41,608 research outputs found
On localizations of quasi-simple groups with given countable center
A group homomorphism is a localization of if for every
homomorphism there exists a unique endomorphism
, such that (maps are acting on the
right). G\"{o}bel and Trlifaj asked in \cite[Problem 30.4(4), p. 831]{GT12}
which abelian groups are centers of localizations of simple groups. Approaching
this question we show that every countable abelian group is indeed the center
of some localization of a quasi-simple group, i.e. a central extension of a
simple group. The proof uses Obraztsov and Ol'shanskii's construction of
infinite simple groups with a special subgroup lattice and also extensions of
results on localizations of finite simple groups by the second author and
Scherer, Th\'{e}venaz and Viruel.Comment: 21 page
Generators and closed classes of groups
We show that in the category of groups, every singly-generated class which is
closed under isomorphisms, direct limits and extensions is also
singly-generated under isomorphisms and direct limits, and in particular is
co-reflective. We also establish several new relations between singly-generated
closed classes.Comment: 22 page
The effect of international trade on mark-ups distribution
This paper presents empirical evidence about the relationship between market openness and markup distribution of manufacturing firms. The empirical analysis uses a panel data set of Spanish firms in the period 1990-2005, with a structural approach that lets us to identify individual mark-ups. The results point out that tougher competition associated to openness reduces the average of marginal costs and prices, while it increases the average firm size. However, the evidence about the effect on average markups and the dispersion of performance variables is weaker. These results partially support the theoretical predictions by the recent literature on efficiency heterogeneity and international trade and, in particular, Melitz and Ottaviano (2008).markups, marginal costs, size, openness
Markups, bargaining power and offshoring: an empirical assessment
This paper tests the pro-competitive effect of imports on product and labour markets for Spanish manufacturing firms in the period 1990-2005. In doing so, it takes into account the type of imported products: final vs intermediate. Markups are estimated following the procedure suggested by Roeger (1995) and including an efficient bargaining model. The observed heterogeneity among firms is parameterized to consider additional product standardization and market concentration. The results support the Imports as Market Discipline hypothesis for importers of final goods, while firms that offshore intermediate inputs show similar markups to non-importers. Additionally, the union bargaining power is smaller the more final-goods oriented imports are and the more homogeneous is the type of goods elaborated by firms.Markups, offshoring, bargaining power
Non-simple localizations of finite simple groups
Often a localization functor (in the category of groups) sends a finite
simple group to another finite simple group. We study when such a localization
also induces a localization between the automorphism groups and between the
universal central extensions. As a consequence we exhibit many examples of
localizations of finite simple groups which are not simple.Comment: 10 page
Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene
We investigate the transmission properties of quasiperiodic or aperiodic
structures based on graphene arranged according to the Cantor sequence. In
particular, we have found self-similar behaviour in the transmission spectra,
and most importantly, we have calculated the scalability of the spectra. To do
this, we implement and propose scaling rules for each one of the fundamental
parameters: generation number, height of the barriers and length of the system.
With this in mind we have been able to reproduce the reference transmission
spectrum, applying the appropriate scaling rule, by means of the scaled
transmission spectrum. These scaling rules are valid for both normal and
oblique incidence, and as far as we can see the basic ingredients to obtain
self-similar characteristics are: relativistic Dirac electrons, a self-similar
structure and the non-conservation of the pseudo-spin. This constitutes a
reduction of the number of conditions needed to observe self-similarity in
graphene-based structures, see D\'iaz-Guerrero et al. [D. S. D\'iaz-Guerrero,
L. M. Gaggero-Sager, I. Rodr\'iguez-Vargas, and G. G. Naumis,
arXiv:1503.03412v1, 2015]
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