83 research outputs found
Photometric detection of internal gravity waves in upper main-sequence stars. II. Combined TESS photometry and high-resolution spectroscopy
Context. Massive stars are predicted to excite internal gravity waves (IGWs)
by turbulent core convection and from turbulent pressure fluctuations in their
near-surface layers. These IGWs are extremely efficient at transporting angular
momentum and chemical species within stellar interiors, but they remain largely
unconstrained observationally. Aims. We aim to characterise the photometric
detection of IGWs across a large number of O and early-B stars in the
Hertzsprung-Russell diagram, and explain the ubiquitous detection of stochastic
variability in the photospheres of massive stars. Methods. We combined
high-precision time-series photometry from the NASA Transiting Exoplanet Survey
Satellite with high-resolution ground-based spectroscopy of 70 stars with
spectral types O and B to probe the relationship between the photometric
signatures of IGWs and parameters such as spectroscopic mass, luminosity, and
macroturbulence. Results. A relationship is found between the location of a
star in the spectroscopic Hertzsprung-Russell diagram and the amplitudes and
frequencies of stochastic photometric variability in the light curves of
massive stars. Furthermore, the properties of the stochastic variability are
statistically correlated with macroturbulent velocity broadening in the
spectral lines of massive stars. Conclusions. The common ensemble morphology
for the stochastic low-frequency variability detected in space photometry and
its relationship to macroturbulence is strong evidence for IGWs in massive
stars, since these types of waves are unique in providing the dominant
tangential velocity field required to explain the observed spectroscopy.Comment: Accepted for publication in A&A. 10 pages and 5 figures (and an
additional 7 pages of appendix tables and figures). Resolution of appendix
figures have been downgraded to meet arXiv's maximum file size of 15Mb. This
version (2ver) is post A&A language editin
Tendinopathyâfrom basic science to treatment
Chronic tendon pathology (tendinopathy), although common, is difficult to treat. Tendons possess a highly organized fibrillar matrix, consisting of type I collagen and various 'minor' collagens, proteoglycans and glycoproteins. The tendon matrix is maintained by the resident tenocytes, and there is evidence of a continuous process of matrix remodeling, although the rate of turnover varies at different sites. A change in remodeling activity is associated with the onset of tendinopathy. Major molecular changes include increased expression of type III collagen, fibronectin, tenascin C, aggrecan and biglycan. These changes are consistent with repair, but they might also be an adaptive response to changes in mechanical loading. Repeated minor strain is thought to be the major precipitating factor in tendinopathy, although further work is required to determine whether it is mechanical overstimulation or understimulation that leads to the change in tenocyte activity. Metalloproteinase enzymes have an important role in the tendon matrix, being responsible for the degradation of collagen and proteoglycan in both healthy patients and those with disease. Metalloproteinases that show increased expression in painful tendinopathy include ADAM (a disintegrin and metalloproteinase)-12 and MMP (matrix metalloproteinase)-23. The role of these enzymes in tendon pathology is unknown, and further work is required to identify novel and specific molecular targets for therapy
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Metalloproteinases and their inhibitorsâdiagnostic and therapeutic opportunities in orthopedics
Matrix metalloproteinases (MMPs) and related enzymes (ADAMs, ADAMTS) and their inhibitors control matrix turnover and function. Recent advances in our understanding of musculoskeletal conditions such as tendinopathy, arthritis, Dupuytren's disease, degenerative disc disease, and bone and soft tissue healing suggest that MMPs have prominant roles. Importantly, MMPs are amenable to inhibition by cheap, safe, and widely available drugs such as the tetracycline antibiotics and the bisphosphonates. This indicates that these MMP inhibitors, if proven effective for any novel indication, may be quickly brought into clinical practice
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