5,841 research outputs found
Equidivisible pseudovarieties of semigroups
We give a complete characterization of pseudovarieties of semigroups whose
finitely generated relatively free profinite semigroups are equidivisible.
Besides the pseudovarieties of completely simple semigroups, they are precisely
the pseudovarieties that are closed under Mal'cev product on the left by the
pseudovariety of locally trivial semigroups. A further characterization which
turns out to be instrumental is as the non-completely simple pseudovarieties
that are closed under two-sided Karnofsky-Rhodes expansion
Joint Distributed Access Point Selection and Power Allocation in Cognitive Radio Networks
Spectrum management has been identified as a crucial step towards enabling
the technology of the cognitive radio network (CRN). Most of the current works
dealing with spectrum management in the CRN focus on a single task of the
problem, e.g., spectrum sensing, spectrum decision, spectrum sharing or
spectrum mobility. In this work, we argue that for certain network
configurations, jointly performing several tasks of the spectrum management
improves the spectrum efficiency. Specifically, we study the uplink resource
management problem in a CRN where there exist multiple cognitive users (CUs)
and access points (APs), with each AP operates on a set of non-overlapping
channels. The CUs, in order to maximize their uplink transmission rates, have
to associate to a suitable AP (spectrum decision), and to share the channels
belong to this AP with other CUs (spectrum sharing). These tasks are clearly
interdependent, and the problem of how they should be carried out efficiently
and distributedly is still open in the literature.
In this work we formulate this joint spectrum decision and spectrum sharing
problem into a non-cooperative game, in which the feasible strategy of a player
contains a discrete variable and a continuous vector. The structure of the game
is hence very different from most non-cooperative spectrum management game
proposed in the literature. We provide characterization of the Nash Equilibrium
(NE) of this game, and present a set of novel algorithms that allow the CUs to
distributively and efficiently select the suitable AP and share the channels
with other CUs. Finally, we study the properties of the proposed algorithms as
well as their performance via extensive simulations.Comment: Accepted by Infocom 2011; Infocom 2011, The 30th IEEE International
Conference on Computer Communication
Dynamical Contents of Unconventional Supersymmetry
The Dirac Hamiltonian formalism is applied to a system in -dimensions
consisting of a Dirac field minimally coupled to Chern-Simons and
connections, and , respectively. This theory is connected
to a supersymmetric Chern-Simons form in which the gravitino has been projected
out (unconventional supersymmetry) and, in the case of a flat background,
corresponds to the low energy limit of graphene. The separation between
first-class and second-class constraints is performed explicitly, and both the
field equations and gauge symmetries of the Lagrangian formalism are fully
recovered. The degrees of freedom of the theory in generic sectors shows that
the propagating states correspond to fermionic modes in the background
determined by the geometry of the graphene sheet and the nondynamical
electromagnetic field. This is shown for the following canonical sectors: i) a
conformally invariant generic description where the spinor field and the
dreibein are locally rescaled; ii) a specific configuration for the Dirac
fermion consistent with its spin, where Weyl symmetry is exchanged by time
reparametrizations; iii) the vacuum sector , which is of interest for
perturbation theory. For the latter the analysis is adapted to the case of
manifolds with boundary, and the corresponding Dirac brackets together with the
centrally extended charge algebra are found. Finally, the
generalization of the gauge group is briefly treated, yielding analogous
conclusions for the degrees of freedom.Comment: 17 pages. Accepted version for publication in JHE
PUBLIC INVESTMENT IN TRANSPORTATION INFRASTRUCTURES AND INDUSTRY PERFORMANCE IN PORTUGAL
The objective of this paper is to evaluate the effects at the industry level of public investment in transportation infrastructures in Portugal. The empirical results are based on VAR/ECM models for the Portuguese economy and for eighteen industries covering the whole spectrum of economic activity in the country. These models consider private-sector output, employment and investment as well as public investment. Empirical results at the aggregate level indicate that public investment has a positive effect on both private inputs as well as on private output and that it affects labor productivity positively. These aggregate results, however, hide a wide variety of industry-level effects. In absolute terms, the industries that benefit the most from public investment are Construction, Trade, Transportation, Finance, Real Estate, and Services. In turn, relative to their size, the industries that benefit the most are Mining, Non-Metal Products, Metal Products, Construction, Restaurants, Transportation, and Finance, and, therefore, public investment tends to shift the industry mix toward these industries. Accordingly, our empirical results suggest that although public investment has been a powerful instrument to enhance the long-term economic performance in Portugal it does so in a way that is rather unbalanced across industries.Infrastructures, Industry Performance, Portugal
Stocks, Flows and Valuation Effects of Foreign Assets and Liabilities: Do They Matter?
Large holdings of foreign assets and liabilities, along with increasing relevance of valuation effects—capital gains or losses—have characterized global financial integration. In this paper, we assess empirically the implications of stocks, flows and valuation adjustments in external crises (current-account reversals, sudden stops and currency crises), sovereign credit ratings and the longrun real exchange rates (RER), in both industrial and developing economies. We find support for the view that foreign assets and liabilities are rather distinctive external holdings with different implications in the occurrence of external crisis. Valuation adjustments have an impact on crises, although quantitatively not very large. Portfolio liabilities (particularly equity) increase the probability of current-account reversals and currency crises, while the likelihood of sudden stops increases with the stock of foreign direct investment (FDI) assets. In the case of sovereign credit ratings, we find a noteworthy effect of the stock and flows of FDI liabilities on improving sovereign ratings. Finally, as for the RER, gross assets and liabilities appear equally important, but components of external holdings have considerably different effects. While the cumulative current account is associated with real depreciation, the valuation effect is strongly linked with real currency appreciations in developing economies.
On the group of a rational maximal bifix code
We give necessary and sufficient conditions for the group of a rational
maximal bifix code to be isomorphic with the -group of , when
is recurrent and is rational. The case where is uniformly
recurrent, which is known to imply the finiteness of , receives
special attention.
The proofs are done by exploring the connections with the structure of the
free profinite monoid over the alphabet of
Joint Access Point Selection and Power Allocation for Uplink Wireless Networks
We consider the distributed uplink resource allocation problem in a
multi-carrier wireless network with multiple access points (APs). Each mobile
user can optimize its own transmission rate by selecting a suitable AP and by
controlling its transmit power. Our objective is to devise suitable algorithms
by which mobile users can jointly perform these tasks in a distributed manner.
Our approach relies on a game theoretic formulation of the joint power control
and AP selection problem. In the proposed game, each user is a player with an
associated strategy containing a discrete variable (the AP selection decision)
and a continuous vector (the power allocation among multiple channels). We
provide characterizations of the Nash Equilibrium of the proposed game, and
present a set of novel algorithms that allow the users to efficiently optimize
their rates. Finally, we study the properties of the proposed algorithms as
well as their performance via extensive simulations.Comment: Revised and Resubmitted to IEEE Transactions on Signal Processin
Zero Mode Effect Generalization for the Electromagnetic Current in the Light Front
We consider in this work the electromagnetic current for a system composed by
two charged bosons and show that it has a structure of many bodies even in the
impulse approximation, when described in the light front time . In terms
of the two-body component for the bound state, the current contains two-body
operators. We discuss the process of pair creation from the interacting photon
and interpret it as a zero mode contribution to the current and its
consequences for the components of currents in the light-front.Comment: 13 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:hep-th/050911
Semántica leibniziana polivalente
Este es un resumen de un desarrollo conjetural de una semántica leibniziana que admite finitos valores de verdad para casi todas las verdades y falsedades de razón e infinitos valores de verdad para alguna verdad y falsedad de razón y todas las verdades y falsedades de hecho.draf
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