559 research outputs found
2D photonic-crystal optomechanical nanoresonator
We present the optical optimization of an optomechanical device based on a
suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based
on a 2D photonic-crystal geometry. We first identify by numerical simulation a
set of geometrical parameters providing a reflectivity higher than 99.8 % over
a 50-nm span. We then study the limitations induced by the finite value of the
optical waist and lateral size of the NWG pattern using different numerical
approaches. The NWG grating, pierced in a suspended InP 265 nm-thick membrane,
is used to form a compact microcavity involving the suspended nano-membrane as
end mirror. The resulting cavity has a waist size smaller than 10 m and a
finesse in the 200 range. It is used to probe the Brownian motion of the
mechanical modes of the nanomembrane
Does reperfusion injury still cause significant mortality after lung transplantation?
ObjectivesSevere reperfusion injury after lung transplantation has mortality rates approaching 40%. The purpose of this investigation was to identify whether our improved 1-year survival after lung transplantation is related to a change in reperfusion injury.MethodsWe reported in March 2000 that early institution of extracorporeal membrane oxygenation can improve lung transplantation survival. The records of consecutive lung transplant recipients from 1990 to March 2000 (early era, n = 136) were compared with those of recipients from March 2000 to August 2006 (current era, n = 155). Reperfusion injury was defined by an oxygenation index of greater than 7 (where oxygenation index = [Percentage inspired oxygen] Ă [Mean airway pressure]/[Partial pressure of oxygen]). Risk factors for reperfusion injury, treatment of reperfusion injury, and 30-day mortality were compared between eras by using Ï2, Fisher's, or Student's t tests where appropriate.ResultsAlthough the incidence of reperfusion injury did not change between the eras, 30-day mortality after lung transplantation improved from 11.8% in the early era to 3.9% in the current era (P = .003). In patients without reperfusion injury, mortality was low in both eras. Patients with reperfusion injury had less severe reperfusion injury (P = .01) and less mortality in the current era (11.4% vs 38.2%, P = .01). Primary pulmonary hypertension was more common in the early era (10% [14/136] vs 3.2% [5/155], P = .02). Graft ischemic time increased from 223.3 ± 78.5 to 286.32 ± 88.3 minutes in the current era (P = .0001). The mortality of patients with reperfusion injury requiring extracorporeal membrane oxygenation improved in the current era (80.0% [8/10] vs 25.0% [3/12], P = .01).ConclusionImproved early survival after lung transplantation is due to less severe reperfusion injury, as well as improvements in survival with extracorporeal membrane oxygenation
The 2022â2023 accretion outburst of the young star V1741 Sgr
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/V1741 Sgr (= SPICY 71482/Gaia22dtk) is a Classical T Tauri star on the outskirts of the Lagoon Nebula. After at least a decade of stability, in mid-2022, the optical source brightened by âŒ3 mag over 2 months, remained bright until early 2023, then dimmed erratically over the next 4 months. This event was monitored with optical and infrared spectroscopy and photometry. Spectra from the peak (October 2022) indicate an EX Lup-type (EXor) accretion outburst, with strong emission from HâI, HeâI, and CaâII lines and CO bands. At this stage, spectroscopic absorption features indicated a temperature of T ⌠4750 K with low-gravity lines (e.g. BaâII and SrâII). By April 2023, with the outburst beginning to dim, strong TiO absorption appeared, indicating a cooler T ⌠3600 K temperature. However, once the source had returned to its pre-outburst flux in August 2023, the TiO absorption and the CO emission disappeared. When the star went into outburst, the sourceâs spectral energy distribution became flatter, leading to bluer colours at wavelengths shorter than âŒ1.6 m and redder colours at longer wavelengths. The brightening requires a continuum emitting area larger than the stellar surface, likely from optically thick circumstellar gas with cooler surface layers producing the absorption features. Additional contributions to the outburst spectrum may include blue excess from hotspots on the stellar surface, emission lines from diffuse gas, and reprocessed emission from the dust disc. Cooling of the circumstellar gas would explain the appearance of TiO, which subsequently disappeared once this gas had faded and the stellar spectrum reemerged.Peer reviewe
Drivers of future alien species impacts: An expertâbased assessment
Understanding the likely future impacts of biological invasions is crucial yet highly challenging given the multiple relevant environmental, socioâeconomic and societal contexts and drivers. In the absence of quantitative models, methods based on expert knowledge are the best option for assessing future invasion trajectories. Here, we present an expert assessment of the drivers of potential alien species impacts under contrasting scenarios and socioecological contexts through the midâ21st century. Based on responses from 36 experts in biological invasions, moderate (20%â30%) increases in invasions, compared to the current conditions, are expected to cause major impacts on biodiversity in most socioecological contexts. Three main drivers of biological invasionsâtransport, climate change and socioâeconomic changeâwere predicted to significantly affect future impacts of alien species on biodiversity even under a bestâcase scenario. Other drivers (e.g. human demography and migration in tropical and subtropical regions) were also of high importance in specific global contexts (e.g. for individual taxonomic groups or biomes). We show that some bestâcase scenarios can substantially reduce potential future impacts of biological invasions. However, rapid and comprehensive actions are necessary to use this potential and achieve the goals of the Postâ2020 Framework of the Convention on Biological Diversity
Fossil Carder Bee's nest from the Hominin locality of Taung, South Africa
The Buxton-Norlim Limeworks southwest of Taung, South Africa, is renowned for the discovery of the first Australopithecus africanus fossil, the âTaung Childâ. The hominin was recovered from a distinctive pink calcrete that contains an abundance of invertebrate ichnofauna belonging to the Coprinisphaera ichnofacies. Here we describe the first fossil beeâs nest, attributed to the ichnogenus Celliforma, from the Plio-Pleistocene of Africa. Petrographic examination of a cell lining revealed the preservation of an intricate organic matrix lined with the calcitic casts of numerous plant trichomesâa nesting behaviour unique to the modern-day carder bees (Anthidiini). The presence of Celliforma considered alongside several other recorded ichnofossils can be indicative of a dry, savannah environment, in agreement with recent work on the palaeoenvironment of Plio-Pleistocene southern Africa. Moreover, the occurrence of ground-nesting bees provides further evidence that the pink calcrete deposits are of pedogenic origin, rather than speleogenic origin as has previously been assumed. This study demonstrates the potential value of insect trace fossils as palaeoenvironmental indicators
G305 Star-forming Region. I. Newly Classified Hot Stars
The relatively nearby star-forming complex G305 is one of the most luminous H II regions in the Galaxy, and it contains several sites and epochs of star formation. Using a combination of near-infrared photometry from "Vista Variables in Via Lactea" ESO Large Public Survey, SDSS-IV APOGEE-2 spectra, and Gaia DR2 photometry and astrometry, we report on 29 OB type, WolfâRayet, and emission-line stars, 18 of which are newly classified. Most of these hot stars belongs to the main sequence, although some stars of class I are also proposed. The mean radial velocity is RV = â41.8 km s^(-1). The average spectroscopic distance is 3.2 ± 1.6 kpc, while the Gaia DR2 average distance is 3.7 ± 1.8 kpc. Eight objects show light-curve variations with amplitudes greater than 0.5 mag in the K S band
- âŠ