• Dopamine D1 receptor activation contributes to light-adapted changes in retinal inhibition to rod bipolar cells.

  Flood, Michael D.; Moore-Dotson, Johnnie M.; Eggers, Erika D.; Univ Arizona, Dept Physiol; Univ Arizona, Dept Biomed Engn (AMER PHYSIOLOGICAL SOC, 2018-08-01)

  Dopamine modulation of retinal signaling has been shown to be an important part of retinal adaptation to increased background light levels, but the role of dopamine modulation of retinal inhibition is not clear. We previously showed that light adaptation causes a large reduction in inhibition to rod bipolar cells, potentially to match the decrease in excitation after rod saturation. In this study, we determined how dopamine D1 receptors in the inner retina contribute to this modulation. We found that D1 receptor activation significantly decreased the magnitude of inhibitory light responses from rod bipolar cells, whereas D1 receptor blockade during light adaptation partially prevented this decline. To determine what mechanisms were involved in the modulation of inhibitory light responses, we measured the effect of D1 receptor activation on spontaneous currents and currents evoked from electrically stimulating amacrine cell inputs to rod bipolar cells. D1 receptor activation decreased the frequency of spontaneous inhibition with no change in event amplitudes, suggesting a presynaptic change in amacrine cell activity in agreement with previous reports that rod bipolar cells lack D1 receptors. Additionally, we found that D1 receptor activation reduced the amplitude of electrically evoked responses, showing that D1 receptors can modulate amacrine cells directly. Our results suggest that D1 receptor activation can replicate a large portion but not all of the effects of light adaptation, likely by modulating release from amacrine cells onto rod bipolar cells. NEW & NOTEWORTHY We demonstrated a new aspect of dopaminergic signaling that is involved in mediating light adaptation of retinal inhibition. This D1 receptor-dependent mechanism likely acts through receptors located directly on amacrine cells, in addition to its potential role in modulating the strength of serial inhibition between amacrine cells. Our results also suggest that another D2/D4 receptor-dependent or dopamine-independent mechanism must also be involved in light adaptation of inhibition to rod bipolar cells.
• Principal 2-blocks and Sylow 2-subgroups

  Taylor, Jay; Schaeffer Fry, Amanda A.; MSU Denver; Univ Arizona, Dept Math (John Wiley & Sons, 2018-07-16)

  Let G be a finite group with Sylow 2-subgroup P. Navarro–Tiep–Vallejo have conjectured that the principal 2-block of N_G(P) contains exactly one irreducible Brauer character if and only if all odd-degree ordinary irreducible characters in the principal 2-block of G are fixed by a certain Galois automorphism. Recent work of Navarro–Vallejo has reduced this conjecture to a problem about finite simple groups. We show that their conjecture holds for all finite simple groups, thus establishing the conjecture for all finite groups.
• Target patterns in a 2D array of oscillators with nonlocal coupling

  Jaramillo, Gabriela; Venkataramani, Shankar; Univ Arizona, Dept Math (Institute of Physics, London, 2018-07-26)

  We analyze the effect of adding a weak, localized, inhomogeneity to a two dimensional array of oscillators with nonlocal coupling. We propose and also justify a model for the phase dynamics in this system. Our model is a generalization of a viscous eikonal equation that is known to describe the phase modulation of traveling waves in reaction–diffusion systems. We show the existence of a branch of target pattern solutions that bifurcates from the spatially homogeneous state when , the strength of the inhomogeneity, is nonzero and we also show that these target patterns have an asymptotic wavenumber that is small beyond all orders in . The strategy of our proof is to pose a good ansatz for an approximate form of the solution and use the implicit function theorem to prove the existence of a solution in its vicinity. The analysis presents two challenges. First, the linearization about the homogeneous state is a convolution operator of diffusive type and hence not invertible on the usual Sobolev spaces. Second, a regular perturbation expansion in does not provide a good ansatz for applying the implicit function theorem since the nonlinearities play a major role in determining the relevant approximation, which also needs to be 'correct' to all orders in . We overcome these two points by proving Fredholm properties for the linearization in appropriate Kondratiev spaces and using a refined ansatz for the approximate solution which was obtained using matched asymptotics.
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  Automating Wavefront Parallelization for Sparse Matrix Computations

  Venkat, Anand; Mohammadi, Mahdi Soltan; Park, Jongsoo; Rong, Hongbo; Barik, Rajkishore; Strout, Michelle Mills; Hall, Mary; Univ Arizona, Dept Comp Sci (IEEE, 2016)

  This paper presents a compiler and runtime framework for parallelizing sparse matrix computations that have loop-carried dependences. Our approach automatically generates a runtime inspector to collect data dependence information and achieves wavefront parallelization of the computation, where iterations within a wavefront execute in parallel, and synchronization is required across wavefronts. A key contribution of this paper involves dependence simplification, which reduces the time and space overhead of the inspector. This is implemented within a polyhedral compiler framework, extended for sparse matrix codes. Results demonstrate the feasibility of using automatically-generated inspectors and executors to optimize ILU factorization and symmetric Gauss-Seidel relaxations, which are part of the Preconditioned Conjugate Gradient (PCG) computation. Our implementation achieves a median speedup of 2.97x on 12 cores over the reference sequential PCG implementation, significantly outperforms PCG parallelized using Intel's Math Kernel Library (MKL), and is within 6% of the median performance of manually-parallelized PCG.
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  Galician coda restrictions and plural clusters

  Colina, S.; Simonet, M.; Univ Arizona, Dept Linguist (WALTER DE GRUYTER, 2014-11)

  The present study investigates the phonology and phonetics of Galician post-vocalic velar nasals. Galician has very strict coda restrictions – it does not allow for complex codas. One exception to this restriction is found in the plurals of words ending in a nasal consonant, which add /s/ to the “right” of a noun or adjective: man ‘hand’, mans ‘hands’; pan ‘bread’, pans ‘breads’. The present study puts forward a proposal, initially based on synchronic, formal phonological grounds, according to which post-vocalic, pre-/s/ nasals in plural forms are not nasal stops, but nasal glides. Their nature as nasal glides allows for their syllabification in the nucleus rather than in the coda, thus preserving (i.e., not violating) the restriction on complex codas. This proposal is then tested with a production experiment based on quantitative acoustic data. The acoustic study reveals indeed a difference in the degree of weakening of post-vocalic nasals, with pre-/s/ nasals in the plural forms showing a significantly higher degree of weakening than pre-/s/ nasals in the singular forms. The article concludes with an Optimality-Theoretic analysis of the phonological facts.

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