High resolution dark field microscopy is becoming an important tool for the investigation of unstained and specifically stained biological molecules. Of primary consideration to the microscopist is the interpretation of image Intensities and the effects of radiation damage to the specimen. Ignoring inelastic scattering, the image intensity is directly related to the collected elastic scattering cross section, σɳ, which is the product of the total elastic cross section, σ and the eficiency of the microscope system at imaging these electrons, η. The number of potentially bond damaging events resulting from the beam exposure required to reduce the effect of quantum noise in the image to a given level is proportional to 1/η. We wish to compare η in three dark field systems.
La fin de l'hiver 2019-2020 est marquée par la succession de tempêtes. Les zones de vents forts répondent à des schémas conceptuels très différent : jet de basses couches, jet en air froid, sting jet, forte instabilité et tempête de pente aval.
The end of winter 2019-2020 is characterised by successive windstorms. The areas of severe winds correspond to various conceptual models: warm jet, cold jet, sting jet, deep convection and downslope windstorm.
