17,988 research outputs found
Overcoming ambiguities in classical and quantum correlation measures
We identify ambiguities in the available frameworks for defining quantum,
classical, and total correlations as measured by discordlike quantifiers. More
specifically, we determine situations for which either classical or quantum
correlations are not uniquely defined due to degeneracies arising from the
optimization procedure over the state space. In order to remove such
degeneracies, we introduce a general approach where correlations are
independently defined, escaping therefore from a degenerate subspace. As an
illustration, we analyze the trace-norm geometric quantum discord for two-qubit
Bell-diagonal states.Comment: 5 pages, 2 figures. v2: Minor corrections. Published versio
Fermionic bound states in Minkowski-space: Light-cone singularities and structure
The Bethe-Salpeter equation for two-body bound system with spin
constituent is addressed directly in the Minkowski space. In order to
accomplish this aim we use the Nakanishi integral representation of the
Bethe-Salpeter amplitude and exploit the formal tool represented by the exact
projection onto the null-plane. This formal step allows one i) to deal with
end-point singularities one meets and ii) to find stable results, up to
strongly relativistic regimes, that settles in strongly bound systems. We apply
this technique to obtain the numerical dependence of the binding energies upon
the coupling constants and the light-front amplitudes for a fermion-fermion
state with interaction kernels, in ladder approximation, corresponding to
scalar-, pseudoscalar- and vector boson exchanges, respectively. After
completing the numerical survey of the previous cases, we extend our approach
to a quark-antiquark system in state, taking both constituent-fermion and
exchanged boson masses, from lattice calculations. Interestingly, the
calculated light-front amplitudes for such a mock pion show peculiar signatures
of the spin degrees of freedom.Comment: 22 pages, 7 figures, bst file include
Geometric classical and total correlations via trace distance
We introduce the concepts of geometric classical and total correlations
through Schatten 1-norm (trace norm), which is the only Schatten p-norm able to
ensure a well-defined geometric measure of correlations. In particular, we
derive the analytical expressions for the case of two-qubit Bell-diagonal
states, discussing the superadditivity of geometric correlations. As an
illustration, we compare our results with the entropic correlations, discussing
both their hierarchy and monotonicity properties. Moreover, we apply the
geometric correlations to investigate the ground state of spin chains in the
thermodynamic limit. In contrast to the entropic quantifiers, we show that the
classical correlation is the only source of 1-norm geometric correlation that
is able to signaling an infinite-order quantum phase transition.Comment: v2: published versio
CHALLENGES TO THE BRAZILIAN AGROFOOD INDUSTRY IN THE GLOBAL MARKET
A globalização da economia mundial vem sendo amplamente discutida,
revolvendo um debate tanto teórico quanto ideológico a respeito
dessa multifacetada transformação, com a qual todos os paÃses vem
se envolvendo. Independente dos rumos dessa discussão, a questão
da competitividade tem se tornado essencial nas relações econômicas
internacionais da última década, quando a maioria dos paÃses
começaram a promover uma abertura tanto aos fluxos de investimento
quanto de comércio.
Abstract
Globalization has been deeply discussed revolving around a theoretical
and ideological contention concerning this many-sided transformation
with which, in one way or another, all countries have become
entangled. Whatever the course of the discussion, competitiveness
has become the key question in the international economic relations
of the last decade, when most countries started opening up their
economies to the external flows of trade and investment. The core of
this analysis indicates the challenges facing Brazil in the international
market when differentiated products appear to dominate trade relation.
The discussion explores the extent to which foreign direct investment
can change the conditions under which the country can
boost its international competitiveness. As it will be argued here, the
process of opening up the Brazilian economy in the 1990s has so far
only consolidated the countrys position as a commodity exporter,
whereas the mainstream of the international market has consisted of
processed and differentiated products
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