Straight Round the Twist: Frustration and Chirality in Smectics-A

Frustration is a powerful mechanism in condensed matter systems, driving both order and co plexity. In smectics, the frustration between macroscopic chirality and equally spaced layers generates textures characterised by a proliferation of defects. In this article, we study several different ground states of the chiral Landau-de Gennes free energy for a smectic liquid crystal. The standard theory finds the twist grain boundary (TGB) phase to be the ground state for chiral type II smectics. However, for very highly chiral systems, the hierarchical helical nanofilament (HN) phase can form and is stable over the TGB.Comment: 9 pages, 3 figures, submitted to J. Interface Focu

Reliable Computation in Noisy Backgrounds Using Real-Time Neuromorphic Hardware

Wang H-P, Chicca E, Indiveri G, Sejnowski TJ. Reliable Computation in Noisy Backgrounds Using Real-Time Neuromorphic Hardware. Presented at the Biomedical Circuits and Systems Conference (BIOCAS), Montreal, Que.Spike-time based coding of neural information, in contrast to rate coding, requires that neurons reliably and precisely fire spikes in response to repeated identical inputs, despite a high degree of noise from stochastic synaptic firing and extraneous background inputs. We investigated the degree of reliability and precision achievable in various noisy background conditions using real-time neuromorphic VLSI hardware which models integrate-and-fire spiking neurons and dynamic synapses. To do so, we varied two properties of the inputs to a single neuron, synaptic weight and synchrony magnitude (number of synchronously firing pre-synaptic neurons). Thanks to the realtime response properties of the VLSI system we could carry out extensive exploration of the parameter space, and measure the neurons firing rate and reliability in real-time. Reliability of output spiking was primarily influenced by the amount of synchronicity of synaptic input, rather than the synaptic weight of those synapses. These results highlight possible regimes in which real-time neuromorphic systems might be better able to reliably compute with spikes despite noisy input

The Power of Poincar\'e: Elucidating the Hidden Symmetries in Focal Conic Domains

Focal conic domains are typically the "smoking gun" by which smectic liquid crystalline phases are identified. The geometry of the equally-spaced smectic layers is highly generic but, at the same time, difficult to work with. In this Letter we develop an approach to the study of focal sets in smectics which exploits a hidden Poincar\'e symmetry revealed only by viewing the smectic layers as projections from one-higher dimension. We use this perspective to shed light upon several classic focal conic textures, including the concentric cyclides of Dupin, polygonal textures and tilt-grain boundaries.Comment: 4 pages, 3 included figure

Sterol content as a character for selecting yeast strains in enology

It could be established that the total sterol content is an individual and reproducible characteristic in Saccharomyces cerevisiae under the same cultural and physiological conditions. Its accumulation in the cells is affected by glucose concentration to different extents in the 18 strains studied. Only some strains undergo glucose catabolite repression in sterol biosynthesis.There was no linear correlation between sterol content in the cells of the 18 strains grown under static or shaken conditions. Under statical conditions significant positive correlations were found between sterol contents and ethanol average production in the 18 strains. On the contrary, in aerobically grown cells significant but negative correlations were found between sterol contents and alcohol production.A new yeast selection characteristic for vinification is proposed.La teneur en stérols comme un caractère de sélection de souches de levures en oenologieNous avons établi que l'accumulation de stérols dans les cellules est un caractère individuel et reproduisible des Saccharomyces cerevisiae dans des conditions égales. Cette accumulation est influencée par la concentration du glucose dans le milieu. Toutes les 18 souches ne subissent pas la répression catabolique de la synthèse de stérols due au glucose.Il n'y a aucune corrélation entre la teneur en stérols en aération continuelle et dans des conditions de semianaérobiose (culture statique). Dans des conditions statiques nous avons trouvé une corrélation significative positive entre la teneur en stérols et la production d'éthanol. Par contre, dans des conditions d'érobiose, les teneurs en stérols présentent aux différentes concentrations de glucose des corrélations significatives négatives avec la production d'éthanol des souches.Dans des conditions de développement statiques la teneur en stérols peut être utilisée comme un nouveau critère de sélection pour obtenir des souches de levures productrices de degrés élevés d'alcool

Quantum phase excitations in Ginzburg-Landau superconductors

We give a straightforward generalization of the Ginzburg-Landau theory for superconductors where the scalar phase field is replaced by an antisymmetric Kalb-Ramond field. We predict that at very low temperatures, where quantum phase effects are expected to play a significant role, the presence of vortices destroys superconductivity.Comment: revtex, 4 pages, no figure

The Feeling of Color: A Haptic Feedback Device for the Visually Disabled

Tapson J, Gurari N, Diaz J, et al. The Feeling of Color: A Haptic Feedback Device for the Visually Disabled. Presented at the Biomedical Circuits and Systems Conference (BIOCAS), Baltimore, MD.We describe a sensory augmentation system designed to provide the visually disabled with a sense of color. Our system consists of a glove with short-range optical color sensors mounted on its fingertips, and a torso-worn belt on which tactors (haptic feedback actuators) are mounted. Each fingertip sensor detects the observed objectpsilas color. This information is encoded to the tactor through vibrations in respective locations and varying modulations. Early results suggest that detection of primary colors is possible with near 100% accuracy and moderate latency, with a minimum amount of training

Comparison of Theory and Direct Numerical Simulations of Drag Reduction by Rodlike Polymers in Turbulent Channel Flows

Numerical simulations of turbulent channel flows, with or without additives, are limited in the extent of the Reynolds number \Re and Deborah number \De. The comparison of such simulations to theories of drag reduction, which are usually derived for asymptotically high \Re and \De, calls for some care. In this paper we present a study of drag reduction by rodlike polymers in a turbulent channel flow using direct numerical simulation and illustrate how these numerical results should be related to the recently developed theory

The cycling of carbon into and out of dust

Observational evidence seems to indicate that the depletion of interstellar carbon into dust shows rather wide variations and that carbon undergoes rather rapid recycling in the interstellar medium (ISM). Small hydrocarbon grains are processed in photo-dissociation regions by UV photons, by ion and electron collisions in interstellar shock waves and by cosmic rays. A significant fraction of hydrocarbon dust must therefore be re-formed by accretion in the dense, molecular ISM. A new dust model (Jones et al., Astron. Astrophys., 2013, 558, A62) shows that variations in the dust observables in the diffuse interstellar medium (nH = 1000 cm^3), can be explained by systematic and environmentally-driven changes in the small hydrocarbon grain population. Here we explore the consequences of gas-phase carbon accretion onto the surfaces of grains in the transition regions between the diffuse ISM and molecular clouds (e.g., Jones, Astron. Astrophys., 2013, 555, A39). We find that significant carbonaceous dust re-processing and/or mantle accretion can occur in the outer regions of molecular clouds and that this dust will have significantly different optical properties from the dust in the adjacent diffuse ISM. We conclude that the (re-)processing and cycling of carbon into and out of dust is perhaps the key to advancing our understanding of dust evolution in the ISM.Comment: 14 pages, 6 figure