903 research outputs found
Generalized Contact Bundles
In this Note, we propose a line bundle approach to odd-dimensional analogues
of generalized complex structures. This new approach has three main advantages:
(1) it encompasses all existing ones; (2) it elucidates the geometric meaning
of the integrability condition for generalized contact structures; (3) in light
of new results on multiplicative forms and Spencer operators, it allows a
simple interpretation of the defining equations of a generalized contact
structure in terms of Lie algebroids and Lie groupoids.Comment: Short Note: 8 pages. Minor revisions. Published in C. R. Math.
Comments welcome
The Dynamic Properties of Alternative Assumptions on Price Adjustment in New Keynesian Models
This paper presents a classification of the different new Phillips curves existing in the literature as a set of choices based on three assumptions: the choice of the structure of price adjustments (Calvo or Taylor), the presence of backward indexation, and the type of price contracts (fixed prices or predetermined prices). The paper suggests study of the dynamic properties of each specification, following different monetary shocks on the growth rate of the money stock. We develop the analytical form of the price dynamics, and we display graphics for the responses of prices, output, and inflation. We show that the choice made for each of the three assumptions has a strong influence on the dynamic properties. Notably, the choice of the price structure, while often considered as unimportant, is indeed the most influential choice concerning the dynamic responses of output and inflation.New Keynesian Phillips Curves, Taylor Price Rule, Calvo Price Rule, Fixed Prices, Predetermined Prices, Disinflation policy.
Booms petroliers et basculements du rapport de force
Chaque boom et chaque crise des prix pĂ©troliers marquent le basculement du rapport de force au profit de lâun des acteurs de lâĂ©conomie pĂ©troliĂšre (pays producteurs, pays consommateurs et multinationales pĂ©troliĂšres). Le principal enjeu de ces basculements rĂ©side dans la prise ou la perte de contrĂŽle du marchĂ© pĂ©trolier par les acteurs. Chacun dâeux ne cherche quâĂ instaurer la politique de prix satisfaisant les objectifs inhĂ©rents aux stratĂ©gies Ă©conomiques nationales, aux relations internationales ou mĂȘme sâaccaparer de la part la plus importante du surplus pĂ©trolier.Mots-clefsBoom pĂ©trolier, crise pĂ©troliĂšre, rapport de force, prix dub pĂ©trole.Code Jel : Q33, Q41, Q4
Locally-adapted convolution-based super-resolution of irregularly-sampled ocean remote sensing data
Super-resolution is a classical problem in image processing, with numerous
applications to remote sensing image enhancement. Here, we address the
super-resolution of irregularly-sampled remote sensing images. Using an optimal
interpolation as the low-resolution reconstruction, we explore locally-adapted
multimodal convolutional models and investigate different dictionary-based
decompositions, namely based on principal component analysis (PCA), sparse
priors and non-negativity constraints. We consider an application to the
reconstruction of sea surface height (SSH) fields from two information sources,
along-track altimeter data and sea surface temperature (SST) data. The reported
experiments demonstrate the relevance of the proposed model, especially
locally-adapted parametrizations with non-negativity constraints, to outperform
optimally-interpolated reconstructions.Comment: 4 pages, 3 figure
PtCl<sub>2</sub>-Catalyzed Rearrangement of Methylenecyclopropanes
Alkylidenecyclopropanes readily convert into cyclobutene derivatives on treatment with catalytic amounts of PtCl2. The reaction is strongly accelerated when performed under an atmosphere of CO (1 atm). The resulting cyclobutenes are isolated in good to excellent yields for substrates bearing aliphatic as well as aromatic substituents R on their olefinic site. If the substituent R, however, is a very electron-rich arene, the cyclobutenes initially formed react further to give dimeric products with a previously unknown 1,2,2a,7a-tetrahydrospiro[cyclobuta[a]indene-7,1â-cyclobutane skeleton. A mechanism accounting for these experimental observations as well as for a deuterium-labeling experiment is proposed which implies reactive intermediates at the nonclassical cation/carbene interface. Furthermore it is shown that the PtCl2-catalyzed cyclobutene formation can be geared with subsequent ring-opening/ring-closing metathesis (ROM/RCM) events. Finally, a convenient âone potâ method for the preparation of the alkylidenecyclopropane substrates used in this study is presented, which is based on a modified JuliaâKocienski olefination of aldehydes with readily available 1-tert-butyl-1H-tetrazol-5-yl-cyclopropyl sulfone under Barbier conditions
A Rhodium-Catalyzed CâH Activation/Cycloisomerization Tandem
A reaction cascade comprising a rhodium-catalyzed CâH activation, a subsequent hydrometalation of an alkylidene cyclopropane in vicinity, regioselective CâC bond activation of the flanking cyclopropane ring, followed by reductive elimination of the resulting metallacycle, opens a new entry into functionalized cycloheptene derivatives. This crossover of CâH activation and higher order cycloaddition has been performed in two different formats, either using alkylidenecyclopropanes with a lateral vinylpyridine moiety or with a pending aldehyde group as the trigger. The reaction tolerates various functional groups, leaves chiral centers α to the reacting sites unaffected, and proceeds with excellent stereoselectivity. Labeling experiments support the proposed mechanism explaining the observed net cycloisomerization process
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