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Sparsity-based detection strategies for faint signals in noise. Application to astrophysical hyperspectral data.
No full textThis thesis deals with the problem of detecting unknown signals at low Signal-to-Noise Ratio. This work focuses on the definition, study and implementation of efficient methods able to discern only-noise observations from those that presumably carry the information of interest in a sparse way. The relevance of these methods is assessed on hyperspectral data as an applicative part.
In the first part of this work, the basic principles of statistical hypothesis testing together with a general overview on sparse representations, estimation and detection are introduced.
In the second part of the manuscript, two statistical hypotheses tests are proposed and studied. Both are adapted to the detection of sparse signals. The behaviors and the relative differences between the tests are theoretically investigated through a detailed study of their analytical and structural characteristics. The tests’ detection performances are compared with those of classical frequentist and Bayesian methods.
According to the three-dimensional data sets considered in the applicative part and to be closer to realistic scenarios involving data acquisition systems, the proposed detection strategies are adapted in order to: i) account for spectrally variable noise; ii) exploit the spectral similarities of neighbors pixels in the spatial domain and iii) exploit the greater accuracy brought by dictionary-based models, which take into account the spatio-spectral blur of information caused by instrumental Point Spread Functions.
The tests are finally applied to massive astrophysical hyperspectral data in the context of the European Southern Observatory’s Multi Unit Spectroscopic Explorer
Entry, Investment and Competition in Telecommunications and Media Markets
No full textThis Ph.D. thesis builds on the new empirical industrial organization (NEIO) literature trying to use market data to determine fundamental market drivers such as demand parameters, entry and investment thresholds or the level and development of competition in the market.
The thesis addresses two sectors: telecommunications (high-speed internet as well as fixed telephony) and media (newspaper sellers).
It is divided in three articles
1) Geographic regulation and cooperative investment in next generation broadband networks
A review of recent literature and practical cases
This article reviews the theoretical and empirical literature on geographic regulation and co-investments in next generation broadband. Alternative telecom operators have continuously invested in their own infrastructure in recent years. After more than a decade since liberalisation, competitive conditions have substantially changed, especially in urban areas. European regulatory authorities have acknowledged this development by starting regional deregulation. Additionally, different forms of cooperative investments in next generation broadband have appeared on the market. The effects of such schemes on competition, investment and welfare crucially depend on the fine details of implementation. For instance, in the case of joint-ventures, it matters how investment costs are shared and how internal and external access prices are determined. In the case of long-term access agreements, it is essential to consider how access tariffs are structured, whether they can adapt to market developments ex-post and whether contracts are signed before or after the investment takes place. Generally, many of these agreements allow for some extent of risk sharing, offering the possibility to increase investment incentives when firms are not risk neutral. It is suggested that regulators consider introducing regulated co-investment agreements complementing current regulation or in some cases even substituting for it, in addition to considering geographically segmented access prices.
2) Entry and Competition in local Newspaper Retail Markets
When two are enough
This article estimates sustainable coverage and competitive effects of entry for Swiss newspaper sellers which sell composite goods, including a range of other products such as food and near-food items. It uses the applied entry threshold ratio methodology from Bresnahan and Reiss (1991), which allows estimation even when the range of products under examination is not exactly defined and when price and quantity data are not available. It is found that under monopoly pricing, single firm entry is sustainable in Communes with a market size of over 482 people (leaving 310 Swiss communes without a selling point). With duopoly prices, instead, a first firm would only be able to enter a market with a market size of 921 people (leaving another 263 Communes without coverage). There are therefore tangible benefits from above duopoly prices in monopoly regions. Thus, a clear and quantifiable trade-off between prices in monopoly regions and coverage exists. Moreover, it is found that a second entrant in this market strongly increases competition, while further entry doesn’t have significant additional competitive effects. From a welfare perspective, therefore, it can be stated that “two is enough” to ensure competition in this market. It is shown that this is not the case in some other retail markets, where entry by a third firm may still significantly affect competition. Finally, using these estimation results, it is shown that public policy, which consisted of having the Government controlled Swiss Post enter the newspaper sellers’ retail market, was not optimal as it was focused on urban areas where neither coverage nor competition could be enhanced, while risking competitive distortions. At the same time, it is shown that there are Communes in which such a Government policy may be welfare enhancing.
3) Competition and Market Strategies in the Swiss Fixed Telephony Market
An estimation of Swisscom’s dynamic residual demand curve
This article develops a market model based on a generalised version of the traditional “dominant firm – competitive fringe” model allowing the incumbent also more competitive conduct than that of a dominant firm. A system of simultaneous equations is developed and direct estimation of the incumbent’s residual demand function is performed by instrumenting the market price with incumbent-specific cost shifting variables as well as other variables. Unlike earlier papers that assess market power in this market, this paper also adjusts the market model to ensure a sufficient level of cointegration and avoid spurious regression results. This necessitates introducing intertemporal effects. While the incumbent’s conduct cannot be directly estimated using this framework, the concrete estimates show that residual demand is inelastic (long run price elasticity of residual demand of -0.12). Such a level of elasticity is, however, only compatible with a profit maximising incumbent in the case of largely competitive conduct (conduct parameter below 0.12 and therefore close to zero). It is therefore found that the Swiss incumbent acted to a great extent competitively in the fixed telephony retail market in the period under review (2004-2012) and that (partial) retail price caps in place can no longer be justified on the basis of a lack of competition
Invecchiamento ovocitario umano: parametri strutturali ed ultrastrutturali
No full textXXVI Ciclo di Dottorato in “Biotecnologie della Riproduzione Umana” – Università “Sapienza” di Roma.
Riassunto 3° anno (anno accademico 2012/2013)
Dottoranda: Claudia Boninsegna
Titolo del progetto di ricerca: “Invecchiamento ovocitario umano: parametri strutturali ed ultrastrutturali”
L’infertilità è definita come l’incapacità di una coppia di concepire dopo un anno o più di rapporti sessuali regolari non protetti. Negli ultimi decenni si è riscontrato un notevole aumento dei tassi di infertilità, dovuto principalmente al ritardo nella programmazione della gravidanza. L’esistenza di una relazione inversa tra età e fertilità femminile è nota da tempo ed è determinata dalla graduale diminuzione che si verifica con l’età sia nella quantità che nella qualità dei gameti femminili, gli ovociti.
Lo scopo di questo lavoro è l’osservazione approfondita, tramite microscopia ottica e microscopia elettronica a trasmissione, dei tratti morfologici che caratterizzando l’invecchiamento ovocitario, sia nel processo fisiologico dell’invecchiamento riproduttivo (reproductive aging, RA), sia nel corso dell’invecchiamento in vitro (in vitro aging, IvA).
Lo studio è stato condotto su 61 ovociti maturi (MII) soprannumerari donati alla ricerca, previa firma di un consenso informato e secondo le leggi vigenti, da 23 pazienti che si sono sottoposte a trattamenti di fecondazione assistita (IVF o ICSI) nel periodo compreso tra Ottobre 2007 e Luglio 2013. I trattamenti sono stati eseguiti presso la UOC OGC03 - Infertilità e FIVET (Prof. C. Aragona) del DAI (Dipartimento di Attività Integrata) di Ginecologia e Ostetricia, Perinatologia e Puericultura (Prof Pierluigi Benedetti Panici) dell’Azienda Policlinico Umberto I, Università “Sapienza” di Roma (DU -Dipartimento Universitario- di Scienze Ginecologico-ostetriche e Scienze Urologiche, Prof Vincenzo Gentile)
Gli ovociti sono stati suddivisi in due gruppi in base all’età delle pazienti: A (età inferiore a 35 anni, 25 ovociti) e B (età uguale o superiore ai 35 anni, 36 ovociti). Un totale di 31 ovociti (13 ovociti nel gruppo A e 18 del gruppo B) sono stati fissati poco dopo il pick up (tempo 0); i rimanenti 30 (12 nel gruppo A e 18 del gruppo B) sono stati fissati dopo 24 ore di coltura.
La successiva analisi di microscopia ottica ed elettronica è stata condotta presso la UO Microscopia elettronica (Prof. Giuseppe Familiari), sezione di Anatomia Umana (Prof. E. Gaudio) del Dipartimento di Scienze Anatomiche, Istologiche, Medico Legali e dell’Apparato Locomotore (Prof. Elio Ziparo) dell’Università “Sapienza” di Roma. Tale analisi è stata condotta in collaborazione con la sezione di Anatomia (Prof. Guido Macchiarelli) del Dipartimento di Scienze della Salute dell’Università degli studi dell’Aquila.
I gruppi in esame erano perciò i seguenti:
• gruppo <35: ovociti MII all’aspirazione di donne con età inferiore a 35 anni
• gruppo <35c: ovociti MII coltivati per 24 h di donne con età inferiore a 35 anni
• gruppo ≥35: ovociti MII all’aspirazione di donne con età uguale o superiore a 35 anni
• gruppo ≥35c: ovociti MII coltivati per 24 h di donne con età uguale o superiore a 35 anni
Per la valutazione della preservazione strutturale (microscopia ottica) e ultrastrutturale (microscopia elettronica a trasmissione) degli ovociti sono stati presi in considerazione diversi parametri morfologici; l’analisi statistica si è concentrata su 5 di essi
- spessore della zona pellucida (zona pellucida thickness, ZPt)
- numero di granuli corticali (cortical granules, CG) per 10 um di superficie lineare
- numero di microvilli (Mv) per 10 um di superficie lineare
- densità degli aggregati di mitocondri e tubuli di reticolo endoplasmatico liscio (mitochondria-smooth endoplasmic reticulum aggregates, M-SER) per 10 um2 di area citoplasmatica
- densità dei complessi di mitocondri e vescicole di reticolo endoplasmatico liscio (mitochondria-vesicle complex, MVC) per 10 um2 di area citoplasmatica
Gli ovociti del gruppo <35 mostrano le caratteristiche ultrastrutturali tipiche degli ovociti MII ideali: MVC piccole e scarsamente rappresentate (densità 0,35±0,26 per 10um2) ed aggregati M-SER ben rappresentati (densità 2,89±0,68 per 10um2), una quantità adeguata di CGs e di Mv (rispettivamente 11±1,41 e 11,18±1,54 per 10um). Lo spessore medio della ZP era 18,32±1,93um.
Negli ovociti del gruppo <35c si osserva un aumento della densità di MVC (1,31±0,36 per 10um2) ed una contemporanea riduzione dei complessi M-SER (1,80±0,35 per 10um2) e, in misura più lieve, dei CG e dei Mv (rispettivamente 11±1,41 e 11,18±1,54 per 10um). Lo spessore medio della ZP era 18,27±1,74um.
Neli ovociti del gruppo ≥35 i MCV sono presenti in numero maggiore (densità 2,05±0,48 per 10um2), i complessi M-SER sono scarsi (0,97±0,28 per 10um2) e si osserva una ulteriore riduzione dei CG e dei Mv (rispettivamente 7,45±1,37 e 6±1 per 10um). Lo spessore medio della ZP era 21,73±1,79um.
Negli ovociti del gruppo ≥35c si osserva un aumento notevole della densità dei MVC (3,19±0,40 per 10um2) e una marcata diminuzione dei complessi M-SER (0,57±0,31 per 10um2). Si osserva anche una riduzione della quantità di CG e di Mv (rispettivamente 2,55±1,37 e 4,73±1,13). Lo spessore medio della ZP era 21,55±1,57um.
Rispetto agli ovociti di “controllo”, appartenenti al primo gruppo (<35), le variazioni numeriche mostrano dunque un andamento graduale, essendo minime nel gruppo <35c, più evidenti nel gruppo ≥35 e molto accentuate nel gruppo ≥35c.
In conclusione, gli ovociti invecchiati in vitro e quelli invecchiati in vivo condividono molte caratteristiche ultrastrutturali tipiche che possono essere considerate markers morfologici di invecchiamento. Inoltre i dati presentati in questo lavoro rivelano che gli ovociti di donne giovani sembrano meno sensibili all’invecchiamento in vitro rispetto a quelli di donne in età avanzata, già soggetti a invecchiamento riproduttivo. Questi ultimi ovociti sembrano subire un invecchiamento in vitro prematuro, che potrebbe spiegare la loro ridotta finestra di fecondazione e la minore competenza di sviluppo
Ricerca indiretta di materia oscura dal Centro Galattico con il telescopio Cherenkov sottomarino per neutrini ANTARES
No full textIn recent years Dark Matter has become one of the major research topics in astrophysics. In one of the most popular scenario the Dark Matter is composed of WIMPs. These particles are present in massive astrophysical onbjects like the Galactic Centre and here they self-annihilate producing Standard Model particles that eventually decay producing neutrinos. In this thesis work we performed an indirect search for Dark Matter trying to detect these neutrinos with the aim of the ANTARES submarine Cherenkov neutrino telescope. The analysis and the results of this research are here presented
Observational constrains on the chemical evolution of high redshift galaxies through 3D spectroscopy.
No full textIn this thesis I investigate the properties of 34 star forming galaxies at z ~3.4, by exploiting data
obtained with the VLT near-infrared integral field spectrometer SINFONI. By using the SINFONI
spectra, along with multi-band photometric images, I investigate the metal content, dynamics and
star formation in these galaxies.
One of the most important results is that z~ 3.4 galaxies deviate from the scaling relations between
mass, star formation rate and metallicity characterizing local and low redshift galaxies (z<2), in the
sense that galaxies at z>3 are characterized by metallicities significantly lower. This deviation
occurring only at z>3 must trace a different galaxy evolutionary mechanism in place at such early
epochs, with respect to galaxies at 0<z<2. However, I show that the deviation from the local scaling
relations is not associated with dynamics of the host galaxy (rotating disks and mergers/interacting
galaxies deviate by the same amount), hence an increased rate of merging cannot be responsible for
such deviations.
By using the integral field spectroscopic information I could map the metallicity in a subsample of
10 galaxies at z ~3.4. These are among the first metallicity gradients measured at such high redshift.
We find that a significant fraction of galaxies are characterized by inverted (positive) metallicity
gradients, i.e. the metallicity increases towards the outer regions, in contrast to what observed locally.
Also for what concerns the metallicity gradients, I found that the occurrence of inverted gradients
is not correlated with the galaxy dynamical properties. A more detailed investigation reveals that
the metallicity anticorrelates with the star formation rate, which peaks in the central region of
galaxies. This result supports the models of smooth gas inflows feeding galaxies at high redshift. In
this scenario the pristine infall both boosts star formation (through the Schmidt-Kennicutt law) and
dilutes the metallicity, generating the observed anti-correlation.
By mapping the distribution of the star formation, and by inverting the Schmidt-Kennicutt relation,
I could also infer the distribution and total content of molecular gas in these z~ 3 galaxies. I found evidence
that the average gas fraction in galaxies at z>3 does not follow the steep increasing evolution
from z=0 to z ~2. Between z~ 2 and z~ 3 the average gas fraction in galaxies remains constant or,
possibly, even decreases. Our findings are marginally consistent with the models expectations on the
evolution of the gas content in galaxies and further support the scenario that the evolution of cosmic
star formation in galaxies is primarily driven by the evolution of the amount of gas in galaxies, and
not by an evolution in the efficiency of star formation.
By combining the information on the gas content and on the metallicity I could infer the galaxy
properties can only be explained by a combination of massive inflows and massive outflows, both
of which a factor of few to several higher than in the host galaxy. Such massive flows in the early
universe are likely responsible for the different properties and deviations of galaxies at z 3 relative
to local and low redshift galaxies.
I further explore the physical mechanisms driving galaxy formation and evolution by comparingmy
observational results with detailed semi-analytical models and cosmological simulations specifically
developed, in collaboration with other teams, to trace the metallicity evolution and distribution in
early galaxies.This work was funded by the Marie Curie Initial Training Network ELIXIR of the European Commission
under contract PITN-GA-2008-214227
