1,564 research outputs found
Characterising the biofilm forming capabilities of Cystic Fibrosis Pseudomonas aeruginosa clinical isolates
Pion scattering in Wilson ChPT
We compute the scattering amplitude for pion scattering in Wilson chiral
perturbation theory for two degenerate quark flavors. We consider two different
regimes where the quark mass m is of order (i) a\Lambda_QCD^2 and (ii)
a^2\Lambda_QCD^3. Analytic expressions for the scattering lengths in all three
isospin channels are given. As a result of the O(a^2) terms the I=0 and I=2
scattering lengths do not vanish in the chiral limit. Moreover, additional
chiral logarithms proportional to a^2\ln M_{\pi}^2 are present in the one-loop
results for regime (ii). These contributions significantly modify the familiar
results from continuum chiral perturbation theory.Comment: 20 pages, 4 figures. V3: Comments on finite size effects and the
axial vector current added, one more reference. To be published in PR
The dynamics of thin vibrated granular layers
We describe a series of experiments and computer simulations on vibrated
granular media in a geometry chosen to eliminate gravitationally induced
settling. The system consists of a collection of identical spherical particles
on a horizontal plate vibrating vertically, with or without a confining lid.
Previously reported results are reviewed, including the observation of
homogeneous, disordered liquid-like states, an instability to a `collapse' of
motionless spheres on a perfect hexagonal lattice, and a fluctuating,
hexagonally ordered state. In the presence of a confining lid we see a variety
of solid phases at high densities and relatively high vibration amplitudes,
several of which are reported for the first time in this article. The phase
behavior of the system is closely related to that observed in confined
hard-sphere colloidal suspensions in equilibrium, but with modifications due to
the effects of the forcing and dissipation. We also review measurements of
velocity distributions, which range from Maxwellian to strongly non-Maxwellian
depending on the experimental parameter values. We describe measurements of
spatial velocity correlations that show a clear dependence on the mechanism of
energy injection. We also report new measurements of the velocity
autocorrelation function in the granular layer and show that increased
inelasticity leads to enhanced particle self-diffusion.Comment: 11 pages, 7 figure
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
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
f_B and f_Bs with maximally twisted Wilson fermions
We present a lattice QCD calculation of the heavy-light decay constants f_B
and f_Bs performed with Nf=2 maximally twisted Wilson fermions, at four values
of the lattice spacing. The decay constants have been also computed in the
static limit and the results are used to interpolate the observables between
the charm and the infinite-mass sectors, thus obtaining the value of the decay
constants at the physical b quark mass. Our preliminary results are f_B=191(14)
MeV, f_Bs=243(14) MeV, f_Bs/f_B=1.27(5). They are in good agreement with those
obtained with a novel approach, recently proposed by our Collaboration (ETMC),
based on the use of suitable ratios having an exactly known static limit.Comment: Proceedings of the 27th International Symposium on Lattice Field
Theory (Lattice 2009), Beijing, China, 2009 July 26-31. 8 pages, 3 figure
O(a^2) cutoff effects in lattice Wilson fermion simulations
In this paper we propose to interpret the large discretization artifacts
affecting the neutral pion mass in maximally twisted lattice QCD simulations as
O(a^2) effects whose magnitude is roughly proportional to the modulus square of
the (continuum) matrix element of the pseudoscalar density operator between
vacuum and one-pion state. The numerical size of this quantity is determined by
the dynamical mechanism of spontaneous chiral symmetry breaking and turns out
to be substantially larger than its natural magnitude set by the value of
Lambda_QCD.Comment: 38 pages, 1 figure, 2 table
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