9,103 research outputs found
Space-Time diversity for NLOS mitigation in TDOA-based positioning systems
This paper studies the potential impact of using space-Time information in the mitigation of the Non-LineOf-Sight condition in mobile subscriber's positioning systems. First of all, this work discusses the positioning problem based on measures of Time Differences Of Arrival departing from a more exact characterization of the signal statistics and including some geometrical restrictions to achieve an improved accurate. Furthermore, a novel approach that integrates signal propagation characteristics to information provided by a suitable timing estimation model based on Cramer Rao Bound for a Rayleigh-fading channel, when antenna arrays are used at the receiver and when a set ofchannel vector estimates are available, has been introduced to study the positive benefits of space-Time diversity. These approaches are evaluated within a realistic simulation scenario.Peer ReviewedPostprint (published version
Stellar clusters in the inner Galaxy and their correlation with cold dust emission
Stars are born within dense clumps of giant molecular clouds, constituting
young stellar agglomerates known as embedded clusters, which only evolve into
bound open clusters under special conditions. We statistically study all
embedded clusters (ECs) and open clusters (OCs) known so far in the inner
Galaxy, investigating particularly their interaction with the surrounding
molecular environment and the differences in their evolution. We first compiled
a merged list of 3904 clusters from optical and infrared clusters catalogs in
the literature, including 75 new (mostly embedded) clusters discovered by us in
the GLIMPSE survey. From this list, 695 clusters are within the Galactic range
|l| < 60 deg and |b| < 1.5 deg covered by the ATLASGAL survey, which was used
to search for correlations with submm dust continuum emission tracing dense
molecular gas. We defined an evolutionary sequence of five morphological types:
deeply embedded cluster (EC1), partially embedded cluster (EC2), emerging open
cluster (OC0), OC still associated with a submm clump in the vicinity (OC1),
and OC without correlation with ATLASGAL emission (OC2). Together with this
process, we performed a thorough literature survey of these 695 clusters,
compiling a considerable number of physical and observational properties in a
catalog that is publicly available. We found that an OC defined observationally
as OC0, OC1, or OC2 and confirmed as a real cluster is equivalent to the
physical concept of OC (a bound exposed cluster) for ages in excess of ~16 Myr.
Some observed OCs younger than this limit can actually be unbound associations.
We found that our OC and EC samples are roughly complete up to ~1 kpc and ~1.8
kpc from the Sun, respectively, beyond which the completeness decays
exponentially. Using available age estimates for a few ECs, we derived an upper
limit of 3 Myr for the duration of the embedded phase... (Abridged)Comment: 39 pages, 9 figures. Accepted for publication in A&A on Sept 16,
2013. The catalog will be available at the CDS after official publication of
the articl
Capital Inflows, Exchange Rate Flexibility, and Credit Booms
The prospects of expansionary monetary policies in the advanced countries for the foreseeable future have renewed the debate over policy options to cope with large capital inflows that are, at least partly, driven by low interest rates in the financial centers. Historically, capital flow bonanzas have often fueled sharp credit expansions in advanced and emerging market economies alike. Focusing primarily on emerging markets, we analyze the impact of exchange rate flexibility on credit markets during periods of large capital inflows. We show that credit grows more rapidly and its composition tilts to foreign currency in economies with less flexible exchange rate regimes, and that these results are not explained entirely by the fact that the latter attract more capital inflows than economies with more flexible regimes. Our findings thus suggest countries with less flexible exchange rate regimes may stand to benefit the most from regulatory policies that reduce banks’ incentives to tap external markets and to lend/borrow in foreign currency; these policies include marginal reserve requirements on foreign lending, currency-dependent liquidity requirements, and higher capital requirement and/or dynamic provisioning on foreign exchange loans.
Cosmological Magnetic Fields from Gauge-Mediated Supersymmetry-Breaking Models
We study the generation of primordial magnetic fields, coherent over
cosmologically interesting scales, by gravitational creation of charged scalar
particles during the reheating period. We show that magnetic fields consistent
with those detected by observation may obtained if the particle mean life
\tau_s is in the range 10^{-14} sec \leq \tau_s \leq 10{-7} sec. We apply this
mechanism to minimal gauge mediated supersymmetry-breaking models, in the case
in which the lightest stau \tilde\tau_1 is the next-to-lightest supersymmetric
particle. We show that, for a large range of phenomenologically acceptable
values of the supersymmetry-breaking scale \sqrt{F}, the generated primordial
magnetic field can be strong enough to seed the galactic dynamo.Comment: 12 pages, Latex. Final version accepted for publication in Phys.
Lett.
Minimal matrices and the corresponding minimal curves on flag manifolds in low dimension
In general C*-algebras, elements with minimal norm in some equivalence class are introduced and characterized. We study the set of minimal hermitian matrices, in the case where the C*-algebra consists of 3 Ă— 3 complex matrices, and the quotient is taken by the subalgebra of diagonal matrices. We thoroughly study the set of minimal matrices particularly because of its relation to the geometric problem of finding minimal curves in flag manifolds. For the flag manifold of 'four mutually orthogonal complex lines' in C4, it is shown that there are infinitely many minimal curves joining arbitrarily close points. In the case of the flag manifold of 'three mutually orthogonal complex lines' in C3, we show that the phenomenon of multiple minimal curves joining arbitrarily close points does not occur.Fil: Andruchow, Esteban. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto CalderĂłn; Argentina. Universidad Nacional de General Sarmiento. Instituto de Ciencias; ArgentinaFil: Mata Lorenzo, Luis E.. Universidad SimĂłn Bolivar; VenezuelaFil: Mendoza, Alberto. Universidad SimĂłn Bolivar; VenezuelaFil: Recht, Lázaro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto CalderĂłn; Argentina. Universidad SimĂłn Bolivar; VenezuelaFil: Varela, Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto CalderĂłn; Argentina. Universidad Nacional de General Sarmiento. Instituto de Ciencias; Argentin
- …