Proxima Centauri b is not a transiting exoplanet

We report Spitzer Space Telescope observations during predicted transits of the exoplanet Proxima Centauri b. As the nearest terrestrial habitable-zone planet we will ever discover, any potential transit of Proxima b would place strong constraints on its radius, bulk density, and atmosphere. Subsequent transmission spectroscopy and secondary-eclipse measurements could then probe the atmospheric chemistry, physical processes, and orbit, including a search for biosignatures. However, our photometric results rule out planetary transits at the 200~ppm level at 4.5$~{\mu}m$, yielding a 3$\sigma$ upper radius limit of 0.4~R_\rm{\oplus} (Earth radii). Previous claims of possible transits from optical ground- and space-based photometry were likely correlated noise in the data from Proxima Centauri's frequent flaring. Follow-up observations should focus on planetary radio emission, phase curves, and direct imaging. Our study indicates dramatically reduced stellar activity at near-to-mid infrared wavelengths, compared to the optical. Proxima b is an ideal target for space-based infrared telescopes, if their instruments can be configured to handle Proxima's brightness.Comment: 8 pages, 3 figures, 2 tables, accepted for publication in MNRA

Transcriptome-wide Mapping Reveals Widespread Dynamic-Regulated Pseudouridylation of ncRNA and mRNA

Pseudouridine is the most abundant RNA modification, yet except for a few well-studied cases, little is known about the modified positions and their function(s). Here, we develop Ψ-seq for transcriptome-wide quantitative mapping of pseudouridine. We validate Ψ-seq with spike-ins and de novo identification of previously reported positions and discover hundreds of unique sites in human and yeast mRNAs and snoRNAs. Perturbing pseudouridine synthases (PUS) uncovers which pseudouridine synthase modifies each site and their target sequence features. mRNA pseudouridinylation depends on both site-specific and snoRNA-guided pseudouridine synthases. Upon heat shock in yeast, Pus7p-mediated pseudouridylation is induced at >200 sites, and PUS7 deletion decreases the levels of otherwise pseudouridylated mRNA, suggesting a role in enhancing transcript stability. rRNA pseudouridine stoichiometries are conserved but reduced in cells from dyskeratosis congenita patients, where the PUS DKC1 is mutated. Our work identifies an enhanced, transcriptome-wide scope for pseudouridine and methods to dissect its underlying mechanisms and function

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Association between gastric electromechanical activity and satiation in dogs

Objective: The objective of this study was to validate the use of impedance for measurement of antral contractions and to determine the relationship between food-induced changes in gastric motility and satiation. Research Methods and Procedures: In Experiment 1, three dogs were implanted with an antral strain gauge and bipolar electrodes for measurement of local tissue impedance. Impedance and strain gauge recordings were obtained simultaneously during antral contractions to correlate impedance changes with contractile events. In Experiment 2, seven dogs were implanted with two pairs of gastric electrodes for simultaneous recording of slow wave activity and impedance. The changes in the rate of slow waves and of antral contractions assessed by impedance during food intake were characterized. Results: Variations in strain gauge amplitude were highly correlated with changes in antral impedance (R2: 0.70 to 0.82, p \u3c 0.05). In Experiment 2, slow wave rate was significantly reduced after food intake and reached a nadir at satiation (5.0 ± 0.3 vs. 3.8 ± 0.5 events/min, p \u3c 0.001). Likewise, the amplitude of antral contractions assessed by variations in impedance was significantly increased after food intake, peaking at satiation (5.3 ± 1.4 vs. 12.2 ± 4.3 Ohms, p \u3c 0.01). Discussion: Measurement of impedance is a reliable tool for assessing gastric contractility. Food ingestion significantly reduces slow wave rate and enhances antral contractions. Peak changes in these two variables occur at the time of satiation. Electrical measurements of both slow waves and impedance may be used to estimate gastric motility and satiation. Copyright © 2007 NAASO