On the quasiparticle description of c=1 CFTs

We show that the description of $c=1$ Conformal Field Theory in terms of quasiparticles satisfying fractional statistics can be obtained from the sine-Gordon model with a chemical potential $A$, in the limit where $A \gg M$. These quasiparticles are related to the excitations of the Calogero-Sutherland (CS) model. We provide a direct calculation of their 2-particle S-matrix using Korepin's method. We also reconsider the computation of the CS S-matrix in terms of particles with fractional charge

Thermodynamics of Fateev's models in the Presence of External Fields

We study the Thermodynamic Bethe Ansatz equations for a one-parameter quantum field theory recently introduced by V.A.Fateev. The presence of chemical potentials produces a kink condensate that modifies the excitation spectrum. For some combinations of the chemical potentials an additional gapless mode appears. Various energy scales emerge in the problem. An effective field theory, describing the low energy excitations, is also introduced.Comment: To appear in Nucl.Phys.

Progettazione e sviluppo di una mano robotica sotto-attuata per robot umanoide bipede

Lo scopo di questo lavoro è la progettazione e lo sviluppo di una mano robotica antropomorfa che possa essere integrata sul robot bipede SABIAN. L'esame dello stato dell'arte verte sulle mani robotiche per robot umanoidi presenti nella letteratura scientifica, con particolare attenzione ai meccanismi di trasmissione. L'obiettivo è quello di progettare una mano facilmente controllabile con un ridotto numero di attuatori che sia in grado di realizzare operazioni di presa anche in ambiente non strutturato e gestualità avanzata. Un'accurata analisi della trasmissione sotto-attuata e l'individuazione di indici globali di performance ha permesso di strutturare una procedura di ottimizzazione volta alla prevenzione dei fenomeni di instabilità della presa. Il dimensionamento del sistema di estensione passivo segue sulla base del Know-How dell'ARTS-lab, che unitamente al controllo, si prefigge lo scopo di replicare la dinamica del dito umano nella fase di chiusura prima della presa. Il lavoro si è concluso con la progettazione della mano e dell'unità di attuazione, puntando l'attenzione all'integrazione dei sensori nella struttura e la realizzazione delle dita

Exactly solvable model for isospin S=3/2 fermionic atoms on an optical lattice

We propose an exact solution of a model describing a low energy behavior of cold isospin S=3/2 fermionic atoms on a one-dimensional optical lattice. Depending on the band filling the effective field theory has a form of a deformed Gross-Neveu model with either $O(7)\times \mathbb{Z}_2$ (half filling) or $U(1)\times O(5)\times \mathbb{Z}_2$ symmetry.Comment: 4 pages, no figures, replaced with the final version to appear in PR

On the relationship between sigma models and spin chains

We consider the two-dimensional $\rm O(3)$ non-linear sigma model with topological term using a lattice regularization introduced by Shankar and Read [Nucl.Phys. B336 (1990), 457], that is suitable for studying the strong coupling regime. When this lattice model is quantized, the coefficient $\theta$ of the topological term is quantized as $\theta=2\pi s$, with $s$ integer or half-integer. We study in detail the relationship between the low energy behaviour of this theory and the one-dimensional spin-$s$ Heisenberg model. We generalize the analysis to sigma models with other symmetries.Comment: To appear in Int. J. MOd. Phys.

The SSSA-MyHand: a dexterous lightweight myoelectric hand prosthesis

The replacement of a missing hand by a prosthesis is one of the most fascinating challenges in rehabilitation engineering. State of art prostheses are curtailed by the physical features of the hand, like poor functionality and excessive weight. Here we present a new multi-grasp hand aimed at overcoming such limitations. The SSSA-MyHand builds around a novel transmission mechanism that implements a semi-independent actuation of the abduction/adduction of the thumb and of the flexion/extension of the index, by means of a single actuator. Thus, with only three electric motors the hand is capable to perform most of the grasps and gestures useful in activities of daily living, akin commercial prostheses with up to six actuators, albeit it is as lightweight as conventional 1-Degrees of Freedom prostheses. The hand integrates position and force sensors and an embedded controller that implements automatic grasps and allows inter-operability with different human-machine interfaces. We present the requirements, the design rationale of the first prototype and the evaluation of its performance. The weight (478 g), force (31 N maximum force at the thumb fingertip) and speed of the hand (closing time: <370 ms), make this new design an interesting alternative to clinically available multi-grasp prostheses

Exactly Solvable Ginzburg-Landau theories of Superconducting Order Parameters coupled to Elastic Modes

We consider two families of exactly solvable models describing thermal fluctuations in two-dimensional superconductors coupled to phonons living in an insulating layer, and study the stability of the superconducting state with respect to vortices. The two families are characterized by one or two superconducting planes. The results suggest that the effective critical temperature increases with the thickness of the insulating layer. Also the presence of the additional superconducting layer has the same effect.Comment: Submitted to Physical Review

Scaling of excitations in dimerized and frustrated spin-1/2 chains

We study the finite-size behavior of the low-lying excitations of spin-1/2 Heisenberg chains with dimerization and next-to-nearest neighbors interaction, J_2. The numerical analysis, performed using density-matrix renormalization group, confirms previous exact diagonalization results, and shows that, for different values of the dimerization parameter \delta, the elementary triplet and singlet excitations present a clear scaling behavior in a wide range of \ell=L/\xi (where L is the length of the chain and \xi is the correlation length). At J_2=J_2c, where no logarithmic corrections are present, we compare the numerical results with finite-size predictions for the sine-Gordon model obtained using Luscher's theory. For small \delta we find a very good agreement for \ell > 4 or 7 depending on the excitation considered.Comment: 4 pages, 4 eps figures, RevTeX 4 class, same version as in PR