1,720,993 research outputs found
The CLAS12 RICH readout electronics: design, development and test
No full textUna delle pi\`u importanti strutture al mondo per lo studio della natura su scala nucleare e subnucleare \`e il Laboratorio Thomas Jefferson, situato in Virginia negli Stati Uniti d'America (JLAB), il quale ha recentemente rinnovato il suo acceleratore di elettroni (CEBAF, Continuous Electron Beam Accelerator) per raggiungere l'energia di 12 GeV/c.
Il principale obiettivo del CEBAF e delle sue quattro sale sperimentali \`e quello di descrivere come le propriet\`a stabili della materia nucleare, quali lo spin semi-intero dei nucleoni, possano essere spiegate in termini dei gradi di libert\`a dei suoi costituenti quali quark e gluoni.
Un innovativo rivelatore ad anelli cherenkov (RICH) \`e stato progettato per lo spettrometro di larga accettanza del CEBAF (CLAS12) allo scopo di migliorare l'identificazione adroni carichi presenti nello stato finale delle degli esperimenti di diffusione e contribuire cos\'i alla complessa rappresentazione multidimensionale del modello attuale.
La tesi descrive l'apparato basilare di CLAS12 dedito alla identificazione delle particelle e presenta il nuovo RICH insieme alla sua struttura e ai suoi principi di funzionamento. La trattazione mette in evidenza gli aspetti tecnologici innovativi, adottati per soddisfare i requisiti di fisica in modo affidabile, ad un costo accettabile e in tempi compatibili con le operazioni gi\`a calendarizzate.
In particolare si sofferma su raffinate valvole fotomoltiplicatrici multianodiche sensibili al singolo fotone (MAPMT) e sulla elettronica di lettura loro associata che \'e stata appositamente sviluppata nell'ambito della progetto di tesi e la cui validazione ha costituito la maggior mole del lavoro.
La descrizione dei circuiti di processamento del segnale, sia analogici che digitali, precede la presentazione delle funzionalit\`a del sistema e la descrizione di come questo sar\`a integrato nella sofisticata architettura di acquisizione dati di CLAS12.
Le prove condotte su banco con generatori di impulsi dimostrano una eccellente sensibilit\`a per segnali la cui ampiezza sia grande solo qualche percento di quella del segnale medio corripondente al singolo fotone. Inoltre sono state utili a sviluppare gli algoritmi di correzione della risposta temporale la cui precisione pu\`o raggiungere il nanonsecondo sull'intero intervallo in carica prodotto dai sensori.
Ulteriori prove con i MAPMT ed una sorgente laser hanno permesso di verificare le prestazioni dell'intera catena, consentito di ottimizzare le procedure e di portare a compimento lo sviluppo della libreria software.
I risultati ottenuti dimostrano la capacit\`a del sistema di accedere alla fenomenologia dei sensori con grande dettaglio (e.g. il crosstalk ottico ovvero la separazione della valanga elettronica tra pixel vicini). Tali peculiari\`a saranno sfruttate durante il ciclo di vita dell'esperimento per controllare lo stato del rivelatore e calibrare i parametri di configurazione utilizzando anche le emissioni termiche dette correnti di buio.
Gli argomenti sono presentati con ordine di complessit\`a crescente con l'ultima parte della tesi dedicata alle prove in condizioni reali. I risultati della campagna di validazione condotta per stabilire la tolleranza alle radiazione delle schede elettroniche cos\'i come i veri e propri esperimenti realizzati con prototipi del RICH di piccola scala sono presentati alla fine.
In conclusione la elettronica sviluppata per il nuovo RICH di CLAS12 \`e stata progettata, realizzata e validata per il suo scopo. Le sue caratteristiche di compattezza, sensibilit\`a e precisione temporale sono potenzialmente interessanti per altre applicazione di imaging in settori diversi quali lo sviluppo di nuovi rivelatori e la medicina nucleare.One of the world leading facilities for the study of nature at nuclear and sub-nuclear scales is the Thomas Jefferson Laboratory in Virginia, USA (JLAB) where the Continuous Electron Beam Accelerator Facility (CEBAF) has been recently upgraded to reach 12 GeV energy.
The main objective of CEBAF and its four experimental halls is to investigate how the stable properties of the matter, like the semi-integer spin of the nucleons, can be explained in terms of degrees of freedom of its constituents, quarks and gluons.
An innovative Ring Imaging Cherenkov detector (RICH) has been designed for the CEBAF Large Acceptance Spectrometer (CLAS12) to improve the identification of the charged hadrons produced in the final state of scattering experiments and help in the representation of the complex multi-dimensional structure of the current model.
The thesis describes the CLAS12 baseline particle identification system and introduces the new RICH module together with its layout and its operating principles.
The dissertation highlights the innovative technological aspects adopted to satisfy the physics requirements at a reasonable cost, in a timely manner and to fit in spectrometer with minimum impact.
In particular the thesis treats the single photon sensitive Multi Anode PhotoMultiplier Tubes (MAPMT) and associated custom electronics that has been developed in the thesis project and whose validation has constituted the largest effort of the thesis work.
The description of the analog and digital signal processing circuits proceeds the presentation of the functionalities of system the description of its integration in the CLAS12 data acquisition architecture.
The tests conducted on bench with pulse generators demonstrate an excellent sensitivity for signal of amplitude just a few percent of the typical photoelectron signal.
Moreover they have been used to develop time response correction algorithms that allow to achieve one nanosecond precision over the entire charge interval spanned by the light sensor output.
Further tests with MAPMTs and a laser source allowed to verify the full chain performance, optimize the procedures and complete the development of the software library.
The obtained results demonstrate the capability of the system to access the detector phenomenology with great detail (e.g. optical crosstalk which is the charge spill over between adjacent pixels). Those peculiarities will be exploited during the life cycle of the experiment to monitor the status of the detector and calibrate the configuration parameters using the dark current of the tubes.
The argument are presented in increasing complexity order with the last part dedicated to real condition testing. The results of the validation campaign conducted to asses the radiation tolerance of the electronics board as well the as small scale complete experiment with RICH prototypes are presented in the end.
In conclusion the readout electronics of the new RICH of CLAS12 was designed, implemented and validate for its scope. For its compactness, sensitivity and time resolution it can be potentially interesting for other imaging application like the development of new detectors and nuclear medicine
Cherenkov light imaging tests with state-of-the-art solid state photon counter for the CLAS12 RICH detector
No full textA large area ring-imaging Cherenkov detector will be operated for hadron identification in the 3GeV/c to 8GeV/c momentum range at the CLAS12 experiment at the upgraded continuous electron beam accelerator facility of Jefferson Lab. The detector, consisting of aerogel radiator, composite mirrors and photon counters, will be built with a hybrid optics design to allow the detection of Cherenkov light for both forward and large angle hadron tracks. The active area has to be densely packed and highly segmented, covering about 1m2 with pixels of 6mm2, and to allow a time resolution of 1. ns. A technology that can offer a cost-effective solution and low material budget could be Silicon Photomultipliers (SiPM) thanks to their high gain at low bias voltage, fast timing, good single-photoelectron resolution and insensitivity to magnetic fields. An investigation is ongoing on samples of 3×3mm2 SiPM of different micro-cell size to assess the single photon detection capability in the presence of high dark count rate due to thermal generation effects, after-pulses or optical cross-talk and to study the response to the moderate radiation damage expected at CLAS12. In this work, a brief review of the latest and most interesting results from these studies will be shown
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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