Microwave Inter-Connections and Switching by means of Carbon Nano-tubes

In this work, carbon nanotube (CNT) based interconnections and switches will be reviewed, discussing the possibility to use nanotubes as potential building blocks for signal routing in microwave networks. In particular, theoretical design of coplanar waveguide (CPW), micro‐strip single‐pole‐single‐throw (SPST) and single‐pole‐double‐throw (SPDT) devices has been performed to predict the electrical performances of CNT‐based RF switching configurations. Actually, by using the semiconductor‐conductor transition obtained by properly biasing the CNTs, an isolation better than 30 dB can be obtained between the ON and OFF states of the switch for very wide bandwidth applications. This happens owing to the shape deformation and consequent change in the band‐gap due to the external pressure caused by the electric field. State‐of‐art for other switching techniques based on CNTs and their use for RF nano‐interconnections is also discussed, together with current issues in measurement techniques

Mechanisms of Step-Stress Degradation In Carbon-Doped 0.15 μm AlGaN/GaN HEMTs for Power RF Applications

We discuss the degradation mechanisms of C-doped 0.15-μm gate AlGaN/GaN HEMTs tested by drain step-stress experiments. Experimental results show that these devices exhibit cumulative degradation effects during the step stress experiments in terms of either (i) transconductance (gm) decrease without any threshold-voltage (VT) change under OFF-state stress, or (ii) both VT and gm decrease under ON-state stress conditions. To aid the interpretation of the experiments, two-dimensional hydrodynamic device simulations were carried out. Based on obtained results, we attribute the gm decrease accumulating under OFF-state stress to hole emission from CN acceptor traps in the gate-drain access region of the buffer, resulting in an increase in the drain access resistance. On the other hand, under ON-state stress, channel hot electrons are suggested to be injected into the buffer under the gate and in the gate-drain region where they can be captured by CN traps, leading to VT and gm degradation, respectively

Progetto di Allestimento della mostra per gli ottant'anni della città universitaria della Sapienza università di Roma

Il progetto allestitivo propone, attraverso dispositivi spaziali e video proiezioni, una lettura cronologica delle diverse fasi che hanno contraddistinto la realizzazione delle sedi dello Studium Urbis romano, dalla sua fondazione, alla realizzazione del luogo storico del palazzo della Sapienza (XVI secolo) con la Chiesa di Sant’Ivo alla Sapienza e la Biblioteca Alessandrina di Francesco Borromini (1642-1660) in cui sono presenti i motivi iconografici dell’identità culturale dell’Ateneo, per proseguire fino alla realizzazione della nuova Città universitaria, costruita per riunire in un’unica sede le discipline storiche, artistico-letterarie e scientifiche fino ad allora sparse in più luoghi della città di Roma. L’esposizione si arricchisce di materiale documentario inedito, frutto del contributo di diversi studiosi e del lavoro di riordino dell’Archivio storico della Sapienza e da riprese realizzate dall’istituto Luce - Cinecittà. L'allestimento ha interessato l'atrio del palazzo del Rettorato ed in particolare la galleria del primo piano

Ant colony optimization for real-world vehicle routing problems

Ant colony optimization (ACO) is a metaheuristic for combinatorial optimization problems. In this paper we report on its successful application to the vehicle routing problem (VRP). First, we introduce the VRP and some of its variants, such as the VRP with time windows, the time dependent VRP, the VRP with pickup and delivery, and the dynamic VRP. These variants have been formulated in order to bring the VRP closer to the kind of situations encountered in the real-world. Then, we introduce the basic principles of ant colony optimization, and we briefly present its application to the solution of the VRP and of its variants. Last, we discuss the applications of ACO to a number of real-world problems: a VRP with time windows for a major supermarket chain in Switzerland; a VRP with pickup and delivery for a leading distribution company in Italy; a time dependent VRP for freight distribution in the city of Padua, Italy, where the travel times depend on the time of the day; and an on-line VRP in the city of Lugano, Switzerland, where customers’ orders arrive during the delivery process

Noise cleaning the precision matrix of short time series

We present a comparison between various algorithms of inference of covariance and precision matrices in small data sets of real vectors of the typical length and dimension of human brain activity time series retrieved by functional magnetic resonance imaging (fMRI). Assuming a Gaussian model underlying the neural activity, the problem consists of denoising the empirically observed matrices to obtain a better estimator of the (unknown) true precision and covariance matrices. We consider several standard noise-cleaning algorithms and compare them on two types of data sets. The first type consists of synthetic time series sampled from a generative Gaussian model of which we can vary the fraction of dimensions per sample q and the strength of off-diagonal correlations. The second type consists of time series of fMRI brain activity of human subjects at rest. The reliability of each algorithm is assessed in terms of test-set likelihood and, in the case of synthetic data, of the distance from the true precision matrix. We observe that the so-called optimal rotationally invariant estimator, based on random matrix theory, leads to a significantly lower distance from the true precision matrix in synthetic data and higher test likelihood in natural fMRI data. We propose a variant of the optimal rotationally invariant estimator in which one of its parameters is optimzed by cross-validation. In the severe undersampling regime (large q) typical of fMRI series, it outperforms all the other estimators. We furthermore propose a simple algorithm based on an iterative likelihood gradient ascent, leading to very accurate estimations in weakly correlated synthetic data sets

Cycling reliability of RF-MEMS switches with Gold–Platinum multilayers as contact material

Contact resistance is the main parameter used for assessing the high cycling reliability of RF microelectromechanical (RF-MEMS) switches. In this paper the use of a modified contact material is tested and compared to pure gold in cycling experiments performed on a RF-MEMS switch in shunt capacitive configuration. The modified contact material is a gold-based multilayer with a thin layer of platinum sandwiched between two layers of gold. The experiment consists in comparing devices with the same layout but with different contact material. While the two types of switch start with similar RF performances, the device with the modified material shows a marked improvement in cycling reliability and a lower series resistance up to 106 cycles when compared to gold contact devices