21 research outputs found
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
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Genetic variability in Irish populations of the invasive zebra mussel, Dreissena polymorpha: discordant estimates of population differentiation from allozymes and microsatellites
Mechanistic modelling of carbon partitioning
Carbon partitioning between alternative sinks is the weak point of all plant growth models, being done using empirically based algorithms. While this approach is effective for simulations, it is unreliable for extrapolation to new conditions, and cannot provide mechanistic understanding of the processes involved. All long-distance carbohydrate transport and partitioning involves the phloem, hence partitioning must be a property of phloem physiology. However, no growth model utilizes the known phloem physiology. Relevant aspects of phloem physiology are discussed and used to produce a minimalist MĂĽnch-based flow model. This model provides a theoretical basis for an unambiguous definition of sink strength, with sink priority being an emergent property of the model. A method to extend this minimalist model is discussed