414 research outputs found
Ecosystem carbon 7 dioxide fluxes after disturbance in forests of North America
Disturbances are important for renewal of North American forests. Here we summarize more than 180 site years of eddy covariance measurements of carbon dioxide flux made at forest chronosequences in North America. The disturbances included stand-replacing fire (Alaska, Arizona, Manitoba, and Saskatchewan) and harvest (British Columbia, Florida, New Brunswick, Oregon, Quebec, Saskatchewan, and Wisconsin) events, insect infestations (gypsy moth, forest tent caterpillar, and mountain pine beetle), Hurricane Wilma, and silvicultural thinning (Arizona, California, and New Brunswick). Net ecosystem production (NEP) showed a carbon loss from all ecosystems following a stand-replacing disturbance, becoming a carbon sink by 20 years for all ecosystems and by 10 years for most. Maximum carbon losses following disturbance (g C m−2y−1) ranged from 1270 in Florida to 200 in boreal ecosystems. Similarly, for forests less than 100 years old, maximum uptake (g C m−2y−1) was 1180 in Florida mangroves and 210 in boreal ecosystems. More temperate forests had intermediate fluxes. Boreal ecosystems were relatively time invariant after 20 years, whereas western ecosystems tended to increase in carbon gain over time. This was driven mostly by gross photosynthetic production (GPP) because total ecosystem respiration (ER) and heterotrophic respiration were relatively invariant with age. GPP/ER was as low as 0.2 immediately following stand-replacing disturbance reaching a constant value of 1.2 after 20 years. NEP following insect defoliations and silvicultural thinning showed lesser changes than stand-replacing events, with decreases in the year of disturbance followed by rapid recovery. NEP decreased in a mangrove ecosystem following Hurricane Wilma because of a decrease in GPP and an increase in ER
Orbital Foregrounds for Ultra-Short Duration Transients
Reflections from objects in Earth orbit can produce sub-second, star-like
optical flashes similar to astrophysical transients. Reflections have
historically caused false alarms for transient surveys, but the population has
not been systematically studied. We report event rates for these orbital
flashes using the Evryscope Fast Transient Engine, a low-latency transient
detection pipeline for the Evryscopes. We select single-epoch detections likely
caused by Earth satellites and model the event rate as a function of both
magnitude and sky position. We measure a rate of
sky hour, peaking at , for flashes morphologically
degenerate with real astrophysical signals in surveys like the Evryscopes. Of
these, sky hour are bright enough to be
visible to the naked eye in typical suburban skies with a visual limiting
magnitude of . These measurements place the event rate of orbital
flashes orders of magnitude higher than the combined rate of public alerts from
all active all-sky fast-timescale transient searches, including neutrino,
gravitational-wave, gamma-ray, and radio observatories. Short-timescale orbital
flashes form a dominating foreground for un-triggered searches for fast
transients in low-resolution, wide-angle surveys. However, events like fast
radio bursts (FRBs) with arcminute-scale localization have a low probability
() of coincidence with an orbital flash, allowing optical surveys
to place constraints on their potential optical counterparts in single images.
Upcoming satellite internet constellations, like SpaceX Starlink, are unlikely
to contribute significantly to the population of orbital flashes in normal
operations.Comment: 8 pages, 4 figure
EvryFlare. III. Temperature Evolution and Habitability Impacts of Dozens of Superflares Observed Simultaneously by Evryscope and TESS
Superflares may provide the dominant source of biologically relevant UV radiation to rocky habitable-zone M-dwarf planets (M-Earths), altering planetary atmospheres and conditions for surface life. The combined line and continuum flare emission has usually been approximated by a 9000 K blackbody. If superflares are hotter, then the UV emission may be 10 times higher than predicted from the optical. However, it is unknown for how long M-dwarf superflares reach temperatures above 9000 K. Only a handful of M-dwarf superflares have been recorded with multiwavelength high-cadence observations. We double the total number of events in the literature using simultaneous Evryscope and Transiting Exoplanet Survey Satellite observations to provide the first systematic exploration of the temperature evolution of M-dwarf superflares. We also increase the number of superflaring M dwarfs with published time-resolved blackbody evolution by ∼10×. We measure temperatures at 2 minutes cadence for 42 superflares from 27 K5–M5 dwarfs. We find superflare peak temperatures (defined as the mean of temperatures corresponding to flare FWHM) increase with flare energy and impulse. We find the amount of time flares emit at temperatures above 14,000 K depends on energy. We discover that 43% of the flares emit above 14,000 K, 23% emit above 20,000 K and 5% emit above 30,000 K. The largest and hottest flare briefly reached 42,000 K. Some do not reach 14,000 K. During superflares, we estimate M-Earths orbiting <200 Myr stars typically receive a top-of-atmosphere UV-C flux of ∼120 W m−2 and up to 103 W m−2, 100–1000 times the time-averaged X-ray and UV flux from Proxima Cen
Frequency of Persistent Tooth Pain after Root Canal Therapy: A Systematic Review and Meta-Analysis
Little is known about the frequency of persistent pain after endodontic procedures, even though pain is a core patient-oriented outcome. We estimated the frequency of persistent pain, regardless of etiology, following endondontic treatment
Frequency of Nonodontogenic Pain after Endodontic Therapy: A Systematic Review and Meta-Analysis
Little is known about ill-defined pain that persists following endodontic procedures, including an estimate of the problem’s magnitude. We conducted a systematic review of prospective studies that reported the frequency of non-odontogenic pain in patients who had undergone endodontic procedures
Frequency of Persistent Tooth Pain after Root Canal Therapy: A Systematic Review and Meta-Analysis
Little is known about the frequency of persistent pain after endodontic procedures, even though pain is a core patient-oriented outcome. We estimated the frequency of persistent pain, regardless of etiology, following endondontic treatment
Radio Astronomy
Contains reports on five research projects.National Aeronautics and Space Administration (Grant NsG-419)National Science Foundation (Grant GP-7046)National Aeronautics and Space Administration (Contract NSR-22-009-120)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U, S. Air Force, under Contract DA 28-043-AMC-02536(E)U. S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-000
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