The BLAST Survey of the Vela Molecular Cloud: Dynamical Properties of the Dense Cores in Vela-D

The Vela-D region, according to the nomenclature given by Murphy & May (1991), of the star forming complex known as the Vela Molecular Ridge (VMR), has been recently analyzed in details by Olmi et al. (2009), who studied the physical properties of 141 pre- and proto-stellar cold dust cores, detected by the ``Balloon-borne Large-Aperture Submillimeter Telescope'' (BLAST) during a much larger (55 sq. degree) Galactic Plane survey encompassing the whole VMR. This survey's primary goal was to identify the coldest, dense dust cores possibly associated with the earliest phases of star formation. In this work, the dynamical state of the Vela-D cores is analyzed. Comparison to dynamical masses of a sub-sample of the Vela-D cores estimated from the 13CO survey of Elia et al. (2007), is complicated by the fact that the 13CO linewidths are likely to trace the lower density intercore material, in addition to the dense gas associated with the compact cores observed by BLAST. In fact, the total internal pressure of these cores, if estimated using the 13CO linewidths, appears to be higher than the cloud ambient pressure. If this were the case, then self-gravity and surface pressure would be insufficient to bind these cores and an additional source of external confinement (e.g., magnetic field pressure) would be required. However, if one attempts to scale down the 13CO linewidths, according to the observations of high-density tracers in a small sample of sources, then most proto-stellar cores would result effectively gravitationally bound.Comment: This paper has 12 pages and 6 figures. Accepted for publication by the Astrophysical Journal on July 19, 201

The Doherty Power Amplifier

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SVILUPPO DI METODI DECONVOLUTIVI PER L’INDIVIDUAZIONE DI SORGENTI INDIPENDENTI SU DATI DI RISONANZA MAGNETICA FUNZIONALE

La tecnica di risonanza magnetica funzionale per immagini (fMRI) è un metodo non invasivo per determinare la distribuzione spaziale e temporale dell’attività cerebrale indotta da compiti sensori, motori e cognitivi. Nel contesto dell’analisi dei dati fMRI, grande sviluppo ha avuto e sta avendo, la tecnica della separazione delle sorgenti nascoste (Blind Source Separation) che, a partire dai segnali misurati, ricerca le sorgenti che li hanno generati nell’ipotesi che queste ultime siano statisticamente indipendenti. Sotto questa forma il metodo prende il nome di Analisi delle Componenti Indipendenti (ICA) e si differenzia dai classici procedimenti di analisi basati sulla regressione, la correlazione o la sottrazione di immagini per il fatto che nessuna ipotesi a priori è necessaria se non quella sull’indipendenza statistica delle sorgenti. Il modello base utilizzato nell’analisi delle componenti indipendenti, come in altri metodi di analisi multivariata, considera i segnali osservati come derivati dal mescolamento istantaneo delle varie sorgenti. Nel caso di dati di risonanza magnetica funzionale, questo modello può risultare inadeguato visto che lo stesso processo cognitivo può generare, in diverse aree cerebrali, variazioni del segnale con una differente dinamica temporale; questo può essere dovuto sia ad una diversa attività neurale, ma anche alla eterogeneità della risposta emodinamica. L’attivazione di due o più voxel (elementi volumetrici di base in cui è suddivisa l’immagine acquisita) che sovrintendono alle medesime funzioni, può risultare ad esempio reciprocamente ritardata a causa dell’inevitabile latenza dei processi emodinamici di base. Tale ritardo si traduce nell’acquisizione di segnali sfasati tra loro e difficilmente identificabili tramite un criterio multivariato istantaneo. In questa tesi presentiamo un approccio al problema di BSS basato su un modello di mescolamento convolutivo: ogni segnale osservato, è generato da sorgenti statisticamente indipendenti, mescolate tra loro dopo aver subito un processo di convoluzione. Questo tipo d’orientamento permette di estendere il modello istantaneo in modo da tenere conto delle differenze in ampiezza, latenza e durata del segnale fMRI nelle varie regioni. L’obiettivo di questa tesi è verificare la bontà del modello convolutivo nel caso di segnali fMRI con le caratteristiche sopradette. Nel primo capitolo di questo elaborato vengono presentati i principi fisici da cui deriva il segnale fMRI e le sue caratteristiche specifiche ed essenziali. Particolare attenzione è riservata alla relazione con la risposta emodinamica cerebrale, alla risoluzione spazio-temporale e alle possibili fonti di rumore che complicano l’acquisizione dei dati. Infine viene proposto un modello lineare della risposta fMRI utile a quantificare la risposta neurale indotta da stimolazioni sensoriali e quindi a valutare l’attivazione di corrispondenti zone cerebrali. Il capitolo secondo introduce i concetti fondamentali della teoria dell’ottimizzazione e dei metodi basati sul gradiente che sono alla base degli algoritmi di separazione delle sorgenti nascoste (BSS). In particolare viene proposta una possibile generalizzazione del metodo del gradiente, applicata a spazi non euclidei. Il capitolo terzo copre il classico problema dell’individuazione e separazione delle sorgenti nascoste, riferendosi in particolare all’ipotesi che queste ultime siano statisticamente indipendenti (ICA). E’ esposto il principio base della non-gaussianità e la sua relazione con l’ICA. Sono rivisti i principi della mutua informazione e della Neg-Entropia unitamente alle relazioni tra questi tre principi fondamentali. Nel quarto capitolo è esposto in maniera dettagliata il problema del mescolamento convolutivo, in cui le sorgenti indipendenti subiscono un processo di filtraggio non più modelizzabile con una semplice matrice scalare. Vengono inoltre presentati una serie di approcci al problema sia in ambito temporale sia in quello frequenziale allo scopo di deconvolvere e separare le sorgenti indipendenti. La traduzione dei concetti teorici in algoritmi pratici per la stima del modello convolutivo sia nel tempo che in frequenza è presentata nel quinto capitolo. L’analisi e l’applicazione, degli algoritmi sviluppati, a segnali fMRI simulati riguarda il contenuto del sesto capitolo; lo scopo è di testarne le potenzialità nel deconvolvere le componenti indipendenti. Il processo convolutivo viene modellizzato tramite l’uso di filtri FIR con i quali è possibile tenere conto delle differenti dinamiche del segnale. Il settimo ed ultimo capitolo, invece, tratta l’applicazione a dati reali acquisiti nel laboratorio di risonanza magnetica dell’Istituto di Fisiologia Clinica del Consiglio Nazionale delle Ricerche di Pisa. Si espongono quindi i risultati ottenuti e si traggono le conclusioni del lavoro svolto. Le elaborazioni svolte sono state effettuate in ambiente Matlab 6.5 della MathWorks

The Spitzer-IRAC Point Source Catalog of the Vela-D Cloud

This paper presents the observations of the Cloud D in the Vela Molecular Ridge, obtained with the IRAC camera onboard the Spitzer Space Telescope at the wavelengths \lambda = 3.6, 4.5, 5.8, 8.0 {\mu}m. A photometric catalog of point sources, covering a field of approximately 1.2 square degrees, has been extracted and complemented with additional available observational data in the millimeter region. Previous observations of the same region, obtained with the Spitzer MIPS camera in the photometric bands at 24 {\mu}m and 70 {\mu}m, have also been reconsidered to allow an estimate of the spectral slope of the sources in a wider spectral range. A total of 170,299 point sources, detected at the 5-sigma sensitivity level in at least one of the IRAC bands, have been reported in the catalog. There were 8796 sources for which good quality photometry was obtained in all four IRAC bands. For this sample, a preliminary characterization of the young stellar population based on the determination of spectral slope is discussed; combining this with diagnostics in the color-magnitude and color-color diagrams, the relative population of young stellar objects in the different evolutionary classes has been estimated and a total of 637 candidate YSOs have been selected. The main differences in their relative abundances have been highlighted and a brief account for their spatial distribution is given. The star formation rate has been also estimated and compared with the values derived for other star forming regions. Finally, an analysis of the spatial distribution of the sources by means of the two-point correlation function shows that the younger population, constituted by the Class I and flat-spectrum sources, is significantly more clustered than the Class II and III sources.Comment: Accepted by Ap

Near- and Far-Infrared Counterparts of Millimeter Dust Cores in the Vela Molecular Ridge Cloud D

The aim of this paper is to identify the young protostellar counterparts associated to dust millimeter cores of the Vela Molecular Ridge Cloud D through new IR observations (H_2 narrow-band at 2.12 micron and N broad band at 10.4 micron) along with an investigation performed on the existing IR catalogues. The association of mm continuum emission with infrared sources from catalogues (IRAS, MSX, 2MASS), JHK data from the literature and new observations, has been established according to spatial coincidence, infrared colours and spectral energy distributions. Only 7 out of 29 resolved mm cores (and 16 out of the 26 unresolved ones) do not exhibit signposts of star formation activity. The other ones are clearly associated with: far-IR sources, H_2 jets or near-IR objects showing a high intrinsic colour excess. The distribution of the spectral indices pertaining to the associated sources is peaked at values typical of Class I objects, while three objects are signalled as candidates Class 0 sources. We remark the high detection rate (30%) of H_2 jets driven by sources located inside the mm-cores. They appear not driven by the most luminous objects in the field, but rather by less luminous objects in young clusters, testifying the co-existence of both low- and intermediate-mass star formation. The presented results reliably describe the young population of VMR-D. However, the statistical evaluation of activity vs inactivity of the investigated cores, even in good agreement with results found for other star forming regions, seems to reflect the limiting sensitivity of the available facilities rather than any property intrinsic to the mm-condensations.Comment: 38 pages. To be published to Astronomy & Astrophysic

Layered double hydroxides with low Al content and new intercalate structures

Layered double hydroxides (LDHs) containing Mg2+ and Al3+ as divalent and trivalent cations, respectively, have been synthesized by a procedure based on hydrolysis of a mixture of metal alcoholates, and have been characterized mainly by Wide Angle X-ray diffraction (WAXD) and Fourier Transform Infrared (FTIR) measurements. The used procedure is suitable to prepare LDHs with Al molar fractions, x(Al)=Al/(Al+Mg), as low as 0.1. The same LDH preparation procedure, for x(Al)<0.1, produces thermally stable intercalates with alkoxy anions, exhibiting layers similar to those of brucite, which maintain a high degree of order only in the hexagonal packing of the hydroxide groups. In particular, the basal periodicity increases from nearly 0.8 nm up to nearly 1.3 nm, due to the parallel staking of hexanolate groups in the clay galleries. (C) 2012 Elsevier B.V. All rights reserved

Spitzer-IRAC survey of molecular jets in Vela-D

We present a survey of H2 jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer -IRAC data between 3.6 and 8.0 micron. Our search has led to the identification of 15 jets and about 70 well aligned knots within 1.2 squared degree. We compare the IRAC maps with observations of the H2 1-0 S(1) line at 2.12 micron, with a Spitzer-MIPS map at 24 and 70 micron, and with a map of the dust continuum emission at 1.2 mm. We find a association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the Young Stellar Objects of VMR-D. We selected all the sources of Class II or earlier which are located close to the jet center and aligned with it.The association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 micron, suggesting they are very young protostars. Three of them are also associated with the most compact jets. The exciting source Spectral Energy Distributions have been modeled by means of the photometric data between 1.2 micron and 1.2 mm. From SEDs fits we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24] - [70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.Comment: Accepted by The Astrophysical Journa

Assessing Social Anxiety Disorder : Psychometric Properties of the Italian Social Phobia Inventory (I-SPIN)

Social Phobia, one of the most common psychological disorders, can cause serious discomfort and impairment in a person’s life. The importance of assessing the specific features of this disorder is well-known. This paper assesses the psychometric properties of the Italian version of the Social Phobia Inventory (I-SPIN)

Performance of a fully automatic lesion detection system for breast DCE-MRI

PURPOSE: To describe and test a new fully automatic lesion detection system for breast DCE-MRI. MATERIALS AND METHODS: Studies were collected from two institutions adopting different DCE-MRI sequences, one with and the other one without fat-saturation. The detection pipeline consists of (i) breast segmentation, to identify breast size and location; (ii) registration, to correct for patient movements; (iii) lesion detection, to extract contrast-enhanced regions using a new normalization technique based on the contrast-uptake of mammary vessels; (iv) false positive (FP) reduction, to exclude contrast-enhanced regions other than lesions. Detection rate (number of system-detected malignant and benign lesions over the total number of lesions) and sensitivity (system-detected malignant lesions over the total number of malignant lesions) were assessed. The number of FPs was also assessed. RESULTS: Forty-eight studies with 12 benign and 53 malignant lesions were evaluated. Median lesion diameter was 6 mm (range, 5-15 mm) for benign and 26 mm (range, 5-75 mm) for malignant lesions. Detection rate was 58/65 (89%; 95% confidence interval [CI] 79%-95%) and sensitivity was 52/53 (98%; 95% CI 90%-99%). Mammary median FPs per breast was 4 (1st-3rd quartiles 3-7.25). CONCLUSION: The system showed promising results on MR datasets obtained from different scanners producing fat-sat or non-fat-sat images with variable temporal and spatial resolution and could potentially be used for early diagnosis and staging of breast cancer to reduce reading time and to improve lesion detection. Further evaluation is needed before it may be used in clinical practice