127,534 research outputs found
Cavity averages for hard spheres in the presence of polydispersity and incomplete data
We develop a cavity-based method which allows to extract thermodynamic
properties from position information in hard-sphere/disk systems. So far, there
are 'available-volume' and 'free-volume' methods. We add a third one, which we
call 'available-volume-after-takeout', and which is shown to be mathematically
equivalent to the others. In applications, where data sets are finite, all
three methods show limitations, and they do this in different parameter ranges.
We illustrate the principal equivalence and the limitations on data from
molecular dynamics -- In particular, we test robustness against missing data.
We have in mind experimental limitations where there is a small polydispersity,
say 4% in the particle radii, but individual radii cannot be determined. We
observe that, depending on the used method, the errors in such a situation are
easily 100% for the pressure and 10kT for the chemical potentials. Our work is
meant as guideline to the experimentalist for choosing the right one of the
three methods, in order to keep the outcome of experimental data analysis
meaningful.Comment: 13 pages, 6 figures. The final publication is available at Springer
via http://dx.doi.org/10.1140/epje/i2015-15097-
The range and nature of effective interactions in hard-sphere solids
Colloidal systems observed in video microscopy are often analysed using the
displacements correlation matrix of particle positions. In non-thermal systems,
the inverse of this matrix can be interpreted as a pair-interaction potential
between particles. If the system is thermally agitated, however, only an
effective interaction is accessible from the correlation matrix. We show how
this effective interaction differs from the non-thermal case by comparing with
high-statistics numerical data from hard-sphere crystals.Comment: 12 pages, 10 figures, Soft Matter 201
Orbitally excited and hybrid mesons from the lattice
We discuss in general the construction of gauge-invariant non-local meson
operators on the lattice. We use such operators to study the - and -wave
mesons as well as hybrid mesons in quenched QCD, with quark masses near the
strange quark mass. The resulting spectra are compared with experiment for the
orbital excitations. For the states produced by gluonic excitations (hybrid
mesons) we find evidence of mixing for non-exotic quantum numbers. We give
predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\
0^{+-}2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde
Comment on "Nucleon spin-averaged forward virtual Compton tensor at large Q^2"
In recent work, Hill and Paz apply the operator product expansion to forward
doubly virtual Compton scattering. The resulting large- form of the
amplitude is compatible with the one we obtain by extrapolation of
low- results from a chiral effective field theory, providing support for
our approach. That paper also presents a result for the two-photon contribution
to the Lamb shift in muonic hydrogen that has a much larger uncertainty than in
previous work. We show that this an overestimate arising from the inclusion of
the proton pole term in the subtracted dispersion relation for .Comment: 3 pages; version accepted for publicatio
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