14 research outputs found
Covers of acts over monoids II
In 1981 Edgar Enochs conjectured that every module has a flat cover and
finally proved this in 2001. Since then a great deal of effort has been spent
on studying different types of covers, for example injective and torsion free
covers. In 2008, Mahmoudi and Renshaw initiated the study of flat covers of
acts over monoids but their definition of cover was slightly different from
that of Enochs. Recently, Bailey and Renshaw produced some preliminary results
on the `other' type of cover and it is this work that is extended in this
paper. We consider free, divisible, torsion free and injective covers and
demonstrate that in some cases the results are quite different from the module
case
The Bose Gas and Asymmetric Simple Exclusion Process on the Half-Line
In this paper we find explicit formulas for: (1) Green's function for a
system of one-dimensional bosons interacting via a delta-function potential
with particles confined to the positive half-line; and (2) the transition
probability for the one-dimensional asymmetric simple exclusion process (ASEP)
with particles confined to the nonnegative integers. These are both for systems
with a finite number of particles. The formulas are analogous to ones obtained
earlier for the Bose gas and ASEP on the line and integers, respectively. We
use coordinate Bethe Ansatz appropriately modified to account for confinement
of the particles to the half-line. As in the earlier work, the proof for the
ASEP is less straightforward than for the Bose gas.Comment: 14 Page
On the nature of Bose-Einstein condensation in disordered systems
We study the perfect Bose gas in random external potentials and show that
there is generalized Bose-Einstein condensation in the random eigenstates if
and only if the same occurs in the one-particle kinetic-energy eigenstates,
which corresponds to the generalized condensation of the free Bose gas.
Moreover, we prove that the amounts of both condensate densities are equal. Our
method is based on the derivation of an explicit formula for the occupation
measure in the one-body kinetic-energy eigenstates which describes the
repartition of particles among these non-random states. This technique can be
adapted to re-examine the properties of the perfect Bose gas in the presence of
weak (scaled) non-random potentials, for which we establish similar results
Properties of baryon resonances from a multichannel partial wave analysis
Properties of nucleon and resonances are derived from a multichannel
partial wave analysis. The statistical significance of pion and photo-induced
inelastic reactions off protons are studied in a multichannel partial-wave
analysis.Comment: 12 pages, 8 Table
Refraction contrast imaging and edge effects in neutron radiography
This paper reports on the edge enhancement and refraction scattering effects in neutron radiography measured at thermal and cold neutron beams with a high resolution 55 mm microchannel plate neutron counting detector. These effects in some cases can enhance the contrast of certain features in the neutron radiographic images. At the same time, the edge effects introduce image distortions, as in case of tomographic reconstructions. The edge effects in radiographies of several steel and aluminum objects are shown for different beam divergences and sample orientations relative to the beam. It is also demonstrated how novel microcapillary neutron collimators can enable refraction and scattering contrast imaging in some cases, where the refraction and scattering angles are relatively large. These collimators can also be used to reduce some refraction artifacts, namely remove bright edges in the transmission image