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Le zooplancton (du grec ancien , « animal ») est un plancton animal. Il se nourrit de matière vivante, certaines espèces étant herbivores et d’autres carnivores. Il descend pendant la nuit vers des eaux plus profondes, et remonte pendant la journée vers la surface, pour se nourrir de phytoplancton attiré par la lumière. Ce mouvement du zooplancton (dit de migration verticale quotidienne) suit un rythme nycthéméral commandé par la lumière du Soleil. Dans les eaux douces, la plupart des espèces zooplanctoniques sont plus actives les deux heures suivant le coucher du soleil, et deux heures avant l'aube. Il en va de même pour la plupart de leurs prédateurs. De nombreuses espèces zooplanctoniques peuvent elles-mêmes émettre de la lumière (bioluminescence), en profondeur ou en surface lorsque la mer est agitée. Le zooplancton contribue à la production de tripton (aussi appelé « pseudoplancton » ) qui rassemble tous les éléments supposés morts (nécromasse) ou d'origine minérale ou o

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ENV-406: Biomineralization: from nature to application

Understanding process and role of biomineralization (minerals formed by living organisms) in context of Earth's evolution,global chemical cycles, climatic changes and remediation.

ENV-220: Fundamentals in ecology

The students will learn the fundamentals in ecology with the goal to perceive the environment beyond its physical and chemical characteristics. Starting from basic concepts, they will acquire mechanistic understanding of biodiversity, ecosystem functioning and global change.

ENV-425: Limnology

Focus is on lakes, rivers and reservoirs as aquatic systems. Specific is the quantitative analyse (incl. exercises) of physical, biogeochemical and sedimentological processes / interactions. The goal is to understand the relevant processes (focus on water quality) from an engineering perspective.

2021

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Grazing function g and collimation angular acceptance

Valentina Previtali

The grazing function g is introduced—a synchrobetatron optical quantity that is analogous (and closely connected) to the Twiss and dispersion functions β, α, η, and η′. It parametrizes the rate of change of total angle with respect to synchrotron amplitude for grazing particles, which just touch the surface of an aperture when their synchrotron and betatron oscillations are simultaneously (in time) at their extreme displacements. The grazing function can be important at collimators with limited acceptance angles. For example, it is important in both modes of crystal collimation operation—in channeling and in volume reflection. The grazing function is independent of the collimator type—crystal or amorphous—but can depend strongly on its azimuthal location. The rigorous synchrobetatron condition g=0 is solved, by invoking the close connection between the grazing function and the slope of the normalized dispersion. Propagation of the grazing function is described, through drifts, dipoles, and quadrupoles. Analytic expressions are developed for g in perfectly matched periodic FODO cells, and in the presence of β or η error waves. These analytic approximations are shown to be, in general, in good agreement with realistic numerical examples. The grazing function is shown to scale linearly with FODO cell bend angle, but to be independent of FODO cell length. The ideal value is g=0 at the collimator, but finite nonzero values are acceptable. Practically achievable grazing functions are described and evaluated, for both amorphous and crystal primary collimators, at RHIC, the SPS (UA9), the Tevatron (T-980), and the LHC.

American Physical Society2009

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Viral Transfer and Inactivation through Zooplankton Trophic Interactions

Virginie Bachmann, Xavier Fernandez Cassi, Niveen Saad Ismail, Tamar Kohn, Margot Ninon Lauren Olive

Waterborne viruses are responsible for numerous diseases and are abundant in aquatic systems. Understanding the fate of viruses in natural systems has important implications for human health. This research quantifies the uptake of bacteriophage T4 and the enteric virus echovirus 11 when exposed to the filter feeders Tetrahymena pyriformis and Daphnia magna, and also examines the potential of viral transfer due to trophic interactions. Experiments co-incubating each species with the viruses over 72-96 hours showed up to 4-log virus removal for T. pyriformis, while direct viral uptake by D. magna was not observed. However, viral uptake by D. magna occurred indirectly by viral transfer from prey to predator, through D. magna feeding on virus loaded T. pyriformis. This predator-prey interaction resulted in 1-log additional virus removal compared to removal by T.pyriformis alone. Incomplete viral inactivation by D. magna was observed through recovery of infective viruses from daphnid tissue. This research furthers our understanding of the impacts of zooplankton filter feeding on viral inactivation and shows the potential for viral transfer through the food chain. The viral-zooplankton interactions observed in these studies indicate that zooplankton may improve water quality through viral uptake or may serve as vectors for infection by accumulating viruses.

2020

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Plancton

Océan

vignette|Animation montrant les découpages possibles en 5, 4, 3 ou 1 seul océan(s). vignette|Le grand océan planétaire, mis en valeur par la projection de Fuller. Un océan est souvent défini, en géogr

Microphagie suspensivore

[[File:BecCanardDontFiltreur.jpg|thumb|Comparaison de deux becs de canards, dont le second (celui du bas ; Anas platyrhynchos) est adapté à la filtration ; beaucoup plus large et plus long que