Downlink and Uplink Cell Association with Traditional Macrocells and Millimeter Wave Small Cells

Millimeter wave (mmWave) links will offer high capacity but are poor at penetrating into or diffracting around solid objects. Thus, we consider a hybrid cellular network with traditional sub 6 GHz macrocells coexisting with denser mmWave small cells, where a mobile user can connect to either opportunistically. We develop a general analytical model to characterize and derive the uplink and downlink cell association in view of the SINR and rate coverage probabilities in such a mixed deployment. We offer extensive validation of these analytical results (which rely on several simplifying assumptions) with simulation results. Using the analytical results, different decoupled uplink and downlink cell association strategies are investigated and their superiority is shown compared to the traditional coupled approach. Finally, small cell biasing in mmWave is studied, and we show that unprecedented biasing values are desirable due to the wide bandwidth.Comment: 30 pages, 9 figures. Submitted to IEEE Transactions on Wireless Communication

Exploring the bulk of the BL Lac object population:1. parsec-scale radio structures

Context. The advent of Fermi is changing our understanding on the radio and gamma-ray emission in Active Galactic Nuclei. Contrary to pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the gamma-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multi-frequency properties are poorly understood and/or have not been investigated in a systematically fashion. Aims. Our main goal is to analyze the radio and gamma-ray emission properties of a sample of 42 BL Lacs selected, for the first time in the literature, with no constraint on their radio and gamma-ray flux densities/emission. Methods. Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the whole sample, we present here fundamental parameters such as radio flux densities, spectral index information, and parsec-scale structure. Moreover, we search for gamma-ray counterparts using data reported in the Second Catalog of Fermi Gamma-ray sources. Results. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. Gamma-ray counterparts are found for 14/42 sources. Conclusions. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing "non classical" properties such as low source compactness, core dominance, no gamma-ray emission and steep radio spectral indexes. A deeper multiwavelength analysis will be needed.Comment: 19 pages, 6 figures, 6 tables, accepted for publication in A&

Thermodynamic Analysis of a Multi-Ejector, CO2, Air-To-Water Heat Pump System

Abstract Nowadays, air conditioning systems for residential and office buildings, contribute largely to the energy consumptions and to the direct and indirect emissions of greenhouse gases. Carbon dioxide (CO2) could be an interesting option to replace traditional HFCs in space heating applications, due to its environmentally friendly characteristics: zero ODP and extremely low GWP, but, in order to spread its use, improvements in performances are needed. In fact, CO2 requires transcritical cycles with high expansion losses. The use of an ejector can reduce these losses and improve the performances up to 30% (depending on the performances of the ejector itself and on the operating conditions). In the a/c applications, characterized by variable operating conditions, multi-ejector systems could be used, where some ejectors work in parallel, in different combination, varying the operating conditions. Currently, a project of DTE-PCU-SPCT Department of ENEA and Industrial Engineering Department of Federico II University of Naples, is in progress, in order to evaluate experimentally the effect of several ejectors geometries on the global performance of a CO2 heat pump working with a transcritical cycle. As a part of this project, a complete heat pump system for production of hot water for sanitary use and for space heating is tested to investigate the effect of the ejector size on the balancing of the global performance of the whole system

Infrared Thermography to an Aluminium Foam Sandwich Structure Subjected to Low Velocity Impact Tests

Abstract This work is the straightforward continuation of previous ones in which vibro-acoustic characteristics of AFS panels were investigated both numerically and experimentally. Herein, the use of infrared thermography (IRT) is exploited to investigate impact damaging of an aluminium foam sandwich panel by monitoring its surface, opposite to the impact, during a low velocity impact test, which is performed with a modified Charpy pendulum. Thermal images, acquired in time sequence during the impact by the infrared camera, are post-processed to get information useful for understanding absorption capabilities and impact damaging mechanisms of this kind of structure

Large-scale radio morphology and nuclear accretion in FRII-low-excitation radio galaxies

Radio galaxies (RGs) are among the most energetic manifestation of the AGN phenomenon and, as such, are extraordinarily relevant to address important unknowns relating accretion and ejection, and to investigate the role of the surrounding environment in shaping the radio morphology. The best candidates for this pioneering study are the RGs classified as FRII-LERGs, since they show both a radio morphology typical of powerful RGs (expected to have a standard accretion disc) and have an inefficient engine, as suggested by their optical spectra. In this work we study the X-ray properties of all the FRII-LERGs of the 3CR sample at z<0.3 testing three possible scenarios: (i) FRII-LERGs are recently switched-off high-excitation RGs (HERGs) with efficient accretion disc; (ii) FRII-LERGs are strongly absorbed HERGs; (iii) FRII-LERGs are inefficient accretors and their large-scale radio emission is mainly determined by the environment. These results will be further supplemented by multi-wavelength observations, with particular attention to the radio band

The magnetic field structure in CTA 102 from high-resolution mm-VLBI observations during the flaring state in 2016-2017

CONTEXT: Investigating the magnetic field structure in the innermost regions of relativistic jets is fundamental to understanding the crucial physical processes giving rise to jet formation, as well as to their extraordinary radiation output up to γ-ray energies. AIMS: We study the magnetic field structure of the quasar CTA 102 with 3 and 7 mm VLBI polarimetric observations, reaching an unprecedented resolution (∼50 μas). We also investigate the variability and physical processes occurring in the source during the observing period, which coincides with a very active state of the source over the entire electromagnetic spectrum. METHODS: We perform the Faraday rotation analysis using 3 and 7 mm data and we compare the obtained rotation measure (RM) map with the polarization evolution in 7 mm VLBA images. We study the kinematics and variability at 7 mm and infer the physical parameters associated with variability. From the analysis of γ-ray and X-ray data, we compute a minimum Doppler factor value required to explain the observed high-energy emission. RESULTS: Faraday rotation analysis shows a gradient in RM with a maximum value of ∼6 × 104⁴ rad m⁻² and intrinsic electric vector position angles (EVPAs) oriented around the centroid of the core, suggesting the presence of large-scale helical magnetic fields. Such a magnetic field structure is also visible in 7 mm images when a new superluminal component is crossing the core region. The 7 mm EVPA orientation is different when the component is exiting the core or crossing a stationary feature at ∼0.1 mas. The interaction between the superluminal component and a recollimation shock at ∼0.1 mas could have triggered the multi-wavelength flares. The variability Doppler factor associated with such an interaction is large enough to explain the high-energy emission and the remarkable optical flare occurred very close in time.Accepted manuscrip

The TeV-emitting radio galaxy 3C 264. VLBI kinematics and SED modeling

Context. In March 2018, the detection by VERITAS of very-high-energy emission (VHE &gt; 100 GeV) from 3C 264 was reported. This is the sixth, and second most distant, radio galaxy ever detected in the TeV regime. Aims: In this article we present a radio and X-ray analysis of the jet in 3C 264. We determine the main physical parameters of the parsec-scale flow and explore the implications of the inferred kinematic structure for radiative models of this γ-ray emitting jet. Methods: The radio data set is comprised of VLBI observations at 15 GHz from the MOJAVE program, and covers a time period of about two years. Through a segmented wavelet decomposition method (WISE code), we estimated the apparent displacement of individual plasma features; we then performed a pixel-based analysis of the stacked image to determine the jet shape. The X-ray data set includes all available observations from the Chandra, XMM, and Swift satellites, and is used, together with archival data in the other bands, to build the spectral energy distribution (SED). Results: Proper motion is mostly detected along the edges of the flow, which appears strongly limb brightened. The apparent speeds increase as a function of distance from the core up to a maximum of ̃11.5 c. This constrains the jet viewing angle to assume relatively small values (θ ≲ 10°). In the acceleration region, extending up to a de-projected distance of ̃4.8 × 104 Schwarzschild radii (̃11 pc), the jet is collimating (r ∝ z0.40 ± 0.04), as predicted for a magnetically-driven plasma flow. By assuming that the core region is indeed magnetically dominated (UB/Ue &gt; 1), the SED and the jet power can be well reproduced in the framework of leptonic models, provided that the high-energy component is associated to a second emitting region. The possibility that this region is located at the end of the acceleration zone, either in the jet layer or in the spine, is explored in the modeling

The TeV-emitting radio galaxy 3C 264. VLBI kinematics and SED modeling

Context. In March 2018, the detection by VERITAS of very-high-energy emission (VHE &gt; 100 GeV) from 3C 264 was reported. This is the sixth, and second most distant, radio galaxy ever detected in the TeV regime. Aims: In this article we present a radio and X-ray analysis of the jet in 3C 264. We determine the main physical parameters of the parsec-scale flow and explore the implications of the inferred kinematic structure for radiative models of this γ-ray emitting jet. Methods: The radio data set is comprised of VLBI observations at 15 GHz from the MOJAVE program, and covers a time period of about two years. Through a segmented wavelet decomposition method (WISE code), we estimated the apparent displacement of individual plasma features; we then performed a pixel-based analysis of the stacked image to determine the jet shape. The X-ray data set includes all available observations from the Chandra, XMM, and Swift satellites, and is used, together with archival data in the other bands, to build the spectral energy distribution (SED). Results: Proper motion is mostly detected along the edges of the flow, which appears strongly limb brightened. The apparent speeds increase as a function of distance from the core up to a maximum of ̃11.5 c. This constrains the jet viewing angle to assume relatively small values (θ ≲ 10°). In the acceleration region, extending up to a de-projected distance of ̃4.8 × 104 Schwarzschild radii (̃11 pc), the jet is collimating (r ∝ z0.40 ± 0.04), as predicted for a magnetically-driven plasma flow. By assuming that the core region is indeed magnetically dominated (UB/Ue &gt; 1), the SED and the jet power can be well reproduced in the framework of leptonic models, provided that the high-energy component is associated to a second emitting region. The possibility that this region is located at the end of the acceleration zone, either in the jet layer or in the spine, is explored in the modeling