Exponential Stabilization of Certain Configurations of the General N-Trailer System

We address the problem of asymptotic stabilization of certain configurations for the general N-trailer system (i.e. for which the hitching point of each trailer is not necessarily located on the rear axle of the preceding vehicle). In general, this system is not flat and, therefore, cannot be transformed into the classical chained form system. However, we show that it can be {\em approximated}, at some configurations, by the chained form system. This allows us to deduce simple time-varying continuous feedbacks which ensure local exponential stability of these particular configurations

Non-Robustness of Continuous Homogeneous Stabilizers for Affine Control Systems

This paper focuses on asymptotic point-stabilization of smooth affine control systems. For asymptotic feedback stabilizers, a simple definition of {robustness} with respect to unmodeled dynamics is adopted. Two theorems are then proved which state sufficient conditions for the {non-robustness} of homogeneous stabilizers. The first theorem, which applies to systems that may contain a drift term, involves a specific class of feedback stabilizers. The second one, which applies to driftless systems and is stated independently of any particular stabilizer, provides a condition related to an eventual loss of rank of the accessibility distribution. One of the consequences of the second result is that, for {chained-form systems}, no (static) continuous homogeneous exponential stabilizer (some of which have been proposed in the literature) can be robust in the sense defined herein. Examples are provided which illustrate a typical application of each result

EDUCACIÓN AMBIENTAL Y SOCIEDAD. SABERES LOCALES PARA EL DESARROLLO Y LA SUSTENTABILIDAD

Este texto contribuye al análisis científico de varias áreas del conocimiento como la filosofía social, la patología, la educación para el cuidado del medio ambiente y la sustentabilidad que inciden en diversas unidades de aprendizaje de la Licenciatura en Educación para la Salud y de la Maestría en Sociología de la SaludLas comunidades indígenas de la sierra norte de Oaxaca México, habitan un territorio extenso de biodiversidad. Sin que sea una área protegida y sustentable, la propia naturaleza de la región ofrece a sus visitantes la riqueza de la vegetación caracterizada por sus especies endémicas que componen un paisaje de suma belleza

Successful Long-Distance Breeding Range Expansion of a Top Marine Predator

Little is known about the effects of large-scale breeding range expansions on the ecology of top marine predators. We examined the effects of a recent range expansion on the breeding and foraging ecology of Laysan albatrosses (Phoebastria immutabilis). Laysan albatrosses expanded from historical breeding colonies in the Central Pacific Ocean to the Eastern Pacific Ocean around central Baja California, Mexico, leading to a 4,000-km shift from colonies located adjacent to the productive transition zone in the Central Pacific to colonies embedded within the eastern boundary current upwelling system of the Eastern Pacific California Current. We use electronic tagging and remote sensing data to examine the consequences of this range expansion on at-sea distribution, habitat use, foraging habitat characteristics, and foraging behavior at sea by comparing birds from historic and nascent colonies. We found the expansion resulted in distinct at-sea segregation and differential access to novel oceanographic habitats. Birds from the new Eastern Pacific colony on Guadalupe Island, Mexico have reduced ranges, foraging trip lengths and durations, and spend more time on the water compared to birds breeding in the Central Pacific on Tern Island, United States. Impacts of the range expansion to the post-breeding season were less pronounced where birds maintained some at-sea segregation but utilized similar habitat and environmental variables. These differences have likely benefited the Eastern Pacific colony which has significantly greater reproductive output and population growth rates. Laysan albatrosses have the plasticity to adapt to distinctly different oceanographic habitats and also provide insight on the potential consequences of range shifts to marine organisms

Natural and Anthropogenic Oil Impacts on Benthic Foraminifera in the Southern Gulf of Mexico

The Campeche Sound is the major offshore oil producing area in the Southern Gulf of Mexico (SGoM). To evaluate the impact of oil related activities in the ocean floor sediments, we analyzed the geochemical (major and trace element, organic carbon and hydrocarbon concentrations) and biological (benthic foraminifera) composition of 62 superficial sediment samples, from 13 to 1336 m water depth. Cluster and Factor analysis of all the variables indicate that their distribution patterns are mainly controlled by differences between the terrigenous and carbonate platforms in the SGoM. Benthic foraminiferal assemblages were abundant and diverse, and their distribution patterns are mainly determined by water depth and sedimentary environment. However, most of the abundant species are opportunistic and/or low-oxygen tolerant, and many of their tests show oil stains and infillings, characteristic of oil polluted locations, suggesting the environment has been modified by natural seepage or oil-related activities. To determine if these conditions are natural or anthropogenic in origin, pre - industrial settings should be studied. Organic carbon (Corg) content (0.6-2.9%) and total hydrocarbon concentrations (PAHs 1.0-29.5 μg k