1,991 research outputs found
Comparison of thread-cutting behaviour in three specialist predatory mites to cope with complex webs of Tetranychus spider mites
Anti-predator defenses provided by complex webs of Tetranychus mites can severely impede the performance of generalist predatory mites, whereas this may not be true for specialist predatory mites. Although some specialist predatory mites have developed morphological protection to reduce the adverse effects of complex webs, little is known about their behavioral abilities to cope with the webs. In this study, we compared thread-cutting behavior of three specialist predatory mites, Phytoseiulus persimilis, Neoseiulus womersleyi and N. californicus, exhibited inside the complex web of T. urticae. No major difference was observed among them in the basic pattern of this behavior, using chelicerae and palps, and in the number of silken threads severed while moving inside the web. These results and observations suggest that each predator species cut many sticky silken threads to move inside the complex web without suffering from serious obstructio
Expanding Space: the Root of all Evil?
While it remains the staple of virtually all cosmological teaching, the
concept of expanding space in explaining the increasing separation of galaxies
has recently come under fire as a dangerous idea whose application leads to the
development of confusion and the establishment of misconceptions. In this
paper, we develop a notion of expanding space that is completely valid as a
framework for the description of the evolution of the universe and whose
application allows an intuitive understanding of the influence of universal
expansion. We also demonstrate how arguments against the concept in general
have failed thus far, as they imbue expanding space with physical properties
not consistent with the expectations of general relativity.Comment: 8 pages, accepted for publication in PAS
Archeops, mapping the CMB sky from large to small angular scales
Archeops is a balloon-borne experiment designed to measure the temperature
fluctuations of the CMB on a large region of the sky () with a high
angular resolution (10 arcminutes) and a high sensitivity ( per
pixel). Archeops will perform a measurement of the CMB anisotropies power
spectrum from large angular scales () to small angular scales
(). Archeops flew for the first time for a test flight in July
1999 from Sicily to Spain and the first scientific flight took place from
Sweden to Russia in January 2001. The data analysis is on its way and I present
here preliminary results, realistic simulations showing the expected accuracy
on the measurement of the power spectrum and perspectives for the incoming
flights (Winter 2001/2003).Comment: 6 pages, 6 figures, proceedings to TAUP2001 conference, LNGS, Italy,
Sept. 200
The flatness problem and
By way of a complete integration of the Friedmann equations, in terms of
observables, it is shown that for the cosmological constant there
exist non-flat FLRW models for which the total density parameter
remains throughout the entire history of the universe. Further, it is
shown that in a precise quantitative sense these models are not finely tuned.
When observations are brought to bear on the theory, and in particular the WMAP
observations, they confirm that we live in just such a universe. The conclusion
holds when the classical notion of is extended to dark energy.Comment: Final form to appear in Physical Review Letters. Further information
at http://grtensor.org/Robertson
Prospectus, November 13, 1996
https://spark.parkland.edu/prospectus_1996/1029/thumbnail.jp
Prospectus, November 20, 1996
https://spark.parkland.edu/prospectus_1996/1030/thumbnail.jp
Hyperparasitoids exploit herbivore-induced plant volatiles during host location to assess host quality and non-host identity
Although consumers often rely on chemical information to optimize their foraging strategies, it is poorly understood how top carnivores above the third trophic level find resources in heterogeneous environments. Hyperparasitoids are a common group of organisms in the fourth trophic level that lay their eggs in or on the body of other parasitoid hosts. Such top carnivores use herbivore-induced plant volatiles (HIPVs) to find caterpillars containing parasitoid host larvae. Hyperparasitoids forage in complex environments where hosts of different quality may be present alongside non-host parasitoid species, each of which can develop in multiple herbivore species. Because both the identity of the herbivore species and its parasitization status can affect the composition of HIPV emission, hyperparasitoids encounter considerable variation in HIPVs during host location. Here, we combined laboratory and field experiments to investigate the role of HIPVs in host selection of hyperparasitoids that search for hosts in a multi-parasitoid multi-herbivore context. In a wild Brassica oleracea-based food web, the hyperparasitoid Lysibia nana preferred HIPVs emitted in response to caterpillars parasitized by the gregarious host Cotesia glomerata over the non-host Hyposoter ebeninus. However, no plant-mediated discrimination occurred between the solitary host C. rubecula and the non-host H. ebeninus. Under both laboratory and field conditions, hyperparasitoid responses were not affected by the herbivore species (Pieris brassicae or P. rapae) in which the three primary parasitoid species developed. Our study shows that HIPVs are an important source of information within multitrophic interaction networks allowing hyperparasitoids to find their preferred hosts in heterogeneous environments
Generation of scalar-tensor gravity effects in equilibrium state boson stars
Boson stars in zero-, one-, and two-node equilibrium states are modeled
numerically within the framework of Scalar-Tensor Gravity. The complex scalar
field is taken to be both massive and self-interacting. Configurations are
formed in the case of a linear gravitational scalar coupling (the Brans-Dicke
case) and a quadratic coupling which has been used previously in a cosmological
context. The coupling parameters and asymptotic value for the gravitational
scalar field are chosen so that the known observational constraints on
Scalar-Tensor Gravity are satisfied. It is found that the constraints are so
restrictive that the field equations of General Relativity and Scalar-Tensor
gravity yield virtually identical solutions. We then use catastrophe theory to
determine the dynamically stable configurations. It is found that the maximum
mass allowed for a stable state in Scalar-Tensor gravity in the present
cosmological era is essentially unchanged from that of General Relativity. We
also construct boson star configurations appropriate to earlier cosmological
eras and find that the maximum mass for stable states is smaller than that
predicted by General Relativity, and the more so for earlier eras. However, our
results also show that if the cosmological era is early enough then only states
with positive binding energy can be constructed.Comment: 20 pages, RevTeX, 11 figures, to appear in Class. Quantum Grav.,
comments added, refs update
Prospectus, January 13, 1997
https://spark.parkland.edu/prospectus_1997/1000/thumbnail.jp
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