2,234 research outputs found
A formula for the number of tilings of an octagon by rhombi
We propose the first algebraic determinantal formula to enumerate tilings of
a centro-symmetric octagon of any size by rhombi. This result uses the
Gessel-Viennot technique and generalizes to any octagon a formula given by
Elnitsky in a special case.Comment: New title. Minor improvements. To appear in Theoretical Computer
Science, special issue on "Combinatorics of the Discrete Plane and Tilings
Arctic octahedron in three-dimensional rhombus tilings and related integer solid partitions
Three-dimensional integer partitions provide a convenient representation of
codimension-one three-dimensional random rhombus tilings. Calculating the
entropy for such a model is a notoriously difficult problem. We apply
transition matrix Monte Carlo simulations to evaluate their entropy with high
precision. We consider both free- and fixed-boundary tilings. Our results
suggest that the ratio of free- and fixed-boundary entropies is
, and can be interpreted as the ratio of the
volumes of two simple, nested, polyhedra. This finding supports a conjecture by
Linde, Moore and Nordahl concerning the ``arctic octahedron phenomenon'' in
three-dimensional random tilings
Two-dimensional random tilings of large codimension: new progress
Two-dimensional random tilings of rhombi can be seen as projections of
two-dimensional membranes embedded in hypercubic lattices of higher dimensional
spaces. Here, we consider tilings projected from a -dimensional space. We
study the limiting case, when the quantity , and therefore the number of
different species of tiles, become large. We had previously demonstrated [ICQ6]
that, in this limit, the thermodynamic properties of the tiling become
independent of the boundary conditions. The exact value of the limiting entropy
and finite corrections remain open questions. Here, we develop a mean-field
theory, which uses an iterative description of the tilings based on an analogy
with avoiding oriented walks on a random tiling. We compare the quantities
so-obtained with numerical calculations. We also discuss the role of spatial
correlations.Comment: Proceedings of the 7th International Conference on Quasicrystals
(ICQ7, Stuttgart), 4 pages, 4 figure
New record of <i>Carapus dubius</i> (Carapidae) off Madagascar?
When checking the identification of the Carapidae in the MNHN collection (MusĂ©um National dâHistoire Naturelle, Paris) a specimen of Eurypleuron owasianum (Matsubara, 1953) (MNHN 1992-0914) caught off Madagascar (20°S, 42°30âE) was found to be incorrectly identified. The specimen is vey close to Carapus dubius (Putnam, 1874), which is known from the Eastern Pacific (Markle and Olney, 1990)
Etude des liens entre les croyances religieuses et spirituelles, la santĂ© et lâĂąge
International audienc
Présence de Sergentomyia schwetzi Adler, Théodor et Parrot (Diptera, Phlebotomidae) dans le Sud marocain
Etude de la précision du satellite lidar GLAS-ICESat pour l'altimétrie des eaux continentales
For the coming century, the control of water resources will be certainly the key of all the stakes for billions of human beings. Unfortunately a reduction in the number of stations is observed with a decline of measurements quality. Remote sensing, which saw the development of numerous satellite radar altimeters and more recently the launch of the satellite lidar ICESat, could be an interesting alternative for the study of the hydrological networks. The objective of this study is to estimate the potential of ICESat for monitoring continental water missions through the cases of the Lake Geneva (Switzerland and France) and rivers of Metropolitan France. Our first axis of study concerned the satellite-based assessment of ICESat on the Lake Geneva by comparing laser data to hydrological gauge water levels. Two hydrological stations (Chillon and Saint Prex) were used to evaluate the accuracy of ICESat elevations. First it was necessary that all data was in the same datum to conduct a consistent comparison. ICESat elevations, which are referenced in the Topex ellipsoid, were converted into orthometric elevations by a translation between Topex ellipsoid and WGS84 and then into the vertical reference IGN69 (RGF93) with the grid RAF98. The shots of water alone were then extracted track by track and the mean elevation calculated for each track was used for the comparison with reference elevations (hydrological gauges). The error RMS is 33 cm (-0.20 cm ± 0.21 cm) without any saturation correction. When the saturation correction is supplied and different from -999.000, the quality of water elevation data is improved : the error RMS is 14 cm (0.01 cm ± 0.10 cm). However GLAS temporal profiles show a slow progressive adaptation of GLAS sensor before proposing correct elevations. On the passage of ICESat from the land to water, the first spots elevations are higher than reference elevation and the following spots from 30 cm to 50 cm. The progressive return to the normal can last 0.2 s. It corresponds to 8 measurements and an adaptation distance of 1.360 km. When the transition footprints are excluded, the accuracy for the ICESat elevation measurements is 5 cm. Besides hydrological objects with a small size (small lakes, small rivers), which can not apply a margin of 1.5 km to remove transition footprints, could not be monitoring using ICESat with a good accuracy. Next the accuracy of ICESat was investigated on French rivers with a width larger than the size of ICESat footprint (about 55 m for the laser 3). The error RMS is 1.15 m (0.03 m ± 1.17 m) due to the time of ICESat adaptation on the passage from land to water. ICESat is not adapted for the monitoring of the continental water resource
Reclaiming human machine nature
Extending and modifying his domain of life by artifact production is one of
the main characteristics of humankind. From the first hominid, who used a wood
stick or a stone for extending his upper limbs and augmenting his gesture
strength, to current systems engineers who used technologies for augmenting
human cognition, perception and action, extending human body capabilities
remains a big issue. From more than fifty years cybernetics, computer and
cognitive sciences have imposed only one reductionist model of human machine
systems: cognitive systems. Inspired by philosophy, behaviorist psychology and
the information treatment metaphor, the cognitive system paradigm requires a
function view and a functional analysis in human systems design process.
According that design approach, human have been reduced to his metaphysical and
functional properties in a new dualism. Human body requirements have been left
to physical ergonomics or "physiology". With multidisciplinary convergence, the
issues of "human-machine" systems and "human artifacts" evolve. The loss of
biological and social boundaries between human organisms and interactive and
informational physical artifact questions the current engineering methods and
ergonomic design of cognitive systems. New developpment of human machine
systems for intensive care, human space activities or bio-engineering sytems
requires grounding human systems design on a renewed epistemological framework
for future human systems model and evidence based "bio-engineering". In that
context, reclaiming human factors, augmented human and human machine nature is
a necessityComment: Published in HCI International 2014, Heraklion : Greece (2014
DNA methylation: a historical perspective
In 1925, 5-methylcytosine was first reported in bacteria. However, its biological importance was not intuitive for several decades. After this initial lag, the ubiquitous presence of this methylated base emerged across all domains of life and revealed a range of essential biological functions. Today, we are armed with the knowledge of the key factors that establish, maintain, and remove DNA methylation and have access to a staggering and rapidly growing number of base-resolution methylation maps. Despite this, several fundamental details about the precise role and interpretation of DNA methylation patterns remain under investigation. Here, we review the field of DNA methylation from its beginning to present day, with an emphasis on findings in mammalian systems, and point the reader to select experiments that form the foundation of this field
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