Analisi e progetto del convertitore risonante LLC

Questa tesi tratta del convertitore risonante LLC. Tutte le varie condizioni di funzionamento sono state accuratamente simulate e si è analizzato nel dettaglio le forme d'onda del convertitore, individuando anche una possibile procedura di sintesi progettuale. Il convertitore di tipo LLC è particolarmente adatto a realizzare alimentatori ad elevata densità di potenza grazie alla possibilità di operare a frequenze molto elevate in virtù delle basse perdite di commutazione, con conseguente vantaggio per gli ingombri ridotti degli elementi filtranti. Inoltre la doppia induttanza prevista altro non è che un unico trasformatore che si deve appositamente costruire con le induttanze di dispersione e magnetizzazione previste in sede di progetto, per cui si tratta di un convertitore con isolamento e a minimo numero di componenti. Sebbene la comprensione del modo di operare di questo convertitore richieda un certo sforzo intellettuale, i benefici della topologia LLC sono tali che se ne prevede un sempre più ampio utilizzo in molte moderne applicazioni come il pilotaggio di TV a schermo piatto e in tutti quegli apparati che necessitano di una certificazione 80+ di eccellenza nell'efficienza energetica

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Beam Scanning Leaky-Wave Antenna with a Reconfigurable Impedance Plane

An electronically-reconfigurable leaky-wave antenna based on metasurfaces is designed and implemented. This innovative antenna consists of a multilayered structure with two (metasurface) impedance planes. The beam scanning at fixed frequency is achieved by electronically tuning the surface impedance of the lower plane using voltage-controlled varactor diodes. The rationale of this solution is that a variation in the impedance profile of the antenna in the direction transversal to propagation affects the phase velocity of the leaky wave and therefore the beam direction

The infrared properties of the new outburst star IRAS 05436-0007 in quiescent phase

We compiled and investigated the infrared/sub-mm/mm SED of the new outburst star IRAS 05436-0007 in quiescent phase. The star is a flat-spectrum source, with an estimated total luminosity of L_bol ~ 5.6 L_sun, typical of low-mass T Tauri stars. The derived circumstellar mass of 0.5 M_sun is rather high among low-mass YSOs. The observed SED differs from the SEDs of typical T Tauri stars and of 4 well-known EXors, and resembles more the SEDs of FU Orionis objects indicating the presence of a circumstellar envelope. IRAS 05436-0007 seems to be a Class II source with an age of approximately 4x10^5 yr. In this evolutionary stage an accretion disk is already fully developed, though a circumstellar envelope may also be present. Observations of the present outburst will provide additional knowledge on the source.Comment: 4 pages, 4 figures, to be published in Astronomy & Astrophysics Letter

The symbiotic star CH Cygni – II. The ejecta from the 1998-2000 active phase

We present Hubble Space Telescope (HST) imaging, a Very Large Array (VLA) radio map (4.74 GHz), optical high-resolution (echelle) spectroscopy and UBV photoelectric photometry of the symbiotic star CH Cyg obtained during its 1998–2000 active phase. The HST imaging, taken during eclipse, shows the central stars are embedded in a nebula extending to 620 ± 150 au for a distance of 270 ± 66 pc. The inner nebula is strongly influenced by the onset of activity and associated outflow in 1998. The surface brightness contours of the contemporaneous radio VLA observation agree well with HST images. Photometric observations of the broad 1999 U-minimum suggest that it is due to the eclipse of the active hot component by the giant on the long-period (14.5 yr) outer orbit. We also find that the onset of the 1998 and the 1992 active periods occur at the same orbital phase of the inner binary. Spectroscopic observations reveal two types of outflow from the active star: a high-velocity (>1200 km s−1) hot star wind sporadically alternating with a more massive outflow indicated by P-Cygni-like profiles. We present evidence connecting the extended nebulosity with the high-velocity shocked outflow, and hence the activity in the central binary

Genomic alterations in rectal tumors and response to neoadjuvant chemoradiotherapy: an exploratory study

<p>Abstract</p> <p>Background</p> <p>Neoadjuvant chemoradiotherapy is the treatment of choice in advanced rectal cancer, even though there are many patients who will not benefit from it. There are still no effective methods for predicting which patients will respond or not. The present study aimed to define the genomic profile of rectal tumors and to identify alterations that are predictive of response in order to optimize therapeutic strategies.</p> <p>Methods</p> <p>Forty-eight candidates for neoadjuvant chemoradiotherapy were recruited and their pretherapy biopsies analyzed by array Comparative Genomic Hybridization (aCGH). Pathologic response was evaluated by tumor regression grade.</p> <p>Results</p> <p>Both Hidden Markov Model and Smoothing approaches identified similar alterations, with a prevalence of DNA gains. Non responsive patients had a different alteration profile from responsive ones, with a higher number of genome changes mainly located on 2q21, 3q29, 7p22-21, 7q21, 7q36, 8q23-24, 10p14-13, 13q12, 13q31-34, 16p13, 17p13-12 and 18q23 chromosomal regions.</p> <p>Conclusions</p> <p>This exploratory study suggests that an in depth characterization of chromosomal alterations by aCGH would provide useful predictive information on response to neoadjuvant chemoradiotherapy and could help to optimize therapy in rectal cancer patients.</p> <p>The data discussed in this study are available on the NCBI Gene Expression Omnibus [GEO: GSE25885].</p

Non di solo arte. Viaggio in Italia tra voci e numeri della giovane arte contemporanea

I giovani artisti in Italia: chi sono, che cosa fanno, quanto guadagnano. Le ambizioni, i percorsi di formazione, i rapporti con il mercato.- Indice #7- Prefazione, Maria Sole Agnelli Teodorani Fabbri e Luigi Guidobono Cavalchini Garofoli #11- L’idea e gli obiettivi del progetto #17- La forcina piegata: un’introduzione alla ricerca #21- Cap.I I risultati in sintesi #25- Cap.II Il sistema dell’arte contemporanea in Italia #29- Cap.III Identikit degli artisti #33- Cap.IV Lavoro artistico e reddito #51- Cap.V I percorsi di formazione #65- Cap.VI L’arte e il suo mercato #77- Cap.VII Le politiche pubbliche #91- Cap.VIII Gli spazi indipendenti #103- Cap.IX Generazioni e opportunità a confronto #111- Cap.X #159- Cap.XI Pensieri sull’arte #181- Cap.XII Alcuni percorsi possibili per l’arte contemporanea in Italia #199- Metodologia della ricerca #203- Rassegna bibliografica ragionata #217- Riferimenti bibliografici #225- Siti web #232- Allegati #23

The Stellar Composition of the Star Formation Region CMa R1 -- III. A new outburst of the Be star component in Z CMa

We report on a recent event in which, after more than a decade of slowly fading, the visual brightness of the massive young binary Z CMa suddenly started to rise by about 1 magnitude in December 1999, followed by a rapid decline to its previous brightness over the next six months. This behaviour is similar to that exhibited by this system around its eruption in February 1987. A comparison of the intrinsic luminosities of the system with recent evolutionary calculations shows that Z CMa may consist of a 16 M_sun B0 IIIe primary star and a ~ 3 M_sun FUOr secondary with a common age of ~ 3 x 10^5 yr. We also compare new high-resolution spectra obtained in Jan. and Feb. 2000, during the recent rise in brightness, with archive data from 1991 and 1996. The spectra are rich in emission lines, which originate from the envelope of the early B-type primary star. The strength of these emission lines increased strongly with the brightness of Z CMa. We interpret the collected spectral data in terms of an accretion disc with atmosphere around the Herbig B0e component of Z CMa, which has expanded during the outbursts of 1987 and 2000. A high resolution profile of the 6300 A [O I] emission line, obtained by us in March 2002 shows an increase in flux and a prominent blue shoulder to the feature extending to ~ -700 km/s, which was much fainter in the pre-outburst spectra. We propose that this change in profile is a result of a strong change in the collimation of a jet, as a result of the outburst at the start of this century.Comment: 22 pages, 12 figures, accepted for publication in MNRA

The Scientific Investigation of Unidentified Aerial Phenomena (UAP) Using Multimodal Ground-based Observatories

Peer reviewedPublisher PD