Dreaming neural networks: forgetting spurious memories and reinforcing pure ones

The standard Hopfield model for associative neural networks accounts for biological Hebbian learning and acts as the harmonic oscillator for pattern recognition, however its maximal storage capacity is $\alpha \sim 0.14$, far from the theoretical bound for symmetric networks, i.e. $\alpha =1$. Inspired by sleeping and dreaming mechanisms in mammal brains, we propose an extension of this model displaying the standard on-line (awake) learning mechanism (that allows the storage of external information in terms of patterns) and an off-line (sleep) unlearning$\&$consolidating mechanism (that allows spurious-pattern removal and pure-pattern reinforcement): this obtained daily prescription is able to saturate the theoretical bound $\alpha=1$, remaining also extremely robust against thermal noise. Both neural and synaptic features are analyzed both analytically and numerically. In particular, beyond obtaining a phase diagram for neural dynamics, we focus on synaptic plasticity and we give explicit prescriptions on the temporal evolution of the synaptic matrix. We analytically prove that our algorithm makes the Hebbian kernel converge with high probability to the projection matrix built over the pure stored patterns. Furthermore, we obtain a sharp and explicit estimate for the "sleep rate" in order to ensure such a convergence. Finally, we run extensive numerical simulations (mainly Monte Carlo sampling) to check the approximations underlying the analytical investigations (e.g., we developed the whole theory at the so called replica-symmetric level, as standard in the Amit-Gutfreund-Sompolinsky reference framework) and possible finite-size effects, finding overall full agreement with the theory.Comment: 31 pages, 12 figure

The scorpion collections (Arachnida, Scorpiones) held in the Museo Regionale di Scienze Naturali of Turin (Italy)

Data and considerations about the history and contents of the scorpion collection housed in the Museo Regionale di Scienze Naturali of Turin (MRSN) are reported. Information on type material and important historical specimens are provided, as well as biographical notes about the major zoologists of the museum

Bollywood: New contexts and new audiences

Coincidiendo con algunos espectaculares éxitos de taquilla a mediados de los 90, el pujante cine popular hindi –Bollywood, de acuerdo con la terminología que acababa entonces de acuñarse– se adentró con paso firme en una nueva era, superando una crisis de creatividad bien apreciable en la década anterior y, sobre todo, renovando fórmulas expresivas en una dirección todavía difícil de determinar, pero indudablemente más atenta al público global que al tradicional espectador local. Limando aquellas aristas formales menos susceptibles de un consumo globalizado (o, simplemente, menos del gusto de un nuevo público joven y urbano en la propia India), asumiendo ciertos riesgos en el tratamiento de problemáticas delicadas y, a la postre, renegociando creativamente la propia herencia de la tradición del cine comercial hindi producido en Mumbai (Bombay), esta sensibilidad neo-Bollywood parece haberse impuesto con fuerza en los últimos quince años, al tiempo que las viejas fórmulas de consumo dejan paso a otras nuevas y, al calor de dicho proceso, se van configurando nuevos públicos que a su vez inciden de manera determinante sobre los propios mecanismos de producciónCoinciding with some spectacular box office hits in the mid-90s, the buoyant popular Hindi cinema –Bollywood in the newly created terminology– firmly went into a new era. It overcame the creativity crisis of the previous decade and, above all, renewed formulas of expression in ways still hard to define, but without any doubt more attentive to the global public than to the traditional local one. This Neo-Bollywood sensitivity has gained strength in the last fifteen years by refining formal elements less acceptable for global consumption (or simply, those that are far removed from the tastes of the young urban Indian public); by taking some risks in the treatment of more controversial issues; and finally, by creatively renegotiating the inherited traditions of the commercial Hindi cinema produced in Mumbai (Bombay). At the same time, the old forms of consumption have given way to new ones and in the process new audiences have emerged that have a decisive impact on the mechanisms of productio

A Broadband Bow-Tie Cavity-Backed Slot for Traveling-Wave Arrays in the Millimeter-Wave Band

The use of bow-tie geometries to enhance the characteristics of a radiating element previously proposed by the authors is presented. The previous element consisted of a broadband cavity-backed slot in transmission configuration. The bow-tie shape of the cavity improves the bandwidth of the element and the bow-tie slot keeps constant the amount of power radiated. The structure is designed for the millimeterwave band. The enhancement of the element performance is shown through simulation results. A fractional bandwidth of more than 100% is achieved in the 70 GHz band, and the radiated power remains almost constant throughout 30 GHz of the bandwidth. These results show a great improvement over the original radiating element. The radiating structure has the ideal characteristics for building series-fed reconfigurable arrays for wide-band applications in the millimeter-wave band.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported in part by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 706334, in part by the Spanish Ministerio de Educaci´on, Cultura y Deporte (Programa para la Formaci´on del Profesorado Universitario) under Grant FPU15/06457 and in other part by the Spanish Ministerio de Econom´ıa y Competitividad, under the project ADDMATE TEC2016-76070-CR3-3-R