celui de la revue en ligne Pambazuka, ainsi que sur le blogue LAMenparle.InterviewMozambique is currently facing one of the most challenging tests of its capacity to resolve the country’s political, economic and social challenges. Politically, a ceasefire agreement signed between the Government of Frente de Libertação de Moçambique (FRELIMO) and the main opposition party, the Resistência Nacional de Moçambique (RENAMO) on 24 August 2014 was short-lived. It only served to clear the way for the country’s general elections on 15 October 2014, at which time the highly contested results by RENAMO brought about another round of military conflict. Economically, the national currency, Metical, has been consistently devaluing against, for example, the South African Rand, the American Dollar and the Euro, when potential gains from newly discovered resources (e.g. offshore gas) have failed to produce any tangible improvement to people’s lives. This, in conjunction with the discovery of hidden debt of 1, 4 billion USD, led partners like the International Monetary Fund (IMF), the World Bank (WB) and the British to suspend further financial aid to the country. It is therefore expected that these political and economic developments will lead to political upheaval if the Government does not address questions fast and adequately. To better understand Mozambique’s current political developments from a political-historical perspective, Fredson Guilengue, Programme Manager at the Rosa Luxemburg Stiftung Southern Africa (RLS) interviewed historian Michel Cahen (MC). Michel Cahen is an authority on Portuguese colonisation in Africa and a political analyst of Portuguese speaking African Countries (PALOPs). He is the Director of Research at the Centre National de la Recherche Scientifique (CNRS) at “Les Afriques dans le monde” Research Centre at the Institute for Political Studies in Bordeaux, France. As an accredited historian of Mozambican and Angolan contemporary history, Cahen has written extensively on Mozambique’s political developments

On Mpc-structures and Symplectic Dirac Operators

We prove that the kernels of the restrictions of symplectic Dirac or symplectic Dirac-Dolbeault operators on natural subspaces of polynomial valued spinor fields are finite dimensional on a compact symplectic manifold. We compute those kernels for the complex projective spaces. We construct injections of subgroups of the symplectic group (the pseudo-unitary group and the stabilizer of a Lagrangian subspace) in the group Mpc and classify G-invariant Mpc-structures on symplectic spaces with a G-action. We prove a variant of Parthasarathy's formula for the commutator of two symplectic Dirac-type operators on a symmetric symplectic space