16,123 research outputs found
Hydrodynamic limit of a disordered lattice gas
We consider a model of lattice gas dynamics in the d-dimensional cubic
lattice in the presence of disorder. If the particle interaction is only mutual
exclusion and if the disorder field is given by i.i.d. bounded random
variables, we prove the almost sure existence of the hydrodynamical limit in
dimension d>2. The limit equation is a non linear diffusion equation with
diffusion matrix characterized by a variational principle
Results from a Non-Perturbative Renormalization of Lattice Operators
We propose a general renormalization method, which avoids completely the use
of lattice perturbation theory. We present the results from its numerical
applications to two-fermion operators on a lattice, at
.Comment: 3 pages postscript file. Contribution to Lattice '9
Non-perturbative renormalization in kaon decays
We discuss the application of the MPSTV non-perturbative method \cite{NPM} to
the operators relevant to kaon decays. This enables us to reappraise the
long-standing question of the rule, which involves
power-divergent subtractions that cannot be evaluated in perturbation theory.
We also study the mixing with dimension-six operators and discuss its
implications to the chiral behaviour of the parameter.Comment: Talk presented at LATTICE96(improvement), LaTeX 3 pages, uses
espcrc2, 2 postscript figure
Lattice computation of structure functions
Recent lattice calculations of hadron structure functions are described.Comment: Plenary talk presented at LATTICE96, LaTeX, 7 pages, 5 figures,
espcrc2.sty and epsfig.sty include
Non-perturbative Renormalization of Lattice Operators
We briefly review and compare three methods (one perturbative, one based on
Ward Identities and one non-perturbative) for the calculation of the
renormalization constants of lattice operators. The following results are
presented: (a) non perturbative renormalization of the operators with light
quarks; (b) the renormalization constants with a heavy (charm) quark mass and
its KLM improvement; (c) the non perturbative determination of the mixing of
the operator.Comment: 9 pages, uuencoded PS file, 8 figures included, 1 tabl
A possible theoretical explanation of metallicity gradients in elliptical galaxies
Models of chemical evolution of elliptical galaxies taking into account
different escape velocities at different galactocentric radii are presented. As
a consequence of this, the chemical evolution develops differently in different
galactic regions; in particular, we find that the galactic wind, powered by
supernovae (of type II and I) starts, under suitable conditions, in the outer
regions and successively develops in the central ones. The rate of star
formation (SFR) is assumed to stop after the onset of the galactic wind in each
region. The main result found in the present work is that this mechanism is
able to reproduce metallicity gradients, namely the gradients in the
index, in good agreement with observational data. We also find that in order to
honor the constant [Mg/Fe] ratio with galactocentric distance, as inferred from
metallicity indices, a variable initial mass function as a function of
galactocentric distance is required. This is only a suggestion since trends on
abundances inferred just from metallicity indices are still uncertain.Comment: 18 pages, LaTeX file with 4 figures using mn.sty, submitted to MNRA
The phase diagrams of iron-based superconductors: theory and experiments
Phase diagrams play a primary role in the understanding of materials
properties. For iron-based superconductors (Fe-SC), the correct definition of
their phase diagrams is crucial because of the close interplay between their
crystallo-chemical and magnetic properties, on one side, and the possible
coexistence of magnetism and superconductivity, on the other. The two most
difficult issues for understanding the Fe-SC phase diagrams are: 1) the origin
of the structural transformation taking place during cooling and its
relationship with magnetism; 2) the correct description of the region where a
crossover between the magnetic and superconducting electronic ground states
takes place. Hence a proper and accurate definition of the structural, magnetic
and electronic phase boundaries provides an extremely powerful tool for
material scientists. For this reason, an exact definition of the thermodynamic
phase fields characterizing the different structural and physical properties
involved is needed, although it is not easy to obtain in many cases. Moreover,
physical properties can often be strongly dependent on the occurrence of
micro-structural and other local-scale features (lattice micro-strain, chemical
fluctuations, domain walls, grain boundaries, defects), which, as a rule, are
not described in a structural phase diagram. In this review, we critically
summarize the results for the most studied 11-, 122- and 1111-type compound
systems, providing a correlation between experimental evidence and theory
DEPENDENCE OF THE CURRENT RENORMALISATION CONSTANTS ON THE QUARK MASS
We study the behaviour of the vector and axial current renormalisation
constants and as a function of the quark mass, . We show that
sizeable and systematic effects are present in the
Wilson and Clover cases respectively. We find that the prescription of
Kronfeld, Lepage and Mackenzie for correcting these artefacts is not always
successful.Comment: Contribution to Lattice'94, 3 pages PostScript, uuencoded compressed
Short note on magnetic impurities in SmFeAsOF (x=0, 0.07) compounds revealed by zero-field As NMR
We have performed zero-field As nuclear magnetic resonance study of
SmFeAsOF (x=0, 0.07) polycrystals in a wide frequency range at
various temperatures. As resonance line was found at around 265 MHz
revealing the formation of the intermetallic FeAs clusters in the new layered
superconductors. We have also demonstrated that NMR is a sensitive tool for
probing the quality of these materials.Comment: Revised authorshi
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