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Multiple Sclerosis (MS) is a chronic autoimmune and inflammatory neurological disorder characterised by episodes of symptom exacerbation, known as relapses. In this study, we investigate the role of environmental factors in relapse occurrence among MS patients, using data from the H2020 BRAINTEASER project. We employed predictive models, including Random Forest (RF) and Logistic Regression (LR), with varying sets of input features to predict the occurrence of relapses based on clinical and pollutant data collected over a week. The RF yielded the best result, with an AUC-ROC score of 0.713. Environmental variables, such as precipitation, NO2, PM2.5, humidity, and temperature, were found to be relevant to the prediction.

Manifold optimization (MO) is a powerful mathematical framework that can be applied to optimize functions over complex geometric structures, which is particularly useful in advanced wireless communication systems, such as reconfigurable intelligent surface (RIS)-aided massive MIMO (mMIMO) and extra-large scale massive MIMO (XL-MIMO) systems. MO provides a structured approach to tackling complex optimization problems. By leveraging the geometric properties of the manifold, more efficient and effective solutions can be found compared to conventional optimization methods. This paper provides a tutorial on MO technique and provides some applications of MO in the context of wireless communications systems. In particular, to corroborate the effectiveness of MO methodology, we explore five application examples in RIS-aided mMIMO system, focusing on fairness, energy efficiency (EE) maximization, intracell pilot reuse interference mitigation, and grant-free (GF) random access (RA).

We use near-infrared (NIR) spectroscopy covering simultaneously the $zJHK$ bands to look for outflowing gas from the nuclear environment of 1H0707-495 taking advantage that this region is dominated by low-ionization broad line region (BLR) lines, most of them isolated. We detect broad components in HI, FeII and OI, at rest to the systemic velocity, displaying full width at half maximum (FWHM) values of ~500 km s$^{-1}$, consistent with its classification as a narrow-line Seyfert~1 AGN. Moreover, most lines display a conspicuous blue-asymmetric profile, modeled using a blueshifted component, whose velocity shift reaches up to ~826 km s$^{-1}$. This last feature can be interpreted in terms of outflowing gas already observed in X-ray and UV lines in 1H0707-495 but not detected before in the low-ionization lines. We discuss the relevance of our findings within the framework of the wind scenario already proposed for this source and suggest that the wind extends well into the narrow line region due to the observation of a blueshifted component in the forbidden line of [SIII] $\lambda$9531., Comment: 21 pages, 11 figures. Accepted to The Astronomical Journal

This chapter delves into the critical aspects of optimizing energy efficiency (EE) in active reconfigurable intelligent surface (RIS)-assisted massive MIMO (M-MIMO) wireless communication systems. We develop a comprehensive and unified theoretical framework to analyze the boundaries of EE within M-MIMO systems integrated with active RIS while adhering to practical constraints. Our research focuses on a formulated EE optimization problem aiming to maximize the EE for active RIS-assisted M-MIMO communication systems. Our goal is to strategically find the number of active RIS elements for outperforming the EE attainable by an entirely passive RIS. Besides, the proposed novel solution has been tailored to the innovative problem. The formulation and solution design consider analytical optimization techniques, such as lagrangian dual transform (LDT) and fractional programming (FP) optimization, facilitating the effective implementation of RIS-aided M-MIMO applications in real-world settings. In particular, our results show that the proposed algorithm can provide up to 120% higher EE than the entirely passive RIS. Besides, we found that the active RIS can operate with less than half of the reflecting elements for the entirely passive RIS. Finally, in view of active RIS achieving the complete utilization of amplification power available, it should be equipped with a reasonable number of reflecting elements above N = 49., Comment: 22 pages, 52 references, 2 tables, and 5 figures

Constraining the physical conditions of the ionized media in the vicinity of an active supermassive black hole (SMBH) is crucial to understanding how these complex systems operate. Metal emission lines such as iron (Fe) are useful probes to trace the gaseous media's abundance, activity, and evolution in these accreting systems. Among these, the FeII emission has been the focus of many prior studies to investigate the energetics, kinematics, and composition of the broad-emission line region (BELR) from where these emission lines are produced. In this work, we present the first simultaneous FeII modeling in the optical and near-infrared (NIR) regions. We use CLOUDY photoionization code to simulate both spectral regions in the wavelength interval 4000-12000 Angstroms. We compare our model predictions with the observed line flux ratios for IZw1 - a prototypical strong FeII-emitting active galactic nuclei (AGN). This allows putting constraints on the BLR cloud density and metal content that is optimal for the production of the FeII emission, which can be extended to IZw1-like sources, by examining a broad parameter space. We demonstrate the salient and distinct features of the FeII pseudo-continuum in the optical and NIR, giving special attention to the effect of micro-turbulence on the intensity of the FeII emission., Comment: 17 pages, 6 figures, 1 table, accepted in MDPI Physics

The DEtection TRansformer (DETR) opened new possibilities for object detection by modeling it as a translation task: converting image features into object-level representations. Previous works typically add expensive modules to DETR to perform Multi-Object Tracking (MOT), resulting in more complicated architectures. We instead show how DETR can be turned into a MOT model by employing an instance-level contrastive loss, a revised sampling strategy and a lightweight assignment method. Our training scheme learns object appearances while preserving detection capabilities and with little overhead. Its performance surpasses the previous state-of-the-art by +2.6 mMOTA on the challenging BDD100K dataset and is comparable to existing transformer-based methods on the MOT17 dataset., Comment: WACV 2024

Channel state information (CSI) estimation is a critical issue in the design of modern massive multiple-input multiple-output (mMIMO) networks. With the increasing number of users, assigning orthogonal pilots to everyone incurs a large overhead that strongly penalizes the system's spectral efficiency (SE). It becomes thus necessary to reuse pilots, giving rise to pilot contamination, a vital performance bottleneck of mMIMO networks. Reusing pilots among the users of the same cell is a desirable operation condition from the perspective of reducing training overheads; however, the intra-cell pilot contamination might worsen due to the users' proximity. Reconfigurable intelligent surfaces (RISs), capable of smartly controlling the wireless channel, can be leveraged for intra-cell pilot reuse. In this paper, our main contribution is a RIS-aided approach for intra-cell pilot reuse and the corresponding channel estimation method. Relying upon the knowledge of only statistical CSI, we optimize the RIS phase shifts based on a manifold optimization framework and the RIS positioning based on a deterministic approach. The extensive numerical results highlight the remarkable performance improvements the proposed scheme achieves (for both uplink and downlink transmissions) compared to other alternatives., Comment: 13 pages, 11 figures, full paper, 1 table

Emission-line studies in the active galactic nuclei (AGNs), particularly those utilizing high spatial resolution, provide the most accurate method to determine critical quantities of the central engine and of the gas a few tens of parsecs away. Using seeing-limited data with spectroscopy, we have explored the extended narrow-line region for a sample of active galactic nuclei (AGNs) with strong, forbidden emission lines that have high-ionization potentials (IP $\gtrsim$ 100 eV). We have studied the optical and near-infrared spectra for these AGNs, extracted and compared their spectral energy distributions, and put constraints on the physical conditions of the region producing the coronal lines. We have realized a novel black hole mass scaling relation with one such prominent coronal line - [Si VI] 1.963 microns, over the 10$^6$ - 10$^8$ M$_{\odot}$ interval, that suggests photoionization by the continuum produced by the accretion disk is the primary physical process at play here. We perform a detailed parameter space study to optimize the emission from these coronal lines in terms of fundamental black hole parameters and test predictions that can be used to measure the kinematics of the extended X-ray emission gas. With the successful launch and first light of the JWST, we are well-poised to refine our findings using the superb angular resolution of the telescope that will allow us to map the inner few parsecs to the central supermassive black holes. This opens up the study of the higher ionization lines that will be spatially resolved by JWST, expanding our sample to tens of hundreds of AGNs, and putting firmer constraints on the physical conditions in the coronal line region., Comment: 3 pages, 1 figure, version matches the published version in Proceedings of the XLV Annual Meeting of the Brazilian Astronomical Society

Double-peaked profiles associated with the broad-line region (BLR) of active galactic nuclei (AGNs) are regarded as the clearest evidence of the presence of an accretion disk. They are most commonly detected by means of optical spectroscopy in the Balmer lines and in the Mg II $\lambda$2798 ultraviolet line. Here, we report the first unambiguous detection of a double-peak broad emission line associated with the O I $\lambda$11297 emission line in the near-infrared (NIR) in the local Seyfert 1 galaxy III Zw 002. Additionally, we detect simultaneously in the spectrum the double-peak emission in the Pa$\alpha$ line and very likely in the He II $\lambda$10830. This is the first time that several broad double-peaked NIR emission lines have been detected simultaneously. The double-peaked profiles are fit using a disk-based model, with an additional Gaussian component attributed to nondisk clouds, which represents the classical BLR. Our results obtained from the fits reveal important parameters, such as disk inclination and geometry. From the double-peaked profile fits, we suggest that the BLR in III Zw 002 has a disk-like geometry, as it extends up to the outer edge of the BLR., Comment: 8 pages, 3 figures, 1 table, published in ApJ Letters

Coronal-Line Forest Active Galactic Nuclei (CLiF AGN) are characterized by strong, high-ionization lines, which are in contrast to what is found in typical AGNs. Here, we carry out an infrared analysis aimed at understanding the spectral energy distribution of six sources from this group. In this work, the properties of the dusty torus for these objects are analyzed. To this purpose, we infer the physical and geometrical properties of the dust structure that surrounds the central region by fitting with models the spectral energy distribution (SED) of CLiF AGNs in the infrared. For this analysis, we compare the results of three models: CLUMPY, SKIRTOR and CAT3D-WIND. Using the Bayesian information criterion, SKIRTOR was found to have the most robust fit to the SEDs in five out of six galaxies. The remaining object was best fitted with CLUMPY. The results indicate that these objects are preferentially Type~I sources, supporting the detection of broad components in the permitted lines, likely associated with the BLR in the near-infrared (NIR) spectra. The best SED fitting indicates that the line of sight gives access to the view of the central source for these objects, but the amount of dusty clouds in the same direction is high, suggesting the hypothesis that they obscure the emission of the continuum produced by the central source and that the obscuration makes the coronal lines to not overlap with the continuum., Comment: 13 pages, 12 figures, submitted to MNRAS

The main requirements for 5G and beyond connectivity include a uniform high quality of service, which can be attained in crowded scenarios by extra-large MIMO (XL-MIMO) systems. Another requirement is to support increasing connected users in (over)crowded machine-type communication (mMTC). In such scenarios, pilot assignment (PA) becomes paramount to reduce pilot contamination and consequently improve spectral efficiency (SE). We propose a novel quasi-optimal low-complexity iterative pilot assignment strategy for XL-MIMO systems based on a genetic algorithm (GA). The proposed GA-based PA procedure turns the quality of service more uniform, taking into account the normalized mean-square error (NMSE) of channel estimation from each candidate of the population. The simulations reveal that the proposed iterative procedure minimizes the channel estimation NMSE averaged over the UEs. The second procedure is the subarray (SA) selection. In XL-MIMO systems, commonly, a UE is close to a SA antenna subset such that a sufficient data rate can be achieved if only a specific SA serves that UE. Thus, a SA selection procedure is investigated to make the system scalable by defining the maximum number of UEs each SA can help. Hence, the SA clusters are formatted based on the PA decision. Furthermore, we introduce an appropriate channel model for XL-MIMO, which considers a deterministic LoS component with a distance-dependent probability of existence combined with a stochastic spatially correlated Rayleigh NLoS fading component. The developed simulations and analyses rely on this suitable channel model under realistic assumptions of pilot contamination and correlated channels., Comment: 29 pages, 6 figures, 2 tables, In Press

A novel random access (RA) scheme for mixed URLLC-mMTC traffic scenario is proposed using realistic statistical models, with the use mode presenting long-term traffic regularity. The traffic is predicted by a long short-term memory neural network, which enables a traffic-aware resource slicing aided by contention access class barring-based procedure. The method combines a grant-free (GF) RA scheme with an intermediate step to congestion alleviation. The protocol trade-off is a small overhead while enabling a higher number of decoded received packets thanks to the intermediate step. Numerical results evaluate the system performance for each procedure and combined solution. A comparison with GF benchmark reveals substantial improvement in system performance., Comment: Submitted to IoT Forum - S\~ao Paulo

We propose a novel random access (RA) protocol that accounts for the network traffic in mixed URLLC-mMTC scenarios. By considering an IoT environment under high mMTC traffic demand, we model the traffic of each service using realistic statistical models, with the mMTC and URLLC use modes presenting a long-term traffic regularity. A long-short term memory (LSTM) neural network (NN) is used as a network traffic predictor, enabling a traffic-aware resource slicing (RS) scheme, aided by a contention access control barring (ACB)-based procedure. The proposed method combines a grant-based RA scheme, where it is introduced an intermediate step in grant-free RA, to deal with collisions. The protocol presents a small overhead, supporting a higher number of packets in a frame thanks to the congestion alleviation enabled by the ACB procedure. Numerical results show the effectiveness in combining the three procedures in terms of accuracy for traffic prediction, resource utilization and channel loading for RS, and increased throughput.% for the proposed LSTM-ACB-based RA protocol. The comparison with a grant-free benchmark reveals substantial improvement in system performance., Comment: Awaiting for publication in 2022 WF-IoT. arXiv admin note: text overlap with arXiv:2303.01159

In this article, we study the uplink (UL) channel of a cellular network of Internet of Things (IoT) devices assisted by a reconfigurable intelligent surface (RIS) with a limited number of reflecting angle configurations. Firstly, we derive an expression of the required transmit power for the machine-type devices (MTDs) to attain a target signal-to-noise ratio (SNR), considering a channel model that accounts for the RIS discretization into sub-wavelength reflecting elements. Such an expression demonstrates that the transmit power depends on the target SNR, the position of the MTD in the service area, and the RIS setup, which includes the number of reflecting elements and the available reflecting angle configurations. Secondly, we develop an expression for the expected battery lifetime (EBL) of the MTDs, which explicitly depends on the MTD transmit power. Numerical simulations on the energy efficiency (EE) evaluated via the EBL demonstrate the benefits of adopting RISs to enable energy-efficient IoT networks., Comment: To appear in Proceedings of the I Symposium on Internet of Things

Green Internet of Things (IoT) aims to enable a sustainable smart world by making energy efficiency (EE) the main performance indicator for IoT hardware and software. With respect to network design, this implies in developing energy-efficient communication protocols and network architectures adapted to the ubiquitousness of the IoT machine-type devices (MTDs) and the sporadic traffic generated by them, keeping a low power consumption at the MTDs-side. In this sense, reconfigurable intelligent surfaces (RISs) have presented the capacity of significantly improving the network coverage using mostly passive reflecting elements, drastically reducing the power expenditure. In this paper, we develop a realistic power consumption model and an expression for the overall system EE for RIS-aided IoT networks that adopt a two time-scale random access (RA) protocol to handle the uplink transmissions. Specifically, during each time slot of the RA protocol, the RIS covers a specific area of interest in the communication cell with a predefined set of phase-shift configurations, changing the channel qualities of the contending MTDs. Numerical results comparing the RA protocol performance reveal that access policies that exploit information of the channel qualities are suitable for green IoT networks, simultaneously attaining competitive EE and throughput combined with low power consumption at the MTDs-side., Comment: To appear in Proceedings of the IEEE 8th World Forum on Internet of Things

3D object tracking is a critical task in autonomous driving systems. It plays an essential role for the system's awareness about the surrounding environment. At the same time there is an increasing interest in algorithms for autonomous cars that solely rely on inexpensive sensors, such as cameras. In this paper we investigate the use of triplet embeddings in combination with motion representations for 3D object tracking. We start from an off-the-shelf 3D object detector, and apply a tracking mechanism where objects are matched by an affinity score computed on local object feature embeddings and motion descriptors. The feature embeddings are trained to include information about the visual appearance and monocular 3D object characteristics, while motion descriptors provide a strong representation of object trajectories. We will show that our approach effectively re-identifies objects, and also behaves reliably and accurately in case of occlusions, missed detections and can detect re-appearance across different field of views. Experimental evaluation shows that our approach outperforms state-of-the-art on nuScenes by a large margin. We also obtain competitive results on KITTI., Comment: Accepted to CVPR 2022 Workshop on Autonomous Driving

Providing minimum quality-of-service (QoS) in crowded wireless communications systems, with high user density, is challenging due to the network structure with limited transmit power budget and resource blocks. Smart resource allocation methods, such as user scheduling, power allocation, and modulation and coding scheme selection, must be implemented to cope with the challenge. Aiming to enhance the number of served users with minimum QoS in the downlink (DL) channel of crowded extra-large scale massive multiple-input multiple-output (XL-MIMO) systems, in this paper we propose a QoS-aware joint user scheduling and power allocation technique. The proposed technique is constituted by two sequential procedures: the clique search-based scheduling (CBS) algorithm for user scheduling followed by optimal power allocation with transmit power budget and minimum achievable rate per user constraints. To accurately evaluate the proposed technique in the XL-MIMO scenario, we propose a generalized non-stationary multi-state channel model based on spherical-wave propagation assuming that users under LoS and NLoS transmission coexist in the same communication cell. Such model considers that users under different channel states experience different propagation aspects both in the multipath fading model and the path loss rule. Numerical results on the achievable sum-rate, number of scheduled users, and distribution of the scheduled users reveal that the proposed CBS algorithm provides a fair coverage over the whole cell area, achieving remarkable numbers of scheduled users when users under the LoS and NLoS channel states coexist in the communication cell., Comment: 12 pages, 12 figures, 1 table

In this work, we study the optical properties of compact radio sources selected from the literature in order to determine the impact of the radio-jet in their circumnuclear environment. Our sample includes 58 Compact Steep Spectrum (CSS) and GigaHertz Peaked Spectrum (GPS) and 14 Megahertz-Peaked spectrum (MPS) radio sources located at $z\leq 1$. The radio luminosity ($L_R$) of the sample varies between Log\,L$_R\sim$ 23.2 and 27.7 W\,Hz$^{-1}$. We obtained optical spectra for all sources from SDSS-DR12 and performed a stellar population synthesis using the {\sc starlight} code. We derived stellar masses (M$_\star$), ages $\langle t_\star \rangle$, star formation rates (SFR), metallicities $\langle Z_\star \rangle$ and internal reddening A$_V$ for all young AGNs of our sample. A visual inspection of the SDSS images was made to assign a morphological class for each source. Our results indicate that the sample is dominated by intermediate to old stellar populations and there is no strong correlation between optical and radio properties of these sources. Also, we found that young AGNs can be hosted by elliptical, spiral and interacting galaxies, confirming recent findings. When comparing the optical properties of CSS/GPS and MPS sources, we do not find any significant difference. Finally, the Mid-Infrared WISE colours analysis suggest that compact radio sources defined as powerful AGNs are, in general, gas-rich systems., Comment: 44 pages, 12 figures, 5 tables, accepted for publication in MNRAS

Using bona-fide black hole (BH) mass estimates from reverberation mapping and the line ratio [SiVI] 1.963$\mu$m/Br$\gamma_{\rm broad}$ as tracer of the AGN ionising continuum, a novel BH-mass scaling relation of the form log($M_{\rm BH}) = (6.40\pm 0.17) - (1.99\pm 0.37) \times$ log ([SiVI]/Br$\gamma_{\rm broad})$, dispersion 0.47 dex, over the BH mass interval, $10^6 - 10^8$ M$_{\odot}$ is found. Following on the geometrically thin accretion disc approximation and after surveying a basic parameter space for coronal lines production, we believe one of main drivers of the relation is the effective temperature of the disc, which is effectively sampled by the [SiVI] 1.963$\mu$m coronal line for the range of BH masses considered. By means of CLOUDY photoionisation models, the observed anti-correlation appears to be formally in line with the thin disc prediction T_disc $\propto {M_{\rm BH}}^{-1/4}$., Comment: 22 pages, 16 figures. Accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:2010.00075

In modern models and simulations of galactic evolution, the star formation in massive galaxies is regulated by an ad hoc active galactic nuclei (AGN) feedback process. However, the physics and the extension of such effects on the star formation history of galaxies is matter of vivid debate. In order to shed some light in the AGN effects over the star formation, we analyzed the inner 500$\times$500pc of a sample of 14 Seyfert galaxies using GMOS and MUSE integral field spectroscopy. We fitted the continuum spectra in order to derive stellar age, metallicity, velocity and velocity dispersion maps in each source. After stacking our sample and averaging their properties, we found that the contribution of young SP, as well as that of AGN featureless continuum both peak at the nucleus. The fraction of intermediate-age SPs is smaller in the nucleus if compared to outer regions, and the contribution of old SPs vary very little within our field of view (FoV). We also found no variation of velocity dispersion or metallicity within our FoV. Lastly, we detected an increase in the dust reddening towards the center of the galaxies. These results lead us to conclude that AGN phenomenon is usually related to a recent star formation episode in the circumnuclear region., Comment: 18 pages, 17 figures. Accepted for publication at MNRAS

In a cell-free massive multiple-input multiple-output (CF-mMIMO) network, multiple access points (APs) actively cooperate to serve users' equipment (UEs). We consider how the random access (RA) problem can be addressed by such a network under the occurrence of pilot collisions. To find a solution, we embrace the user-centric perspective, which basically dictates that only a preferred set of APs needs to serve a UE. Due to the success of the strongest-user collision resolution (SUCRe) protocol for cellular (Ce) mMIMO, we extend it by considering the new setting. Besides, we establish that the user-centric perspective naturally equips a CF network with robust fundamentals for resolving collisions. We refer to this foundation as spatial separability, which enables multiple colliding UEs to access the network simultaneously. We then propose two novel RA protocols for CF-mMIMO: i) the baseline cell-free (BCF) that resolves collisions with the concept of spatial separability alone, and ii) the cell-free SUCRe (CF-SUCRe) that combines SUCRe and spatial separability principle to resolve collisions. We evaluate our proposed RA protocols against the Ce-SUCRe. Respectively, the BCF and CF-SUCRe can support 7x and 4x more UEs' access on average compared to the Ce-SUCRe with an average energy efficiency gain based on total power consumed (TPC) by the network per access attempt of 52x and 340x. Among our procedures, even with a higher overhead, the CF-SUCRe is superior to BCF regarding TPC per access attempt. This is because the combination of methods for collision resolution allows many APs to be disconnected from the RA process without sacrificing much the performance. Finally, our numerical results presented in this work can be reproduced using the code package available on: github.com/victorcroisfelt/cf-ra-spatial-separability., Comment: 14 pages, 8 figures

The recent extra-large scale massive multiple-input multiple-output (XL-MIMO) systems are seen as a promising technology for providing very high data rates in increased user-density scenarios. Spatial non-stationarities and visibility regions (VRs) appear across the XL-MIMO array since its large dimension is of the same order as the distances to the user-equipments (UEs). Due to the increased density of UEs in typical applications of XL-MIMO systems and the scarcity of pilots, the design of random access (RA) protocols and scheduling algorithms become challenging. In this paper, we propose a joint RA and scheduling protocol, namely non-overlapping VR XL- MIMO (NOVR-XL) RA protocol, which takes advantage of the different VRs of the UEs for improving RA performance, besides seeking UEs with non-overlapping VRs to be scheduled in the same payload data pilot resource. Our results reveal that the proposed scheme achieves significant gains in terms of sum rate compared with traditional RA schemes, as well as reducing access latency and improving connectivity performance as a whole., Comment: 10pages, 6 figures, 2 tables. Index terms: Random-access protocol, grant-based protocols, massive MIMO, XL-MIMO, non-stationarity, visibility region (VR), scheduling

In this second paper in the series, we carefully analyze the observational properties of the optical FeII and NIR CaII triplet in Active Galactic Nuclei, as well as the luminosity, black hole mass, and Eddington ratio in order to define the driving mechanism behind the properties of our sample. The CaII shows an inverse Baldwin effect, bringing out the particular behavior of this ion with respect to the other low-ionization lines such as H$\beta$. We performed a Principal Component Analysis, where 81.2% of the variance can be explained by the first three principal components drawn from the FWHMs, luminosity, and equivalent widths. The first principal component (PC1) is primarily driven by the combination of black hole mass and luminosity with a significance over 99.9%, which in turn is reflected in the strong correlation of the PC1 with the Eddington ratio. The observational correlations are better represented by the Eddington ratio, thus it could be the primary mechanism behind the strong correlations observed in the CaII-FeII sample. Since calcium belongs to the $\alpha$-elements, the FeII/CaII flux ratio can be used as a chemical clock for determining the metal content in AGN and trace the evolution of the host galaxies. We confirm the de-enhancement of the ratio FeII/CaII by the Eddington ratio, suggesting a metal enrichment of the BLR in intermediate-$z$ with respect to low-$z$ objects. A larger sample, particularly at $z$>2, is needed to confirm the present results., Comment: 35 pages, 16 figures, 4 tables. Accepted for publication in ApJ

Characterizing high-z quasar environments is key to understanding the co-evolution of quasars and the surrounding galaxies. To restrict their global picture, we statistically examine the g-dropout galaxy overdensity distribution around 570 faint quasar candidates at z ~ 4, based on the Hyper Suprime-Cam Subaru Strategic Program survey. We compare the overdensity significances of g-dropout galaxies around the quasars with those around g-dropout galaxies, and find no significant difference between their distributions. A total of 4 (22) out of the 570 faint quasars, 0.7_{-0.4}^{+0.4} (3.9_{-0.8}^{+0.8}) %, are found to be associated with the > 4 sigma overdense regions within an angular separation of 1.8 (3.0) arcmin, which is the typical size of protoclusters at this epoch. This is similar to the fraction of g-dropout galaxies associated with the > 4 sigma overdense regions. This result is consistent with our previous work that 1.3_{-0.9}^{+0.9} % and 2.0_{-1.1}^{+1.1} % of luminous quasars detected in the Sloan Digital Sky Survey exist in the > 4 sigma overdense regions within 1.8 and 3.0 arcmin separations, respectively. Therefore, we suggest that the galaxy number densities around quasars are independent of their luminosity, and most quasars do not preferentially appear in the richest protocluster regions at z ~ 4. The lack of an apparent positive correlation between the quasars and the protoclusters implies that: i) the gas-rich major merger rate is relatively low in the protocluster regions, ii) most high-z quasars may appear through secular processes, or iii) some dust-obscured quasars exist in the protocluster regions., Comment: 12 pages, 4 figures

Coronal-Line Forest Active Galactic Nuclei (CLiF AGN) are characterized by strong high-ionization lines, which contrast to what is found in most AGNs. Here, we carry out a multiwavelength analysis aimed at understanding the physical processes in the Narrow Line Region (NLR) of these objects and unveiling if they are indeed a special class of AGN. By comparing coronal emission-line ratios we conclude that there are no differences between CLiF and non-CLiF AGNs. We derive physical conditions of the narrow line region (NLR) gas and found electron densities in the range $3.6\times$10$^{2}$ - $1.7\times$10$^{4}$ cm$^{-3}$ and temperatures of $3.7\times$10$^{3}$ - $6.3\times$10$^{4}$ K, suggesting that the ionization mechanism is associated primarily with photoionization by the AGN. We suggest a NLR dominated by matter-bounded clouds to explain the high-ionization line spectrum observed. The mass of the central black hole, derived from the stellar velocity dispersion show that most of the objects have values in the interval 10$^{7-8}$~M$\odot$. Our results imply that CLiF AGN is not a separate category of AGNs. In all optical/near-infrared emission-line properties analyzed, they represent an extension to the low/high ends of the distribution within the AGN class., Comment: 30 pages, 25 figures, to be published in MNRAS

Getting insights on the shape and nature of the ionizing continuum in astronomical objects is often done via indirect methods as high energy photons are absorbed by our Galaxy. This work explores the ionization continuum of active galactic nuclei (AGN) using the ubiquitous coronal lines. Using bona-fide BH mass estimates from reverberation mapping and the line ratio [Si VI] 1.963 micron/Br$\gamma_{\rm broad}$ as tracer of the AGN ionizing continuum, a novel BH-mass scaling relation of the form log($M_{\rm BH}) = (6.40\pm 0.17) - (1.99\pm 0.37) \times$ log ([Si VI]/Br$\gamma_{\rm broad})$, over the BH mass interval, $10^6 - 10^8$ M$_{\odot}$ with dispersion 0.47 dex is found. Following on the thin accretion disc approximation and after surveying a basic parameter space for coronal lines production, we believe that a key parameter driving this anti-correlation is the effective temperature of the accretion disc, this being effectively sampled by the coronal line gas. Accordingly, the observed anti-correlation becomes formally in line with the thin accretion disc prediction $T_{\rm{disc}} \propto {M_{\rm BH}}^{-1/4}$., Comment: 16 pages, 6 figures. Submitted to ApJ

Extra-large massive multiple-input multiple-output (XL-MIMO) systems is a new concept, where spatial non-stationarities allow activate a high number of user equipments (UEs). This paper focuses on a grant-based random access (RA) approach in the novel XL-MIMO channel scenarios. Modifications in the classical Strongest User Collision Resolution (SUCRe) protocol have been aggregated to explore the visibility regions (VRs) overlapping in XL-MIMO. The proposed grant-based RA protocol takes advantage of this new degree of freedom for improving the number of access attempts and accepted UEs. As a result, the proposed grant-based protocol for XL-MIMO systems is capable of reducing latency in the pilot allocation step., Comment: 12 pages, 5 figures, accepted paper in the IEEE Communications Letters

We consider the recently proposed extra-large scale massive multiple-input multiple-output (XL-MIMO) systems, with some hundreds of antennas serving a smaller number of users. Since the array length is of the same order as the distance to the users, the long-term fading coefficients of a given user vary with the different antennas at the base station (BS). Thus, the signal transmitted by some antennas might reach the user with much more power than that transmitted by some others. From a green perspective, it is not effective to simultaneously activate hundreds or even thousands of antennas, since the power-hungry radio frequency (RF) chains of the active antennas increase significantly the total energy consumption. Besides, a larger number of selected antennas increases the power required by linear processing, such as precoding matrix computation, and short-term channel estimation. In this paper, we propose four antenna selection (AS) approaches to be deployed in XL-MIMO systems aiming at maximizing the total energy efficiency (EE). Besides, employing some simplifying assumptions, we derive a closed-form analytical expression for the EE of the XL-MIMO system, and propose a straightforward iterative method to determine the optimal number of selected antennas able to maximize it. The proposed AS schemes are based solely on long-term fading parameters, thus, the selected antennas set remains valid for a relatively large time/frequency intervals. Comparing the results, we find that the genetic-algorithm based AS scheme usually achieves the best EE performance, although our proposed highest normalized received power AS scheme also achieves very promising EE performance in a simple and straightforward way., Comment: 24 pages, 7 figures, 1 table and 22 references

We investigate the statistical properties of eigenvalues of pseudo-Hermitian random matrices whose eigenvalues are real or complex conjugate. It is shown that when the spectrum splits into separated sets of real and complex conjugate eigenvalues, the real ones show characteristics of an intermediate incomplete spectrum, that is, of a so-called thinned ensemble. On the other hand, the complex ones show repulsion compatible with cubic-order repulsion of non normal matrices for the real matrices, but higher order repulsion for the complex and quaternion matrices.

We report the rest-frame ultraviolet luminosity function of $g$-dropout galaxies in 177 protocluster candidates (PC UVLF) at $z\sim4$ selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess towards the bright-end. This excess can not be explained by the contribution of only active galactic nuclei, and we also find that this is more significant in higher dense regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at $z\sim4$. We also estimate the star formation rate density (SFRD) in protocluster regions as $\simeq 6-20\%$ of the cosmic SFRD, based on the measured PC UVLF after correcting for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a non-negligible contribution to the cosmic SFRD at $z\sim4$, as previously suggested by simulations. Our results suggest that protoclusters are essential components for the galaxy evolution at $z\sim4$., Comment: 22 pages, 16 figures, Accepted for publication in ApJ

Optical Fe II emission is a strong feature in quasar spectra originating in the broad-line region (BLR). The difficulty in understanding the complex Fe II pseudo-continuum has led us to search for other reliable, simpler ionic species such as Ca II. In this first part of the series, we confirm the strong correlation between the strengths of two emission features, the optical Fe II and the NIR Ca II, both from observations and photoionization modelling. With the inclusion of an up-to-date compilation of observations with both optical Fe II and NIR Ca II measurements, we span a wider and more extended parameter space and confirm the common origin of these two spectral features with our photoionization models using CLOUDY. Taking into account the effect of dust into our modelling, we constrain the BLR parameter space (primarily, in terms of the ionization parameter and local cloud density) as a function of the strengths of Fe II and Ca II emission., Comment: 21 pages, 12 figures, 1 table; accepted for publication in ApJ

We present near-infrared spectroscopy of the NLS1 galaxy PHL1092 (z=0.394), the strongest FeII emitter ever reported, combined with optical and UV data. We modeled the continuum and the broad emission lines using a power-law plus a black body function and Lorentzian functions, respectively. The strength of the FeII emission was estimated using the latest FeII templates in the literature. We re-estimate the ratio between the FeII complex centered at 4570Ang and the broad component of H-Beta, R_FeII, obtaining a value of 2.58, nearly half of that previously reported (R_FeII=6.2), but still placing PHL1092 among extreme FeII emitters. The FWHM found for low ionization lines are very similar (FWHM~1200km/s), but significantly narrower than those of the Hydrogen lines (FWHM(H-Beta)~1900km/s). Our results suggest that the FeII emission in PHL1092 follows the same trend as in normal FeII emitters, with FeII being formed in the outer portion of the BLR and co-spatial with CaII, and OI, while H-Beta is formed closer to the central source. The flux ratio between the UV lines suggest high densities, log(n_H)~13.0 cm^{-3}, and a low ionization parameter, log(U)~-3.5. The flux excess found in the FeII bump at 9200Ang after the subtraction of the NIR FeII template and its comparison with optical FeII emission suggests that the above physical conditions optimize the efficiency of the ly-Alpha fluorescence process, which was found to be the main excitation mechanism in the FeII production. We discuss the role of PHL1092 in the Eigenvector 1 context., Comment: Accepted for publication at MNRAS

The use of massive multiple-input multiple-output (MIMO) to serve a crowd of user equipments (UEs) is challenged by the deficit of pilots. Assuming that the UEs are intermittently active, this problem can be addressed by a shared access to the pilots and a suitable random access (RA) protocol. The strongest-user collision resolution (SUCRe) is a previously proposed RA protocol that often privileges the UEs closer to the base station (BS). In contrast, we propose a novel RA protocol using a decentralized pilot power allocation method that aims at a fairer performance. The proposed access class barring with power control (ACBPC) protocol allows each UE to estimate, without additional overhead, how many UEs collided for the chosen pilot and calculate an ACB factor, which is then used to determine the pilot retransmission probability in the next protocol step. The results show that the proposed ACBPC protocol is superior to SUCRe in terms of providing a fair connectivity for very crowded networks, although still being distributed and uncoordinated as the original SUCRe protocol., Comment: 12 pages, 4 figures

We present VLT/SINFONI observations of 35 quasars at 2.1 < z < 3.2, the majority of which were selected from the Clusters Around Radio-Loud AGN (CARLA) survey. CARLA quasars have large CIV-based black hole (BH) masses (M(BH) > 10^9 Msun) and powerful radio emission (P(500MHz) > 27.5 W/Hz). We estimate Ha-based M(BH), finding a scatter of 0.35 dex compared to CIV. We evaluate several recipes for correcting CIV-based masses, which reduce the scatter to 0.24 dex. The radio power of the radio-loud quasars is at most weakly correlated with the interconnected quantities Ha-width, L(5100A) and M(BH), suggesting that it is governed by different physical processes. However, we do find a strong inverse correlation between CIV blueshift and radio power linked to higher Eddington ratios and L(5100A). Under standard assumptions, the BH growth time is longer than the cosmic age for many CARLA quasars, suggesting that they must have experienced more efficient growth in the past. If these BHs were growing from seeds since the epoch of reionization, it is possible that they grew at the Eddington limit like the quasars at z ~ 6-7, and then continued to grow at the reduced rates observed until z ~ 2-3. Finally, we study the relation between M(BH) and environment, finding a weak positive correlation between M(BH) and galaxy density measured by CARLA., Comment: MNRAS, accepted (28 pages, 22 figures)

Characterizing the variability of the extragalactic sources used for calibration in the Atacama Large Millimeter/Sub-millimeter Array (ALMA) is key to assess the flux scale uncertainty of science observations. To this end, we model the variability of 39 quasars which have been used by ALMA as secondary flux calibrators using continuous time stochastic processes. This formalism is specially adapted to the multi-frequency, quasi-periodic sampling which characterizes the calibration monitoring of ALMA. We find that simple mixtures of Ornstein-Uhlenbeck processes can describe well the flux and spectral index variability of these sources for Bands 3 and 7 (91.5 and 103.5, and 343.5 GHz, respectively). The spectral shape of the calibrators are characterized by negative spectral indices, mostly between $-0.35$ and $-0.80$, and with additional concavity. The model provides forecasts, interpolations, and uncertainty estimations for the observed fluxes that depend on the intrinsic variability of the source. These can be of practical use for the ALMA data calibrator survey and data quality assurance.

We present spectra and near-infrared images of a sample of faint radio sources initially selected as promising high-redshift radio galaxy (HzRG) candidates. We have determined redshifts for a total of 13 radio galaxies with redshifts ranging from $0.52\le z \le 5.72$. Our sample probes radio luminosities that are almost an order of magnitude fainter than previous large samples at the highest redshifts. We use near-infrared photometry for a subsample of these galaxies to calculate stellar masses using simple stellar population models, and find stellar masses to be in the range $10^{10.8} - 10^{11.7} M_\odot$. We then compare our faint radio galaxies with brighter radio galaxies at $z\ge2$ from the literature. We find that fainter radio galaxies have lower Ly$\alpha$ luminosities and narrower full width at half maxima compared to the bright ones, implying photoionisation by weaker AGN. We also rule out the presence of strong shocks in faint HzRGs. The stellar masses determined for faint HzRGs are lower than what has been observed for brighter ones. We find that faint HzRG population in the redshift range $2-4$ forms a bridge between star-forming and narrow-line AGN, whereas the ones at $z>4$ are dominated by star-formation, and may be building up their stellar mass through cold accretion of gas. Finally, we show that the overall redshift evolution of radio sizes at $z>2$ is fully compatible with increased inverse Compton scattering losses at high redshifts., Comment: 26 pages (including 2 appendices), 17 figures, accepted for publication in MNRAS

Massive MIMO is considered to be one of the key technologies in the emerging 5G systems, but also a concept applicable to other wireless systems. Exploiting the large number of degrees of freedom (DoFs) of massive MIMO essential for achieving high spectral efficiency, high data rates and extreme spatial multiplexing of densely distributed users. On the one hand, the benefits of applying massive MIMO for broadband communication are well known and there has been a large body of research on designing communication schemes to support high rates. On the other hand, using massive MIMO for Internet-of-Things (IoT) is still a developing topic, as IoT connectivity has requirements and constraints that are significantly different from the broadband connections. In this paper we investigate the applicability of massive MIMO to IoT connectivity. Specifically, we treat the two generic types of IoT connections envisioned in 5G: massive machine-type communication (mMTC) and ultra-reliable low-latency communication (URLLC). This paper fills this important gap by identifying the opportunities and challenges in exploiting massive MIMO for IoT connectivity. We provide insights into the trade-offs that emerge when massive MIMO is applied to mMTC or URLLC and present a number of suitable communication schemes. The discussion continues to the questions of network slicing of the wireless resources and the use of massive MIMO to simultaneously support IoT connections with very heterogeneous requirements. The main conclusion is that massive MIMO can bring benefits to the scenarios with IoT connectivity, but it requires tight integration of the physical-layer techniques with the protocol design., Comment: Submitted for publication

The orthogonal frequency division multiplexing (OFDM) transmission has shown promise in applications of visible light communication (VLC). However, the variation of the nonlinearity of the optical power emitted by the high power light emitting diode (HPLED) as a function of current and temperature implies in drastic OFDM-VLC performance degradation. The first part of this work, experimentally confirms and models this degradation due to temperature in a high power white HPLED. The higher attenuation at high frequencies, which is inherent to the HPLED and which is accentuated by the effect of the intrinsic capacitance of the photodiode, is another factor of degradation due to the reduction of the signal-to-noise ratio (SNR) at the receiver for such frequencies. For the mitigation of these effects, we propose a pre-distortion and digital pre-equalization scheme using a luminous feedback signal in the transmitter module. The system is modeled so that the operating points are mathematically deduced and evaluated by simulations and by an experimental setup. By allowing the linearization of the transmitted light signal and the maintenance of an average SNR in all OFDM subcarriers, the performance improvement is confirmed in comparison with other schemes, such as with non-predistortion, pre-distortion with fixed parameters, and simple post-equalization., Comment: 25 pages, 14 figures, 2 tables

To exploit the benefits of massive multiple-input multiple-output (M-MIMO) technology in scenarios where base stations (BSs) need to be cheap and equipped with simple hardware, the computational complexity of classical signal processing schemes for spatial multiplexing of users shall be reduced. This calls for suboptimal designs that perform well the combining/precoding steps and simultaneously achieve low computational complexities. An approach based on the iterative Kaczmarz algorithm (KA) has been recently investigated, assuring well execution without the knowledge of second order moments of the wireless channels in the BS, and with easiness, since no tuning parameters, besides the number of iterations, are required. In fact, the randomized version of KA (rKA) has been used in this context due to global convergence properties. Herein, modifications are proposed on this first rKA-based attempt, aiming to improve its performance-complexity trade-off solution for M-MIMO systems. We observe that long-term channel effects degrade the rate of convergence of the rKA-based schemes. This issue is then tackled herein by means of a hybrid rKA initialization proposal that lands within the region of convexity of the algorithm and assures fairness to the communication system. The effectiveness of our proposal is illustrated through numerical results which bring more realistic system conditions in terms of channel estimation and spatial correlation than those used so far. We also characterize the computational complexity of the proposed rKA scheme, deriving upper bounds for the number of iterations. A case study focused on a dense urban application scenario is used to gather new insights on the feasibility of the proposed scheme to cope with the inserted BS constraints., Comment: 36 pages, 5 figures, full paper

We have obtained three-dimensional maps of the universe in $\sim200\times200\times80$ comoving Mpc$^3$ (cMpc$^3$) volumes each at $z=5.7$ and $6.6$ based on a spectroscopic sample of 179 galaxies that achieves $\gtrsim80$\% completeness down to the Ly$\alpha$ luminosity of $\log(L_{\rm Ly\alpha}/[\mathrm{erg\ s^{-1}}])=43.0$, based on our Keck and Gemini observations and the literature. The maps reveal filamentary large-scale structures and two remarkable overdensities made out of at least 44 and 12 galaxies at $z=5.692$ (z57OD) and $z=6.585$ (z66OD), respectively, making z66OD the most distant overdensity spectroscopically confirmed to date with $>10$ spectroscopically confirmed galaxies. We compare spatial distributions of submillimeter galaxies at $z\simeq 4-6$ with our $z=5.7$ galaxies forming the large-scale structures, and detect a $99.97\%$ signal of cross correlation, indicative of a clear coincidence of dusty star-forming galaxy and dust unobscured galaxy formation at this early epoch. The galaxies in z57OD and z66OD are actively forming stars with star formation rates (SFRs) $\gtrsim5$ times higher than the main sequence, and particularly the SFR density in z57OD is 10 times higher than the cosmic average at the redshift (a.k.a. the Madau-Lilly plot). Comparisons with numerical simulations suggest that z57OD and z66OD are protoclusters that are progenitors of the present-day clusters with halo masses of $\sim10^{14}\ \mathrm{M_\odot}$., Comment: 17 pages, 11 figures, Accepted for Publication in ApJ

This paper proposes a detailed investigation on the uplink (UL) performance of massive multiple-input-multiple-output (maMIMO) systems employing maximum-ratio combining at the receiver. While most papers in maMIMO literature assume orthogonal frequency-division multiplexing (OFDM), current standards like LTE employ single-carrier (SC) waveform in the UL due to several benefits. We thus perform a systemic comparison between two fundamental schemes: the time-reversal MRC (TRMRC) operating under SC, and the frequency-domain MRC (FDMRC) employed with OFDM. It was recently shown that TRMRC outperforms FDMRC in terms of achievable rates, since SC systems do not require the cyclic prefix (CP) of OFDM. On the other hand, the computational complexity of TRMRC algorithm is higher than that of FDMRC, even when efficient solutions are employed (e.g., fast convolution with the overlap-and-add method). Hence, the best scheme for the UL maMIMO systems still remains an open question. The main contribution of this paper is the comparison of the total energy efficiency of both TRMRC and FDMRC when used in the UL of maMIMO systems. Our results show that, for current typical system parameters, FDMRC/OFDM achieves a higher total energy efficiency than TRMRC/SC. However, if the cell radius is below 300m and/or the computational efficiency increases by 30% regarding the current processors, the TRMRC under SC waveform becomes more attractive for the UL of maMIMO systems., Comment: 27 pages, 03 tables, and 08 figures

To provide the vast exploitation of the large number of antennas on massive multiple-input-multiple-output (M-MIMO), it is crucial to know as accurately as possible the channel state information in the base station. This knowledge is canonically acquired through channel estimation procedures conducted after a pilot signaling phase, which adopts the widely accepted time-division duplex scheme. However, the quality of channel estimation is very impacted either by pilot contamination or by spatial correlation of the channels. There are several models that strive to match the spatial correlation in M-MIMO channels, the exponential correlation model being one of these. To observe how the channel estimation and pilot contamination are affected by this correlated fading model, this work proposes to investigate an M-MIMO scenario applying the standard minimum mean square error channel estimation approach over uniform linear arrays and uniform planar arrays (ULAs and UPAs, respectively) of antennas. Moreover, the elements of the array are considered to contribute unequally on the communication, owing to large-scale fading variations over the array. Thus, it was perceived that the spatially correlated channels generated by this combined model offer a reduction of pilot contamination, consequently the estimation quality is improved. The UPA acquired better results regarding pilot contamination since it has been demonstrated that this type of array generates stronger levels of spatial correlation than the ULA. In contrast to the favorable results in channel estimation, the channel hardening effect was impaired by the spatially correlated channels, where the UPA imposes the worst performance of this effect for the discussed model., Comment: 26 pages, 9 figures

In this paper, we have analyzed the performance-complexity tradeoff of {a selective} likelihood ascent search (LAS) algorithm initialized by a linear detector, such as matched filtering (MF), zero forcing (ZF) and minimum mean square error (MMSE), {and considering an optimization factor $\rho$ from the bit flipping rule}. The scenario is the uplink of a massive MIMO (M-MIMO) system, and the {analysis has }been developed by means of computer simulations. With the increasing number of base station (BS) antennas, the classical detectors become inefficient. Therefore, the LAS is employed for performance-complexity tradeoff improvement. Using an adjustable optimized threshold on the bit flip rule of LAS, much better solutions have been achieved in terms of BER with no further complexity increment, indicating that there is an optimal threshold for each scenario. Considering a $32\times32$ antennas scenario, {the large-scale MIMO system equipped with the proposed LAS detector with} factor $\rho$ = 0.8 {requires} 5 dB less {in terms of SNR than the conventional LAS of the} literature ($\rho$ = 1.0) to achieve the same bit error rate of $10^{-3}$.

We investigate the effects of pilot assignment in multi-cell massive multiple-input multiple-output systems. When deploying a large number of antennas at base station (BS), and linear detection/precoding algorithms, the system performance in both uplink (UL) and downlink (DL) is mainly limited by pilot contamination. This interference is proper of each pilot, and thus system performance can be improved by suitably assigning the pilot sequences to the users within the cell, according to the desired metric. We show in this paper that UL and DL performances constitute conflicting metrics, in such a way that one cannot achieve the best performance in UL and DL with a single pilot assignment configuration. Thus, we propose an alternative metric, namely total capacity, aiming to simultaneously achieve a suitable performance in both links. Since the PA problem is combinatorial, and the search space grows with the number of pilots in a factorial fashion, we also propose a low complexity suboptimal algorithm that achieves promising capacity performance avoiding the exhaustive search. Besides, the combination of our proposed PA schemes with an efficient power control algorithm unveils the great potential of the proposed techniques in providing improved performance for a higher number of users. Our numerical results demonstrate that with 64 BS antennas serving 10 users, our proposed method can assure a 95%-likely rate of 4.2 Mbps for both DL and UL, and a symmetric 95%-likely rate of 1.4 Mbps when serving 32 users.

We report the discovery of the most distant radio galaxy to date, TGSS1530 at a redshift of $z=5.72$ close to the presumed end of the Epoch of Reionisation. The radio galaxy was selected from the TGSS ADR1 survey at 150 MHz for having to an ultra-steep spectral index, $\alpha^{\textrm{150 MHz}}_{\textrm{1.4 GHz}} = -1.4$ and a compact morphology obtained using VLA imaging at 1.4 GHz. No optical or infrared counterparts for it were found in publicly available sky surveys. Follow-up optical spectroscopy at the radio position using GMOS on Gemini North revealed the presence of a single emission line. We identify this line as Lyman alpha at $z=5.72$, because of its asymmetric line profile, the absence of other optical/UV lines in the spectrum and a high equivalent width. With a Ly$\alpha$ luminosity of $5.7 \times 10^{42}$ erg s$^{-1}$ and a FWHM of $370$ km s$^{-1}$, TGSS1530 is comparable to `non-radio' Lyman alpha emitters (LAEs) at a similar redshift. However, with a radio luminosity of $\log L_{\textrm{150 MHz}} = 29.1$ W Hz$^{-1}$ and a deconvolved physical size $3.5$ kpc, its radio properties are similar to other known radio galaxies at $z>4$. Subsequent $J$ and $K$ band imaging using LUCI on the Large Binocular Telescope resulted in non-detection of the host galaxy down to $3\sigma$ limits of $J>24.4$ and $K>22.4$ (Vega). The $K$ band limit is consistent with $z>5$ from the $K-z$ relation for radio galaxies, suggesting stellar mass limits using simple stellar population models of $M_{\textrm{stars}}< 10^{10.5}$ $M_\odot$. Its high redshift coupled with relatively small radio and Ly$\alpha$ sizes suggest that TGSS1530 may be a radio galaxy in an early phase of its evolution., Comment: 11 pages, 7 figures. Latest published version 10 October 2018

On 2015 November 13, the small artificial object designated WT1190F entered the Earth atmosphere above the Indian Ocean offshore Sri Lanka after being discovered as a possible new asteroid only a few weeks earlier. At ESA's SSA-NEO Coordination Centre we took advantage of this opportunity to organize a ground-based observational campaign, using WT1190F as a test case for a possible similar future event involving a natural asteroidal body., Comment: Icarus, In Press. 5 pages, 2 figures

We present the cross-correlation between 151 luminous quasars ($M_{ \mathrm{UV}} < -26$) and 179 protocluster candidates at $z \sim 3.8$, extracted from the Wide imaging survey ($ \sim 121~ $deg$^2$) performed with a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at $ > 4 \sigma $. The distributions of the distance between quasars and the nearest protoclusters and the significance of the overdensity at the position of quasars are statistically identical to those found for $g$-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of $g$-dropout galaxies around quasars is slightly higher than that around $g$-dropout galaxies on $1.0 - 2.5$ pMpc scales, while at $ < 0.5$ pMpc that around quasars tends to be lower. We also find that quasars with higher UV-luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which the luminous quasar at $z \sim4 $ resides in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasars may be suppressing star formation in their close vicinity., Comment: 15 pages, 11 figures, accepted for publication in PASJ special issue

Massive MIMO communication systems have been identified as one of the most prominent technologies of the next generation wireless standards, such as 5G, due to the large gains in energy and spectral efficiency that can be achieved. In the asymptotic condition of infinite number of antennas at the base station (BS), the performance bottleneck of these systems is due to the pilot contamination effect, i.e., the directional interference arising from users in adjacent cells that reuse the same set of orthogonal training sequences, and thus the interference seen by each user is determined by the pilot sequence assigned to him. We show in this paper that the system performance can be improved by appropriately assigning the pilot sequences to the users, in the so-called pilot allocation scheme. Depending on the optimization metric adopted, it is more advantageous to a user with certain long- term fading coefficient be assigned to a specific pilot sequence, whose interference can be completely estimated in advance by the BS by only knowing the long term fading coefficients of users in adjacent cells. Besides, if the objective is to maximize the number of users with a target quality of service, we have shown that the pilot allocation schemes can be combined with power control algorithms, resulting in much more improvements for the system. For unitary frequency reuse factor, we have found that the data throughput provided for 95% of the users increases when applying power control algorithm from 134kbps to 1.461Mbps with no pilot allocation, while this performance gain provided by power control changes from 793kbps to 6.743Mbps when pilot allocation is employed. If the reuse factor increases to 3, a 95%-likely data throughput of 17.310Mbps can be assured when pilot allocation and power control are suitably combined., Comment: 21 pages, 5 figures; submitted paper for a journal

We study the compatibility of large quasar groups with the concordance cosmological model. Large Quasar Groups are very large spatial associations of quasars in the cosmic web, with sizes of 50-250h^-1 Mpc. In particular, the largest large quasar group known, named Huge-LQG, has a longest axis of ~860h^-1 Mpc, larger than the scale of homogeneity (~260 Mpc), which has been noted as a possible violation of the cosmological principle. Using mock catalogues constructed from the Horizon Run 2 cosmological simulation, we found that large quasar groups size, quasar member number and mean overdensity distributions in the mocks agree with observations. The Huge-LQG is found to be a rare group with a probability of 0.3 per cent of finding a group as large or larger than the observed, but an extreme value analysis shows that it is an expected maximum in the sample volume with a probability of 19 per cent of observing a largest quasar group as large or larger than Huge-LQG. The Huge-LQG is expected to be the largest structure in a volume at least 5.3 +- 1 times larger than the one currently studied., Comment: 16 pages, 12 figures, accepted for publication in MNRAS, Revised June 22: corrected typo in the name of one of the author, corrected typos in general, revised introduction and extreme value theory section

We present a study of FeII emission in the near-infrared region (NIR) for 25 active galactic nuclei (AGNs) to obtain information about the excitation mechanisms that power it and the location where it is formed. We employ a NIR FeII template derived in the literature and found that it successfully reproduces the observed FeII spectrum. The FeII bump at 9200 Angstroms detected in all objects studied confirms that Lyman-alpha fluorescence is always present in AGNs. The The correlation found between the flux of the 9200 Angstroms bump, the 1 micron lines and the optical FeII imply that Lyman-alpha fluorescence plays an important role in the FeII production. We determined that at least 18% of the optical FeII is due to this process while collisional excitation dominates the production of the observed FeII. The line profiles of FeII 10502, OI 11287, CaII 8664 and Paschen-beta were compared to gather information about the most likely location where they are emitted. We found that FeII, OI and CaII have similar widths and are, on average, 30% narrower than Paschen-beta. Assuming that the clouds emitting the lines are virialized, we show that the FeII is emitted in a region twice as far from the central source than Paschen-beta. The distance though strongly varies: from 8.5 light-days for NGC4051 to 198.2 light-days for Mrk509. Our results reinforce the importance of the FeII in the NIR to constrain critical parameters that drive its physics and the underlying AGN kinematics as well as more accurate models aimed at reproducing this complex emission., Comment: Accepted for publication in The Astrophysical Journal