1,161 research outputs found
Perturbative renormalisation of quark bilinear operators for overlap fermions with and without stout links and improved gauge action
We calculate lattice renormalisation constants of local and one-link quark
operators for overlap fermions and improved gauge actions in one-loop
perturbation theory. For the local operators we stout smear the SU(3) links in
the fermionic action. Using the popular tadpole improved L\"uscher-Weisz
actions at and we present numerical values for the Z
factors in the scheme (partly as function of the stout smearing
strength). We compare various levels of mean field (tadpole) improvement which
have been applied to our results.Comment: 7 page
How ions distribute in a drying porous medium: A simple model
Salt crystallization at surfaces is an important problem for buildings and monuments. We do not consider the formation of salt crystals as such, but focus on transport properties of ions in a drying porous medium. We deal with the first phase of the drying process, where the water is still uniformly distributed throughout the medium. An approximate model is presented, which accounts for both convection and diffusion. It is shown that the key parameter is the Peclet number at the evaporating surface, PehL/D, where h, L, , and D are the drying rate, sample size, porosity, and diffusion constant, respectively. When Pe1 (diffusion dominates over convection) the ions remain uniformly distributed throughout the system. Strong accumulation at the evaporating surface occurs for Pe1 (convection dominates over diffusion). Crossover behavior is found for Pe1. Therefore, it is likely that the first crystals will be formed both in the bulk and at the interfaces of the material when Pe1. For high values of Pe the density peak at the evaporating surface will reach the saturation concentration long before it is reached in the bulk of the material. As a consequence, the salt starts to crystallize at the interfaces
A review of salt transport in porous media : assessment methods and salt reduction treatments
It is an unpalatable fact that while objects can deteriorate through lack of care and attention, they can also deteriorate as a result of inappropriate and misguided interventions. This is particularly the case with regard to salt-related deterioration problems. A successful treatment outcome using aqueous salt reduction methods demands an understanding of the transport processes involved as well as detailed information regarding the characteristics and specific situation of the individual object. The use of poultice materials to reduce the salt content of salt deteriorated objects is a long established technique in conservation. However, due to the complex nature of salt problems within historic structures the result of such interventions can be variable and unpredictable. The amount and depth to which salts are mobilised, and where they are transported to, is dependent on the inter-relationship between the poultice and the substrate, the drying conditions and also the initial salt distribution. This paper examines the current scientific understanding of salt and moisture transport processes, and the extent to which this knowledge can feed back into the practical arena, to aid the conservator. Moreover, areas where further research is required are identified. In particular, the importance of pre- and post treatment investigations is highlighted, showing how, in combination with knowledge of salt and moisture transport mechanisms, these can give useful indications regarding treatment options. The role of selective salt extraction and the post treatment behaviour of residual salts are discussed
Accelerating Hasenbusch's acceleration of Hybrid Monte Carlo
Hasenbusch has proposed splitting the pseudo-fermionic action into two parts,
in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a
different splitting, also using clover-improved Wilson fermions. An additional
speed-up between 5 and 20% over the original proposal was achieved in
production runs.Comment: Poster presented by H. Stueben at Lattice2003, meta-data correcte
On the metallicity gradient of the Galactic disk
Aims: The iron abundance gradient in the Galactic stellar disk provides
fundamental constraints on the chemical evolution of this important Galaxy
component. However the spread around the mean slope is, at fixed Galactocentric
distance, larger than estimated uncertainties. Methods: To provide quantitative
constraints on these trends we adopted iron abundances for 265 classical
Cepheids (more than 50% of the currently known sample) based either on
high-resolution spectra or on photometric metallicity indices. Homogeneous
distances were estimated using near-infrared Period-Luminosity relations. The
sample covers the four disk quadrants and their Galactocentric distances range
from ~5 to ~17 kpc. Results: A linear regression over the entire sample
provides an iron gradient of -0.051+/-0.004 dex/kpc. The above slope agrees
quite well, within the errors, with previous estimates based either on Cepheids
or on open clusters covering similar Galactocentric distances. However, once we
split the sample in inner (Rg < 8 kpc) and outer disk Cepheids we found that
the slope (-0.130+/-0.015 dex/kpc) in the former region is ~3 times steeper
than the slope in the latter one (-0.042+/-0.004 dex/kpc). We found that in the
outer disk the radial distribution of metal-poor (MP, [Fe/H]<-0.02 dex) and
metal-rich (MR) Cepheids across the four disk quadrants does not show a clear
trend when moving from the innermost to the external disk regions. We also
found that the relative fractions of MP and MR Cepheids in the 1st and in the
3rd quadrant differ at 8 sigma (MP) and 15 sigma (MR) level.Comment: 6 pages, 6 figures, A&A accepte
Reply to "Comment on `Lattice determination of Sigma - Lambda mixing' "
In this Reply, we respond to the above Comment. Our computation [Phys. Rev. D
91 (2015) 074512] only took into account pure QCD effects, arising from quark
mass differences, so it is not surprising that there are discrepancies in
isospin splittings and in the Sigma - Lambda mixing angle. We expect that these
discrepancies will be smaller in a full calculation incorporating QED effects.Comment: 5 page
Multiple Scattering: Dispersion, Temperature Dependence, and Annular Pistons
We review various applications of the multiple scattering approach to the
calculation of Casimir forces between separate bodies, including dispersion,
wedge geometries, annular pistons, and temperature dependence. Exact results
are obtained in many cases.Comment: 15 pages, 12 figures, contributed to the Festschrift for Emilio
Elizald
Axial and tensor charge of the nucleon with dynamical fermions
We present preliminary results for the axial and tensor charge of the nucleon
obtained from simulations with N_f=2 clover fermions. A comparison with chiral
perturbation theory is attempted.Comment: Talk presented at Lattice2004(weak), Fermilab, June 21-26, 2004, 3
pages, 3 figures, v2: one reference added, v3: acknowledgement extende
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