Synthesis of neural networks for spatio-temporal spike pattern recognition and processing

The advent of large scale neural computational platforms has highlighted the lack of algorithms for synthesis of neural structures to perform predefined cognitive tasks. The Neural Engineering Framework offers one such synthesis, but it is most effective for a spike rate representation of neural information, and it requires a large number of neurons to implement simple functions. We describe a neural network synthesis method that generates synaptic connectivity for neurons which process time-encoded neural signals, and which makes very sparse use of neurons. The method allows the user to specify, arbitrarily, neuronal characteristics such as axonal and dendritic delays, and synaptic transfer functions, and then solves for the optimal input-output relationship using computed dendritic weights. The method may be used for batch or online learning and has an extremely fast optimization process. We demonstrate its use in generating a network to recognize speech which is sparsely encoded as spike times.Comment: In submission to Frontiers in Neuromorphic Engineerin

Quasilocal Energy in FRW Cosmology

This paper presents a calculation of the quasilocal energy of a generic FRW model of the universe. The results have the correct behavior in the small-sphere limit and vanish for the empty Milne universe. Higher order corrections are found when comparing these results to classical calculations of cosmological energy. This case is different from others in the literature chiefly in that it involves a non-stationary spacetime. This fact can be used to differentiate between the various formulations of quasilocal energy. In particular, the formulation due to Brown and York is compared to that of Epp. Only one of these is seen to have the correct classical limit.Comment: The article has been revised for publication in Classical and Quantum Gravity. All calculations remain unchanged. A discussion of Epp's formulation and additional references have been adde

Bragg waveguides with low-index liquid cores

The spectral properties of light confined to low-index media by binary layered structures is discussed. A novel phase-based model with a simple analytical form is derived for the approximation of the center of arbitrary bandgaps of binary layered structures operating at arbitrary effective indices. An analytical approximation to the sensitivity of the bandgap center to changes in the core refractive index is thus derived. Experimentally, significant shifting of the fundamental bandgap of a hollow-core Bragg fiber with a large cladding layer refractive index contrast is demonstrated by filling the core with liquids of various refractive indices. Confirmation of these results against theory is shown, including the new analytical model, highlighting the importance of considering material dispersion. The work demonstrates the broad and sensitive tunability of Bragg structures and includes discussions on refractive index sensing.Kristopher J. Rowland, Shahraam Afshar V., Alexander Stolyarov, Yoel Fink, and Tanya M. Monr

Suspended core fibers for the transmission of cylindrical vector modes

Date of Publication: 28 October 2016This paper presents a study of propagation of radially and azimuthally polarized cylindrical vector modes in six-strut suspended core fibers based on finite element simulations. The study shows large effective index differences in order of 10-⁻³-10⁻² of these modes can be achieved in the suspended core fibers with core diameter of less than 2 μm, material index 1.45 of silica to 2.0 of tellurite and wavelength of 750 nm, allowing the stable propagation of the first higher order modes in doughnut shape within these fibers. The effective index difference and the field intensity of these cylindrical vector modes can be tuned by selecting appropriate fiber material and core size. The study shows that the suspended core fiber can be a competitive candidate for fiber-based highresolution stimulated emission depletion (STED) nanoscopy application.Hong Ji, Yinlan Ruan, Shahraam Afshar Vahid, Heike Ebendorff-Heidepriem, and Tanya M. Monr

3-Form Flux Compactification of Salam-Sezgin Supergravity

The compactification of 6 dimensional Salam-Sezgin model in the presence of 3-form flux H is investigated. We find a torus topology for this compactification with two cusps which are the places of branes, while at the limit of large size L of the compact direction we also obtain sphere topology. This resembles the Randall-Sundrum I,II model. The branes at one of the cusps can be chosen to be 3- and 4-branes which fill our 4-dimensional space together with the fact that H=0 at this position restores the Lorentz symmetry. This compactification also provides an example for the so-called `time warp' solution, [0812.5107 [hep-th]]. According to a no-go theorem in $d\ne 6$, the time warp compactification violates the null energy condition. While the theorem is quiet for d=6, our model gives a time warp compactification which satisfies the null energy condition. We also derive the four dimensional effective Planck mass which is not obvious due to the time warp nature of the solution.Comment: 19 pages, 5 fig

Gravity duals for logarithmic conformal field theories

Logarithmic conformal field theories with vanishing central charge describe systems with quenched disorder, percolation or dilute self-avoiding polymers. In these theories the energy momentum tensor acquires a logarithmic partner. In this talk we address the construction of possible gravity duals for these logarithmic conformal field theories and present two viable candidates for such duals, namely theories of massive gravity in three dimensions at a chiral point.Comment: 15 pages, 1 figure, invited plenary talk at the First Mediterranean Conference on Classical and Quantum Gravity, v2: published version, corrected typo in left eq. (5

Testing foundations of quantum mechanics with photons

The foundational ideas of quantum mechanics continue to give rise to counterintuitive theories and physical effects that are in conflict with a classical description of Nature. Experiments with light at the single photon level have historically been at the forefront of tests of fundamental quantum theory and new developments in photonics engineering continue to enable new experiments. Here we review recent photonic experiments to test two foundational themes in quantum mechanics: wave-particle duality, central to recent complementarity and delayed-choice experiments; and Bell nonlocality where recent theoretical and technological advances have allowed all controversial loopholes to be separately addressed in different photonics experiments.Comment: 10 pages, 5 figures, published as a Nature Physics Insight review articl

The Relationship Between Age and Mental Health Among Adults in Iran During the COVID-19 Pandemic

The evidence on the predictors of mental health in the COVID-19 pandemic has revealed contradictory findings, which prevent effective screening for mental health assistance. This study aims to identify the predictors of mental health issues, specifically examining age as a nonlinear predictor. Based on a survey of 474 adults using snowball sampling under the COVID-19 pandemic during April 1th–10th, 2020, in Iran, we found that age had a curvilinear relationship with nonsomatic pain, depression, and anxiety. Specifically, it predicted pain, depression, and anxiety disorders, negatively among adults younger than 45 years, yet positively among seniors older than 70 years. Adults who were female, were unsure about their chronic diseases, or exercised less were more likely to have mental health issues. This study, being the first paper to examine age curvilinearly, suggests future research to pay more attention to nonlinear predictors of mental health disorders in the COVID-19 pandemic

The GRA Beam-Splitter Experiments and Particle-Wave Duality of Light

Grangier, Roger and Aspect (GRA) performed a beam-splitter experiment to demonstrate the particle behaviour of light and a Mach-Zehnder interferometer experiment to demonstrate the wave behaviour of light. The distinguishing feature of these experiments is the use of a gating system to produce near ideal single photon states. With the demonstration of both wave and particle behaviour (in two mutually exclusive experiments) they claim to have demonstrated the dual particle-wave behaviour of light and hence to have confirmed Bohr's principle of complementarity. The demonstration of the wave behaviour of light is not in dispute. But we want to demonstrate, contrary to the claims of GRA, that their beam-splitter experiment does not conclusively confirm the particle behaviour of light, and hence does not confirm particle-wave duality, nor, more generally, does it confirm complementarity. Our demonstration consists of providing a detailed model based on the Causal Interpretation of Quantum Fields (CIEM), which does not involve the particle concept, of GRA's which-path experiment. We will also give a brief outline of a CIEM model for the second, interference, GRA experiment.Comment: 24 pages, 4 figure