6,221 research outputs found
The presence of webbing affects the oviposition rate of two-spotted spider mites, Tetranychus urticae (Acari: Tetranychidae)
Several species of tetranychid mites including Tetranychus urticae Koch (Acari: Tetranychidae) construct complicated three-dimensional webs on plant leaves. These webs provide protection against biotic and abiotic stress. As producing web is likely to entail a cost, mites that arrive on a leaf with web are expected to refrain from producing it, because they will gain the benefit of protection from the existing web. Mites that produce less web may then allocate resources that are not spent on web construction to other fitness-enhancing activities, such as laying eggs. To test this, the oviposition rate of T. urticae adult females was examined on leaves with web. As a control, we used leaves where the web had been removed, hence both types of leaves had been exposed to conspecifics previously and were thus damaged. On leaves with web, the oviposition rate of T. urticae females was higher than on leaves where the web had been removed. Therefore, the presence of web constructed by conspecifics enhanced the oviposition rate of T. urticae females. This provides indirect evidence that mites use the web constructed by conspecifics and thereby save resources that can be allocated to other traits that enhance reproductive succes
Schwarzschild-like black holes: Light-like trajectories and massless scalar absorption
Black holes are among the most intriguing objects in nature. They are
believed to be fully described by General Relativity (GR), and the
astrophysical black holes are expected to belong to the Kerr family, obeying
the no-hair theorems. Alternative theories of gravity or parameterized
deviations of GR allow black hole solutions, which have additional parameters
other than mass and angular momentum. We analyze a Schwarzschild-like metric,
proposed by Johannsen and Psaltis, characterized by its mass and a deformation
parameter. We compute the absorption cross section of massless scalar waves for
different values of this deformation parameter and compare it with the
corresponding scalar absorption cross section of the Schwarzschild black hole.
We also present analytical approximations for the absorption cross section in
the high-frequency regime. We check the consistence of our results comparing
the numerical and analytical approaches, finding excellent agreement.Comment: 8 pages, 14 figure
Quantum Critical Point in the Spin Glass-Kondo Transition in Heavy Fermion Systems
The Kondo-Spin Glass competition is studied in a theoretical model of a Kondo
lattice with an intra-site Kondo type exchange interaction treated within the
mean field approximation, an inter-site quantum Ising exchange interaction with
random couplings among localized spins and an additional transverse field in
the x direction, which represents a simple quantum mechanism of spin flipping.
We obtain two second order transition lines from the spin-glass state to the
paramagnetic one and then to the Kondo state. For a reasonable set of the
different parameters, the two second order transition lines do not intersect
and end in two distinct QCP.Comment: 20 pages; 1 figure; to appear in Physical Review
Forecasting Spanish Elections
The behavior of the individual Spanish voter has come to be rather well-understood, thanks to a growing research literature. However, no models have appeared to explain, or to forecast, national election outcomes. The presence of this research gap contrasts sharply with the extensive election forecasting work done on other leading Western democracies. Here we fill this gap. The model, developed from core political economy theory, is parsimonious but statistically robust. Further, it promises considerable prediction accuracy of Spanish general election outcomes, six months before the contest actually occurs. After presenting the model, and carrying out extensive regression diagnostics, we offer an ex ante forecast of the 2012 general election.
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