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SuperAGILE: an X-Ray monitor for a gamma mission
Full text linkLa Tesi di Dottorato di Ricerca, svolta all’IASF CNR/INAF di Roma sotto la supervisione del dott. Enrico Costa, contiene lo studio delle prestazioni scientifiche dello strumento SuperAGILE. SuperAGILE è il monitor a raggi X di AGILE, missione su satellite dell’ASI composta da due strumenti, sensibili rispettivamente nelle bande di energia 15-40 keV e 30 MeV-50 GeV, il cui lancio è previsto per la fine del 2005. SuperAGILE è uno strumento a maschera codificata, con rivelatore a microstrip di silicio e maschera di tungsteno.
Oggetto della mia Tesi di Dottorato è lo studio delle prestazioni scientifiche di SuperAGILE e delle più importanti criticità dello strumento: misura dell’uniformità delle prestazioni del circuito XAA1.2 dell’elettronica di lettura, della sua stabilità termica e della stabilità per variazioni della tensione di alimentazione, studio dell’interazione dei raggi cosmici nel circuito con misure sperimentali e stima del flusso aspettato in orbita, misura delle prestazioni scientifiche del modello da volo di SuperAGILE e, infine, studio dell’effetto della disuniformità di soglia sulle immagini.
Le misure dell’uniformità di prestazioni dell’XAA1.2, della stabilità termica (tra –20° C e +40° C) e della stabilità per variazioni della tensione di alimentazione si effettuano con una scheda di acquisizione dedicata e stimolando il circuito per mezzo di un generatore di impulsi di tensione all’interno della scheda. Dalle misure si trova una variazione dei segnali di indirizzo dell’XAA1.2 (fondamentali per ricostruire le immagini delle sorgenti in Cielo) sulla scala dei 10° C.
Lo studio dell’effetto dell’interazione dei raggi cosmici nel circuito, non progettato per applicazioni spaziali, riguarda il latch-up (aumento delle correnti di alimentazione che può danneggiare il chip per surriscaldamento) e il SEU (variazione di un bit nella memoria con perdita di programmazione) e l’effetto della dose assorbita sulla linearità e sul consumo. La misure sperimentali sono state effettuate irraggiando l’XAA1.2 con ioni (da 16O a 197Au) all’esperimento dedicato SIRAD dell’acceleratore Tandem nei Laboratori Nazionali INFN di Legnaro presso Padova. Al variare del LET, che misura l’energia per unità di lunghezza rilasciata dalle particelle cariche nel silicio, si misura la sezione d’urto di latch-up e SEU. Ad intervalli regolari si effettuano misure di linearità con l’impulso di calibrazione per studiare l’effetto della dose. Stimando il flusso di ioni in orbita con il codice CREME96 e usando un modello approssimato che tiene conto della spallazione dei protoni, ho trovato che il tasso aspettato di latch-up e SEU in orbita è minore di un evento per tutta la durata di AGILE e che l’effetto della dose assorbita è trascurabile.
La Tesi di Dottorato contiene anche la caratterizzazione del modello da volo di SuperAGILE, che consiste nel misurare con l’impulso di carica la linearità e il rumore dell’elettronica di lettura dopo il montaggio degli XAA1.2, dopo la procedura di burn-in (accensione della scheda programmata in configurazione nominale all’interno di un forno a 75° C per 240 ore consecutive) e dopo l’integrazione del rivelatore. Dalle misure si trova che il burn-in non produce variazioni di prestazioni e che, dopo il montaggio del rivelatore, il rumore dell’elettronica di lettura è pari a circa 7.5 keV FWHM mentre l’energia di soglia è circa 19 keV. Il rumore dell’elettronica è stato misurato anche tramite l’acquisizione di sorgenti di raggi X (241Am, 57Co, 109Cd e righe di fluorescenza del Ba) e i valori trovati sono in buon accordo con le misure con l’impulso di carica.
La Tesi contiene anche la discussione delle principali problematiche affrontate durante la scrittura di programmi per l’analisi dei dati raccolti in laboratorio. A causa del gran numero di pixel del rivelatore di SuperAGILE, infatti, la linearità e il rumore (sia con impulso di carica che con sorgenti di raggi X) devono essere stimate in modo automatico, senza l’immissione di parametri dall’utente.
Infine, ho stimato l’effetto della disuniformità dell’energia di soglia sulle immagini di SuperAGILE generando immagini del fondo sul rivelatore, applicando diversi modelli di disuniformità di soglia e decodificando le immagini del cielo. Mentre l’attuale livello di uniformità di soglia non è sufficiente per poter osservare sorgenti deboli con integrazioni dell’ordine di 106 s, l’equalizzazione fine digitale delle soglie del circuito, tramite un DAC a 3 bit, permette di ottenere una uniformità sufficiente per poter effettuare osservazioni per 106 s.The Ph.D. Thesis, performed at IASF CNR/INAF in Rome under the supervision of dr. Enrico Costa, contains the study of the scientific performances of the SuperAGILE instrument. SuperAGILE is the X-ray monitor of AGILE, satellite-borne mission of ASI whose payload is composed of two instruments, sensitive in the 15-40 keV and 30 MeV-50 GeV energy bands respectively, and whose launch is foreseen in late 2005. SuperAGILE is a coded aperture instrument with silicon microstrip detector and tungsten coded mask.
Topic of my Ph.D. Thesis is the study of the SuperAGILE scientific performances and criticalities: measurement of the performances uniformity of the XAA1.2 front-end electronic circuit, of its thermal stability and of its stability toward supply voltage variations, study of the cosmic rays interaction in the front-end circuit with experimental measurements and estimate of the expected flux in orbit, measurements of the scientific performances of the SuperAGILE flight model and finally study of the impact of the threshold non uniformity on the images.
The measurements of the performances uniformity of the XAA1.2, of its thermal stability (between –20° C and +40° C) and of the stability toward supply voltage variations are performed using a dedicated acquisition board feeding the chip with a pulse generator contained in the board. From the measurements a variation of the XAA1.2 address signals (used to reconstruct the images of the sources in the Sky) on the 10° C scale is found.
The study of the effect of the cosmic rays interaction in the XAA1.2 chip, that is not designed as a radiation hard component for space applications, concerns the latch-up (sudden increase of the supply currents that can damage the chip due to overheating) and the SEU (bit flip in the memory registers with loss of chip configuration) and the effect of the absorbed dose on the linearity and power consumption. The measurements have been performed with ions irradiation (from 16O to 197Au) at the SIRAD facility of the Tandem accelerator in the Laboratori Nazionali INFN in Legnaro near Padova. With different values of LET, a measure of the energy released per unit length by the charged particles in silicon, the latch-up and SEU cross-section values are measured. During the irradiation linearity measurements using the test pulse generator are performed in order to study the total dose effect. Evaluating the ions flux in orbit with the CREME96 code and using an approximated model to take into account the proton spallation, I have found that the expected latch-up and SEU rate in orbit is less than one event during all the AGILE duration and that the total dose effect is negligible.
My Ph.D. Thesis contains also the characterization of the SuperAGILE flight model, performed measuring the linearity and the noise of the front-end electronics after the XAA1.2 integration, after the burn-in procedure (by supplying the board in nominal configuration inside an oven at 75° C for 240 hours long) and after the detector integration. From the measurements I have found no performance degradation after the burn-in procedure. After the detector integration the noise in the front-end electronic is about 7.5 keV FWHM while the energy threshold is about 19 keV. The noise in the front-end electronic has been measured also using X-ray sources (241Am, 57Co, 109Cd and Ba fluorescence lines) and the measured values are in good agreement with the test pulse measurements.
My Thesis contains also the discussion of the most important topics in the development of data analysis programs. Because of the big number of the SuperAGILE detector pixels, linearity and noise (using both test pulse generator and X-ray sources) need to be estimated automatically, without requiring the user to provide specific parameters.
Finally, the Thesis contains an estimate of the threshold non uniformity on SuperAGILE images by means of background detector images generation applying different non uniformity threshold models. By decoding the resulting Sky images I have found that, while the nominal threshold uniformity does not allow to observe faint sources with exposures of order 106 s, the uniformity level obtained with the digital fine threshold equalization (3 bit DAC), allows expose for 106 s long
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
In viaggio con la regina Cristina. Lettere di Orazio Del Monte e Cesare Macchiati (1667)
No full textEdizione commentata di 16 lettere scritte da Orazio Del Monte e dal protomedico Cesare Macchiati al cardinale Decio Azzolino giuniore durante il secondo viaggio in Svezia della regina Cristina (aprile-giugno 1667).</p
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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