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Self-organizing memristive nanowire connectomes have been exploited for physical (in materia) implementation of brain-inspired computing paradigms. Despite the emergent behavior was shown to rely on weight plasticity at single junction/synapse level and wiring plasticity involving topological changes, a shift to multiterminal paradigms is needed to unveil dynamics at the network level. Here, we report on tomographical evidence of memory engrams(or memory traces) in nanowire connectomes, i.e., chemical and physical changes in biological neural substrates supposed to endow the representation of experience stored in the brain. An experimental/modeling approach shows that spatially correlated short-term plasticity effects can turn into long-lasting engram memory patterns inherently related to network topology inhomogeneities. The ability to exploit both encoding and consolidation of information on the same physical substrate would open radically new perspectives for in materiacomputing, while offering to neuroscientists an alternative platform to understand the role of memory in learning and knowledge.

This paper proposes the characterization of stimulation and detection equipment in the design of wearable brain-computer interfaces based on visually evoked potentials. In particular, methods for the characterization of the optical output of commercial smart glasses, and for the calibration of a low-cost electroencephalograph are presented and discussed. The reported results show that, by proper characterization and calibration, consumer-grade equipment is suitable for brain-computer interface applications. Moreover, unexpected harmonics of the visual stimuli have to be taken into account by suitable processing. Finally, the electroencephalograph shows an adequate linear behavior, but its gain error of around 10% should be corrected by calibration in some applications.

In this work, the calibration of a commercial, low-cost electroencephalograph (Olimex EEG-SMT) is presented. Several works report about many wearable neural interfaces based on this device. On the contrary, metrological characterization of this electroencephalograph is lacking. The work reports that preliminary calibration results on this device showed good linearity but also a magnitude error around 8%, with a substantial dependence on frequency. This may lead to incorrect interpretations of the harmonic content of the observed brain-generated electrical potentials. Consequently, for applications based on neural activity monitoring, a metrological calibration of the electroencephalograph is important. Moreover, the proposed calibration method can be adapted to other similar devices.

The knowledge of the spatial distribution of the electrical conductivity of metallic nanowire networks (NWN) is important for tailoring the performance in applications. This work focuses on Electrical Resistance Tomography (ERT), a technique that maps the electrical conductivity of a sample from several resistance measurements performed on its border. We show that ERT can be successfully employed for NWN characterisation if a dedicated measurement protocol is employed. When applied to other materials, ERT measurements are typically performed with a constant current excitation; we show that, because of the peculiar microscopic structure and behaviour of metallic NWN, a constant voltage excitation protocols is preferable. This protocol maximises the signal to noise ratio in the resistance measurements—and thus the accuracy of ERT maps—while preventing the onset of sample alterations.

Graphene has become the focus of extensive research efforts and it can now be produced in wafer-scale. For the development of next generation graphene-based electronic components, electrical characterization of graphene is imperative and requires the measurement of work function, sheet resistance, carrier concentration and mobility in both macro-, micro- and nano-scale. Moreover, commercial applications of graphene require fast and large-area mapping of electrical properties, rather than obtaining a single point value, which should be ideally achieved by a contactless measurement technique. We demonstrate a comprehensive methodology for measurements of the electrical properties of graphene that ranges from nano- to macro- scales, while balancing the acquisition time and maintaining the robust quality control and reproducibility between contact and contactless methods. The electrical characterisation is achieved by using a combination of techniques, including magneto-transport in the van der Pauw geometry, THz time-domain spectroscopy mapping and calibrated Kelvin probe force microscopy. The results exhibit excellent agreement between the different techniques. Moreover, we highlight the need for standardized electrical measurements in highly controlled environmental conditions and the application of appropriate weighting functions.

A calibration/verification testbed for electrical energy meters is under development at the Istituto Nazionale di Ricerca Metrologica, the National Metrology Institute of Italy. The testbed will be employed for the calibration of commercial static power energy meters under low power conditions and for simulating the verification in the field of energy meters under real operational conditions. The activity is in collaboration with the Ministry for Economic Development and aims to the future development of regulatory documents for energy metering verification.

This paper addresses the calibration of lock-in amplifiers in the low frequency range. A simple but effective calibration setup implemented at INRIM is described. This includes a stable low-voltage source, composed of a digital sine wave generator and a cascade of two voltage dividers, one inductive and one resistive. The magnitude error is the lock-in magnitude error, which can be determined with an uncertainty of the order of 10−4 or better, that is, two orders of magnitude lower than the typical lock-in accuracy specification. The system can operate with an input voltage from 0.1 µV to 10 µV and a frequency from a few hertz to about 1 kHz. The performances of the calibration setup were evaluated at 1 µV and 10 μV at 20 Hz and 103 Hz and compared with those of another existing setup, implemented at METAS, through a direct comparison in the framework of an EURAMET research project.

We propose a simple algorithm to locate the "corner" of an L-curve, a function often used to select the regularisation parameter for the solution of ill-posed inverse problems. The algorithm involves the Menger curvature of a circumcircle and the golden section search method. It efficiently finds the regularisation parameter value corresponding to the maximum positive curvature region of the L-curve. The algorithm is applied to some commonly available test problems and compared to the typical way of locating the l-curve corner by means of its analytical curvature. The application of the algorithm to the data processing of an electrical resistance tomography experiment on thin conductive films is also reported., Comment: 11 pages, 6 figures. Keywords: inverse problem, ill-posed problem, regularization parameter, L-curve, golden section search, Menger curvature, electrical resistance tomography

Young Researcher Meeting, Rome 2019 Fabio Agostini, Lorenzo Aiello, Claudia Antolini, Guerino Avallone, Anna Silvia Baldi, Alessandro Buzzelli, Alessandro Cultrera, Domenico D'Agostino, Rocco D’Agostino, Marco Di Stefano, Luca Giovannelli, Marina Migliaccio, Elisa Nichelli, Lorenzo Pagnanini, Davide Pietrobon, Luca Pizzimento, Emanuela Pusceddu, Matteo Serra, Francesco Stellato, Giorgio Viavattene. The Young Researcher Meeting celebrated its 10th anniversary with a four-day conference held at the University of Rome “Tor Vergata” on 18th - 21st June 2019. It was, indeed, 2009 when a group of PhD students at this same university seeded the idea of starting a series of informal meetings for young researchers to foster discussion on progress in active research fields of Physics and related disciplines. Over the last ten years, the Young Researcher Meeting has become an awaited yearly appointment and it has been hosted by several universities and research institutes. The itinerant character reflects one of the main goals of the event: promoting interdisciplinary and international collaborations among young researchers. The program of the 10th edition was organized in sessions covering six main topics: Applied Physics, Astrophysics and Cosmology, Biophysics, Matter Physics, Particle Physics and Theoretical Physics. It included 40 plenary talks and a polyhedric poster session with 60 original contributions. The conference opening day had as exclusive setting Villa Mondragone, a beautiful XVI century villa overlooking the city of Rome. One of the highlights of the day was an engaging round table discussion on the link between Physics and Industry, during which panelists Dr D. Ricci Pacifici and Dr N. Said, both physicists pursuing a career in the private sector, together with representatives of AKKA Technologies, exchanged their views. The discussion and the interaction with the audience was moderated by Dr E. Nichelli. Two invited keynote speakers have further contributed to the program of the conference: Dr M. Lattanzi, from INFN Ferrara, who discussed the current status and challenges in cosmology, and Dr C. Attaccalite of the Centre Interdisciplinaire de Nanoscience de Marseille, who presented a lucid analysis of the story of academic publishing “from Galileo to Nature”. The consolidated format of the conference also foresees visits to the research facilities that are present in the area where the meeting is hosted. At this edition, participants had the unique opportunity to join a visit to the INFN-National Laboratories of Frascati, which was introduced by the talks of Dr P. Gianotti and Dr A. Balerna. Finally, on the last day of the conference, a guided tour of ancient Rome was offered to the participants who strolled through the streets of the eternal city. The present volume of papers contains a selection of the contributions presented at the conference as either talks or posters. They cover topics on Applied Physics, Astrophysics and Cosmology, Biophysics, Matter Physics, Particle Physics and Theoretical Physics. List of Conference Webpage, ACKNOWLEDGEMENTS, Photos, Logos are available in this pdf.

Electronic applications of large-area graphene films require rapid and accurate methods to map their electrical properties. Here we present the first electrical resistance tomography (ERT) measurements on large-area graphene samples, obtained with a dedicated measurement setup and reconstruction software. The outcome of an ERT measurement is a map of the graphene electrical conductivity. The same setup allows to perform van der Pauw (vdP) measurements of the average conductivity. We characterised the electrical conductivity of chemical-vapour deposited graphene samples by performing ERT, vdP and scanning terahertz time-domain spectroscopy (TDS), the last one by means of a commercial instrument. The measurement results are compared and discussed, showing the potential of ERT as an accurate and reliable technique for the electrical characterization of graphene samples. The work is part of the European project 'GRACE–Developing electrical characterisation methods for future graphene electronics', code 16NRM01. This project has received funding from the European Metrology Programme for Innovation and Research (EMPIR) programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

It has already been reported that 1/f noise in graphene can be dominated by fluctuations of charge carrier mobility. We show here that the increasing damage induced by oxygen plasma on graphene samples result in two trends: at low doses, the magnitude of the 1/f noise increases with the dose; and at high doses, it decreases with the dose. This behaviour is interpreted in the framework of 1/f noise generated by carrier mobility fluctuations where the concentration of mobility fluctuation centers and the mean free path of the carriers are competing factors.

GRACE - Developing electrical characterisation methods for future graphene electronics is a 2016 Normative Joint Research Project of the European Metrology Programme for Innovation and Research. The project focuses on the measurement of the electrical properties of graphene. Its objectives are to develop validated measurement methods and protocols, including fast-throughput examples. The work is performed in collaboration with international standardisation committees, with an aim to initiate and develop dedicated documentary standards.

The Electrical Resistance Tomography (ERT) technique is applied to the measurement of sheet conductance maps of both uniform and patterned conductive thin films. Images of the sheet conductance spatial distribution, and local conductivity values are obtained. Test samples are tin oxide films on glass substrates, with electrical contacts on the sample boundary, some samples are deliberately patterned in order to induce null conductivity zones of known geometry while others contain higher conductivity inclusions. Four-terminal resistance measurements among the contacts are performed with a scanning setup. The ERT reconstruction is performed by a numerical algorithm based on the total variation regularization and the L-curve method. ERT correctly images the sheet conductance spatial distribution of the samples. The reconstructed conductance values are in good quantitative agreement with independent measurements performed with the van der Pauw and the four-point probe methods., Comment: IEEE Transactions on Instrumentation and Measurement

In this paper Electrical Resistance Tomography is applied to recover maps of sheet conductance of commercial metal-oxide thin films, chosen as test material. Results are compared to nominal specifications and van der Pauw, four-point probe measurements. It is shown how Electrical Resistance Tomography can measure with good accuracy the nominal conductance value in uniform samples and also identify resistivity inhomogeneities in altered samples. The choice of the reconstruction algorithm is also briefly discussed.

We report experimental and theoretical evidence of the different mechanisms that lead to doping of Si nanowires upon molecular adsorption of two paradigmatic Lewis bases. Pyridine genuinely dopes the nanowires by injecting charge carriers. Ethanol, on the other hand, simply modifies the dielectric screening conditions, allowing the reactivation of preexisting electrically passive impurities, and thus cannot control neither the nature (n- vs p-type) nor the concentration of the carriers. (C) 2013 AIP Publishing LLC.

The characterization of the intrinsic electrical properties of large surface area materials such as mesoporous nanocrystalline (nc-TiO2), requires one to avoid sensor-like responses to external agents. Both an appropriate sample configuration and a suitable measurement protocol are mandatory. In this work, both the stack and planar contacts configurations were studied, the latter giving evidence which is potentially useful for space charge limited (SCL) current investigations in order to study the band-gap states (BGSs) properties in nc-TiO2. Moreover, in the absence of a suitable measurement protocol, standard dye sensitized solar cells (DSSCs) electrode films show apparent SCL current behaviour, as a consequence of the surface electrical transport contribution due to the physisorbed water on the hydroxylated metal oxide large surface area. This feature recalls the typical results of electrolyte filled systems, in which an exponential distribution of trap states is reported; it is not expected to be an intrinsic feature of the nc-TiO2 trap states distribution. In the absence of adsorbates, no deviation from an ohmic regime is observed in standard electrodes, while in planar configuration samples, the SCL regime is accessible and shows a different BGS signature. The nature of electrical contacts, ohmic in this situation, is also discussed.