3,995 research outputs found
Measuring the Initial Mass Function of Low Mass Stars and Brown Dwarfs
I review efforts to determine the form and any lower limit to the initial
mass function in the Galactic disk, using observations of low-mass stars and
brown dwarfs in the field, young clusters and star forming regions. I focus on
the methodologies that have been used and the uncertainties that exist due to
observational limitations and to systematic uncertainties in calibrations and
theoretical models. I conclude that whilst it is possible that the low-mass
IMFs deduced from the field and most young clusters are similar, there are too
many problems to be sure; there are examples of low-mass cluster IMFs that
appear to be very discrepant and the IMFs for brown dwarfs in the field and
young clusters have yet to be reconciled convincingly.Comment: From a series of lectures presented at the Evry-Schatzman school on
Low-mass stars and the transition from stars to brown dwarfs, edited by C.
Charbonnel, C. Reyle, M. Schultheis. To appear in the EAS Conference Series.
47p
The parallax view: the military origins of holography
The title of this piece is meant to evoke at least three sources. The first – and perhaps the only obvious one – concerns the ability of holograms to display parallax, a shifting of visual viewpoint that allows a three-dimensional image to reveal background objects behind those in the foreground. This parallax view is a unique feature of holograms as visual media. A second allusion is to the American film The Parallax View (1974, director A. J. Pakula), a rather paranoid thriller focusing on conspiracy theories concerning government and corporations. To a casual observer, the bare details of the military origins of holography suggest just such cynical and centrally-directed development, although I hope to dispel such simplistic ideas here. And a third passing reference is to the book The Parallax View (2006) by Slavoj Zizek, a wide-ranging and deep exploration of duality in political views, ontological interpretations and scientific methods, among other topics.
Zizek’s theme, as well as Pakula’s, is relevant to my approach, which focuses on a parallax of both practice and intent. During the first successful decade of holography, conflicting viewpoints developed between distinct communities: the militarily-guided engineers who invented practical holography, and the later imaging scientists and artisans who stressed three-dimensionality and other attributes instead of the original goal of optical image processing. I argue that distinct groups of users had different perceptions of what holography is and what it is for
Supporting Focus and Context Awareness in 3D Modelling Tasks Using Multi-Layered Displays
Most 3D modelling software have been developed for conventional 2D displays, and as such, lack support for true depth perception. This contributes to making polygonal 3D modelling tasks challenging, particularly when models are complex and consist of a large number of overlapping components (e.g. vertices, edges) and objects (i.e. parts). Research has shown that users of 3D modelling software often encounter a range of difficulties, which collectively can be defined as focus and context awareness problems. These include maintaining position and orientation awarenesses, as well as recognizing distance between individual components and objects in 3D spaces. In this paper, we present five visualization and interaction techniques we have developed for multi-layered displays, to better support focus and context awareness in 3D modelling tasks. The results of a user study we conducted shows that three of these five techniques improve users' 3D modelling task performance
Real-time Cosmology
In recent years the possibility of measuring the temporal change of radial
and transverse position of sources in the sky in real time have become
conceivable thanks to the thoroughly improved technique applied to new
astrometric and spectroscopic experiments, leading to the research domain we
call Real-time cosmology. We review for the first time great part of the work
done in this field, analysing both the theoretical framework and some endeavor
to foresee the observational strategies and their capability to constrain
models. We firstly focus on real time measurements of the overall redshift
drift and angular separation shift in distant source, able to trace background
cosmic expansion and large scale anisotropy, respectively. We then examine the
possibility of employing the same kind of observations to probe peculiar and
proper acceleration in clustered systems and therefore the gravitational
potential. The last two sections are devoted to the short time future change of
the cosmic microwave background, as well as to the temporal shift of the
temperature anisotropy power spectrum and maps. We conclude revisiting in this
context the effort made to forecast the power of upcoming experiments like
CODEX, GAIA and PLANCK in providing these new observational tools.Comment: 44 pages, 23 figures. References added; revised text, tables and
plots. Accepted for publication in Physics Report
The implications of embodiment for behavior and cognition: animal and robotic case studies
In this paper, we will argue that if we want to understand the function of
the brain (or the control in the case of robots), we must understand how the
brain is embedded into the physical system, and how the organism interacts with
the real world. While embodiment has often been used in its trivial meaning,
i.e. 'intelligence requires a body', the concept has deeper and more important
implications, concerned with the relation between physical and information
(neural, control) processes. A number of case studies are presented to
illustrate the concept. These involve animals and robots and are concentrated
around locomotion, grasping, and visual perception. A theoretical scheme that
can be used to embed the diverse case studies will be presented. Finally, we
will establish a link between the low-level sensory-motor processes and
cognition. We will present an embodied view on categorization, and propose the
concepts of 'body schema' and 'forward models' as a natural extension of the
embodied approach toward first representations.Comment: Book chapter in W. Tschacher & C. Bergomi, ed., 'The Implications of
Embodiment: Cognition and Communication', Exeter: Imprint Academic, pp. 31-5
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