Delay and throughput characterization in random networks

Data e Ora : Friday, December 3, 2010 - 15:00
Relatore : Dr. Kostas Stamatiou
Affiliazione : DEI
Luogo : Aula Magna A. Lepschy
Descrizione :

We study the problem of evaluating the delay and throughput in networks with randomly distributed nodes. We examine scenarios wheretransmission takes place directly from the source to the destination(single-hop) or via a series of dedicated relays (multi-hop). In the single-hop case, a specific physical layer is considered based on frequency hopping and coding, and the dependence of the network throughput on salient physical-layer parameters is determined. In the multi-hop case, we derive an expression for the mean total delay from the source to the destination and derive the delay-optimal number of hops. We describe the application of these results in multi-hop networks with randomly distributed and mutually interfering routes.

Dispersion and aberration cancellation with entangled photons and their applications

Data e Ora : Friday, November 19, 2010 - 11:00
Relatore : Prof. Alexander Sergienko
Affiliazione : Boston University, USA
Luogo : Aula Magna A. Lepschy
Descrizione :

The flexibility and high information capacity of entangled states has been so far demonstrated in several areas of quantum communication and quantum computing. We developed recently several new techniques for precise optical measurement in optical life sciences, telecommunication, and nanotechnology. They take advantage of quantum entanglement and usually exceed traditional optical approaches both in resolution and in the amount of obtained information about the system under evaluation.
The even-order dispersion cancellation effect provided superior accuracy in quantum optical coherence tomography by eliminating dispersive broadening of low-coherence interference pattern. We recently designed novel type of quantum interferometer allowing observation of both even- and odd-order spectral dispersion cancellation effects in a single experiment. The precise evaluation of polarization mode dispersion in telecommunication routers and characterization of dispersion-engineered nanodevices such as bandgap structures could benefit from the unusual possibility of independently evaluating even- and odd-order dispersion coefficients.
A spatial counterpart of the dispersion cancellation effect that leads to the removal of even-order aberrations has been recently demonstrated. This correlated imaging approach could enhance the resolution of optical imaging and microscopy in biomedical applications by eliminating detrimental effects of aberration.

Advances in integrated quantum photonics

Data e Ora : Friday, October 8, 2010 - 11:00
Relatore : Dr. Alberto Peruzzo
Affiliazione : Centre for Quantum Photonics, University of Bristol, UK
Luogo : Aula Magna `A. Lepschy`
Descrizione :

We report our latest work in integrated quantum photonics (IQP) within Silica-on-Silicon waveguide chips. Amongst several demonstrations, near-unit fidelity quantum interference and two-photon entangling logic operation, the first integrated quantum metrology experiments beating the standard quantum limit, a compiled version of Shor`s quantum factoring algorithm on a waveguide chip and multiport interferometers on integrated devices that rely on multimode interference are shown. Moving forward to new materials, arrays of 21 evanescently coupled waveguides, were fabricated in SiON chips to implement quantum walks and a generalised form of two-photon non-classical interference, which were observed via two photon correlation. All these demonstrations illustrate the importance of integrated optics for future quantum technology.

Monotone minimal perfect hashing, z-fast tries, and prefix search.

Data e Ora : Wednesday, April 21, 2010 - 16:30
Relatore : Prof. Sebastiano Vigna
Affiliazione : Universita` di Milano
Luogo : Aula Magna `A. Lepschy`
Descrizione :

A minimal perfect hash function maps a set S of n keys into the set {0,1,..., n−1} bijectively. Classical results state that minimal perfect hashing is possible in constant time using a structure occupying space close to the lower bound of log e bits per element. In monotone minimal perfect hashing the bijection is required to preserve the lexicographical ordering of the keys. A monotone minimal perfect hash function can be seen as a very weak form of index that provides ranking just on the set S (and answers randomly outside of S). Our goal is to minimise the description size of the hash function: we show that, for a set S of n elements out of a universe of 2^w elements, O(n log log w) bits are sufficient to hash monotonically with evaluation time O(log w). Alternatively, we can get space O(n log w) bits with O(1) query time. As a consequence, it is possible to search a sorted table with O(1) accesses to the table (using additional O(n log log w) bits). Our results are based on the z-fast trie, a new, truly linear kind of trie that lends itself easily to probabilistic or blind versions. We also discuss briefly how a variant of the z-fast trie provides space-optimal results for weak prefix searches (i.e., prefix searches with a guarantee that the result will be non-empty).

Omnidirectional vision: from calibration to robot motion estimation

Data e Ora : Friday, February 26, 2010 - 15:00
Relatore : Dr. Davide Scaramuzza
Affiliazione : ETH Zurich, Autonomous Systems Lab, Zurich, Switzerland
Luogo : Aula Magna `A. Lepschy`
Descrizione :

Cameras are having a large impact on our society, every cell-phone is equipped with a camera and in the very near future all cars will feature cameras to improve traffic safety and even clothing will be equipped with integrated cameras. While cameras are continuing to pervade our daily lives, optics developers are working on increasing the field of view of the cameras. If the field of view of a camera exceeds 180 degrees, it is called an omnidirectional camera. Up until three years ago, these cameras were too heavy, expensive, and bulky to be integrated in commercial products. However today, omnidirectional cameras have become sufficiently small to be installed in cars and even carried on small lightweight helicopters. The market of these cameras is increasing and accordingly, the demand for software that enables their use in the real world is rising. In this talk, I will present how to combine omnidirectional vision and robotics in two applications: ground robots and micro aerial vehicles. After a brief overview on omnidirectional vision, I will show some result on vehicle motion estimation for ground vehicles and autonomous flight of micro helicopters by just using a single miniature omnidirectional camera a sole input.