3,368 research outputs found
Le système monétaire européen : Un point de vue nord américain
Is the european monetary System (EMS) a useful approach to the problems it is meant to solve and to the pursuit of the objectives that its promoters have set for themselves? A review by the authors of a number of economic motives which underly the creation of the EMS leads them to conclude that the various economic problems which the european readily blame on floating exchange rates find in fact their origins in the economic policies pursued by the national governments. Moreover, the authors consider that the defense of parities in the EMS, either through intervention in the exchange markets or by other means, can involve high economic costs and that in the longer run market forces always triumph when parities no longer reflect the fundamental positions of the respective economies. Among the other factors which limit the usefulness of the EMS the authors identify the continuing lack of macro-economic policy coordination by participating countries, its regional character, the underestimation of the importance of the american dollar in the international monetary system and the impact of its fluctuations on european currencies and the tendency of the EMS to harmonize inflation rates at a higher level than should be aimed for. The authors therefore conclude that it is doubtful that the EMS constitutes a useful instrument of economic policy and that efforts towards european monetary union based on such a system of parities can be successful under present circumstances
Characterizing and attributing the warming trend in sea and land surface temperatures
Because of low-frequency internal variability, the observed and underlying warming trends in temperature series can be markedly different. Important differences in the observed nonlinear trends in hemispheric temperature series suggest that the northern and southern hemispheres have responded differently to the changes in the radiative forcing. Using recent econometric techniques, we can reconcile such differences and show that all sea and land temperatures share similar time series properties and a common underlying warming trend having a dominant anthropogenic origin. We also investigate the interhemispheric temperature asymmetry (ITA) and show that the differences in warming between hemispheres are in part driven by anthropogenic forcing but that most of the observed rapid changes is likely due to natural variability. The attribution of changes in ITA is relevant since increases in the temperature contrast between hemispheres could potentially produce a shift in the Intertropical Convergence Zone and alter rainfall patterns. The existence of a current slowdown in the warming and its causes are also investigated. The results suggest that the slowdown is a common feature in global and hemispheric sea and land temperatures that can, at least partly, be attributed to changes in anthropogenic forcing.info:eu-repo/semantics/publishedVersio
Financing sustainable agriculture and mitigation
Key messages:
- Smallholder farmers and forestry producers have a crucial role to play in food security, sustainable land use and emissions reductions initiatives.
- Producers and investors alike require appropriate incentive structures to facilitate participation in sustainable land use initiatives.
- A networked financing approach—Inari—may provide an innovative response to financing sustainable land use via intelligent diversification and addressing the finance needs of smallholders.
- Diversification requires the development of a more holistic risk model for investment in smallholder agriculture and forestry, which will be tested in a number of developing countries in 2013 and 2014
Generalized nonuniform dichotomies and local stable manifolds
We establish the existence of local stable manifolds for semiflows generated
by nonlinear perturbations of nonautonomous ordinary linear differential
equations in Banach spaces, assuming the existence of a general type of
nonuniform dichotomy for the evolution operator that contains the nonuniform
exponential and polynomial dichotomies as a very particular case. The family of
dichotomies considered allow situations for which the classical Lyapunov
exponents are zero. Additionally, we give new examples of application of our
stable manifold theorem and study the behavior of the dynamics under
perturbations.Comment: 18 pages. New version with minor corrections and an additional
theorem and an additional exampl
Molecular Evolution in Time Dependent Environments
The quasispecies theory is studied for dynamic replication landscapes. A
meaningful asymptotic quasispecies is defined for periodic time dependencies.
The quasispecies' composition is constantly changing over the oscillation
period. The error threshold moves towards the position of the time averaged
landscape for high oscillation frequencies and follows the landscape closely
for low oscillation frequencies.Comment: 5 pages, 3 figures, Latex, uses Springer documentclass llncs.cl
Actions of the braid group, and new algebraic proofs of results of Dehornoy and Larue
This article surveys many standard results about the braid group with
emphasis on simplifying the usual algebraic proofs.
We use van der Waerden's trick to illuminate the Artin-Magnus proof of the
classic presentation of the algebraic mapping-class group of a punctured disc.
We give a simple, new proof of the Dehornoy-Larue braid-group trichotomy,
and, hence, recover the Dehornoy right-ordering of the braid group.
We then turn to the Birman-Hilden theorem concerning braid-group actions on
free products of cyclic groups, and the consequences derived by Perron-Vannier,
and the connections with the Wada representations. We recall the very simple
Crisp-Paris proof of the Birman-Hilden theorem that uses the Larue-Shpilrain
technique. Studying ends of free groups permits a deeper understanding of the
braid group; this gives us a generalization of the Birman-Hilden theorem.
Studying Jordan curves in the punctured disc permits a still deeper
understanding of the braid group; this gave Larue, in his PhD thesis,
correspondingly deeper results, and, in an appendix, we recall the essence of
Larue's thesis, giving simpler combinatorial proofs.Comment: 51`pages, 13 figure
Heun Functions and the energy spectrum of a charged particle on a sphere under magnetic field and Coulomb force
We study the competitive action of magnetic field, Coulomb repulsion and
space curvature on the motion of a charged particle. The three types of
interaction are characterized by three basic lengths: l_{B} the magnetic
length, l_{0} the Bohr radius and R the radius of the sphere. The energy
spectrum of the particle is found by solving a Schr\"odinger equation of the
Heun type, using the technique of continued fractions. It displays a rich set
of functioning regimes where ratios \frac{R}{l_{B}} and \frac{R}{l_{0}} take
definite values.Comment: 12 pages, 5 figures, accepted to JOPA, november 200
Exponential dichotomies of evolution operators in Banach spaces
This paper considers three dichotomy concepts (exponential dichotomy, uniform
exponential dichotomy and strong exponential dichotomy) in the general context
of non-invertible evolution operators in Banach spaces. Connections between
these concepts are illustrated. Using the notion of Green function, we give
necessary conditions and sufficient ones for strong exponential dichotomy. Some
illustrative examples are presented to prove that the converse of some
implication type theorems are not valid
A Generalization of the Convex Kakeya Problem
Given a set of line segments in the plane, not necessarily finite, what is a
convex region of smallest area that contains a translate of each input segment?
This question can be seen as a generalization of Kakeya's problem of finding a
convex region of smallest area such that a needle can be rotated through 360
degrees within this region. We show that there is always an optimal region that
is a triangle, and we give an optimal \Theta(n log n)-time algorithm to compute
such a triangle for a given set of n segments. We also show that, if the goal
is to minimize the perimeter of the region instead of its area, then placing
the segments with their midpoint at the origin and taking their convex hull
results in an optimal solution. Finally, we show that for any compact convex
figure G, the smallest enclosing disk of G is a smallest-perimeter region
containing a translate of every rotated copy of G.Comment: 14 pages, 9 figure
Measuring Galaxy Asymmetries in 3D
One of the commonly used non-parametric morphometric statistics for galaxy
profiles and images is the asymmetry statistic. With an eye to current and
upcoming large neutral hydrogen (HI) surveys, we develop a 3D version of the
asymmetry statistic that can be applied to datacubes. This statistic is more
resilient to variations due to the observed geometry than 1D asymmetry
measures, and can be successfully applied to lower spatial resolutions (3-4
beams across the galaxy major axis) than the 2D statistic. We have also
modified the asymmetry definition from an `absolute difference' version to a
`squared difference' version that removes much of the bias due to noise
contributions for low signal-to-noise observations. Using a suite of mock
asymmetric cubes we show that the background-corrected, squared difference 3D
asymmetry statistic can be applied to many marginally resolved galaxies in
large wide-area HI surveys such as WALLABY on the Australian SKA Pathfinder
(ASKAP).Comment: 14 pages, Accepted to MNRA
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