Data e Ora : Tuesday, December 22, 2009 - 15:30
Relatore : Dr. Stefano Minardi
Affiliazione : Center Ultra Optics, Institute of Applied Physics, Friedrich Schiller University, Jena, Germania
Luogo : Sala riunioni 201 DEI A
Descrizione :

In interferometria stellare, correlazioni del primo e del secondo ordine della luce proveniente da due o piu` telescopi sono utilizzate per ricostruire immagini ad altissima risoluzione di oggetti astronomici. La misura delle correlazioni richiede che il tragitto della luce dalla stella al correlatore possa essere controllata con elevatissima precisione. Cio` pone dei vincoli tecnologici stringenti all`infrastruttura dell`interferometro, specialmente nel caso delle correlazioni del primo ordine (interferometria di Michelson). In questa presentazione mostrero` alcuni risultati ottenuti recentemente all`Universita` di Jena volti a dimostrare l`utilita` delle fibre ottiche per il miglioramento delle prestazioni dell`interferometria stellare di Michelson. Proposte per l`uso delle fibre ottiche nel caso delle correlazioni del secondo ordine (interferometria Hanbury Brown & Twiss) saranno inoltre discusse.

Data e Ora : Monday, December 21, 2009 - 15:00
Relatore : Dr. Cristian Bonato
Affiliazione : Huygens Laboratory, Leiden Institute of Physics, The Netherlands
Luogo : Aula Magna `A. Lepschy`
Descrizione :

Hybrid quantum information systems hold great promises for the development of quantum communication and computing due to the possibility to exploit different quantum systems at the best of their potentials. For example, in order to build a quantum network, photons are excellent candidates for long-distance transmission while quantum states of matter are preferred for local storage and processing. Hybrid (photon-matter) systems can also be used to effectively enable strong nonlinear interactions between single photons, which are a prerequisite for optical quantum computing. In the talk, we will focus on quantum dots in micropillar cavities, describing some quantum information schemes involving photon polarization and the spin of a single electron trapped in the dot. Such schemes are based on spin-selective reflection in the weak-coupling regime of cavity quantum electrodynamics. In particular we will describe coherent state transfer between the photon and the spin, a CNOT gate (where the spin is the control qubit and the photon polarization is the target qubit) and a spin-assisted photonic Bell-state analyzer. Finally, we discuss the practical implementation of the proposed schemes in oxide-apertured micropillar cavities. In particular we show experimentally that such cavities support high-quality Hermite-Gaussian transverse optical modes. We then introduce a technique, based on the creation of small surface defects by means of a focused intense laser beam, to permanently tune the optical properties of the microcavity without damaging the cavity quality. This technique allows polarization-selective tuning of the frequencies of the modes on a 150-GHz range and can be used to make the fundamental cavity mode polarization-degenerate, as it is needed for quantum information applications.

Data e Ora : Monday, November 23, 2009 - 11:00
Relatore : Prof. Luca Mari
Affiliazione : Universit� Carlo Cattaneo - LIUC
Luogo : Aula Magna `A. Lepschy`
Descrizione :

A partire dalla constatazione che negli ultimi anni vari atenei italiani hanno attivato laboratori dedicati ai sistemi RFId, il seminario introdurr� un quadro di riferimento, in prospettiva strategica, organizzativa e tecnologica, sullo stato di adozione dei sistemi RFId in Italia, proponendo qualche considerazione sul ruolo che i laboratori universitari stanno svolgendo al proposito. Sar� quindi presentato il `business model` del Lab#ID, il laboratorio sui sistemi RFId dell`Universit� Cattaneo - LIUC, e saranno discusse in via esemplificativa le caratteristiche pi� rilevanti di alcuni dei circa 30 progetti realizzati dal Lab#ID finora, cercando di trarne alcune idee sui trend, sia applicativi che tecnologici, che emergono da questa esperienza. Una breve analisi, in logica di survey, sar� anche dedicata ai circa 80 progetti di applicazioni RFId che sono stati candidati alle prime due edizioni dell`RFId Italia Award (2008 e 2009), di cui il Lab#ID � stato coorganizzatore.

Data e Ora : Wednesday, September 30, 2009 - 15:00
Relatore : Prof. Ugo Bardi
Affiliazione : Universita` di Firenze
Luogo : Aula Magna `A. Lepschy`
Descrizione :

Esistono diverse definizioni di sistemi complessi. Una che pu� essere utilizzata in modo proficuo per modellizzarli � che sono quelli che mostrano perlomeno un ciclo di feedback e, di conseguenza, la propriet� definita come `omeostasi`. Definiti in questo modo, i sistemi complessi non sono necessariamente complicati e la propriet� di omeostasi si verifica anche in semplici sistemi fisici che mostrano transizioni di fase. Le stesse propriet� si trovano in sistemi molto pi� strutturati come sistemi sociali ed economici che possono essere modellizzati con tecniche di `system dynamics`. Mostreremo qui come questi modelli possono descrivere quantitativamente alcuni sistemi socioeconomici come l`estrazione del petrolio, la caccia alle balene del secolo XIX, la corsa all`oro in California e altri. Questi sistemi mostrano una rapida crescita seguita da un collasso dovuto al sovrasfruttamento della risorsa. Questo tipo di modellizazione � stata applicata a sistemi planetari fin dagli anni 1960 per la serie di studi nota in Italia come `I Limiti dello Sviluppo`. Questi modelli si sono rivelati in grado di seguire l`andamento del sistema socio-economico e ecologico mondiale fino ad oggi e ne prevedono il collasso a breve scadenza.

Data e Ora : Thursday, June 18, 2009 - 14:00
Relatore : Prof. Osvaldo Simeone
Affiliazione : New Jersey Institute of Technology, Newark, NJ (USA)
Luogo : Aula Magna `A. Lepschy`
Descrizione :

According to the property-rights model of cognitive radio, the primary terminals own a given bandwidth and may decide to lease it for a fraction of time to secondary nodes in exchange for appropriate remuneration. In this talk, an implementation of spectrum leasing is proposed whereby remuneration takes place in the form of cooperative transmission. On the one hand, the primary link attempts to maximize its quality of service in terms of either rate or probability of outage, accounting for the possible contribution from cooperation. On the other hand, nodes in the secondary ad hoc network compete among themselves for transmission within the leased time-slot. At first, a centralized implementation is investigated and cast in the framework of Stackelberg games. Then, a decentralized and opportunistic variant is studied that is based on HARQ protocols and auctions. Analysis and numerical results show that spectrum leasing based on trading secondary spectrum access for cooperation is a promising framework for cognitive radio.

Data e Ora : Wednesday, June 17, 2009 - 10:00
Relatore : Dr. Andreas Willig
Affiliazione : Technische Universitaet Berlin, Germany
Luogo : Aula Magna `A. Lepschy`
Descrizione :

Wireless sensor networks are networks of small and cheap sensor nodes, which on the one hand provides means (sensors, actuators) to interface with the physical world, and which on the other hand can use wireless technology to locally interact with each other and to increase the robustness of the network. In this talk first a brief introduction to the concept of wireless sensor networks, with consideration of domestic applications. In the second part it is demonstrated by example how the resource constraints found in wireless sensor networks (memory, processing power, radio resources) influence the design of communication protocols.

Data e Ora : Thursday, June 11, 2009 - 15:00
Relatore : Ing. Filippo Gioachin
Affiliazione : Department of Computer Science, University of Illinois at Urbana-Champaign, IL (USA)
Luogo : Aula Magna `A. Lepschy`
Descrizione :

Debugging applications is known to be a difficult task. Debugging parallel applications is even harder due to the distributed nature of parallel processing. Furthermore, when a problem appears only on thousands of processors, modern parallel debuggers are unusable since they become too slow at such scale. In this talk I will present scalable techniques to improve the proficiency of debugging parallel applications in the context of message-passing. As the ambiguity of the title suggests, I will focus on two issues. On one side, how to debug parallel applications that leverage the concept of virtualization as a way of parallelization. On the other hand, how we can effectively employ virtualization techniques to debug applications on very large systems using fewer processors. These techniques will be presented in the context of the Charm++ runtime system, and CharmDebug, the parallel debugging tool tailored to Charm++ applications.

Data e Ora : Friday, May 8, 2009 - 15:00
Relatore : Dr. Yan Huang
Affiliazione : Shenyang Institute of Automation, Chinese Academy of Sciences
Luogo : Aula Magna `A. Lepschy`
Descrizione :

Wireless sensor networks (WSN), which integrates the functions of data collection, data processing and wireless communication, reinforces human ability in information obtaining. There are abundant research topics which are considerably challenging in WSN. As fundamental issues, deployment and localization are basis for the applications of WSN. The deployment, to place sensor nodes with proper strategy to meet some particular requests, determines WSN performance of target detection. Localization in WSN includes node localization and target localization. The former is the premise of the latter, and affects the precision of target tracking. Deployment and localization of WSN applied in target tracking are studied as follows: 1) Considering great cooperative capability of sensor nodes, present a deployment strategy based on detection fusion. 2) Present multipath error analysis of Radio Interferometric Positioning System and propose a modified Particle Swarm Optimization based localization method for it. 3) Design two tracking algorithms based on a distributed particle filter and discuss performance metrics in terms of tracking performance, communication cost, energy cost, and tracking response time.

Data e Ora : Wednesday, April 22, 2009 - 14:30
Relatore : Ing. Maurizio Dusi
Affiliazione : Universita` di Brescia
Luogo : Aula Magna `A. Lepschy`
Descrizione :

L`utilizzo di tunnel a livello applicativo rappresenta una minaccia di sicurezza per ogni rete protetta da firewall e Application Level Gateway. Incapsulare protocolli soggetti a restrizioni di sicurezza, come peer-to-peer, e-mail, chat, all`interno di protocolli ritenuti sicuri o necessari, come HTTP e SSH, permette di eludere le politiche di sicurezza della rete, persino quelle basate sulla ispezione del contenuto dei pacchetti. Scopo del seminario e` fornire un`introduzione alle tecniche di classificazione statistica di traffico. In prima battuta, verranno analizzati i risultati che tali tecniche raggiungono in presenza di traffico in chiaro. Successivamente, verranno discussi schemi per il riconoscimento di traffico sopra tunnel HTTP e SSH, presentando i risultati conseguiti dal gruppo di ricerca dell`Universita` di Brescia.

Data e Ora : Tuesday, April 14, 2009 - 15:00
Relatore : Dr. Larry Hubbard
Affiliazione : Fundus Photograph Reading Center, Dept. of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, WI (USA)
Luogo : Aula Magna `A. Lepschy`
Descrizione :

The international systems for classification of diabetic retinopathy and age-related macular degeneration, two major blinding diseases, were adapted from systems from two US clinical trials: the Early Treatment Diabetic Retinopathy Study and the Age-Related Eye Disease Study. These procedures evolved from exploratory efforts at the University of Wisconsin - Madison. This talk will examine the approaches used to develop such disease classifications, for the purpose of assessing how computerized image processing might be used to extend, and perhaps replace, manual evaluation of ocular images.

Data e Ora : Wednesday, March 18, 2009 - 15:00
Relatore : Prof. Tom La Porta
Affiliazione : Penn State University, USA
Luogo : Aula Magna `A. Lepschy`
Descrizione :

In this talk I discuss the interaction of policy on algorithms for resource assignment in mission-oriented wireless sensor networks. We consider two forms of resource assignment: assigning specific sensors to tasks and allocating bandwidth to data sources. When assigning sensors to tasks we parameterize policy; i.e., we introduce variables and set their values to capture policy and influence our resource allocation within the framework of our algorithms. When allocating bandwidth, we enforce policy with hard constraints. We show the impact of policy in both cases using simulation.

Data e Ora : Thursday, February 26, 2009 - 15:00
Relatore : Prof. Pierluigi Crescenzi
Affiliazione : Dipartimento di Sistemi e Informatica, Universita` di Firenze
Luogo : Sala Riunioni DEI/G
Descrizione :

An edge-Markovian process with birth-rate p and death-rate q generates sequences of graphs (G[0], G[1], G[2],...) with the same node set [n] such that G[t] is obtained from G[t−1] as follows: if e is not in E(G[t−1]) then e is in E(G[t]) with probability p, and if e is in E(G[t−1]) then e is not in E(G[t]) with probability q. Clementi et al. (PODC 2008) analyzed thoroughly information dissemination in such dynamic graphs, by establishing bounds on their flooding time - flooding is the gossip mechanism in which every node becoming aware of an information at step t forwards this information to all its neighbors at all forthcoming steps t′ > t. Despite its many advantages in term of simplicity and robustness, flooding suffers from its high bandwidth consumption. In this talk we show that flooding in dynamic graphs can be implemented in a more parsimonious manner, so that to save bandwidth, yet preserving efficiency in term of simplicity and completion time. For a positive integer k, we say that the flooding protocol is k-active if each node forwards an information only during the k time steps immediately following the step at which the node receives that information for the first time. We define the reachability threshold for the flooding protocol as the smallest integer k such that, for any source s in [n], the k-active flooding protocol from s completes (i.e., reaches all nodes), and we establish tight bounds for this parameter. We show that, for a large spectrum of parameters p and q, the reachability threshold is by several orders of magnitude smaller than the flooding time. In particular, we show that it is even constant whenever the ratio p/(p + q) exceeds log n/n. Moreover, we also show that being active for a number of steps equal to the reachability threshold (up to a multiplicative constant) allows the flooding protocol to complete in optimal time, i.e., in asymptotically the same number of steps as when being perpetually active. These results demonstrate that flooding can be implemented in a practical and efficient manner in dynamic graphs. The main ingredient in the proofs of our results is a reduction lemma enabling to overcome the time dependencies in edge-Markovian dynamic graphs. This is a joint work with Herve Baumann and Pierre Fraigniaud.