187 research outputs found
Applicazione della metodologia S.M.E.D. alla trafilatura di superconduttori
Questa tesi è stata svolta in collaborazione con Outokumpu Copper Superconductors Italy, azienda che opera nel campo dei superconduttori. L’obiettivo della nostra tesi è stato quello di applicare, sugli impianti presenti nello stabilimento di Fornaci di Barga, i principi della metodologia S.M.E.D. Lo scopo del lavoro è stato quello di aumentare la produttività degli impianti al fine di rispettare gli obiettivi di produzione per il biennio 2005-2006. La prima fase del nostro studio è stata la formazione degli operatori, come prevede la suddetta metodologia ed in seguito si è proseguito con l’analisi dei metodi e dei tempi di lavoro. E’ stato analizzato un intero reparto (C.I.M.), costituito da più macchine, con lo scopo di trovare possibili miglioramenti nelle fasi di set up e di fabbricazione. La metodologia è stata applicata anche ad una macchina denominata “Bull Block Oto” facente parte di un altro reparto. Una volta realizzate tutte le modifiche proposte, sono stati quantificati i risultati
Co-existence Between a Radar System and a Massive MIMO Wireless Cellular System
In this paper we consider the uplink of a massive MIMO communication system
using 5G New Radio-compliant multiple access, which is to co-exist with a radar
system using the same frequency band. We propose a system model taking into
account the reverberation (clutter) produced by the radar system at the massive
MIMO receiver. Then, we propose several linear receivers for uplink
data-detection, ranging by the simple channel-matched beamformer to the
zero-forcing and linear minimum mean square error receivers for clutter
disturbance rejection. Our results show that the clutter may have a strong
effect on the performance of the cellular communication system, but the use of
large-scale antenna arrays at the base station is key to provide increased
robustness against it, at least as far as data-detection is concerned.Comment: To be presented at 2018 IEEE SPAWC, Kalamata, Greece, June 201
Energy-Efficient Power Control in Cell-Free and User-Centric Massive MIMO at Millimeter Wave
In a cell-free massive MIMO architecture a very large number of distributed
access points simultaneously and jointly serves a much smaller number of mobile
stations; a variant of the cell-free technique is the user-centric approach,
wherein each access point just serves a reduced set of mobile stations. This
paper introduces and analyzes the cell-free and user-centric architectures at
millimeter wave frequencies, considering a training-based channel estimation
phase, and the downlink and uplink data transmission phases. First of all, a
multiuser clustered millimeter wave channel model is introduced in order to
account for the correlation among the channels of nearby users; second, an
uplink multiuser channel estimation scheme is described along with
low-complexity hybrid analog/digital beamforming architectures. Third, the
non-convex problem of power allocation for downlink global energy efficiency
maximization is addressed. Interestingly, in the proposed schemes no channel
estimation is needed at the mobile stations, and the beamforming schemes used
at the mobile stations are channel-independent and have a very simple
structure. Numerical results show the benefits granted by the power control
procedure, that the considered architectures are effective, and permit
assessing the loss incurred by the use of the hybrid beamformers and by the
channel estimation errors.Comment: To appear on the IEEE Transactions on Green Communications and
Networking; originally submitted on April 24, 2018 and finally accepted for
publication on March 24, 201
Manufacture of a MoO3 coated copper made device
In this report we describe the procedure to manufacture a model of a cylindrical RF cavity made in copper and coated with a 100 nm thick layer of molybdenum trioxide. The device is 100 mm long, has an internal diameter of 60 mm and an external diameter of 80 mm. The cylindrical device was carefully divided into four sections to make possible the coating on the internal curved surfaces polished to a roughness < 10 nm. The molybdenum trioxide has been deposed utilizing a thermal evaporation technique with a dedicated high vacuum chamber equipped with a high-temperature Alumina crucible working in the temperature range of 400° - 600° C
A Methodology to Characterize Power Control Systems for Limiting Exposure to Electromagnetic Fields Generated by Massive MIMO Antennas
The fifth-generation (5G) New Radio (NR) cellular network has been launched recently. The assignment of new spectrum bands and the widespread use of Massive MIMO (MaMIMO) and beamforming techniques for better radio coverage are two major features of the new architecture. They imply both opportunities and challenges, one of the most daring one among the latter ones is the research for methods to assess human exposure to electromagnetic fields radiated by the base stations. The long-term time-varying behavior and spatial multiplexing feature of the MaMIMO antennas, along with the radio resource utilization and adoption of Time-Division Duplexing (TDD), requires that the assessment of exposure to electromagnetic fields radiated by 5G systems is based on a statistical approach that relies on the space and time distribution of the radiated power. That, in turn, is determined through simulations based on the actual maximum transmitted power - defined as the 95 th percentile of the empirical distribution obtained from historical data of radiated power - rather than on the nominal one. To ensure that exposure limits are never exceeded, a monitoring and control system (usually referred to as Power Lock (PL)) that limits the transmitted power can be used. In this paper we propose a methodology, independent from the specific technical solution implemented by the manufacturer, to characterize such control systems and determine their capability to limit the average power transmitted over a given time interval to a value that keeps the corresponding average exposure to electromagnetic fields below a specified value. Experimental results show the effectiveness of the methodology and that it can also be used to identify when the PL interacts with the higher levels of the MaMIMO system architecture
Swift J201424.9+152930: discovery of a new deeply eclipsing binary with 491 s and 3.4 h modulations
We report on the discovery of a new X-ray pulsator, Swift J201424.9+152930
(Sw J2014). Owing to its X-ray modulation at 491 s, it was discovered in a
systematic search for coherent signals in the archival data of the Swift X-ray
Telescope. To investigate the nature of Sw J2014, we performed multi-wavelength
follow-up observations with space-borne (Swift and XMM-Newton) and ground-based
(the 1.5-m Loiano Telescope and the 3.6-m Telescopio Nazionale Galileo)
instruments. The X-ray spectrum of Sw J2014 can be described by a hard and
highly absorbed power law. The optical observations made it possible to single
out the optical counterpart to this source, which displays several variable
emission lines and total eclipses lasting ~20 min. Total eclipses of similar
length were observed also in X-rays. The study of the eclipses, allowed us to
infer a second periodicity of 3.44 h, which we interpret as the orbital period
of a close binary system. We also found that the period has not significantly
changed over a ~7 yr timespan. Based on the timing signatures of Sw J2014, and
its optical and X-ray spectral properties, we suggest that it is a close binary
hosting an accreting magnetic white dwarf. The system is therefore a
cataclysmic variable of the intermediate polar type and one of the very few
showing deep eclipses.Comment: 12 pages, 8 figures, 5 tables; minor changes to match the final MNRAS
versio
A magnetar powering the ordinary monster GRB 130427A?
We present the analysis of the extraordinarily bright Gamma-Ray Burst (GRB)
130427A under the hypothesis that the GRB central engine is an
accretion-powered magnetar. In this framework, initially proposed to explain
GRBs with precursor activity, the prompt emission is produced by accretion of
matter onto a newly-born magnetar, and the observed power is related to the
accretion rate. The emission is eventually halted if the centrifugal forces are
able to pause accretion. We show that the X-ray and optical afterglow is well
explained as the forward shock emission with a jet break plus a contribution
from the spin-down of the magnetar. Our modelling does not require any
contribution from the reverse shock, that may still influence the afterglow
light curve at radio and mm frequencies, or in the optical at early times. We
derive the magnetic field ( G) and the spin period (
ms) of the magnetar and obtain an independent estimate of the minimum
luminosity for accretion. This minimum luminosity results well below the prompt
emission luminosity of GRB 130427A, providing a strong consistency check for
the scenario where the entire prompt emission is the result of continuous
accretion onto the magnetar. This is in agreement with the relatively long spin
period of the magnetar. GRB 130427A was a well monitored GRB showing a very
standard behavior and, thus, is a well-suited benchmark to show that an
accretion-powered magnetar gives a unique view of the properties of long GRBs.Comment: 5 pages, 1 figure, accepted for publication in MNRAS Letter
Complex chromosome rearrangements related 15q14 microdeletion plays a relevant role in phenotype expression and delineates a novel recurrent syndrome
Complex chromosome rearrangements are constitutional structural rearrangements involving three or more chromosomes or having more than two breakpoints. These are rarely seen in the general population but their frequency should be much higher due to balanced states with no phenotypic presentation. These abnormalities preferentially occur de novo during spermatogenesis and are transmitted in families through oogenesis
The host-galaxy response to the afterglow of GRB 100901A
For Gamma-Ray Burst 100901A, we have obtained Gemini-North and Very Large
Telescope optical afterglow spectra at four epochs: one hour, one day, three
days and one week after the burst, thanks to the afterglow remaining unusually
bright at late times. Apart from a wealth of metal resonance lines, we also
detect lines arising from fine-structure levels of the ground state of Fe II,
and from metastable levels of Fe II and Ni II at the host redshift (z =
1.4084). These lines are found to vary significantly in time. The combination
of the data and modelling results shows that we detect the fall of the Ni II 4
F9/2 metastable level population, which to date has not been observed. Assuming
that the population of the excited states is due to the UV-radiation of the
afterglow, we estimate an absorber distance of a few hundred pc. This appears
to be a typical value when compared to similar studies. We detect two
intervening absorbers (z = 1.3147, 1.3179). Despite the wide temporal range of
the data, we do not see significant variation in the absorption lines of these
two intervening systems.Comment: 17 pages, 9 figures. Accepted by Monthly Notices of the Royal
Astronomical Society on Jan 11th 201
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