Soliton Stability in Systems of Two Real Scalar Fields

In this paper we consider a class of systems of two coupled real scalar fields in bidimensional spacetime, with the main motivation of studying classical or linear stability of soliton solutions. Firstly, we present the class of systems and comment on the topological profile of soliton solutions one can find from the first-order equations that solve the equations of motion. After doing that, we follow the standard approach to classical stability to introduce the main steps one needs to obtain the spectra of Schr\"odinger operators that appear in this class of systems. We consider a specific system, from which we illustrate the general calculations and present some analytical results. We also consider another system, more general, and we present another investigation, that introduces new results and offers a comparison with the former investigations.Comment: 16 pages, Revtex, 3 f igure

Rehybridization of electronic structure in compressed two-dimensional quantum dot superlattices

Two-dimensional superlattices of organically passivated 2.6-nm silver quantum dots were prepared as Langmuir monolayers and transferred to highly oriented pyrolytic graphite substrates. The structural and electronic properties of the films were probed with variable temperature scanning tunneling microscopy. Particles passivated with decanethiol (interparticle separation distance of ∼1.1±0.2 nm) exhibited Coulomb blockade and staircase. For particles passivated with hexanethiol or pentanethiol (interparticle separation distance of ∼0.5±0.2 nm), the single-electron charging was quenched, and the redistribution of the density of states revealed that strong quantum mechanical exchange, i.e., wave-function hybridization, existed among the particles in these films

Mapping the dialog act annotations of the LEGO corpus into ISO 24617-2 communicative functions

ISO 24617-2, the ISO standard for dialog act annotation, sets the ground for more comparable research in the area. However, the amount of data annotated according to it is still reduced, which impairs the development of approaches for automatic recognition. In this paper, we describe a mapping of the original dialog act labels of the LEGO corpus, which have been neglected, into the communicative functions of the standard. Although this does not lead to a complete annotation according to the standard, the 347 dialogs provide a relevant amount of data that can be used in the development of automatic communicative function recognition approaches, which may lead to a wider adoption of the standard. Using the 17 English dialogs of the DialogBank as gold standard, our preliminary experiments have shown that including the mapped dialogs during the training phase leads to improved performance while recognizing communicative functions in the Task dimension.info:eu-repo/semantics/publishedVersio

Automatic recognition of the general-purpose communicative functions defined by the ISO 24617-2 standard for dialog act annotation

From the perspective of a dialog system, it is important to identify the intention behind the segments in a dialog, since it provides an important cue regarding the information that is present in the segments and how they should be interpreted. ISO 24617-2, the standard for dialog act annotation, defines a hierarchically organized set of general-purpose communicative functions which correspond to different intentions that are relevant in the context of a dialog. We explore the automatic recognition of these communicative functions in the DialogBank, which is a reference set of dialogs annotated according to this standard. To do so, we propose adaptations of existing approaches to flat dialog act recognition that allow them to deal with the hierarchical classification problem. More specifically, we propose the use of an end-to-end hierarchical network with cascading outputs and maximum a posteriori path estimation to predict the communicative function at each level of the hierarchy, preserve the dependencies between the functions in the path, and decide at which level to stop. Furthermore, since the amount of dialogs in the DialogBank is small, we rely on transfer learning processes to reduce overfitting and improve performance. The results of our experiments show that our approach outperforms both a flat one and hierarchical approaches based on multiple classifiers and that each of its components plays an important role towards the recognition of general-purpose communicative functions.info:eu-repo/semantics/publishedVersio

Confining potential in a color dielectric medium with parallel domain walls

We study quark confinement in a system of two parallel domain walls interpolating different color dielectric media. We use the phenomenological approach in which the confinement of quarks appears considering the QCD vacuum as a color dielectric medium. We explore this phenomenon in QCD_2, where the confinement of the color flux between the domain walls manifests, in a scenario where two 0-branes (representing external quark and antiquark) are connected by a QCD string. We obtain solutions of the equations of motion via first-order differential equations. We find a new color confining potential that increases monotonically with the distance between the domain walls.Comment: RevTex4, 5 pages, 1 figure; version to appear in Int. J. Mod. Phys.

End-to-end multi-level dialog act recognition

The three-level dialog act annotation scheme of the DIHANA corpus poses a multi-level classification problem in which the bottom levels allow multiple or no labels for a single segment. We approach automatic dialog act recognition on the three levels using an end-to-end approach, in order to implicitly capture relations between them. Our deep neural network classifier uses a combination of word- and character-based segment representation approaches, together with a summary of the dialog history and information concerning speaker changes. We show that it is important to specialize the generic segment representation in order to capture the most relevant information for each level. On the other hand, the summary of the dialog history should combine information from the three levels to capture dependencies between them. Furthermore, the labels generated for each level help in the prediction of those of the lower levels. Overall, we achieve results which surpass those of our previous approach using the hierarchical combination of three independent per-level classifiers. Furthermore, the results even surpass the results achieved on the simplified version of the problem approached by previous studies, which neglected the multi-label nature of the bottom levels and only considered the label combinations present in the corpus.info:eu-repo/semantics/publishedVersio

A curiosity model for artificial agents

Curiosity is an inherent characteristic of the animal instinct, which stimulates the need to obtain further knowledge and leads to the exploration of the surrounding environment. In this document we present a computational curiosity model, which aims at simulating that kind of behavior on artificial agents. This model is influenced by the two main curiosity theories defended by psychologists – Curiosity Drive Theory and Optimal Arousal Model. By merging both theories, as well as aspects from other sources, we concluded that curiosity can be defined in terms of the agent’s personality, its level of arousal, and the interest of the object of curiosity. The interest factor is defined in terms of the importance of the object of curiosity to the agent’s goals, its novelty, and surprise. To assess the performance of the model in practice, we designed a scenario consisting of virtual agents exploring a tile-based world, where objects may exist. The performance of the model in this scenario was evaluated in incremental steps, each one introducing a new component to the model. Furthermore, in addition to empirical evaluation, the model was also subjected to evaluation by human observers. The results obtained from both sources show that our model is able to simulate curiosity on virtual agents and that each of the identified factors has its role in the simulation.info:eu-repo/semantics/acceptedVersio