Leakage Subspace Precoding and Scheduling for Physical Layer Security in Multi-User XL-MIMO Systems

We investigate the achievable secrecy sum-rate in a multi-user XL-MIMO system, on which user distances to the base station become comparable to the antenna array dimensions. We show that the consideration of spherical-wavefront propagation inherent to these set-ups is beneficial for physical-layer security, as it provides immunity against eavesdroppers located in similar angular directions that would otherwise prevent secure communication under classical planar-wavefront propagation. A leakage subspace precoding strategy is also proposed for joint secure precoding and user scheduling, which allows to improve the secrecy sum-rate compared to conventional zero-forcing based strategies, under different eavesdropper collusion strategies.Comment: 5 pages and 4 figures. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

On the Effect of Correlation on the Capacity of Backscatter Communication Systems

We analyse the effect of correlation between the forward and backward links on the capacity of backscatter communication systems. To that aim, we obtain an analytical expression for the average capacity under a correlated Rayleigh product fading channel, as well as closed-form asymptotic expressions for the high and low signal-to-noise ratio (SNR) regimes. Our results show that correlation is indeed detrimental for a fixed target SNR; contrarily to the common belief, we also see that correlation can be actually beneficial in some instances when a fixed power budget is considered.Comment: This work has been submitted for publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

The ultracool dwarf DENIS-P J104814.7-395606. Chromospheres and coronae at the low-mass end of the main-sequence

We have obtained an XMM-Newton observation and a broad-band spectrum from the ultraviolet to the near infrared with X-Shooter for one of the nearest M9 dwarfs, DENIS-P J1048-3956 (4pc). We integrate these data by a compilation of activity parameters for ultracool dwarfs from the literature with the aim to advance our understanding of these objects by comparing them to early-M type dwarf stars and the Sun. Our deep XMM-Newton observation has led to the first X-ray detection of DENIS-P J1048-3956 (log Lx = 25.1) as well as the first measurement of its V band brightness (V = 17.35mag). Flux-flux relations between X-ray and chromospheric activity indicators are here for the first time extended into the regime of the ultracool dwarfs. The approximate agreement of DENIS-P J1048-3956 and other ultracool dwarfs with flux-flux relations for early-M dwarfs suggests that the same heating mechanisms work in the atmospheres of ultracool dwarfs, albeit weaker as judged from their lower fluxes. The observed Balmer decrements of DENIS-P J1048-3956 are compatible with optically thick plasma in LTE at low, nearly photospheric temperature or optically thin LTE plasma at 20000K. Describing the decrements with CaseB recombination requires different emitting regions for Halpha and the higher Balmer lines. The high observed Halpha/Hbeta flux ratio is also poorly fitted by the optically thin models. We derive a similarly high value for the Halpha/Hbeta ratio of vB10 and LHS2065 and conclude that this may be a characteristic of ultracool dwarfs. We add DENIS-P J1048-3956 to the list of ultracool dwarfs detected in both the radio and the X-ray band. The Benz-Guedel relation between radio and X-ray luminosity of late-type stars is well-known to be violated by ultracool dwarfs. We speculate on the presence of two types of ultracool dwarfs with distinct radio and X-ray behavior.Comment: accepted for publication in Astronomy & Astrophysic

First record of Triops gadensis Korn and García-de-Lomas, 2010 (Crustacea: Notostraca) in Córdoba Province, southern Spain

We studied a Triops population from a Mediterranean temporary pond located in Guadalcázar, a township in the western part of Córdoba Province. There are four morphologically similar species of Triops occurring in the SW Iberian Peninsula. In particular, the two species found in southern Andalusia, T. baeticus and T. gadensis, cannot reliably be told apart based on known morphological characters. We thus used sequences of 12S rDNA as a molecular marker to soundly identify the population to species rank. Our results demonstrate that the Triops population studied belongs to T. gadensis. This result is rather unexpected given that the species was thought to be restricted to a small distribution range along the Atlantic coast in Cádiz Province. The population is located at approximately 170 km from previously known sites of T. gadensis and shows a previously unknown haplotype, the sixth 12S haplotype reported for the species. We thus suggest that the population has high conservation value, and its habitat, including the surroundings, should be legally protected. We further propose that an open habitat type as pastureland should be retained for the surroundings of the site in order to support its ecological function in the frame of meta-populations dynamics, and as a possible source population from which new localities could be populated via passive dispersal

Forecasts on the contamination induced by unresolved point sources in primordial non-Gaussianity beyond Planck

In this paper we present forecasts of the contamination on different shapes of the primordial non-Gaussianity fnl parameter \u2013 detectable on future Cosmic Microwave Background (CMB) high\u2013resolution anisotropy maps \u2013 produced by unresolved ex- tragalactic point sources at frequencies of cosmological interest (45\u2013375 GHz). We consider two scenarios: an ideal (noiseless) mission and a possible future space-borne satellite, with instrumental characteristics similar to the ones proposed for the Cos- mic Origins Explorer (COrE). The local, equilateral, orthogonal and flat shapes are considered in both temperature (intensity) and polarized emission data. The angular power spectrum and bispectrum of extragalactic point sources are estimated by state- of-the-art models of source number counts. The impact of all the most relevant (far\u2013IR and radio selected) source populations on these shapes at COrE frequencies is studied. The results of this analysis show that unresolved extragalactic point sources should not induce a very relevant non-Gaussian signal in the frequency range 100\u2013200GHz, thus not preventing a correct estimate of the CMB primordial fnl parameter. Polariza- tion information allows one to significantly reduce the error\u2013bars in the fnl parameter and the bias induced by unresolved sources and, hence, to widen the range of frequen- cies for fnl studies. On the contrary, at \u3bd 225GHz, important non-Gaussian deviations in CMB anisotropy maps are expected due to unresolved extragalactic sources

Intraoperative goal directed hemodynamic therapy in noncardiac surgery: a systematic review and meta-analysis

Background: The goal directed hemodynamic therapy is an approach focused on the use of cardiac output and related parameters as end-points for fluids and drugs to optimize tissue perfusion and oxygen delivery. Primary aim: To determine the effects of intraoperative goal directed hemodynamic therapy on postoperative complications rates. Methods: A meta-analysis was carried out of the effects of goal directed hemodynamic therapy in adult noncardiac surgery on postoperative complications and mortality using Preferred Reporting Items for Systematic Reviews and Meta-Analyses methodology. A systematic search was performed in Medline PubMed, Embase, and the Cochrane Library (last update, October 2014). Inclusion criteria were randomized clinical trials in which intraoperative goal directed hemodynamic therapy was compared to conventional fluid management in noncardiac surgery. Exclusion criteria were trauma and pediatric surgery studies and that using pulmonary artery catheter. End-points were postoperative complications (primary) and mortality (secondary). Those studies that fulfilled the entry criteria were examined in full and subjected to quantifiable analysis, predefined subgroup analysis (stratified by type of monitor, therapy, and hemodynamic goal), and predefined sensitivity analysis. Results: 51 RCTs were initially identified, 24 fulfilling the inclusion criteria. 5 randomized clinical trials were added by manual search, resulting in 29 randomized clinical trials in the final analysis, including 2654 patients. A significant reduction in complications for goal directed hemodynamic therapy was observed (RR: 0.70, 95% CI: 0.62-0.79, p < 0.001). No significant decrease in mortality was achieved (RR: 0.76, 95% CI: 0.45-1.28, p = 0.30). Quality sensitive analyses confirmed the main overall results. Conclusions: Intraoperative goal directed hemodynamic therapy with minimally invasive monitoring decreases postoperative complications in noncardiac surgery, although it was not able to show a significant decrease in mortality rate