59,607 research outputs found
Invoking Voids in the Archive
No full textThis is the author accepted manuscript. The final version is available from Camera Austria via the DOI in this recor
Optimizing Compton camera performance
No full textAmore realistic simulation approach is used to study the behavior of the Compton camera in
this thesis than previous studies to date. The Compton camera differs from gamma cameras
in that the collimator is replaced by a detector known as the ‘scatterer’. Gamma rays may be
Compton scattered in the scatterer and subsequently detected by an ‘absorber’ which is the
equivalent of the detector in a gamma camera. By measuring the energies and the positions
of the points on the scatterer and the absorber where the incident and scattered gamma rays
interacted with the detectors, an image of the source can be reconstructed. Because there is
no collimator present, the potential sensitivity of the Compton camera is much higher than
the gamma camera, resulting in reduced acquisition times.
Most of the work described in this thesis was done with the GEANT4 Monte Carlo
simulation software. GEANT4 has been proven to be very robust and efficient in modelling
physics problems of radiation transport and interactions with matter in complex geometries.
Four major studies are carried out to estimate and optimize the performance of this
novel equipment. The first study takes a look at the scatterer’s imaging parameters with
the aim of prescribing an optimal scatterer material and geometry. In the second study,
the contribution of the absorber to the overall Compton camera performance is evaluated,
considering detector material, interaction type and geometry. The third study explores the
limitations imposed by the detector energy threshold and dead time on the Compton camera
performance, using a simplified model of the general electronic architecture. An evaluation
of Compton camera for scintimammography was performed in the fourth study. For
this study, three dual-head Compton camera models (Si/CZT, Si/LaBr₃:Ce and Si/NaI(Tl)
Compton cameras) were simulated, and the effect of scintillation photons’ interactions with
the photomultipliers was implemented.
The results show that silicon of about 1 cm thickness would be adequate as the Compton
camera scatterer. Analyses suggest however, that the choice of silicon is not completely
flawless. Doppler broadening for this detector material contributes as much as 7.3 mm
and 2.4 mm to full-width-at-half-maximum (FWHM) image resolution at 140.5 keV and
511 keV respectively. On the other hand, detector spatial resolution which accounts for
the least image degradation at 140.5 keV is found to be the dominant degrading factor
at 511 keV, suggesting that the absorber parameters play major roles in image resolution
at higher diagnostic energies. Findings further suggest that cadmium zinc telluride (CZT)
would be themost suitable detector as the absorber since thematerial demonstrated the highest efficiency and least positioning error due to multiple interactions as well as good spatial
resolution. The inclusion of the energy threshold and detector dead time at 140.5 keV, reduced
the Compton camera detection efficiency by 48% and 17% respectively, but improved
the image resolution from 10.7 mm to 9.5 mm at the source-to-scatterer distance of 5 cm.
At 511 keV, the inclusion of these parameters reduced the efficiency by 6% and 13% respectively,
but made no significant difference on the camera resolution. For a challenging
detection case in scintimammography, 5 mm breast tumours of tumour/background uptakes
of 10:1 and 6:1 at 511 keV were used. The best signal-to-noise ratio (SNR) was attained
for the Si/CZT Compton camera model, with the SNR values of 12.2 and 5.3.
It is therefore envisioned that with an optimal camera geometry, improved reconstruction
technique and adequate filter algorithm, the combination of Si and CZT as the scatterer
and the absorber of the Compton camera would make a very promising imaging system for
nuclear medicine studies at higher gamma ray energies where the collimated SPECT systems
perform very poorly due to increased septal penetration. It is equally evident from the
studies that with improved technology, new detectors such as LaBr₃:Ce could replace the
traditional NaI(Tl) detector as imaging detectors
Il racconto arabo di oggi e di domani
No full textAnalisi degli sviluppi più recenti del racconto arabo, ambito nel quale si registra negli ultimi decesnni una continua sperimentazione, con il ricorso a una molteplicità di stili e di linguaggi.
Oggetto di studio è la creazione letteraria a partire dal XXI secolo, attraverso le voci di autori provenienti da tutti i paesi arabi
Automated camera ranking and selection using video content and scene context
No full textPhDWhen observing a scene with multiple cameras, an important problem to solve is to automatically
identify “what camera feed should be shown and when?” The answer to this question is of interest
for a number of applications and scenarios ranging from sports to surveillance. In this thesis we
present a framework for the ranking of each video frame and camera across time and the camera
network, respectively. This ranking is then used for automated video production. In the first stage
information from each camera view and from the objects in it is extracted and represented in a way
that allows for object- and frame-ranking. First objects are detected and ranked within and across
camera views. This ranking takes into account both visible and contextual information related to
the object. Then content ranking is performed based on the objects in the view and camera-network
level information. We propose two novel techniques for content ranking namely: Routing Based
Ranking (RBR) and Multivariate Gaussian based Ranking (MVG). In RBR we use a rule based
framework where weighted fusion of object and frame level information takes place while in MVG
the rank is estimated as a multivariate Gaussian distribution. Through experimental and subjective
validation we demonstrate that the proposed content ranking strategies allows the identification of
the best-camera at each time.
The second part of the thesis focuses on the automatic generation of N-to-1 videos based on the
ranked content. We demonstrate that in such production settings it is undesirable to have frequent
inter-camera switching. Thus motivating the need for a compromise, between selecting the best
camera most of the time and minimising the frequent inter-camera switching, we demonstrate that
state-of-the-art techniques for this task are inadequate and fail in dynamic scenes. We propose three
novel methods for automated camera selection. The first method (¡go f ) performs a joint optimization
of a cost function that depends on both the view quality and inter-camera switching so that a
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Abstract ii
pleasing best-view video sequence can be composed. The other two methods (¡dbn and ¡util) include
the selection decision into the ranking-strategy. In ¡dbn we model the best-camera selection
as a state sequence via Directed Acyclic Graphs (DAG) designed as a Dynamic Bayesian Network
(DBN), which encodes the contextual knowledge about the camera network and employs the past
information to minimize the inter camera switches. In comparison ¡util utilizes the past as well
as the future information in a Partially Observable Markov Decision Process (POMDP) where the
camera-selection at a certain time is influenced by the past information and its repercussions in
the future. The performance of the proposed approach is demonstrated on multiple real and synthetic
multi-camera setups. We compare the proposed architectures with various baseline methods
with encouraging results. The performance of the proposed approaches is also validated through
extensive subjective testing
Voci di scrittori arabi di oggi e di domani
No full textIl volume fornisce una panoramica sulla creazione letteraria a partire dall'inizio del XXI secolo fino ai giorni nostri, attraverso le voci di autori provenienti da Maghreb e Mashreq, dando spazio soprattutto alle letterature "emergenti", come quelle dei paesi del Golfo, della Mauritania e del Sudan
Nuove acquisizioni sull'aterosclerosi: placca vulnerabile
No full textNuove acquisizioni sull’aterosclerosi: la placca vulnerabile
Marina Camera
Dip. Scienze Farmacologiche, Università degli Studi di Milano e Centro Cardiologico Monzino IRCCS Milano.
L'aterosclerosi è una patologia infiammatoria, degenerativa, a lenta progressione, caratterizzata dalla presenza di placche aterosclerotiche che possono andare incontro a rottura. L’evento trombotico conseguente alla rottura della placca è responsabile degli eventi cardiovascolari, quali angina instabile, infarto del miocardio e ictus cerebrale.
Studi anatomo-patologici e clinici hanno ormai chiarito che il rischio di rottura è legato più alle caratteristiche istomorfologiche della placca che alle sue dimensioni e al grado di stenosi luminale che essa provoca. Placche instabili sono caratterizzate da un grosso core lipidico, un cappuccio fibroso sottile, un ricco infiltrato di cellule infiammatorie macrofagiche e scarse cellule muscolari lisce. Negli ultimi due decenni, particolare attenzione è stata rivolta al concetto di "placca vulnerabile" come strumento per migliorare la stratificazione del rischio cardiovascolare e per portare, potenzialmente, a nuove opzioni terapeutiche invasive e non per prevenire e curare la malattia cardiovascolare aterotrombotica. È inoltre ipotizzabile che nei prossimi anni le nuove tecniche di imaging ad alta risoluzione saranno in grado di individuare le caratteristiche fondamentali che definiscono una placca vulnerabile che rischia di rompersi. Per ogni placca aterosclerotica potrebbe quindi essere generato un sistema di valutazione finalizzato a valutare il rischio specifico di instabilità con lo scopo di identificare prospetticamente gli eventi coronarici acuti. Inoltre, l'associazione di specifiche informazioni morfologiche con marcatori sistemici di vulnerabilità potrebbe consentire, in un prossimo futuro, di prevedere il rischio reale di infarto miocardico acuto per ogni singolo paziente
More Accurate Pinhole Camera Calibration with Imperfect Planar Target
No full textThis paper presents a novel approach to camera calibration that improves final accuracy with respect to standard methods using precision planar targets, even if now inaccurate, unmeasured, roughly planar targets can be used. The work builds on a recent trend in camera calibration, namely concurrent optimization of scene structure together with the intrinsic camera parameters. A novel formulation is presented that allows maximum likelihood estimation in the case of inaccurate targets, as it extends the camera extrinsic parameters into a tight parametrization of the whole scene structure. It furthermore observes the special characteristics of multi-view perspective projection of planar targets. Its natural extensions to stereo camera calibration and hand-eye calibration are also presented. Experiments demonstrate improvements in the parametrization of the camera model as well as in eventual stereo reconstruction
A new camera for high-resolution infrared imaging of works of art
No full textA new camera – SIRIS (scanning infrared imaging system) – developed at the National Gallery in London allows high-resolution images to be made in the near infrared region (900–1700 nm). The camera is based on a commercially available 320 × 256 pixel indium gallium arsenide area array sensor. This relatively small sensor is moved across the focal plane of the camera using two orthogonal translation stages to give images of c. 5000 × 5000 pixels. The main advantages of the SIRIS camera over scanning infrared devices or sequential image capture and mosaic assembly are its comparative portability and rapid image acquisition – making a 5000 × 5000 pixel image takes less than 20 minutes. The SIRIS camera can operate at a range of resolutions; from around 2.5 pixels per millimetre over an area of up to 2 × 2 m to 10 pixels per millimetre when examining an area measuring 0.5 × 0.5 m. The development of the mechanical, optical and electronic components of the camera, including the design of a new lens, is described. The software used to control image capture and to assemble the individual frames into a seamless mosaic image is mentioned. The camera was designed primarily to examine underdrawings in paintings; preliminary results from test targets and paintings imaged in situ are presented and the quality of the images compared with those from other cameras currently used for this application
Biblioteca della Camera di Commercio a Palazzo Pallavicino, Genova
No full textLa nuova biblioteca della Camera di Commercio di Genova si colloca all’interno del palazzo Tobia Pallavicino, aggiungendosi al sistema di edifici per la cultura di strada nuova (tra cui i musei di Palazzo Bianco, Palazzo Rosso e Palazzo Doria Tursi, la sede del Municipio presso Palazzo Tursi). Per inserire i nuovi spazi nel complesso programma di eventi che si sviluppa all’interno di questo sistema, è necessario che la nuova biblioteca appaia come luogo accogliente, accessibile, pubblico. Per questo motivo la nuova biblioteca dovrà mostrarsi all’interno di palazzo Tobia Pallavicino con chiarezza, rendendo evidente il suo ruolo urbano, pur all’interno dell’edificio esistente.
Il sistema di strada nuova sembra suggerire una strategia di intervento, fornendo interventi esemplari, che possono guidare la nostra proposta per la nuova biblioteca. Nell’immediato dopoguerra infatti, di fronte alle rilevanti distruzioni causate dai bombardamenti, Franco Albini e Franca Helg intervengono nei musei di Palazzo Bianco e Palazzo Rosso, facendosi mediatori tra il pubblico, gli edifici storici e gli oggetti esposti. Albini ed Helg non intervengono sugli spazi, semplicemente li disseminano di segni ed oggetti che ne suggeriscono possibili usi, ne sottolineano rapporti spaziali, definendo così un nuovo insieme di possibili relazioni. Proponiamo di rimuovere il solaio che copre la sala centrale del piano fondi e costituisce l’attuale pavimento del cortile interno. Rimosso il solaio, si mostra la possibilità di utilizzare la sala centrale del piano fondi come stanza a cielo aperto (il cortile infatti è già coperto), illuminata naturalmente dall’alto, ed accessibile direttamente dalla quota di piazza del Ferro. La sala viene così occupata da una grande stanza quadrata, interamente rivestita di libri. La nuova stanza dei libri stabilisce una relazione con le grandi sale di lettura europee. Al di là delle sue dimensioni relativamente ridotte (un cubo di 7,50 m di lato), la stanza dei libri attribuisce alla collezione della biblioteca della Camera di Commercio un ruolo esplicitamente monumentale, adeguato al sistema urbano in cui si va ad inserire. Dalla quota superiore, provenendo da via Garibaldi, è possibile entrare nel Palazzo, attraversare la sala “del Bergamasco” e affacciarsi sulla stanza dei libri. In un sorprendente capovolgimento, una voragine di libri si apre al di sotto del cortile settecentesco. Il cortile appare letteralmente fondato sulla collezione di libri della Camera di Commercio
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