765 research outputs found

    Integration of Action and Language Knowledge: A Roadmap for Developmental Robotics

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    “This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.”This position paper proposes that the study of embodied cognitive agents, such as humanoid robots, can advance our understanding of the cognitive development of complex sensorimotor, linguistic, and social learning skills. This in turn will benefit the design of cognitive robots capable of learning to handle and manipulate objects and tools autonomously, to cooperate and communicate with other robots and humans, and to adapt their abilities to changing internal, environmental, and social conditions. Four key areas of research challenges are discussed, specifically for the issues related to the understanding of: 1) how agents learn and represent compositional actions; 2) how agents learn and represent compositional lexica; 3) the dynamics of social interaction and learning; and 4) how compositional action and language representations are integrated to bootstrap the cognitive system. The review of specific issues and progress in these areas is then translated into a practical roadmap based on a series of milestones. These milestones provide a possible set of cognitive robotics goals and test scenarios, thus acting as a research roadmap for future work on cognitive developmental robotics.Peer reviewe

    Tuning the crystallinity parameters in macroporous titania films

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    Although macroporous titania scaffolds are used for many different applications, not much is known about the importance of the synthesis strategy on the resulting materials' properties. We present a comparative study on the influence of different colloidal titania precursors for direct co-deposition with poly(methyl methacrylate) (PMMA) beads on the properties of the resulting macroporous scaffolds after calcination. The colloidal titania precursors for the film assembly differ in their size and initial crystallinity, ranging from amorphous sol-gel clusters to already crystalline pre-formed particles of 4 nm, 6 nm and 20 nm in size, as well as a combination of sol-gel and nanoparticle precursors in the so-called `Brick and Mortar' approach. The type of the precursor greatly influences the morphology, texture and the specific crystallinity parameters of the macroporous titania scaffolds after calcination such as the size of the crystalline domains, packing density of the crystallites in the macroporous walls and interconnectivity between the crystals. Moreover, the texture and the crystallinity of the films can be tuned by postsynthesis processing of the films such as calcination at different temperatures, which can be also preceded by a hydrothermal treatment. The ability to adjust the porosity, the total surface area and the crystallinity parameters of the crystalline macroporous films by selecting suitable precursors and by applying different post-synthetic treatments provides useful tools to optimize the film properties for different applications

    Doppler Shift in Andreev Reflection from a Moving Superconducting Condensate in Nb/InAs Josephson Junctions

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    We study narrow ballistic Josephson weak links in a InAs quantum wells contacted by Nb electrodes and find a dramatic magnetic-field suppression of the Andreev reflection amplitude, which occurs even for in-plane field orientation with essentially no magnetic flux through the junction. Our observations demonstrate the presence of a Doppler shift in the energy of the Andreev levels, which results from diamagnetic screening currents in the hybrid Nb/InAs-banks. The data for conductance, excess and critical currents can be consistently explained in terms of the sample geometry and the McMillan energy, characterizing the transparency of the Nb/InAs-interface.Comment: 4 pages, 5 figures, title modifie

    Sonoluminescence: Nature's Smallest BlackBody

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    The Spectrum of the light emitted by a sonoluminescing bubble is extremely well fit by the spectrum of a blackbody. Furthermore the radius of emission can be smaller than the wavelength of the light. Consequences, for theories of sonoluminescence are discussed.Comment: 8 pages, 3 Figure

    Deep Autoencoding Models for Unsupervised Anomaly Segmentation in Brain MR Images

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    Reliably modeling normality and differentiating abnormal appearances from normal cases is a very appealing approach for detecting pathologies in medical images. A plethora of such unsupervised anomaly detection approaches has been made in the medical domain, based on statistical methods, content-based retrieval, clustering and recently also deep learning. Previous approaches towards deep unsupervised anomaly detection model patches of normal anatomy with variants of Autoencoders or GANs, and detect anomalies either as outliers in the learned feature space or from large reconstruction errors. In contrast to these patch-based approaches, we show that deep spatial autoencoding models can be efficiently used to capture normal anatomical variability of entire 2D brain MR images. A variety of experiments on real MR data containing MS lesions corroborates our hypothesis that we can detect and even delineate anomalies in brain MR images by simply comparing input images to their reconstruction. Results show that constraints on the latent space and adversarial training can further improve the segmentation performance over standard deep representation learning

    Excitonic Effects on Optical Absorption Spectra of Doped Graphene

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    We have performed first-principles calculations to study optical absorption spectra of doped graphene with many-electron effects included. Both self-energy corrections and electron-hole interactions are reduced due to the enhanced screening in doped graphene. However, self-energy corrections and excitonic effects nearly cancel each other, making the prominent optical absorption peak fixed around 4.5 eV under different doping conditions. On the other hand, an unexpected increase of the optical absorbance is observed within the infrared and visible-light frequency regime (1 ~ 3 eV). Our analysis shows that a combining effect from the band filling and electron-hole interactions results in such an enhanced excitonic effect on the optical absorption. These unique variations of the optical absorption of doped graphene are of importance to understand relevant experiments and design optoelectronic applications.Comment: 15 pages, 5 figures; Nano Lett., Article ASAP (2011

    Ab-initio calculation of the electronic and optical excitations in polythiophene: effects of intra- and interchain screening

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    We present an calculation of the electronic and optical excitations of an isolated polythiophene chain as well as of bulk polythiophene. We use the GW approximation for the electronic self-energy and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. The inclusion of interchain screening in the case of bulk polythiophene drastically reduces both the quasi-particle band gap and the exciton binding energies, but the optical gap is hardly affected. This finding is relevant for conjugated polymers in general.Comment: 4 pages, 1 figur

    Molecular geometry optimization with a genetic algorithm

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    We present a method for reliably determining the lowest energy structure of an atomic cluster in an arbitrary model potential. The method is based on a genetic algorithm, which operates on a population of candidate structures to produce new candidates with lower energies. Our method dramatically outperforms simulated annealing, which we demonstrate by applying the genetic algorithm to a tight-binding model potential for carbon. With this potential, the algorithm efficiently finds fullerene cluster structures up to C60{\rm C}_{60} starting from random atomic coordinates.Comment: 4 pages REVTeX 3.0 plus 3 postscript figures; to appear in Physical Review Letters. Additional information available under "genetic algorithms" at http://www.public.iastate.edu/~deaven

    Optical absorption spectra of finite systems from a conserving Bethe-Salpeter equation approach

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    We present a method for computing optical absorption spectra by means of a Bethe-Salpeter equation approach, which is based on a conserving linear response calculation for electron-hole coherences in the presence of an external electromagnetic field. This procedure allows, in principle, for the determination of the electron-hole correlation function self-consistently with the corresponding single-particle Green function. We analyze the general approach for a "one-shot" calculation of the photoabsorption cross section of finite systems, and discuss the importance of scattering and dephasing contributions in this approach. We apply the method to the closed-shell clusters Na_4, Na^+_9 and Na^+_(21), treating one active electron per Na atom.Comment: 9 pages, 3 figure

    Excitonic effects in solids described by time-dependent density functional theory

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    Starting from the many-body Bethe-Salpeter equation we derive an exchange-correlation kernel fxcf_{xc} that reproduces excitonic effects in bulk materials within time-dependent density functional theory. The resulting fxcf_{xc} accounts for both self-energy corrections and the electron-hole interaction. It is {\em static}, {\em non-local} and has a long-range Coulomb tail. Taking the example of bulk silicon, we show that the α/q2- \alpha / q^2 divergency is crucial and can, in the case of continuum excitons, even be sufficient for reproducing the excitonic effects and yielding excellent agreement between the calculated and the experimental absorption spectrum.Comment: 6 pages, 1 figur
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