RESUMO
La influenza, enfermedad respiratoria altamente contagiosa causada por un influenza virus, se ha presentado desde tiempos remotos. En tiempos de Hipócrates se describieron eventos con todas las características de probables epidemias de influenza sucedidas en la época helénica. El término se originó en Italia, siglo XV, pues las epidemias sucedidas en esa época se atribuían a la "influencia de las estrellas". No se puede determinar cuándo ocurrirá una pandemia; sin embargo, se sabe que se presenta con cierta regularidad. La primera epidemia de influenza descrita como tal y generalmente aceptada, ocurrió en Europa en diciembre de 1173; la primera pandemia descrita que afectó a Europa, Asia y el Norte de África fue en 1580, y la primera que afectó al Continente Americano ocurrió en 1647¹. Es por ello que la Organización Mundial de la Salud solicitó a los países participantes desarrollar los planes de preparación y respuesta para hacer frente a esta eventualidad. México participa por medio de numerosas entidades a nivel federal, instituciones y organismos nacionales con el objeto de proteger a la población de una pandemia mediante acciones efectivas y oportunas. El Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, desarrolló una estrategia propia basándose en las seis líneas de acción contenidas en el Plan Nacional, lo que le permitirá tener las guías y elementos necesarios para formular su propio Plan de Preparación y Respuesta ante una Pandemia de Influenza. Las seis líneas de acción de acuerdo con el Plan Nacional son: 7. Difusión y comunicación social, 2. Coordinación, 3. Vigilancia epidemiológica, 4. Atención médica, 5. Reserva estratégica y 6. Investigación y desarrollo. Se describen los preparativos, curso y resultados de un simulacro de pandemia de influenza.
Influenza is a highly contagious disease caused by a virus; the disease is known since the times of Hippocrates, who described events with all the characteristics of influenza epidemics during his times. Apparently, the term was coined in Italy during the XV century because the disease was attributed to the "influence" of the stars. The first formally described influenza epidemic probably dates back to December 1173; the first pandemic, in 1580, affected Europe, Asia and North Africa; the first affecting the American Continent occurred in 1647. The countries from the WHO have been asked to develop plans to face the real possibility of a new pandemic, this caused by an avian virus; Mexico has participated through the joint effort of many institutions at federal, state and municipal levels, including the Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas (National Institute of Respiratory Diseases) were we have developed a strategy of six lines of action to face this pandemia: Diffusion and social communication, coordination, epidemiologic surveillance, medical services, strategic reserve, development and research. The preparations, course and results of an influenza pandemic simulacrum are described.
RESUMO
The dissociative sticking coefficient for CH4 on Pt(111) has been measured as a function of both gas temperature (Tg) and surface temperature (Ts) using effusive molecular beam and angle-integrated ambient gas dosing methods. The experimental results are used to optimize the three parameters of a microcanonical unimolecular rate theory (MURT) model of the reactive system. The MURT calculations allow us to extract transition state properties from the data as well as to compare our data directly to other molecular beam and thermal equilibrium sticking measurements. We find a threshold energy for dissociation of E0 = 52.5 +/- 3.5 kJ mol(-1). Furthermore, the MURT with an optimized parameter set provides for a predictive understanding of the kinetics of this C-H bond activation reaction, that is, it allows us to predict the dissociative sticking coefficient of CH4 on Pt(111) for any combination of Ts and Tg even if the two are not equal to one another, indeed, the distribution of molecular energy need not even be thermal. Comparison of our results to those from recent thermal equilibrium catalysis studies on CH4 reforming over Pt nanoclusters ( approximately 2 nm diam) dispersed on oxide substrates indicates that the reactivity of Pt(111) exceeds that of the Pt nanocatalysts by several orders of magnitude.
RESUMO
The dissociative sticking coefficient for C2H6 on Pt(111) has been measured as a function of both gas temperature (Tg) and surface temperature (Ts) using effusive molecular beam and angle-integrated ambient gas dosing methods. A microcanonical unimolecular rate theory (MURT) model of the reactive system is used to extract transition state properties from the data as well as to compare our data directly with supersonic molecular beam and thermal equilibrium sticking measurements. We report for the first time the threshold energy for dissociation, E0 = 26.5 +/- 3 kJ mol(-1). This value is only weakly dependent on the other two parameters of the model. A strong surface temperature dependence in the initial sticking coefficient is observed; however, the relatively weak dependence on gas temperature indicates some combination of the following (i) not all molecular excitations are contributing equally to the enhancement of sticking, (ii) that strong entropic effects in the dissociative transition state are leading to unusually high vibrational frequencies in the transition state, and (iii) energy transfer from gas-phase rovibrational modes to the surface is surprisingly efficient. In other words, it appears that vibrational mode-specific behavior and/or molecular rotations may play stronger roles in the dissociative adsorption of C2H6 than they do for CH4. The MURT with an optimized parameter set provides for a predictive understanding of the kinetics of this C-H bond activation reaction, that is, it allows us to predict the dissociative sticking coefficient of C2H6 on Pt(111) for any combination of Ts and Tg even if the two are not equal to one another.
