3,064 research outputs found
The human hand and foot in evolution and art : the effects of wearing footwear
The structures of the human hands and feet are shaped by evolution and its effects on the brain, skeleton and other structures, and on behavior. We used measurements obtained of hands and feet from living humans in Europe, the Americas (South and North) and Australia and images of hands and feet in cave art, paintings, and photographs obtained from the Web including some from Africa. We used the ratios of the third finger/width of hand and second toe/width of foot. We hypothesized that hand ratios would not have changed over millennia whereas, because of the use of footwear and mechanical locomotion, the ratios obtained from feet could have changed significantly. Here we report that statistical analyses and modeling confirmed our initial hypothesi
Definition of the stimulated emission threshold in high- nanoscale lasers through phase-space reconstruction
Nanoscale lasers sustain few optical modes so that the fraction of
spontaneous emission funnelled into the useful (lasing) mode is high
(of the order of few 10) and the threshold, which traditionally
corresponds to an abrupt kink in the light in- light out curve, becomes
ill-defined. We propose an alternative definition of the threshold, based on
the dynamical response of the laser, which is valid even for lasers.
The laser dynamics is analyzed through a reconstruction of its phase-space
trajectory for pulsed excitation. Crossing the threshold brings about a change
in the shape of the trajectory and in the area contained in it. An unambiguous
definition of the threshold in terms of this change is shown theoretically and
illustrated experimentally in a photonic crystal laser
An Explicit Framework for Interaction Nets
Interaction nets are a graphical formalism inspired by Linear Logic
proof-nets often used for studying higher order rewriting e.g. \Beta-reduction.
Traditional presentations of interaction nets are based on graph theory and
rely on elementary properties of graph theory. We give here a more explicit
presentation based on notions borrowed from Girard's Geometry of Interaction:
interaction nets are presented as partial permutations and a composition of
nets, the gluing, is derived from the execution formula. We then define
contexts and reduction as the context closure of rules. We prove strong
confluence of the reduction within our framework and show how interaction nets
can be viewed as the quotient of some generalized proof-nets
Creation, doubling, and splitting, of vortices in intracavity second harmonic generation
We demonstrate generation and frequency doubling of unit charge vortices in a
linear astigmatic resonator. Topological instability of the double charge
harmonic vortices leads to well separated vortex cores that are shown to
rotate, and become anisotropic, as the resonator is tuned across resonance
WATER\u2013BUDGET AS A TOOL TO EVALUATE THE SUSTAINABLE USE OF GROUNDWATER RESOURCES (ISONZO PLAIN, NE ITALY)
Water budget, hydrogeology, Soča/Isonzo River, climate chang
Comparison of Recoil-Induced Resonances (RIR) and Collective Atomic Recoil Laser (CARL)
The theories of recoil-induced resonances (RIR) [J. Guo, P. R. Berman, B.
Dubetsky and G. Grynberg, Phys. Rev. A {\bf 46}, 1426 (1992)] and the
collective atomic recoil laser (CARL) [ R. Bonifacio and L. De Salvo, Nucl.
Instrum. Methods A {\bf 341}, 360 (1994)] are compared. Both theories can be
used to derive expressions for the gain experienced by a probe field
interacting with an ensemble of two-level atoms that are simultaneously driven
by a pump field. It is shown that the RIR and CARL formalisms are equivalent.
Differences between the RIR and CARL arise because the theories are typically
applied for different ranges of the parameters appearing in the theory. The RIR
limit considered in this paper is , while the CARL
limit is , where is the magnitude of the
difference of the wave vectors of the pump and probe fields, is the
width of the atomic momentum distribution and is a recoil
frequency. The probe gain for a probe-pump detuning equal to zero is analyzed
in some detail, in order to understand how the gain arises in a system which,
at first glance, might appear to have vanishing gain. Moreover, it is shown
that the calculations, carried out in perturbation theory have a range of
applicability beyond the recoil problem. Experimental possibilities for
observing CARL are discussed.Comment: 16 pages, 1 figure. Submitted to Physical Review
Disentangling the influence of urbanization and invasion on endemic geckos in tropical biodiversity hot spots : a case study of Phyllodactylus martini (Squamata: Phyllodactylidae) along an Urban Gradient in Curaçao
Author Posting. © Peabody Museum of Natural History, 2016. This article is posted here by permission of Peabody Museum of Natural History for personal use, not for redistribution. The definitive version was published in Bulletin of the Peabody Museum of Natural History 57(2016): 147–164, doi:10.3374/014.057.0209.Predicting the response of endemic species to urbanization has emerged as a fundamental challenge
in 21st century conservation biology. The factors that underlie population declines of reptiles
are particularly nebulous, as these are often the least understood class of vertebrates in a given
community. In this study, we assess correlations between feeding ecology and phenotypic traits of
the Lesser Antillean endemic Dutch leaf-toed gecko, Phyllodactylus martini, along an urban gradient
in the Caribbean island of Curaçao. There has been a marked decline of this species in developed
habitats associated with the invasive tropical house gecko Hemidactylus mabouia. We find
a correlation between aspects of locomotor morphology and prey in undeveloped habitats that is
absent in developed habitats. Analyses of stomach contents further suggest that Phyllodactylus
martini alters primary prey items in developed areas. However, changes in prey promote the overlap
in foraging niches between Phyllodactylus martini and Hemidactylus mabouia, suggesting that
direct resource competition is contributing to the decline of Phyllodactylus martini. In addition to
competitive exclusion, we suggest that the urban extirpation of Phyllodactylus martini could also
be attributed to a top-down control on population growth by Hemidactylus mabouia. Colonizations
of walls put Phyllodactylus martini in direct contact with Hemidactylus mabouia increasing
the chances for predation events, as evidenced by our observation of a predation event on a Phyllodactylus
martini juvenile by an adult Hemidactylus mabuoia. In total, our results add to a growing
body of literature demonstrating the threat that invasive synanthropic reptiles pose to
endemics that might otherwise be able to cope with increased urbanization pressures
- …
