1,721,000 research outputs found
Pseudo-random Aloha for Enhanced Collision-recovery in RFID
No full textIn this letter we motivate the need to revisit the MAC protocol used in Gen2 RFID system in order to leverage receiver structures with Collision Recovery capabilities at the PHY layer. To this end we propose a simple variant of the Framed Slotted-ALOHA where slot selection is not random, as in the classical scheme, but instead computed deterministically by a pseudo-random function of the message to be transmitted and the frame index. Deterministic slot selection enables Inter-frame Successive Interference Cancellation (ISIC) without changing the PHY modulation and coding format of legacy RFID standard. By means of simulations we show that ISIC can bring 20-25% gain in throughput with respect to traditional intra-slot SIC
Dispersion of passive tracers in a velocity field with non-δ-correlated noise
No full textThe diffusive properties in velocity fields whose small scales are parameterized by non-δ-correlated noise is investigated using multiscale technique. The analytical expression of the eddy diffusivity tensor is found for a two-dimensional (2D) steady shear flow and it is an increasing function of the characteristic noise decorrelation time τ. In order to study a generic flow v, a small-τ expansion is performed and the first correction O(τ) to the effective diffusion coefficients is evaluated. This is done using two different approaches and it results that at the order τ the problem with a colored noise is equivalent to the δ-correlated case provided by a renormalization of the velocity field v↦ṽ depending on τ. Two examples of 2D closed-streamlines velocity field are considered and in both the cases an enhancement of the diffusion is found
Analisi sperimentale dei processi di trasporto nei suoli in condizioni di non equilibrio
No full text
Spectral properties of quantum N-body systems versus chaotic properties of their mean-field approximations
No full textWe present numerical evidence that in a system of interacting bosons there exists a correspondence between the spectral properties of the exact quantum Hamiltonian and the dynamical chaos of the associated mean-field evolution. This correspondence, analogous to the usual quantum-classical correspondence, is related to the formal parallel between the second quantization of the mean field, which generates the exact dynamics of the quantum N-body system, and the first qnantization of classical canonical coordinates. The limit of infinite density and the thermodynamic limit are then briefly discussed
Performance Analysis of Coded Cooperation over Time-Variant Channels
No full textWe contribute to the evaluation of the performance
of a relaying technique called coded cooperation. This cooperation scheme involves two or more mobile stations (MS) that reciprocally transmit portions of their codewords through independent fading channels so as to achieve diversity. Performance analysis in the literature considers two extreme cases of temporal variability for the fading channel: the block fading (BF) model for channels that remain constant during the transmission of the whole codeword and the fast fading (FF) one for independent identically distributed channel gains over the time. In this paper we extend the analysis to more realistic propagation scenarios where the channel response varies over the time with a correlation function that depends on the MSs’ velocity. We derive analytical bounds on the average bit error probability and we validate the results by numerical simulations for a varying degree of channel correlation, ranging from the BF to the FF case.
Numerical results show that the performance gain provided by the cooperation with respect to the non-cooperative case decreases as the MSs move faster
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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