28,754 research outputs found

    Inhibitory control of feature selectivity in an object motion sensitive circuit of the retina

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    Object motion sensitive (OMS) W3-retinal ganglion cells (W3-RGCs) in mice respond to local movements in a visual scene but remain silent during self-generated global image motion. The excitatory inputs that drive responses of W3-RGCs to local motion were recently characterized, but which inhibitory neurons suppress W3-RGCs’ responses to global motion, how these neurons encode motion information, and how their connections are organized along the excitatory circuit axis remains unknown. Here, we find that a genetically identified amacrine cell (AC) type, TH2-AC, exhibits fast responses to global motion and slow responses to local motion. Optogenetic stimulation shows that TH2-ACs provide strong GABAA receptor-mediated input to W3-RGCs but only weak input to upstream excitatory neurons. Cell-type-specific silencing reveals that temporally coded inhibition from TH2-ACs cancels W3-RGC spike responses to global but not local motion stimuli and, thus, controls the feature selectivity of OMS signals sent to the brain

    Long-run dynamics of the U.S. patent classification system

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    Almost by definition, radical innovations create a need to revise existing classification systems. In this paper, we argue that classification system changes and patent reclassification are common and reveal interesting information about technological evolution. To support our argument, we present three sets of findings regarding classification volatility in the U.S. patent classification system. First, we study the evolution of the number of distinct classes. Reconstructed time series based on the current classification scheme are very different from historical data. This suggests that using the current classification to analyze the past produces a distorted view of the evolution of the system. Second, we study the relative sizes of classes. The size distribution is exponential so classes are of quite different sizes, but the largest classes are not necessarily the oldest. To explain this pattern with a simple stochastic growth model, we introduce the assumption that classes have a regular chance to be split. Third, we study reclassification. The share of patents that are in a different class now than they were at birth can be quite high. Reclassification mostly occurs across classes belonging to the same 1-digit NBER category, but not always. We also document that reclassified patents tend to be more cited than non-reclassified ones, even after controlling for grant year and class of origin

    Topological triviality of smoothly knotted surfaces in 4-manifolds

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    Some generalizations and variations of the Fintushel-Stern rim surgery are known to produce smoothly knotted surfaces. We show that if the fundamental groups of their complements are cyclic, then these surfaces are topologically unknotted. Using a twist-spinning construction from high-dimensional knot theory, we construct examples of knotted surfaces whose complements have cyclic fundamental groups.Comment: Final version; appeared in AMS Transactions. 15 pages, 2 figure

    Spin-orbit coupling in the metallic and spin-liquid phases of Na4Ir3O8

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    It has recently been proposed that Na4Ir3O8 is a weak Mott insulator at ambient pressure, supporting a three-dimensional spin liquid phase with a spinon Fermi surface. This proposal is consistent with recent experimental findings that the material becomes a metal upon increasing pressure or doping. In this work, we investigate the effect of the spin-orbit coupling arising from 5d Ir moments both in the metallic and spin liquid phases of Na4Ir3O8. The effective Hubbard model in terms of pseudospin j=1/2 Ir states is derived and its consequences to both metallic and spin liquid phases are studied. In particular, the model leads to enhanced Wilson ratio and strong temperature dependence of the Hall coefficient.Comment: 8 pages, 9 figure

    Double point surgery and configurations of surfaces

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    We introduce a new operation, double point surgery, on immersed surfaces in a 4-manifold, and use it to construct knotted configurations of surfaces in many 4-manifolds. Taking branched covers, we produce smoothly exotic actions of Z/m x Z/n on simply connected 4-manifolds with complicated fixed-point sets.Comment: Final version; to appear in Journal of Topology. Removed assertion about the restriction of the Z/m x Z/n action to the Z/m and Z/n subgroup

    Halperin-Saslow modes as the origin of the low temperature anomaly in NiGa2S4NiGa_2S_4

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    The absence of magnetic long range order in the triangular lattice spin-1 antiferromagnet NiGaNiGa_2SS_4haspromptedthesearchforanovelquantumgroundstate.Inparticular,severalexperimentssuggestthepresenceofalinearlydispersingmodedespitenolongrangemagneticorder.WeshowthattheanomalouslowtemperaturepropertiesofNiGa has prompted the search for a novel quantum ground state. In particular, several experiments suggest the presence of a linearly dispersing mode despite no long-range magnetic order. We show that the anomalous low temperature properties of NiGa_2SS_4$ can naturally be explained by the formulation developed by Halperin and Saslow where the linearly dispersing Halperin-Saslow mode may exist in the background of frozen spin moments and zero net magnetization. We provide highly non-trivial consistency checks on the existing experimental data and suggest future experiments that can further confirm the existence of the Halperin-Saslow mode. Our results place strong constraints on any microscopic theory of this material.Comment: 5 pages, 1 figur

    Creative Placemaking: Building Partnerships to Create Change

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    Arts, artists, and creative strategies can be critical vehicles for planning to achieve social, economic, and community goals. Creative placemaking is one type of arts-led planning that incorporates both stakeholder participation and community goals. Yet, questions exist around who participates in the creative placemaking process and to what end. Our study discusses a case where a state-sponsored workshop brings people from diverse backgrounds together to facilitate community development and engagement through creative placemaking. In particular, the event discussed in this study highlights how a one-shot intervention can reshape perceptions of creative placemaking held by planners, non-planners, artists, and non-artists. Our study also shows that while pre-workshop participants tended to identify resource-based challenges, post-workshop participants focused more on initiating collaborations and being responsive to community needs. The different attitudes before and after the state-sponsored workshop demonstrate the importance of facilitating stakeholder understanding and engagement for successful creative placemaking

    What are Current Best Approaches Companies are Using for Performance Management for Wage Employees?

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    Academic journals mainly focus on performance management for white-collar employees and lack resources on best practices for wage employees. In response, we have consulted with two renowned professors at the ILR School for advice and also interviewed an HR manager at GE Aviation to find out how leading firms manage performance of hourly-wage workers in practice by probing into three major components of how they 1) approach goal-setting, 2) manage the performance evaluation process, and 3) align performance results with other HR programs
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