29,599 research outputs found

    A General Expression for Symmetry Factors of Feynman Diagrams

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    The calculation of the symmetry factor corresponding to a given Feynman diagram is well known to be a tedious problem. We have derived a simple formula for these symmetry factors. Our formula works for any diagram in scalar theory (ϕ3\phi^3 and ϕ4\phi^4 interactions), spinor QED, scalar QED, or QCD.Comment: RevTex 11 pages with 10 figure

    "We are setting ourselves on fire to keep everyone else warm"-what does the recovery look like for NHS staff?

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    Recovery from the pandemic will be as challenging as the pandemic itself, argue Christina Pagel and Edward Palmer

    State Dependence of Stimulus-Induced Variability Tuning in Macaque MT

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    Behavioral states marked by varying levels of arousal and attention modulate some properties of cortical responses (e.g. average firing rates or pairwise correlations), yet it is not fully understood what drives these response changes and how they might affect downstream stimulus decoding. Here we show that changes in state modulate the tuning of response variance-to-mean ratios (Fano factors) in a fashion that is neither predicted by a Poisson spiking model nor changes in the mean firing rate, with a substantial effect on stimulus discriminability. We recorded motion-sensitive neurons in middle temporal cortex (MT) in two states: alert fixation and light, opioid anesthesia. Anesthesia tended to lower average spike counts, without decreasing trial-to-trial variability compared to the alert state. Under anesthesia, within-trial fluctuations in excitability were correlated over longer time scales compared to the alert state, creating supra-Poisson Fano factors. In contrast, alert-state MT neurons have higher mean firing rates and largely sub-Poisson variability that is stimulus-dependent and cannot be explained by firing rate differences alone. The absence of such stimulus-induced variability tuning in the anesthetized state suggests different sources of variability between states. A simple model explains state-dependent shifts in the distribution of observed Fano factors via a suppression in the variance of gain fluctuations in the alert state. A population model with stimulus-induced variability tuning and behaviorally constrained information-limiting correlations explores the potential enhancement in stimulus discriminability by the cortical population in the alert state.Comment: 36 pages, 18 figure

    Extreme distributions of ground winds /3 to 150 meters/ at Cape Kennedy, Florida

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    Statistical analysis of wind distribution probabilities at Cape Kenned

    The Use of Algal Cultures in Experiments Concerned with Water Supply Problems

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    Rapid and routine methods for isolating and culturing algae are essential for laboratory studies of those algae which create problems in water supplies and for the development of methods for their control. Just as the bacteriologist must isolate the bacteria in order to study their actions under various conditions, so too, the applied phycologist must now follow essentially the same procedure with the algae. Matheson has emphasized this need in his recent report to the 1952 Congress of the International Water Supply Association
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