Molecular Gas in Spiral Galaxies

In this review, I highlight a number of recent surveys of molecular gas in nearby spiral galaxies. Through such surveys, more complete observations of the distribution and kinematics of molecular gas have become available for galaxies with a wider range of properties (e.g., brightness, Hubble type, strength of spiral or bar structure). These studies show the promise of both interferometers and single-dish telescopes in advancing our general understanding of molecular gas in spiral galaxies. In particular, I highlight the contributions of the recent BIMA Survey of Nearby Galaxies (SONG).Comment: 8 pages, 1 figure. To appear in the proceedings of the 4th Cologne-Bonn-Zermatt-Symposium, "The Dense Interstellar Medium in Galaxies", which was held in Zermatt, Switzerland in September 200

Theory of Star Formation

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation -- turbulence, magnetic fields, and self-gravity -- are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.Comment: 120 pages, to appear in ARAA. No changes from v1 text; permission statement adde

Modeling and simulation of cracking in quasi-fragile materials by using phase field method application to concrete

International audienceThis paper is devoted to the application of the phase field method to the case of damage in con-crete, in the particular framework of multiscale mechanics using 3D representative elemen-tary volumes (REVs) at the mesoscale. More specifically, this work consists in the treatment of instabilities in the crack propagation modeling in isotropic elastic solids, which may arise due to the dependency of Miehe scheme with respect to the choice of time step. Our al-gorithm allows for modeling crack propagation within complex microstructures, in a robust manner that is independent of the choice of time step. Several cases of concrete mesostruc-tures exhibiting different aggregate shapes have been analyzed under classical tension and compression loadings

Hybrid nanocomposites through colloidal interactions between crystalline polysaccharide nanoparticles and oxide precursors

International audienceThis chapter is devoted to the presentation of hybrid nanocomposite materials obtained through the interaction of colloidal crystalline polysaccharides and precursors of oxide phases. It also includes a preliminary introduction to the chemistry and physical chemistry of the polysaccharide nanocrystals, mainly cellulose and chitin. The main approaches and processes employed for the synthesis of the nanocomposites are described for different oxide families: silica, transition metals and metal oxides, phosphate and carbonate phases, and graphene oxide. Additionally, the properties of the materials are mentioned, and described in more details when they result from a combination of polysaccharide and oxide phases (typically for mechanical and optical properties). Globally, this chapter aims at giving a comprehensive review of the innovating research undertaken in the field and providing starting knowledge for nonspecialist readers