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Research (6)

LIBRO

In Research ,
Written by Friday, 21 March 2014 08:59

Circuiti Elettrici  Seconda edizione

Renzo Perfetti

Zanichelli, 2013


La seconda edizione di Circuiti elettrici mantiene la collaudata impostazione basata su una graduale esposizione della teoria, con particolare attenzione alle tecniche di risoluzione dei problemi, descritte in forma algoritmica e illustrate attraverso numerosi esempi svolti. Alcuni argomenti sono presentati secondo un nuovo ordine, più funzionale alle esigenze didattiche. Molti esempi sono stati aggiornati.


Sito web del libro:

http://www.zanichelli.it/ricerca/prodotti/9788808178886/renzo-perfetti/circuiti-elettrici/

ARTICOLO

In Research ,
Written by Friday, 21 March 2014 08:52

Recurrent neural network for approximate nonnegative matrix factorization

Giovanni Costantini, Renzo Perfetti, Massimiliano Todisco

 

 

A recurrent neural network solving the approximate nonnegative matrix factorization (NMF) problem is presented in this paper. The proposed network is based on the Lagrangian approach, and exploits a partial dual method in order to limit the number of dual variables. Sparsity constraints on basis or activation matrices are included by adding a weighted sum of constraint functions to the least squares reconstruction error. However, the corresponding Lagrange multipliers are computed by the network dynamics itself, avoiding empirical tuning or a validation process. It is proved that local solutions of the NMF optimization problem correspond to as many stable steady-state points of the network dynamics. The validity of the proposed approach is verified through several simulation examples concerning both synthetic and real-world datasets for feature extraction and clustering applications.

To be published in Neurocomputing (2014)

ARTICOLO

In Research ,
Written by Thursday, 20 March 2014 09:42
Retinal Blood Vessel Segmentation using Line Operators and Support Vector Classification
     
Elisa Ricci            Renzo Perfetti

IEEE Transactions on Medical Imaging vol. 26, N. 10, 2007


Abstract. In the framework of computer-aided diagnosis of eye diseases, retinal vessel segmentation based on line operators is proposed. A line detector, previously used in mammography, is applied to the green channel of the retinal image. It is based on the evaluation of the average grey level along lines of fixed length passing through the target pixel at different orientations. Two segmentation methods are considered. The first uses the basic line detector whose response is thresholded to obtain unsupervised pixel classification. As a further development we employ two orthogonal line detectors along with the grey level of the target pixel to construct a feature vector for supervised classification using a support vector machine (SVM). The effectiveness of both methods is demonstrated through receiver operating characteristic (ROC) analysis on two publicly available databases of color fundus images.

ARTICOLO

In Research ,
Written by Thursday, 20 March 2014 09:22

 

SINGLE-SIDED OBJECTIVE SPEECH INTELLIGIBILITY ASSESSMENT BASED ON SPARSE SIGNAL REPRESENTATION

Giovanni Costantini, Massimiliano Todisco, Renzo Perfetti, Andrea Paoloni, Giovanni Saggio

2012 IEEE INTERNATIONAL WORKSHOP ON MACHINE LEARNING FOR SIGNAL PROCESSING, SEPT. 23–26, 2012, SANTANDER, SPAIN

 

Transcription of speech signals, originating from a
lawful interception, is particularly important in the forensic
phonetics framework. These signals are often degraded and
the transcript may not replicate what was actually
pronounced. In the absence of the clean signal, the only way
to estimate the level of accuracy that can be obtained in the
transcription is to develop an objective methodology for
intelligibility measurements. In this paper a method based
on the Normalized Spectrum Envelope (NSE) and Sparse
Non-negative Matrix Factorization (SNMF) is proposed to
evaluate the signal intelligibility. The approaches are tested
with three different noise types and the results are compared
with the speech intelligibility scores measured by subjective
tests. The results of the experiments show a high correlation
between objective measurements and subjective evaluations.
Therefore, the proposed methodology can be successfully
used in order to establish whether a given intercepted signal
can be transcribed with sufficient reliability.





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