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Mazzarella G.,Consorzio Interuniversitario per le Science Fisiche della Materia | Salasnich L.,Consorzio Interuniversitario per le Science Fisiche della Materia | Salasnich L.,CNR Institute of Neuroscience
Romanian Reports in Physics | Year: 2015

We consider a finite number N of interacting bosonic atoms at zero temperature confined in a one-dimensional double-well trap and study this system by using the two-site Bose-Hubbard (BH) Hamiltonian. For systems with N = 2, N = 3, and N = 4 bosons we analytically solve the eigenproblem associated to this Hamiltonian and find its lowest energetic state. We investigate the structure of the ground state by varying the strength of the boson-boson interaction from the strongly attractive regime to the deep repulsive one. We characterize the ground state of the two-site BH Hamiltonian by calculating the Fisher information F, the coherence visibility _, and the entanglement entropy S. For these quantities we provide analytical formulas that we use to study F, _, and S as functions of the interaction between the particles. We discuss the difference existing, in the deep repulsive regime, between the case with an even number of bosons and that with an odd number of particles, both in the structure of the lowest energetic state and in the behavior of the three above ground-state characterizing parameters. © 2015, Editura Academiei Romane. All rights reserved.

Diwakar S.,University of Pavia | Diwakar S.,Consorzio Interuniversitario per le Science Fisiche della Materia | Diwakar S.,Amrita University | Lombardo P.,University of Pavia | And 3 more authors.
PLoS ONE | Year: 2011

Local field-potentials (LFPs) are generated by neuronal ensembles and contain information about the activity of single neurons. Here, the LFPs of the cerebellar granular layer and their changes during long-term synaptic plasticity (LTP and LTD) were recorded in response to punctate facial stimulation in the rat in vivo. The LFP comprised a trigeminal (T) and a cortical (C) wave. T and C, which derived from independent granule cell clusters, co-varied during LTP and LTD. To extract information about the underlying cellular activities, the LFP was reconstructed using a repetitive convolution (ReConv) of the extracellular potential generated by a detailed multicompartmental model of the granule cell. The mossy fiber input patterns were determined using a Blind Source Separation (BSS) algorithm. The major component of the LFP was generated by the granule cell spike Na + current, which caused a powerful sink in the axon initial segment with the source located in the soma and dendrites. Reproducing the LFP changes observed during LTP and LTD required modifications in both release probability and intrinsic excitability at the mossy fiber-granule cells relay. Synaptic plasticity and Golgi cell feed-forward inhibition proved critical for controlling the percentage of active granule cells, which was 11% in standard conditions but ranged from 3% during LTD to 21% during LTP and raised over 50% when inhibition was reduced. The emerging picture is that of independent (but neighboring) trigeminal and cortical channels, in which synaptic plasticity and feed-forward inhibition effectively regulate the number of discharging granule cells and emitted spikes generating "dense" activity clusters in the cerebellar granular layer. © 2011 Diwakar et al.

Politano A.,University of Calabria | Politano A.,Autonomous University of Madrid | Marino A.R.,University of Calabria | Chiarello G.,University of Calabria | Chiarello G.,Consorzio Interuniversitario per le Science Fisiche della Materia
Journal of Chemical Physics | Year: 2010

High-resolution electron energy loss spectroscopy was used to study the coadsorption of alkali metals (Na, K) and oxygen on clean and CO-modified Ni(111) surfaces. We unambiguously show that on an alkali-precovered surface, the alkali-O bond was not formed upon O2 exposure. On the contrary, the alkali-O bond was readily observed by exposing to O2 the Ni(111) surface precovered with an alkali+CO phase. This enhanced oxidation rate of alkali metals in the presence of CO molecules was ascribed to the short-range CO-induced modification of the electronic charge of alkali-metal adatoms. © 2010 American Institute of Physics.

Spagnolo N.,University of Rome La Sapienza | Spagnolo N.,Consorzio Interuniversitario per le Science Fisiche della Materia | Sciarrino F.,University of Rome La Sapienza | Sciarrino F.,Instituto Nazionale Of Ottica | De Martini F.,University of Rome La Sapienza
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We show that the quantum states generated by universal optimal quantum cloning of a single photon represent a universal set of quantum superpositions resilient to decoherence. We adopt the Bures distance as a tool to investigate the persistence of quantum coherence of these quantum states. According to this analysis, the process of universal cloning realizes a class of quantum superpositions that exhibits a covariance property in lossy configuration over the complete set of polarization states in the Bloch sphere. © 2010 The American Physical Society.

Tolu S.,University of Granada | Vanegas M.,University of Genoa | Luque N.R.,University of Granada | Garrido J.A.,Consorzio Interuniversitario per le Science Fisiche della Materia | Ros E.,University of Granada
Biological Cybernetics | Year: 2012

This study proposes an adaptive control architecture based on an accurate regression method called Locally Weighted Projection Regression (LWPR) and on a bio-inspired module, such as a cerebellar-like engine. This hybrid architecture takes full advantage of themachine learning module (LWPR kernel) to abstract an optimized representation of the sensorimotor space while the cerebellar component integrates this to generate corrective terms in the framework of a control task. Furthermore, we illustrate how the use of a simple adaptive error feedback term allows to use the proposed architecture even in the absence of an accurate analytic reference model. The presented approach achieves an accurate control with low gain corrective terms (for compliant control schemes). We evaluate the contribution of the different components of the proposed scheme comparing the obtained performance with alternative approaches. Then, we show that the presented architecture can be used for accurate manipulation of different objects when their physical properties are not directly known by the controller. We evaluate how the scheme scales for simulated plants of high Degrees of Freedom (7-DOFs). © Springer-Verlag 2012.

Johannessen C.,University of Manchester | Blanch E.W.,University of Manchester | Villani C.,University of Rome La Sapienza | Abbate S.,University of Brescia | And 6 more authors.
Journal of Physical Chemistry B | Year: 2013

The Raman optical activity (ROA) spectra of both enantiomers of 2-Br-hexahelicene in chloroform solution have been measured in the range 1700-300 cm-1. Density functional theory (DFT) calculations accurately reproduce the observed features. The most intense ROA features are also the most intense Raman features, in the region 1350-1400 cm-1, and correspond to the so-called D-modes, which play a major role in coronene and other PAHs (polycyclic aromatic hydrocarbons). Together with a detailed analysis of the normal mode structure, the polarizability tensors for the intense Raman features are investigated and related to the principal characteristics of helicene systems, namely, chirality and π-conjugation. Through electron-phonon coupling analysis, we propose a mechanism that justifies the intense ROA signals. © 2013 American Chemical Society.

Tolu S.,University of Granada | Vanegas M.,University of Genoa | Garrido J.A.,Consorzio Interuniversitario per le Science Fisiche della Materia | Luque N.R.,University of Granada | Ros E.,University of Granada
International Journal of Neural Systems | Year: 2013

In this work, a basic cerebellar neural layer and a machine learning engine are embedded in a recurrent loop which avoids dealing with the motor error or distal error problem. The presented approach learns the motor control based on available sensor error estimates (position, velocity, and acceleration) without explicitly knowing the motor errors. The paper focuses on how to decompose the input into different components in order to facilitate the learning process using an automatic incremental learning model (locally weighted projection regression (LWPR) algorithm). LWPR incrementally learns the forward model of the robot arm and provides the cerebellar module with optimal pre-processed signals. We present a recurrent adaptive control architecture in which an adaptive feedback (AF) controller guarantees a precise, compliant, and stable control during the manipulation of objects. Therefore, this approach efficiently integrates a bio-inspired module (cerebellar circuitry) with a machine learning component (LWPR). The cerebellar-LWPR synergy makes the robot adaptable to changing conditions. We evaluate how this scheme scales for robot-arms of a high number of degrees of freedom (DOFs) using a simulated model of a robot arm of the new generation of light weight robots (LWRs). © 2013 World Scientific Publishing Company.

Alfinito E.,University of Salento | Alfinito E.,Consorzio Interuniversitario per le Science Fisiche della Materia | Reggiani L.,Consorzio Interuniversitario per le Science Fisiche della Materia | Reggiani L.,University of Salento
Journal of Physics Condensed Matter | Year: 2013

By considering a set of experiments carried out on bacteriorhodopsin in vitro by Casuso et al (2007 Phys. Rev. E 76 041919), we extract the conductance as function of the applied voltage. The microscopic interpretation of experiments shows that charge transfer is ruled by a direct tunneling (DT) mechanism at low bias and by a Fowler-Nordheim (FN) tunneling mechanism at high bias. A nucleation region at the cross-over between the DT and FN regimes can be identified. A theoretical analysis of conductance fluctuations is performed by calculating the corresponding variance and the probability density functions (PDFs): these constitute a powerful indicator in order to understand the internal dynamics of the system. Conductance fluctuations are non-Gaussian and follow well the standard generalized Gumbel distributions G(a). In particular, at low bias, the PDFs are bimodal and can be resolved in at least a couple of G(a) functions with different values of the shape parameter a. The nucleation region is characterized by a single Gumbel distribution, G(1). At increasing bias, the G(1) distribution turns in a bimodal distribution. We discuss possible correlations between the voltage dependence of the G(a) and the microscopic mechanisms that determine the electrical response of the system. © 2013 IOP Publishing Ltd.

Reggiani L.,University of Salento | Reggiani L.,Consorzio Interuniversitario per le Science Fisiche della Materia | Shiktorov P.,Lithuanian Academy of Sciences | Starikov E.,Lithuanian Academy of Sciences | Gruinskis V.,Lithuanian Academy of Sciences
Fluctuation and Noise Letters | Year: 2012

The quantum fluctuation dissipation theorem (QFDT) in the Callen-Welton [ Phys. Rev. 83 (1951) 34] form is critically revisited. We show that the role of the system eigenvalues is in general not correctly accounted for by the accepted form of the QFDT. As a consequence, a series of quantum results claimed in the literature, like the presence of zero point fluctuations, the violation of the quantum regression hypothesis, the non-white spectrum of the Langevin force, etc. emerge as a consequence of an incorrect application of the theorem. In this context the case of the single harmonic oscillator is illustrated as a typical example where the accepted form of the QFDT is proven to fail. © 2012 World Scientific Publishing Company.

Politano A.,University of Calabria | Marino A.R.,University of Calabria | Formoso V.,University of Calabria | Formoso V.,Consorzio Interuniversitario per le Science Fisiche della Materia | And 2 more authors.
AIP Advances | Year: 2011

Water interaction with quasi-freestanding graphene deposited on Pt(111) has been investigated by using vibrational spectroscopy. Loss measurements show that water molecules dosed at room temperature can dissociate giving rise to C-H bonds. The formation of the C-H bonds strongly attenuates the optical phonons of the graphene sheet. On the other hand, at 100 K water has been found to adsorb only in molecular state. Present findings should be taken into account in engineering graphene-based devices which should work at atmospheric pressure and at room temperature. © Copyright 2011 Author(s).

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