Multiplicative versus additive noise in multi-state neural networks

The effects of a variable amount of random dilution of the synaptic couplings in Q-Ising multi-state neural networks with Hebbian learning are examined. A fraction of the couplings is explicitly allowed to be anti-Hebbian. Random dilution represents the dying or pruning of synapses and, hence, a static disruption of the learning process which can be considered as a form of multiplicative noise in the learning rule. Both parallel and sequential updating of the neurons can be treated. Symmetric dilution in the statics of the network is studied using the mean-field theory approach of statistical mechanics. General dilution, including asymmetric pruning of the couplings, is examined using the generating functional (path integral) approach of disordered systems. It is shown that random dilution acts as additive gaussian noise in the Hebbian learning rule with a mean zero and a variance depending on the connectivity of the network and on the symmetry. Furthermore, a scaling factor appears that essentially measures the average amount of anti-Hebbian couplings.Comment: 15 pages, 5 figures, to appear in the proceedings of the Conference on Noise in Complex Systems and Stochastic Dynamics II (SPIE International

Erratum: “Seed layer technique for high quality epitaxial manganite films” [AIP Advances 6, 085109 (2016)]

No abstract available

A Multiagent Approach to Qualitative Navigation in Robotics

Navigation in unknown unstructured environments is still a difficult open problem in the field of robotics. In this PhD thesis we present a novel approach for robot navigation based on the combination of landmark-based navigation, fuzzy distances and angles representation and multiagent coordination based on a bidding mechanism. The objective has been to have a robust navigation system with orientation sense for unstructured environments using visual information. To achieve such objective we have focused our efforts on two main threads: navigation and mapping methods, and control architectures for autonomous robots. Regarding the navigation and mapping task, we have extended the work presented by Prescott, so that it can be used with fuzzy information about the locations of landmarks in the environment. Together with this extension, we have also developed methods to compute diverting targets, needed by the robot when it gets blocked. Regarding the control architecture, we have proposed a general architecture that uses a bidding mechanism to coordinate a group of systems that control the robot. This mechanism can be used at different levels of the control architecture. In our case, we have used it to coordinate the three systems of the robot (Navigation, Pilot and Vision systems) and also to coordinate the agents that compose the Navigation system itself. Using this bidding mechanism the action actually being executed by the robot is the most valued one at each point in time, so, given that the agents bid rationally, the dynamics of the biddings would lead the robot to execute the necessary actions in order to reach a given target. The advantage of using such mechanism is that there is no need to create a hierarchy, such in the subsumption architecture, but it is dynamically changing depending on the specific situation of the robot and the characteristics of the environment. We have obtained successful results, both on simulation and on real experimentation, showing that the mapping system is capable of building a map of an unknown environment and use this information to move the robot from a starting point to a given target. The experimentation also showed that the bidding mechanism we designed for controlling the robot produces the overall behavior of executing the proper action at each moment in order to reach the target

The signal-to-noise analysis of the Little-Hopfield model revisited

Using the generating functional analysis an exact recursion relation is derived for the time evolution of the effective local field of the fully connected Little-Hopfield model. It is shown that, by leaving out the feedback correlations arising from earlier times in this effective dynamics, one precisely finds the recursion relations usually employed in the signal-to-noise approach. The consequences of this approximation as well as the physics behind it are discussed. In particular, it is pointed out why it is hard to notice the effects, especially for model parameters corresponding to retrieval. Numerical simulations confirm these findings. The signal-to-noise analysis is then extended to include all correlations, making it a full theory for dynamics at the level of the generating functional analysis. The results are applied to the frequently employed extremely diluted (a)symmetric architectures and to sequence processing networks.Comment: 26 pages, 3 figure

An associative network with spatially organized connectivity

We investigate the properties of an autoassociative network of threshold-linear units whose synaptic connectivity is spatially structured and asymmetric. Since the methods of equilibrium statistical mechanics cannot be applied to such a network due to the lack of a Hamiltonian, we approach the problem through a signal-to-noise analysis, that we adapt to spatially organized networks. The conditions are analyzed for the appearance of stable, spatially non-uniform profiles of activity with large overlaps with one of the stored patterns. It is also shown, with simulations and analytic results, that the storage capacity does not decrease much when the connectivity of the network becomes short range. In addition, the method used here enables us to calculate exactly the storage capacity of a randomly connected network with arbitrary degree of dilution.Comment: 27 pages, 6 figures; Accepted for publication in JSTA

Influence of synthesis conditions on properties of green-reduced graphene oxide

[EN] Green reduction of graphene oxide (GO) was performed using ascorbic acid (AA) in the presence of poly(sodium 4-styrenesulfonate), which resulted in reduced graphene oxide (PSS-rGO) with excellent solubility and stability in water. Large rGO sheets of 4 mu m(2) area and 1.1-nm thickness were obtained. The measurements showed that noncovalent functionalization with PSS molecules prevented rGO from aggregation. The parameters of graphite oxidation process and AA: GO w/w ratio were evaluated, and the obtained results showed that the properties of the reduced material (PSS-rGO) can be tailored by proper selection and adjustment of these parameters.The authors thank the European Commission for their financial support through the project no. NMP3-SL-2010-246073.Pruna, A.; Pullini, D.; Busquets, D. (2013). Influence of synthesis conditions on properties of green-reduced graphene oxide. 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On metastable configurations of small-world networks

We calculate the number of metastable configurations of Ising small-world networks which are constructed upon superimposing sparse Poisson random graphs onto a one-dimensional chain. Our solution is based on replicated transfer-matrix techniques. We examine the denegeracy of the ground state and we find a jump in the entropy of metastable configurations exactly at the crossover between the small-world and the Poisson random graph structures. We also examine the difference in entropy between metastable and all possible configurations, for both ferromagnetic and bond-disordered long-range couplings.Comment: 9 pages, 4 eps figure

Creative, Convergent, and Social: Prospects for Mobile Computing

This paper highlights the over-arching themes salient in the rapidly converging mobile computing industry. Increasingly, the developers of mobile devices and services are looking toward exploratory, non-determinist or, user-driven development methodologies in an effort to cultivate products that consumers will consistently pay for. These include Design Thinking, Living Labs, and other forms of ethnography that embrace serendipity, playfulness, error, and other human responses that have previously rested outside the orthodoxy of technology design. Secondly, the mobile device is likely the world\u27s foremost social computer. Mobile vendors seeking to foster the production, propagation, and consumption of content on mobile devices are increasingly viewing the challenge as a complex social phenomenon, not a merely a well-defined technology problem. Research illustrating these themes is presented