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Phillips W.A.,University of Stirling | Phillips W.A.,Frankfurt Institute of Advanced Studies
Behavioral and Brain Sciences | Year: 2013

Life is preserved and enhanced by coordinated selectivity in local neural circuits. Narrow receptive-field selectivity is necessary to avoid the curse-of-dimensionality, but local activities can be made coherent and relevant by guiding learning and processing using broad coordinating contextual gain-controlling interactions. Better understanding of the functions and mechanisms of those interactions is therefore crucial to the issues Clark examines. © 2013 Cambridge University Press.

Zhi Q.,TU Darmstadt | Zhi Q.,Helmholtz Center for Heavy Ion Research | Zhi Q.,Guizhou Normal University | Caurier E.,University of Strasbourg | And 7 more authors.
Physical Review C - Nuclear Physics | Year: 2013

We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilities of the r-process waiting-point nuclei at the magic neutron numbers N=50, 82, and 126. The calculations include contributions from allowed Gamow-Teller and first-forbidden transitions. We find good agreement with the measured half-lives for the N=50 nuclei with charge numbers Z=28-32 and for the N=82 nuclei 129Ag and 130Cd. The contribution of forbidden transitions reduce the half-lives of the N=126 waiting-point nuclei significantly, while they have only a small effect on the half-lives of the N=50 and 82 r-process nuclei. © 2013 American Physical Society.

Erler J.,Friedrich - Alexander - University, Erlangen - Nuremberg | Erler J.,University of Tennessee at Knoxville | Erler J.,Oak Ridge National Laboratory | Langanke K.,Helmholtz Center for Heavy Ion Research | And 7 more authors.
Physical Review C - Nuclear Physics | Year: 2012

We present a systematics of fission barriers and fission lifetimes for the whole landscape of superheavy elements (SHE), i.e., nuclei with Z100. The fission lifetimes are also compared with the α-decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parametrizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. The computation of fission lifetimes takes care of the crucial ingredients of the large-amplitude collective dynamics along the fission path, as self-consistent collective mass and proper quantum corrections. We discuss the different topologies of fission landscapes which occur in the realm of SHE (symmetric versus asymmetric fission, regions of triaxial fission, bimodal fission, and the impact of asymmetric ground states). The explored region is extended deep into the regime of very neutron-rich isotopes as they are expected to be produced in the astrophysical r process. © 2012 American Physical Society.

Phillips W.A.,University of Stirling | Phillips W.A.,Frankfurt Institute of Advanced Studies
Information (Switzerland) | Year: 2012

This paper discusses concepts of self-organized complexity and the theory of Coherent Infomax in the light of Jaynes's probability theory. Coherent Infomax, shows, in principle, how adaptively self-organized complexity can be preserved and improved by using probabilistic inference that is context-sensitive. It argues that neural systems do this by combining local reliability with flexible, holistic, context-sensitivity. Jaynes argued that the logic of probabilistic inference shows it to be based upon Bayesian and Maximum Entropy methods or special cases of them. He presented his probability theory as the logic of science; here it is considered as the logic of life. It is concluded that the theory of Coherent Infomax specifies a general objective for probabilistic inference, and that contextual interactions in neural systems perform functions required of the scientist within Jaynes's theory. © 2012 by the authors.

Schurhoff T.,Frankfurt Institute of Advanced Studies | Schurhoff T.,Goethe University Frankfurt | Schramm S.,Frankfurt Institute of Advanced Studies | Schramm S.,Goethe University Frankfurt | And 2 more authors.
Astrophysical Journal Letters | Year: 2010

Recent neutron star observations suggest that the masses and radii of neutron stars may be smaller than previously considered, which would disfavor a purely nucleonic equation of state (EoS). In our model, we use a flavor SU(3) sigma model that includes Δ resonances and hyperons in the EoS. We find that if the coupling of the Δ resonances to the vector mesons is slightly smaller than that of the nucleons, we can reproduce both the measured mass-radius relationship and the extrapolated EoS. © 2010 The American Astronomical Society. All rights reserved.

Chandrapala T.N.,Hong Kong University of Science and Technology | Shi B.E.,Hong Kong University of Science and Technology | Triesch J.,Frankfurt Institute of Advanced Studies
5th Joint International Conference on Development and Learning and Epigenetic Robotics, ICDL-EpiRob 2015 | Year: 2015

Neural development in the visual cortex depends on the visual experience during the so-called critical period. Recent experiments have shown that under normal conditions rodents develop binocular receptive fields which have similar orientation preferences for the left and right eyes. In contrast, under conditions of monocular deprivation during the critical period, this orientation alignment does not happen. Here we propose a computational model to explain the process of orientation alignment, its underlying mechanisms, and its failure in case of monocular deprivation or uncorrelated binocular inputs. Our model is based on the recently proposed Active Efficient Coding framework that jointly develops eye movement control and sensory representations. Our model suggests that the active maintenance of a binocular visual field, which leads to correlated visual inputs from the two eyes, is essential for the process of orientation alignment. This behavior is analogous to vergence control in primates. However, due to the fact that rodents have large receptive fields with low spatial frequency tuning, the coordination of the eyes need not be very precise. The model also suggests that it is not necessary that coordinated binocular vision be maintained continuously in order for orientation alignment to develop. © 2015 IEEE.

Chandrapala T.N.,Hong Kong University of Science and Technology | Shi B.E.,Hong Kong University of Science and Technology | Triesch J.,Frankfurt Institute of Advanced Studies
Proceedings of the International Joint Conference on Neural Networks | Year: 2015

A number of unsupervised learning algorithms seeking to account for the receptive field properties of simple cells in the mammalian primary visual cortex have been proposed. Among these are principal component analysis and sparse coding. While it appears that the receptive field properties learned by sparse coding match those measured in cortical cells better than those learned by principal component analysis, it is still not clear why biological neural systems might prefer to use sparse codes. In this paper we explore another reason why sparse representations might be preferred over principal component analysis by studying the utility of different coding schemes in an adaptive behaving agent. We suggest that the qualitative properties of representations based on sparse coding are more stable in the presence of changes in the input statistics than those of representations based on principal component analysis. We demonstrate this by examining representations learned on binocular visual input with different disparity distributions. Our results show that in encoding retinal disparity, the properties of sparse codes are more stable, and that this has important implications in adaptive agents, where the statistics change over time. In particular, in an agent who jointly learns a representation for binocular visual inputs along with a vergence control policy, the learned behavior is unstable when actions are driven by PCA based representations, but stable and self-calibrating when driven by sparse coding based representations. © 2015 IEEE.

Yue X.,Massachusetts General Hospital | Biederman I.,University of Southern California | Mangini M.C.,Concordia College | Malsburg C.V.D.,Frankfurt Institute of Advanced Studies | Amir O.,University of Southern California
Vision Research | Year: 2012

Shape representation is accomplished by a series of cortical stages in which cells in the first stage (V1) have local receptive fields tuned to contrast at a particular scale and orientation, each well modeled as a Gabor filter. In succeeding stages, the representation becomes largely invariant to Gabor coding (Kobatake & Tanaka, 1994). Because of the non-Gabor tuning in these later stages, which must be engaged for a behavioral response (Tong, 2003; Tong et al., 1998), a V1-based measure of shape similarity based on Gabor filtering would not be expected to be highly correlated with human performance when discriminating complex shapes (faces and teeth-like blobs) that differ metrically on a two-choice, match-to-sample task. Here we show that human performance is highly correlated with Gabor-based image measures (Gabor simple and complex cells), with values often in the mid 0.90s, even without discounting the variability in the speed and accuracy of performance not associated with the similarity of the distractors. This high correlation is generally maintained through the stages of HMAX, a model that builds upon the Gabor metric and develops units for complex features and larger receptive fields. This is the first report of the psychophysical similarity of complex shapes being predictable from a biologically motivated, physical measure of similarity. As accurate as these measures were for accounting for metric variation, a simple demonstration showed that all were insensitive to viewpoint invariant (nonaccidental) differences in shape. © 2012 Elsevier Ltd.

PubMed | Frankfurt Institute of Advanced Studies, University of Southern California and National Institute of Mental Health
Type: Journal Article | Journal: Attention, perception & psychophysics | Year: 2016

It is widely accepted that after the first cortical visual area, V1, a series of stages achieves a representation of complex shapes, such as faces and objects, so that they can be understood and recognized. A major challenge for the study of complex shape perception has been the lack of a principled basis for scaling of the physical differences between stimuli so that their similarity can be specified, unconfounded by early-stage differences. Without the specification of such similarities, it is difficult to make sound inferences about the contributions of later stages to neural activity or psychophysical performance. A Web-based app is described that is based on the Malsburg Gabor-jet model (Lades et al., 1993), which allows easy specification of the V1 similarity of pairs of stimuli, no matter how intricate. The model predicts the psycho physical discriminability of metrically varying faces and complex blobs almost perfectly (Yue, Biederman, Mangini, von der Malsburg, & Amir, 2012), and serves as the input stage of a large family of contemporary neurocomputational models of vision.

Van Hees H.,Goethe University Frankfurt | Van Hees H.,Frankfurt Institute of Advanced Studies
European Journal of Physics | Year: 2014

In this comment, we demonstrate that the example of a DC-conducting wire of finite length as an example for the application of the Biot-Savart law is flawed due to the non-conservation of electric charge for such an unphysical setting. The implications drawn in [1] on the restrictions of Ampères circuital law in integral form are unnecessary as long as only physically realizable situations obeying the charge-conservation law are considered. © 2014 IOP Publishing Ltd.

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