Removing chambers in Bruhat-Tits buildings

We introduce and study a family of countable groups constructed from Euclidean buildings by "removing" suitably chosen subsets of chambers

Random groups and nonarchimedean lattices

We consider models of random groups in which the typical group is of intermediate rank (in particular, it is not hyperbolic). These models are parallel to M. Gromov's well-known constructions and include for example a "density model" for groups of intermediate rank. The main novelty is the higher rank nature of the random groups. They are randomization of certain families of lattices in algebraic groups (of rank 2) over local fields

Use of Aggregate Emission Reduction Cost Functions in Designing Optimal Regional SO2 Abatement Strategies

The 1990 Canadian long-range transport of air pollutants and acid deposition report divided North America into 40 sources of emission and 15 sensitive receptor sites. For the purpose of national policy making and international negotiation, the use of these large sources and few receptors may prove adequate. Due to inadequate information regarding cost of reducing emissions from each point source, it was felt necessary to design a method to generate cost functions for emission regions. The objective of this study was to develop aggregate cost functions that relate the cost of SO2 emission reductions to the amount of reduction achieved. The cost curves generated presume the application of control technologies to achieve a mandated regional emission reduction in the year 2000. The study has also assumed that trading will take place among plants within a region. The emissions inventories (GECOT and AIRS for the USA and RDIS for Canada) were used as the major source of data for the study. Cost functions were derived for forty emission regions. The functional forms that best fits estimated costs are either quadratic, power or linear in specifications. Furthermore, the cost functions indicted substantial variation (differences in marginal costs of removal) across emission regions. Preliminary analysis using Environment Canada’s Integrated Assessment Modelling platform indicated that strategies that make use of these functions and environmental goals will cost the industry and government the minimum amount compared to those that relay on quantitative emission reductions. Considering the findings of studies that indicated exposure of several watersheds to excess depositions of SO2 compared to critical loads, policy makers should examine ways of reducing emissions beyond what is already committed for the year 2005 or 2010. Future work will investigate interregional trading, especially between the bordering states of the USA and provinces of Canada based on these cost functions.long-range transport; air pollutants; acid deposition; North America ; sources; emission; cost functions; Canada; long-range transport; air pollutants; acid deposition; sources-receptors; SO2; cost curves; control technologies; USA; Integrated Assessment Modelling

Modeling Stiffness and Damping in Rotational Degrees of Freedom Using Multibond Graphs

A contribution is proposed for the modeling of mechanical systems using multibond graphs. When modeling a physical system, it may be needed to catch the dynamic behavior contribution of the joints between bodies of the system and therefore to characterize the stiffness and damping of the links between them. The visibility of where dissipative or capacitive elements need to be implemented to represent stiffness and damping in multibond graphs is not obvious and will be explained. A multibond graph architecture is then proposed to add stiffness and damping in hree rotational degrees of freedom. The resulting joint combines the spherical joint multibond graph relaxed causal constraints while physically representing three concatenated revolute joints. The mathematical foundations are presented, and then illustrated through the modeling and simulation of an inertial navigation system; in which stiffness and damping between the gimbals are taken into account. This method is particularly useful when modeling and simulating multibody systems using Newton-Euler formalism in multibond graphs. Future work will show how this method can be extended to more complex systems such as rotorcraft blades' connections with its rotor hub.Fondation Airbus Grou

El impacto de las remesas en Guatemala ¿Alivio a la pobreza o factor de desarrollo?

Con su numerosa emigración hacia Estados Unidos, Guatemala hace parte los principales países receptores de remesas en América latina. Frente a este fenómeno, presente en toda Latinoamérica, políticos, académicos y organizaciones internacionales se han interesado en el impacto que tienen las remesas para el desarrollo de los países de la región. Este artículo estudia el caso de Guatemala y busca mostrar qué consecuencias económicas y sociales generan estas transferencias de dinero en la sociedad de Guatemala, país con significativos índices de emigración a los Estados Unidos. Para lograr tal objetivo, el presente artículo caracteriza los emigrantes guatemaltecos que envían remesas, estudia el perfil de los hogares receptores de las mimas, y la forma cómo estas son utilizadas. Posteriormente, se muestra que las remesas representan una ayuda significativa para los hogares más pobres, permitiéndoles aumentar el consumo de bienes de primera necesidad y tener acceso a educación y salud. A su vez se observa cuáles son los factores que permiten convertir las remesas en actividades productivas que contribuyen al desarrollo del país, pero también se advierte sobre las limitantes en el uso de estos recursos. Por último, se mostrará la posición del Estado guatemalteco frente a la emigración de sus ciudadanos, las remesas y las políticas públicas formuladas en relación a éstos dos fenómenos

On algebraic damping close to inhomogeneous Vlasov equilibria in multi-dimensional spaces

We investigate the asymptotic damping of a perturbation around inhomogeneous stable stationary states of the Vlasov equation in spatially multi-dimensional systems. We show that branch singularities of the Fourier-Laplace transform of the perturbation yield algebraic dampings. In two spatial dimensions, we classify the singularities and compute the associated damping rate and frequency. This 2D setting also applies to spherically symmetric self-gravitating systems. We validate the theory using a toy model and an advection equation associated with the isochrone model, a model of spherical self-gravitating systems.Comment: 37 pages, 10 figure

Multi-physic system simplification method applied to a helicopter flight axis active control

A helicopter flight axis control, which is a complex multi-physic system, is modelled using an energetic based graphical tool: the Energetic Macroscopic Representation. Elements of the system are mainly composed of passive technologies and their number tends to increase year after year to improve the pilots comfort by adding new functions. A new methodology is proposed to transform the system into a new active one by replacing some hydro-mechanical elements by a new controllable active mechanical source. The challenge is to simplify the flight control architecture while preserving the global behaviour of the system