10,601 research outputs found
Large Scale Structure: Setting the Stage for the Galaxy Formation Saga
Over the past three decades the established view of a nearly homogeneuous,
featureless Universe on scales larger than a few Megaparsec has been completely
overhauled. In particular through the advent of ever larger galaxy redshift
surveys we were revealed a galaxy distribution displaying an intriguing
cellular pattern in which filamentary and wall-like structures, as well as huge
regions devoid of galaxies, are amongst the most conspicuous morphological
elements. In this contribution we will provide an overview of the present
observational state of affairs concerning the distribution of galaxies and the
structure traced out by the matter distribution in our Universe. In conjunction
with the insight on the dynamics of the structure formation process obtained
through the mapping of the peculiar velocities of galaxies in our local
Universe and the information on the embryonic circumstances that prevailed at
the epoch of Recombination yielded by the various Cosmic Microwave Background
experiments, we seek to arrive at a more or less compelling theoretical
framework of structure formation.The main aspects of this framework of the rise
of structure through gravitational instability can probably be most readily
appreciated through illustrative examples of various scenarios, as for instance
provided by some current state-of-the-art N-body simulations. We will
subsequently wrap up the observational and theoretical evidence for the
emergence and evolution of structure in the Universe by sketching the stage for
the ultimate Holy Grail of late 20th century astrophysics, understanding the
saga of the formation of what arguably are the most prominent and at the same
time intoxicatingly beautiful and intriguing denizens of our Cosmos, the {\it
galaxies}.Comment: 25 pages, 7 figures. Invited Review at `The most distant radio
galaxies' KNAW Colloquium, Amsterdam, October 1997, eds Best et al., Kluwer.
25 pages of LaTex including 7 postscript (bitmapped) figures. Uses
knawproc.cl
Consensus Emerging from the Bottom-up: the Role of Cognitive Variables in Opinion Dynamics
The study of opinions e.g., their formation and change, and their effects
on our society by means of theoretical and numerical models has been one of
the main goals of sociophysics until now, but it is one of the defining topics
addressed by social psychology and complexity science. Despite the flourishing
of different models and theories, several key questions still remain
unanswered. The aim of this paper is to provide a cognitively grounded
computational model of opinions in which they are described as mental
representations and defined in terms of distinctive mental features. We also
define how these representations change dynamically through different
processes, describing the interplay between mental and social dynamics of
opinions. We present two versions of the model, one with discrete opinions
(voter model-like), and one with continuous ones (Deffuant-like). By means of
numerical simulations, we compare the behaviour of our cognitive model with the
classical sociophysical models, and we identify interesting differences in the
dynamics of consensus for each of the models considered.Comment: 14 pages, 8 figure
Debates—Stochastic subsurface hydrology from theory to practice: why stochastic modeling has not yet permeated into practitioners?
This is the peer reviewed version of the following article: [Sanchez-Vila, X., and D. Fernà ndez-Garcia (2016), Debates—Stochastic subsurface hydrology from theory to practice: Why stochastic modeling has not yet permeated into practitioners?, Water Resour. Res., 52, 9246–9258, doi:10.1002/2016WR019302], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/2016WR019302/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingWe address modern topics of stochastic hydrogeology from their potential relevance to real modeling efforts at the field scale. While the topics of stochastic hydrogeology and numerical modeling have become routine in hydrogeological studies, nondeterministic models have not yet permeated into practitioners. We point out a number of limitations of stochastic modeling when applied to real applications and comment on the reasons why stochastic models fail to become an attractive alternative for practitioners. We specifically separate issues corresponding to flow, conservative transport, and reactive transport. The different topics addressed are emphasis on process modeling, need for upscaling parameters and governing equations, relevance of properly accounting for detailed geological architecture in hydrogeological modeling, and specific challenges of reactive transport. We end up by concluding that the main responsible for nondeterministic models having not yet permeated in industry can be fully attributed to researchers in stochastic hydrogeology.Peer ReviewedPostprint (author's final draft
- …