Design and optimization of a compact laser-driven proton beamline

Laser-accelerated protons, generated by irradiating a solid target with a short, energetic laser pulse at high intensity (I > 1018W·cm-2), represent a complementary if not outperforming source compared to conventional accelerators, due to their intrinsic features, such as high beam charge and short bunch duration. However, the broadband energy spectrum of these proton sources is a bottleneck that precludes their use in applications requiring a more reduced energy spread. Consequently, in recent times strong effort has been put to overcome these limits and to develop laser-driven proton beamlines with low energy spread. In this paper, we report on beam dynamics simulations aiming at optimizing a laser-driven beamline - i.e. a laser-based proton source coupled to conventional magnetic beam manipulation devices - producing protons with a reduced energy spread, usable for applications. The energy range of investigation goes from 2 to 20 MeV, i.e. the typical proton energies that can be routinely obtained using commercial TW-power class laser systems. Our beamline design is capable of reducing the energy spread below 20%, still keeping the overall transmission efficiency around 1% and producing a proton spot-size in the range of 10 mm2. We briefly discuss the results in the context of applications in the domain of Cultural Heritage

Design and optimization of a laser-PIXE beamline for material science applications

Multi-MeV proton beams can be generated by irradiating thin solid foils with ultra-intense (>10^18 W/cm^2) short laser pulses. Several of their characteristics, such as high bunch charge and short pulse duration, make them a complementary alternative to conventional radio frequency-based accelerators. A potential material science application is the chemical analysis of cultural heritage (CH) artifacts. The complete chemistry of the bulk material (ceramics, metals) can be retrieved through sophisticated nuclear techniques such as particle-induced X-ray emission (PIXE). Recently, the use of laser-generated proton beams was introduced as diagnostics in material science (laser-PIXE or laser-driven PIXE): Coupling laser-generated proton sources to conventional beam steering devices successfully enhances the capture and transport of the laser-accelerated beam. This leads to a reduction of the high divergence and broad energy spread at the source. The design of our hybrid beamline is composed of an energy selector, followed by permanent quadrupole magnets aiming for better control and manipulation of the final proton beam parameters. This allows tailoring both, mean proton energy and spot sizes, yet keeping the system compact. We performed a theoretical study optimizing a beamline for laser-PIXE applications. Our design enables monochromatizing the beam and shaping its final spot size. We obtain spot sizes ranging between a fraction of mm up to cm scale at a fraction of nC proton charge per shot. These results pave the way for a versatile and tunable laserPIXE at a multi-Hz repetition rate using modern commercially available laser systems

Esercizi di Teoria dei Segnali

Il presente lavoro, attualmente alla sua terza edizione, raccoglie numerosi spunti emersi in tanti anni di esperienza didattica svolta dagli autori presso l'Università degli Studi di Brescia, prima nella Laurea quinquennale in Ingegneria Elettronica, quindi nelle Lauree triennali nel settore dell'Ingegneria dell'Informazione dei nuovi ordinamenti. I temi considerati sono legati agli argomenti classici della teoria dei segnali nel continuo, alle variabili casuali e ai processi stocastici, al campionamento ed alla quantizzazione. Nell'impostazione si è tenuto conto delle esigenze della nuova Laurea triennale, per cui il rigore matematico è stato a volte sacrificato per semplificare la presentazione di qualche argomento specifico. Il testo è strutturato in otto capitoli di esercizi completamente risolti, corredati di un ricco capitolo di complementi nel quale si richiamano alcuni dei principali argomenti della teoria dei segnali al ne di completare la trattazione. In ogni capitolo vengono presentati vari esercizi completamente risolti (circa 70), nonché ulteriori esercizi suggeriti (circa 140), di numerosi dei quali (circa 70) viene indicata la soluzione. Nel Capitolo 1 vengono presentati gli esempi riguardanti le operazioni elementari sui segnali, la convoluzione e la correlazione, sia per segnali di energia che per segnali di potenza (periodici e non periodici). Il Capitolo 2 considera la rappresentazione vettoriale dei segnali, focalizzando l'attenzione sul concetto di ortogonalità e distanza tra segnali, e sull'approssimazione ai minimi errori quadrati di un segnale rispetto ad una base. L'analisi di Fourier viene presentata nel Capitolo 3. L'attenzione viene posta sia sul calcolo della trasformata di Fourier e dello sviluppo in serie di Fourier di un segnale, che sull'applicazione delle principali proprietà della trasformata. I sistemi vengono introdotti nel Capitolo 4, focalizzando l'attenzione sui segnali deterministici. Viene trattato sia il problema della classificazione generale di un sistema (in termini di linearità, invarianza alla traslazione, memoria, causalità, stabilità), che il calcolo del segnale di uscita a fronte di uno specifico segnale applicato in ingresso. Particolare attenzione viene posta sull'analisi dei sistemi lineari tempo-invarianti (LTI), effettuata sia nei tempi che nelle frequenze. Nel Capitolo 5 vengono presentati numerosi esempi sulla caratterizzazione di una variabile casuale, discreta o continua, sull'indipendenza ed incorrelazione di più variabili casuali, sulle funzioni di variabili casuali e sui valori attesi condizionati. Nel Capitolo 6 viene trattata la caratterizzazione di un processo stocastico, focalizzando principalmente l'attenzione sui segnali periodici con fase casuale, sui processi gaussiani e sui processi di tipo PAM (Pulse Amplitude Modulation). Il filtraggio di un processo stocastico viene analizzato nel Capitolo 7. Nel Capitolo 8 viene trattato il problema del campionamento e della quantizzazione di un segnale, sia deterministico che stocastico. La nutrita sezione dedicata ai complementi è suddivisa in varie parti che trattano, rispettivamente, la rappresentazione vettoriale dei segnali, le principali proprietà della trasformata di Fourier e della delta di Dirac, una descrizione delle principali caratteristiche dei sistemi a tempo continuo, le variabili casuali e i processi stocastici, ed infine le operazioni di campionamento e quantizzazione di un segnale. Alcuni testi classici sono inne elencati, come riferimenti per la parte di teoria, nella sezione dedicata alla bibliografia. In particolare, sono stati citati alcuni testi che trattano più o meno tutti gli argomenti presentati in questo lavoro (e.g., [1], [2], [3], [4], [5], [8], [12], [13], [14], [15], [21], [22]), altri che descrivono in maggior dettaglio la rappresentazione vettoriale dei segnali [7], [8], la trasformata di Fourier [18], [24], le variabili casuali ed i processi stocastici [19], [16], [20], [6], [9], [11], [23], [10], i sistemi [17]. In letteratura sono presenti molti altri testi validi che non sono stati citati per non appesantire troppo la trattazione. Ulteriore materiale di supporto (e.g., errata corrige, lucidi di alcune lezioni di teoria, soluzioni di alcuni degli esercizi proposti, nuovi esercizi suggeriti, ...) può essere reso disponibile contattando gli autori, oppure sul sito web: http://www.ing.unibs.it/spier/libro.html. Gli autori sono grati sin d'ora nei confronti di coloro che avessero suggerimenti e consigli per migliorare sia i contenuti che la presentazione, o a tutti coloro che volessero segnalare eventuali errori ed imprecisioni. Tali suggerimenti possono essere diretti agli autori tramite posta elettronica agli indirizzi: [email protected], [email protected]

Top-Down and Bottom-Up Semantic Indexing of Multimedia

The aim of this work consists in proposing a dual approach for the sake of semantic indexing of audio-visual documents. We present two dierent algorithms based respectively on a bottom-up and a top-down strategy. Considering the top-down approach, we propose an algorithm which implements a nite-state machine and uses low-level motion indices extracted from an MPEG compressed bit-stream. Simulation results show that the proposed method can eectively detect the presence of relevant events in sport programs. Using the bottom-up approach, the indexing is performed by means of Hidden Markov Models (HMM), with an innovative approach: the input signal is considered as a non-stationary stochastic process, modeled by a HMM in which each state is associated with a different property of audio-visual material. Several samples from the MPEG-7 content set have been analyzed using the proposed scheme, demonstrating the performance of the overall approach to provide insights about the content of audio-visual programmes. Moreover, what appears quite attractive instead is to use low-level descriptors in providing a feedback for non-expert users of the content of the described audio-visual programme. The experiments have demonstrated that, by adequate visualization or presentation, low-level features carry instantly semantic information about the programme content, given a certain programme category, which may thus help the viewer to use such low-level information for navigation or retrieval of relevant events

Semantic Indexing of Sport Program Sequences by Audio-Visual Analysis

Semantic indexing of sports videos is a subject of great interest to researchers working on multimedia content characterization. Sports programs appeal to large audiences and their efficient distribution over various networks should contribute to widespread usage of multimedia services. In this paper, we propose a semantic indexing algorithm for soccer programs which uses both audio and visual information for content characterization. The video signal is processed first by extracting low-level visual descriptors from the MPEG compressed bit-stream. The temporal evolution of these descriptors during a semantic event is supposed to be governed by a controlled Markov chain. This allows to determine a list of those video segments where a semantic event of interest is likely to be found, based on the maximum likelihood criterion. The audio information is then used to refine the results of the video classification procedure by ranking the candidate video segments in the list so that the segments associated to the event of interest appear in the very first positions of the ordered list. The proposed method is applied to goal detection. Experimental results show the effectiveness of the proposed cross-modal approach

EVENT RECOGNITION IN SPORT PROGRAMS USING LOW-LEVEL MOTION INDICES

In this paper we present a semantic video indexing algorithm based on finite-state machines and low-level motion indices extracted from the MPEG compressed bit-stream. The problem of semantic video indexing is actually of great interest due to the wide diffusion of large video databases. In literature we can find many video indexing algorithms, based on various types of low-level features, but the problem of semantic indexing is less studied and surely it is a great challenging one. The proposed algorithm is an example of solution to the problem of finding a semantic relevant event (e.g., scoring of a goal in a soccer game) in case of specific categories of audio-visual programmes. The simulation results show that the proposed algorithm can effectively detect the presence of goals and other relevant events in sport programs

A cooperative Top-Down/Bottom-Up Technique for Motion Field Segmentation

The segmentation of video sequences into regions underlying a coherent motion is one of the most useful processing for video analysis and coding. In this paper, we propose an algorithm that exploits the advantages of both top-down and bottom-up techniques for motion eld segmentation. To remove camera motion, a global motion estimation and compensation is rst performed. Local motion estimation is then carried out relying on a traslational motion model. Starting from this motion eld, a two-stage analysis based on ane models takes place. In the rst stage, using a top-down segmentation technique, macro-regions with coherent ane motion are extracted. In the second stage, the segmentation of each macro-region is rened using a bottom-up approach based on a motion vector clustering. In order to further improve the accuracy of the spatio-temporal segmentation, a Markov Random Field (MRF)-inspired motion-and-intensity based renement step is performed to adjust objects boundaries

A Markov Chain Model for Semantic Indexing of Sport Program Sequences

In this paper, we propose a semantic indexing algorithm based on the controlled Markov chain modeling framework. Controlled Markov chain models are used to describe the temporal evolution of low-level visual descriptors extracted from the MPEG compressed bit-stream. To reduce the number of false detections given by the proposed video-processing algorithm, we have considered also the audio signal. In particular we have evaluated the "loudeness" associated to each video segments identified by the analysis carried out on the video signal. The intensity of the "loudness" has then been used to order the selected video segments. In this way, the segments associated to interesting events appear in the very first positions of the ordered list, and the number of false detections can be greatly reduced. The proposed algorithm has been conceived for soccer game video sequences, and the simulation results have shown the effectiveness of the proposed algorithm

Efficient digital pre-filtering for least squares linear approximation

In this paper we propose a very simple FIR pre-filter for near optimal least-squares linear approximation of discrete time signals. At first, a greedy least square approximation of the desired signal is derived using an efficient digital pre-processing filter, then the usual linear interpolation is applied to obtain the final result. This leads to a non interpolating reconstruction of the signal, with good reconstruction quality and very limited computational cost. The basic formalism adopted to design the pre-filter has been derived from the framework introduced by Blu et Unser. To demonstrate the usability and the effectiveness of the approach, the proposed method has been applied to the problem of natural image resampling, which is typically applied when the image undergoes successive rotations. The performance obtained are very interesting, and the required computational effort is extremely low