Evidence is accumulating for a rapid diversification of birds following the K–Pg extinction. Recent molecular divergence dating studies suggest that birds radiated explosively during the first few ...million years of the Paleocene; however, fossils from this interval remain poorly represented, hindering our understanding of morphological and ecological specialization in early neoavian birds. Here we report a small fossil bird from the Nacimiento Formation of New Mexico, constrained to 62.221–62.517 Ma. This partial skeleton represents the oldest arboreal crown group bird known. Phylogenetic analyses recovered Tsidiiyazhi abini gen. et sp. nov. as a member of the Sandcoleidae, an extinct basal clade of stem mousebirds (Coliiformes). The discovery of Tsidiiyazhi pushes the minimum divergence ages of as many as nine additional major neoavian lineages into the earliest Paleocene, compressing the duration of the proposed explosive post–K–Pg radiation of modern birds into a very narrow temporal window parallel to that suggested for placental mammals. Simultaneously, Tsidiiyazhi provides evidence for the rapid morphological (and likely ecological) diversification of crown birds. Features of the foot indicate semizygodactyly (the ability to facultatively reverse the fourth pedal digit), and the arcuate arrangement of the pedal trochleae bears a striking resemblance to the conformation in owls (Strigiformes). Inclusion of fossil taxa and branch length estimates impacts ancestral state reconstructions, revealing support for the independent evolution of semizygodactyly in Coliiformes, Leptosomiformes, and Strigiformes, none of which is closely related to extant clades exhibiting full zygodactyly.
Management of postoperative bacterial endophthalmitis was explored in the Endophthalmitis Vitrectomy Study37 in 1995, which has underpinned the core protocols in treatment ever since. While surgical ...techniques have continued to evolve, little has changed in the overall clinical management as no further large randomized controlled trials have taken place. We review the literature addressing the incidence of endophthalmitis, pathogens, antibiotic therapies, and the role of vitrectomy. We suggest an update to management protocols based on available evidence. While vitreous culture remains the gold standard for diagnosis, new techniques allow bacterial identification after antibiotic administration, so injection should be initiated immediately. Current antibiotic regimes are comprehensive and do not need changing. Intravitreal antibiotics should not be repeated at 48 hours after initial treatment. Vitrectomy should be considered instead if the clinical picture is not improving.
Assignment of complex molecular structures from nuclear magnetic resonance (NMR) data can be prone to interpretational mistakes. Residual dipolar couplings and residual chemical shift anisotropy ...provide a spatial view of the relative orientations between bonds and chemical shielding tensors, respectively, regardless of separation. Consequently, these data constitute a reliable reporter of global structural validity. Anisotropic NMR parameters can be used to evaluate investigators' structure proposals or structures generated by computer-assisted structure elucidation. Application of the method to several complex structure assignment problems shows promising results that signal a potential paradigm shift from conventional NMR data interpretation, which may be of particular utility for compounds not amenable to x-ray crystallography.
Microbes sense and respond to their environment with small molecules, and discovering these molecules and identifying their functions informs chemistry, biology, and medicine. As part of a study of ...molecular exchanges between termite-associated actinobacteria and pathogenic fungi, we uncovered a remarkable fungal metabolite, homodimericin A, which is strongly upregulated by the bacterial metabolite bafilomycin C1. Homodimericin A is a hexacyclic polyketide with a carbon backbone containing eight contiguous stereogenic carbons in a C20 hexacyclic core. Only half of its carbon atoms have an attached hydrogen, which presented a significant challenge for NMR-based structural analysis. In spite of its microbial production and rich stereochemistry, homodimericin A occurs naturally as a racemic mixture. A plausible nonenzymatic reaction cascade leading from two identical achiral monomers to homodimericin A is presented, and homodimericin A’s formation by this path, a six-electron oxidation, could be a response to oxidative stress triggered by bafilomycin C1.
Studying the evolution and biogeographic distribution of dinosaurs during the latest Cretaceous is critical for better understanding the end-Cretaceous extinction event that killed off all non-avian ...dinosaurs. Western North America contains among the best records of Late Cretaceous terrestrial vertebrates in the world, but is biased against small-bodied dinosaurs. Isolated teeth are the primary evidence for understanding the diversity and evolution of small-bodied theropod dinosaurs during the Late Cretaceous, but few such specimens have been well documented from outside of the northern Rockies, making it difficult to assess Late Cretaceous dinosaur diversity and biogeographic patterns. We describe small theropod teeth from the San Juan Basin of northwestern New Mexico. These specimens were collected from strata spanning Santonian - Maastrichtian. We grouped isolated theropod teeth into several morphotypes, which we assigned to higher-level theropod clades based on possession of phylogenetic synapomorphies. We then used principal components analysis and discriminant function analyses to gauge whether the San Juan Basin teeth overlap with, or are quantitatively distinct from, similar tooth morphotypes from other geographic areas. The San Juan Basin contains a diverse record of small theropods. Late Campanian assemblages differ from approximately coeval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. We also provide evidence that erect and recurved morphs of a Richardoestesia-like taxon represent a single heterodont species. A late Maastrichtian assemblage is dominated by a distinct troodontid. The differences between northern and southern faunas based on isolated theropod teeth provide evidence for provinciality in the late Campanian and the late Maastrichtian of North America. However, there is no indication that major components of small-bodied theropod diversity were lost during the Maastrichtian in New Mexico. The same pattern seen in northern faunas, which may provide evidence for an abrupt dinosaur extinction.
Abstract Diabetic retinopathy is a complication of diabetes that is caused by changes in the blood vessels of the retina. The symptoms can blur or distort the patient’s vision and are a main cause of ...blindness. Exudates are one of the primary signs of diabetic retinopathy. Detection of exudates by ophthalmologists normally requires pupil dilation using a chemical solution which takes time and affects patients. This paper investigates and proposes a set of optimally adjusted morphological operators to be used for exudate detection on diabetic retinopathy patients’ non-dilated pupil and low-contrast images. These automatically detected exudates are validated by comparing with expert ophthalmologists’ hand-drawn ground-truths. The results are successful and the sensitivity and specificity for our exudate detection is 80% and 99.5%, respectively.
Determination of relative configuration is frequently a rate-limiting step in the characterization of small organic molecules. Solution NMR-based nuclear Overhauser effect and scalar J-coupling ...constants can provide useful spatial information but often fail when stereocenters are separated by more than 4–5 Å. Residual dipolar couplings (RDCs) can provide a means of assigning relative configuration without limits of distance between stereocenters. However, sensitivity limits their application. Chemical shift is the most readily measured NMR parameter, and partial molecular alignment can reveal the anisotropic component of the chemical shift tensor, manifested as residual chemical shift anisotropy (RCSA). Hence, 13C RCSAs provide information on the relative orientations of specific structural moieties including nonprotonated carbons and can be used for stereochemical assignment. Herein, we present two robust and sensitive methods to accurately measure and apply 13C RCSAs for stereochemical assignment. The complementary techniques are demonstrated with five molecules representing differing structural classes.
The extinction of the dinosaurs Brusatte, Stephen L.; Butler, Richard J.; Barrett, Paul M. ...
Biological reviews of the Cambridge Philosophical Society,
20/May , Volume:
90, Issue:
2
Journal Article
Peer reviewed
Open access
ABSTRACT
Non‐avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and ...changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long‐term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinction's tempo and causes. Little support exists for a global, long‐term decline across non‐avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large‐bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.
We propose a reconfigurable dual-sense linear-to-circular polarization (LCP) converter in the form of a VO2-based metasurface. VO2 is a phase change material (PCM) that is useful for low-loss mmWave ...devices, being transparent in its insulating state and metallic when heated. The device operates in the satellite communications uplink portion of Ka-band (27.5-31 GHz). It consists of a four-layer meanderline metasurface with two overlapping configurations, rotated relatively by 90° in- plane, for right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) conversion. Each configuration is interrupted by VO2 patches with double spiral NiCr microheaters along the meandered traces. Under dc bias, the VO2 of one trace changes from insulator to conductor, activating the configuration. The simulated design exhibits axial ratio (AR) <inline-formula> <tex-math notation="LaTeX">\le0.99 </tex-math></inline-formula> dB and insertion loss (IL) <inline-formula> <tex-math notation="LaTeX">\le2.59 </tex-math></inline-formula>, for both RHCP and LHCP conversion. After verifying the dual-sense RF design in simulation, single-sense LCP conversion was measured. The measured results are for LHCP conversion with AR <inline-formula> <tex-math notation="LaTeX">\le2.1 </tex-math></inline-formula> dB and IL <inline-formula> <tex-math notation="LaTeX">\le4.0 </tex-math></inline-formula> dB. The LHCP conversion also has 1-dB AR from 30.2-32.4 GHz and 3-dB AR from 27-38 GHz (26% circular polarization bandwidth). This study demonstrates for the first time LCP conversion using a transmission-mode reconfigurable metasurface in Ka-band using VO2 PCM, and simple dc activation network.
A great diversity of crustacean zooplankton found in inland and coastal waters produce embryos that settle into bottom sediments to form an egg bank. Embryos from these banks can remain dormant for ...centuries, creating a reservoir of genetic diversity. A large body of literature describes the ecological and evolutionary importance of zooplankton egg banks. However, literature on the physiological traits behind dormancy in crustacean zooplankton are limited. Most data on the physiology of dormancy comes from research on one species of anostracan, the brine shrimp, Artemia franciscana. Anoxia-induced dormancy in this species is facilitated by a profound and reversible acidification of the intracellular space. This acidification is accompanied by a reversible depletion of adenosine triphosphate (ATP). The present study demonstrates that acidification of the intracellular space also occurs in concert with a depletion of nucleoside triphosphates (NTPs) in the Antarctic copepod, Boeckella poppei. Like A. franciscana, the depletion of NTPs and acidification are rapidly reversed during aerobic recovery in B. poppei. These data provide the first comparative evidence that extreme dormancy under anoxia in crustacean zooplankton is associated with intracellular acidification and an ability to recover from the depletion of ATP.
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