1,882 research outputs found
A polynomial rooting approach for synchronization in multipath channels using antenna arrays
The estimation of the delay of a known training signal received
by an antenna array in a multipath channel is addressed.
The effect of the co-channel interference is taken
into account by including a term with unknown spatial correlation.
The channel is modeled as an unstructured FIR
filter. The exact maximum likelihood (ML) solution for
this problem is derived, but it does not have a simple dependence
on the delay. An approximate estimator that is
asymptotically equivalent to the exact one is presented. Using
an appropriate reparameterization, it is shown that the
delay estimate is obtained by rooting a low-order polynomial,
which may be of interest in applications where fast
feedforward synchronization is needed.Peer ReviewedPostprint (published version
A free-energy stable nodal discontinuous Galerkin approximation with summation-by-parts property for the Cahn-Hilliard equation
We present a nodal Discontinuous Galerkin (DG) scheme for the Cahn-Hilliard
equation that satisfies the summation-by-parts simultaneous-approximation-term
(SBP-SAT) property. The latter permits us to show that the discrete free-energy
is bounded, and as a result, the scheme is provably stable. The scheme and the
stability proof are presented for general curvilinear three-dimensional
hexahedral meshes. We use the Bassi-Rebay 1 (BR1) scheme to compute interface
fluxes, and an IMplicit-EXplicit (IMEX) scheme to integrate in time. Lastly, we
test the theoretical findings numerically and present examples for two and
three-dimensional problems
A reduced-complexity and asymptotically efficient time-delay estimator
This paper considers the problem of estimating the time delays of multiple replicas of a known signal received by an array of antennas. Under the assumptions that the noise and co-channel interference (CCI) are spatially colored Gaussian processes and that the spatial signatures are arbitrary, the maximum likelihood (ML) solution to the general time delay estimation problem is derived. The resulting criterion for the delays yields consistent and asymptotically efficient estimates. However, the criterion is highly non-linear, and not conducive to simple minimization procedures. We propose a new cost function that is shown to provide asymptotically efficient delay estimates. We also outline a heuristic way of deriving this cost function. The form of this new estimator lends itself to minimization by the computationally attractive iterative quadratic maximum likelihood (IQML) algorithm. The existence of simple yet accurate initialization schemes based on ESPRIT and identity weightings makes the approach viable for practical implementation.Peer ReviewedPostprint (published version
Reuse of nesting scrapes by Kentish Plovers
We studied reuse of nesting scrapes within breeding seasons by Kentish Plovers (Charadrius alexandrinus) in an inland lake of southern Spain over six years. Overall, 5.6% of original nests were reused at least once. We tested whether nest reuse is adaptive, but found no differences in breeding success between those pairs that reused nests and those that did not. We also tested whether nest reuse should be more frequent when scrapes are difficult to excavate than when it is easier to excavate them, and found that nests on hard substrates were more frequently reused than nests on soft substrates, and that nest reuse was more frequent in the second half of the season, when the nesting substrate is harder, than in the first half of the season. This suggests that nest reuse may save Kentish Plovers some energy.Peer Reviewe
Usurpación de nidos de quebrantahuesos (Gypaetus barbatus) e interacciones interespecíficas por la ocupación del nido en el Pirineo central (Aragón)
El quebrantahuesos es una especie catalogada como “en peligro de extinción” en Europa, cuya fracción reproductora en los Pirineos se ha estimado en 125 unidades reproductoras (UR). En el Pirineo central (Aragón) en los últimos 15 años se ha producido un incremento de la población reproductora acompañado de un progresivo descenso de la productividad cuyas causas son objeto de discusión y pueden deberse a diversos factores. El periodo de reproducción del quebrantahuesos es muy extenso y coincide con el de otras rapaces que compiten por los emplazamientos de los nidos. Esto implica una importante inversión de tiempo y energía, por lo que la usurpación de nidos podría tener efectos negativos sobre el éxito reproductor. En Aragón entre 2005 y 2010 fueron usurpados 107 nidos de quebrantahuesos pertenecientes a 52 de las 72 UR controladas. La mayor parte de los nidos (95,3% de los casos; n = 102) fueron usurpados por buitre leonado (Gyps fulvus), aunque también por alimoche común (Neophron percnopterus) (4,7% de los casos; n = 5). El Pirineo Axial acogió tanto el mayor porcentaje de UR con nidos usurpados como la UR con un mayor número de nidos usurpados. No se encontraron diferencias significativas en cuanto a la productividad entre UR que habían sufrido usurpación y los que no la habían padecido. El buitre leonado posee una similar distribución espacial y parecidos requerimientos ecológicos al quebrantahuesos, mayor corpulencia y agresividad así como similar fenología de puesta temprana. El aumento demográfico del buitre leonado en Aragón podría estar provocando una mayor usurpación de nidos de quebrantahuesos en los Pirineos.El presente trabajo se ha elaborado dentro del Convenio Marco de Colaboración suscrito entre el Gobierno de Aragón y la FCQ (2008-2011), por el cual se desarrollaron diferentes acciones del Plan de Recuperación del quebrantahuesos en Aragón (D. 45/2003). Pascual López-López disfruta de una beca postdoctoral del programa “Juan de la Cierva” del Ministerio de Economía y Competitividad (referencia JCI-2011-09588)
Modeling Lexicon Emergence as Concept Emergence in Networks
Amodel for lexicon emergence in social networks is presented. The model
is based on a modified version of classic Naming Games, where agents’ knowledge
is represented by means of formal contexts. That way it is possible to represent the
effect interactions have on individual knowledge as well as the dynamics of global
knowledge in the network.Ministerio de Economía y Competitividad TIN2013-41086-PJunta de Andalucía TIC-606
Complex concept lattices for simulating human prediction in sport
In order to address the study of complex systems, the detection of patterns in their dynamics
could play a key role in understanding their evolution. In particular, global patterns are required
to detect emergent concepts and trends, some of them of a qualitative nature. Formal concept analysis
(FCA) is a theory whose goal is to discover and extract knowledge from qualitative data (organized
in concept lattices). In complex environments, such as sport competitions, the large amount of information
currently available turns concept lattices into complex networks. The authors analyze how to
apply FCA reasoning in order to increase confidence in sports predictions by means of detecting regularities
from data through the management of intuitive and natural attributes extracted from publicly
available information. The complexity of concept lattices -considered as networks with complex topological
structure- is analyzed. It is applied to building a knowledge based system for confidence-based
reasoning, which simulates how humans tend to avoid the complexity of concept networks by means of
bounded reasoning skills.Ministerio de Ciencia e Innovación TIN2009-09492Junta de Andalucía TIC-606
Qualitative Reasoning on Complex Systems from Observations
A hybrid approach to phenomenological reconstruction of Complex
Systems (CS), using Formal Concept Analysis (FCA) as main tool for conceptual
data mining, is proposed. To illustrate the method, a classic CS is selected
(cellular automata), to show how FCA can assist to predict CS evolution under
different conceptual descriptions (from different observable features of the CS).Junta de Andalucía TIC-606
Simulating Language Dynamics by Means of Concept Reasoning
A problem in the phenomenological reconstruction of Complex
Systems (CS) is the extraction of the knowledge that elements playing
in CS use during its evolution. This problem is important because
such a knowledge would allow the researcher to understand the global
behavior of the system [1,2]. In this paper an approach to partially solve
this problem by means of Formal Concept Analysis (FCA) is described in
a particular case, namely Language Dynamics. The main idea lies in the
fact that global knowledge in CS is naturally built by local interactions
among agents, and FCA could be useful to represent their own knowledge.
In this way it is possible to represent the effect of interactions
on individual knowledge as well as the dynamics of global knowledge.
Experiments in order to show this approach are given using WordNet.Ministerio de Ciencia e Innovación TIN2009-09492Junta de Andalucía TIC-606
Confidence-Based Reasoning with Local Temporal Formal Contexts
Formal Concept Analysis (FCA) is a theory whose goal is to discover and to extract Knowledge from qualitative data. It provides tools for reasoning with implication basis (and association rules). In this paper we analyse how to apply FCA reasoning to increase confidence in sports betting, by means of detecting temporal regularities from data. It is applied to build a Knowledge based system for confidence reasoning.Ministerio de Ciencia e Innovación TIN2009-09492Junta de Andalucía TIC-606
- …