1,220 research outputs found
Exploring the phase structure of lattice QCD with twisted mass quarks
The phase structure of zero temperature twisted mass lattice QCD is
investigated. We find strong metastabilities in the plaquette observable when
the untwisted quark mass sweeps across zero.Comment: Talks presented at Lattice2004(spectrum), 6 pages, 6 figure
Lattice Spacing Dependence of the First Order Phase Transition for Dynamical Twisted Mass Fermions
Lattice QCD with Wilson fermions generically shows the phenomenon of a first
order phase transition. We study the phase structure of lattice QCD using
Wilson twisted mass fermions and the Wilson plaquette gauge action are used in
a range of beta values where such a first order phase transition is observed.
In particular, we investigate the dependence of the first order phase
transition on the value of the lattice spacing. Using only data in one phase
and neglecting possible problems arising from the phase transition we are able
to perform a first scaling test for physical quantities using this action.Comment: 15 pages, 7 figures, typo corrected, web-list of authors correcte
Self similar Barkhausen noise in magnetic domain wall motion
A model for domain wall motion in ferromagnets is analyzed. Long-range
magnetic dipolar interactions are shown to give rise to self-similar dynamics
when the external magnetic field is increased adiabatically. The power spectrum
of the resultant Barkhausen noise is of the form , where
can be estimated from the critical exponents for interface
depinning in random media.Comment: 7 pages, RevTex. To appear in Phys. Rev. Let
Twisted mass fermions: neutral pion masses from disconnected contributions
Twisted mass fermions allow light quarks to be explored but with the
consequence that there are mass splittings, such as between the neutral and
charged pion. Using a direct calculation of the connected neutral pion
correlator and stochastic methods to evaluate the disconnected correlations, we
determine the neutral pion mass. We explore the dependence on lattice spacing
and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the
splitting which is linked, via chiral PT, to the nature of the phase transition
at small quark mass.Comment: 6 pages, poster (hadron spectrum and quark masses) at Lattice
2005,Dublin, July 25-3
Plant-phenotypic changes induced by parasitoid ichnoviruses enhance the performance of both unparasitized and parasitized caterpillars
There is increasing awareness that interactions between plants and insects can be mediated by microbial symbionts. Nonetheless, evidence showing that symbionts associated with organisms beyond the second trophic level affect plant-insect interactions are restricted to a few cases belonging to parasitoid-associated bracoviruses. Insect parasitoids harbour a wide array of symbionts which, like bracoviruses, can be injected into their herbivorous hosts to manipulate their physiology and behaviour. Yet, the function of these symbionts in plant-based trophic webs remains largely overlooked. Here, we provide the first evidence of a parasitoid-associated symbiont belonging to the group of ichnoviruses which affects the strength of plant-insect interactions. A comparative proteomic analysis shows that, upon parasitoid injection of calyx fluid containing ichnovirus particles, the composition of salivary glands of caterpillars changes both qualitatively (presence of two viral-encoded proteins) and quantitatively (abundance of several caterpillar-resident enzymes, including elicitors such as glucose oxidase). In turn, plant phenotypic changes triggered by the altered composition of caterpillar oral secretions affect the performance of herbivores. Ichnovirus manipulation of plant responses to herbivory leads to benefits for their parasitoid partners in terms of reduced developmental time within the parasitized caterpillar. Interestingly, plant-mediated ichnovirus-induced effects also enhance the performances of unparasitized herbivores which in natural conditions may feed alongside parasitized ones. We discuss these findings in the context of ecological costs imposed to the plant by the viral symbiont of the parasitoid. Our results provide intriguing novel findings about the role played by carnivore-associated symbionts on plant-insect-parasitoid systems and underline the importance of placing mutualistic associations in an ecological perspective
- âŠ