3,096 research outputs found
Convergent evolution of levee building behavior among distantly related ant species in a floodplain ant assemblage
Flooding impacts ground nesting ant colonies by destroying the infrastructure housing and organizing societal function. Here, we report the convergent evolution in distantly related ant species of a behavioral trait that minimizes costs of flooding: the construction of earthen levees around nest entrances. In a South American floodplain ecosystem, we observed five ant species constructing prominent earthen berms encircling nest entrances shortly after large rainfall events. In four of these species, experimental flooding of nests demonstrated that earthen berms sufficed to prevent floodwaters from entering the below ground portions of the nest. Additional manipulations revealed that levee breaching caused, pronounced, and extended reductions in food collection for two distantly related species. Foraging was preempted by the allocation of workers to repair the internal structure of the nest. These findings represent convergent evolution of a functionally important nest construction behavior in response to comparable selective forces
Properties of equations of the continuous Toda type
We study a modified version of an equation of the continuous Toda type in 1+1
dimensions. This equation contains a friction-like term which can be switched
off by annihilating a free parameter \ep. We apply the prolongation method,
the symmetry and the approximate symmetry approach. This strategy allows us to
get insight into both the equations for \ep =0 and \ep \ne 0, whose
properties arising in the above frameworks are mutually compared. For \ep =0,
the related prolongation equations are solved by means of certain series
expansions which lead to an infinite- dimensional Lie algebra. Furthermore,
using a realization of the Lie algebra of the Euclidean group , a
connection is shown between the continuous Toda equation and a linear wave
equation which resembles a special case of a three-dimensional wave equation
that occurs in a generalized Gibbons-Hawking ansatz \cite{lebrun}. Nontrivial
solutions to the wave equation expressed in terms of Bessel functions are
determined.
For \ep\,\ne\,0, we obtain a finite-dimensional Lie algebra with four
elements. A matrix representation of this algebra yields solutions of the
modified continuous Toda equation associated with a reduced form of a
perturbative Liouville equation. This result coincides with that achieved in
the context of the approximate symmetry approach. Example of exact solutions
are also provided. In particular, the inverse of the exponential-integral
function turns out to be defined by the reduced differential equation coming
from a linear combination of the time and space translations. Finally, a Lie
algebra characterizing the approximate symmetries is discussed.Comment: LaTex file, 27 page
Maximum solutions of normalized Ricci flows on 4-manifolds
We consider maximum solution , , to the normalized
Ricci flow. Among other things, we prove that, if is a smooth
compact symplectic 4-manifold such that and let
, be a solution to (1.3) on whose Ricci curvature
satisfies that and additionally , then there exists an , and a sequence of points
, , satisfying that, by passing to a
subsequence, , in the -pointed
Gromov-Hausdorff sense for any sequence , where
, , are complete complex hyperbolic orbifolds
of complex dimension 2 with at most finitely many isolated orbifold points.
Moreover, the convergence is in the non-singular part of
and
, where
(resp. ) is the Euler characteristic (resp. signature) of
.Comment: 23 page
Einstein--Maxwell--Dilaton metrics from three--dimensional Einstein--Weyl structures
A class of time dependent solutions to Einstein--Maxwell-dilaton
theory with attractive electric force is found from Einstein--Weyl structures
in (2+1) dimensions corresponding to dispersionless Kadomtsev--Petviashvili and
Toda equations. These solutions are obtained from time--like
Kaluza--Klein reductions of solitons.Comment: 12 pages, to be published in Class.Quantum Gra
High Momentum Probes of Nuclear Matter
We discuss how the chemical composition of QCD jets is altered by final state
interactions in surrounding nuclear matter. We describe this process through
conversions of leading jet particles. We find that conversions lead to an
enhancement of kaons at high transverse momentum in Au+Au collisions at RHIC,
while their azimuthal asymmetry v_2 is suppressed.Comment: Contribution to the 4th international workshop High-pT physics at LHC
09, Prague; 6 pages, 6 figure
IBIS/PICsIT in-flight performances
PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy
detector of the IBIS telescope on-board the INTEGRAL satellite. PICsIT operates
in the gamma-ray energy range between 175 keV and 10 MeV, with a typical energy
resolution of 10% at 1 MeV, and an angular resolution of 12 arcmin within a
\~100 square degree field of view, with the possibility to locate intense point
sources in the MeV region at the few arcmin level. PICsIT is based upon a
modular array of 4096 independent CsI(Tl) pixels, ~0.70 cm^2 in cross-section
and 3 cm thick. In this work, the PICsIT on-board data handling and science
operative modes are described. This work presents the in-flight performances in
terms of background count spectra, sensitivity limit, and imaging capabilities.Comment: 8 pages, 4 figures. Accepted for publication on A&A, special issue on
First Science with INTEGRA
The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848
IGR J16318-4848 is the prototype and one of the more extreme examples of the
new class of highly obscured Galactic X-ray sources discovered by INTEGRAL. A
monitoring campaign on this source has been carried out by XMM-Newton and
INTEGRAL, consisting in three simultaneous observations performed in February,
March and August 2004. The long-term variability of the Compton-thick
absorption and emission line complexes will be used to probe the properties of
the circumstellar matter. A detailed timing and spectral analysis of the three
observations is performed, along with the reanalysis of the XMM-Newton
observation performed in February 2003. The results are compared with
predictions from numerical radiative transfer simulations to derive the
parameters of the circumstellar matter. Despite the large flux dynamic range
observed (almost a factor 3 between observations performed a few months apart),
the source remained bright (suggesting it is a persistent source) and
Compton-thick (NH >1.2x10^24 cm-2). Large Equivalent Width (EW) emission lines
from Fe Kalpha, Fe Kbeta and Ni Kalpha were present in all spectra. The
addition of a Fe Kalpha Compton Shoulder improves the fits, especially in the
2004 observations. Sporadic occurrences of rapid X-ray flux risings were
observed in three of the four observations. The Fe Kalpha light curve followed
the continuum almost instantaneously, suggesting that the emission lines are
produced by illumination of small-scale optically-thick matter around the
high-energy continuum source. Using the iron line EW and Compton Shoulder as
diagnostic of the geometry of the matter, we suggest that the obscuring matter
is in a flattened configuration seen almost edge-on.Comment: accepted by Astronomy and Astrophysic
Einstein-Maxwell gravitational instantons and five dimensional solitonic strings
We study various aspects of four dimensional Einstein-Maxwell multicentred
gravitational instantons. These are half-BPS Riemannian backgrounds of minimal
N=2 supergravity, asymptotic to R^4, R^3 x S^1 or AdS_2 x S^2. Unlike for the
Gibbons-Hawking solutions, the topology is not restricted by boundary
conditions. We discuss the classical metric on the instanton moduli space. One
class of these solutions may be lifted to causal and regular multi `solitonic
strings', without horizons, of 4+1 dimensional N=2 supergravity, carrying null
momentum.Comment: 1+30 page
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