310 research outputs found
Un commento altomedievale al De arithmetica di Boezio
L'article comporte une étude et une édition d'un commentaire du Xème siècle sur le de arithmetica de Boèce.Ce commentaire garde la trace de l'enseignement de Remi d'AuxerreStudio e edizione di un commento del secolo X sul De arithmetica di Boezio. Il commento è da mettere in relazione con l'insegnamento di Remigio d'Auxerr
Magnetar giant flare high-energy emission
High energy ( keV) emission has been detected persisting for several
tens of seconds after the initial spike of magnetar giant flares. It has been
conjectured that this emission might arise via inverse Compton scattering in a
highly extended corona generated by super-Eddington outflows high up in the
magnetosphere. In this paper we undertake a detailed examination of this model.
We investigate the properties of the required scatterers, and whether the
mechanism is consistent with the degree of pulsed emission observed in the tail
of the giant flare. We conclude that the mechanism is consistent with current
data, although the origin of the scattering population remains an open
question. We propose an alternative picture in which the emission is closer to
that star and is dominated by synchrotron radiation. The observations
of the December 2004 flare modestly favor this latter picture. We assess the
prospects for the Fermi Gamma-Ray Space Telescope to detect and characterize a
similar high energy component in a future giant flare. Such a detection should
help to resolve some of the outstanding issues.Comment: 20 pages, 14 figure
Why do some asthma patients respond poorly to glucocorticoid therapy?
Glucocorticosteroids are the first-line therapy for controlling airway inflammation in asthma. They bind intracellular glucocorticoid receptors to trigger increased expression of anti-inflammatory genes and suppression of pro-inflammatory gene activation in asthmatic airways. In the majority of asthma patients, inhaled glucocorticoids are clinically efficacious, improving lung function and preventing exacerbations. However, 5–10 % of the asthmatic population respond poorly to high dose inhaled and then systemic glucocorticoids. These patients form a category of severe asthma associated with poor quality of life, increased morbidity and mortality, and constitutes a major societal and health care burden. Inadequate therapeutic responses to glucocorticoid treatment is also reported in other inflammatory conditions such as rheumatoid arthritis and inflammatory bowel disease; however, asthma represents the most studied steroid-refractory disease. Several cellular and molecular events underlying glucocorticoid resistance in asthma have been identified involving abnormalities of glucocorticoid receptor signaling pathways. These events have been strongly related to immunological dysregulation, genetic, and environmental factors such as cigarette smoking or respiratory infections. A better understanding of the multiple mechanisms associated with glucocorticoid insensitivity in asthma phenotypes could improve quality of life for people with asthma but would also provide transferrable knowledge for other inflammatory diseases. In this review, we provide an update on the molecular mechanisms behind steroid-refractory asthma. Additionally, we discuss some therapeutic options for treating those asthmatic patients who respond poorly to glucocorticoid therapy
Keck and Gemini spectral characterization of Lucy mission fly-by target (152830) Dinkinesh
Recently, the inner main belt asteroid (152830) Dinkinesh was identified as
an additional fly-by target for the Lucy mission. The heliocentric orbit and
approximate absolute magnitude of Dinkinesh are known, but little additional
information was available prior to its selection as a target. In particular,
the lack of color spectrophotometry or spectra made it impossible to assign a
spectral type to Dinkinesh from which its albedo could be estimated. We set out
to remedy this knowledge gap by obtaining visible wavelength spectra with the
Keck telescope on 2022 November 23 and with Gemini-South on 2022 December 27.
The spectra measured with the Keck I/Low Resolution Imaging Spectrometer (LRIS)
and the Gemini South/Gemini Multi-Object Spectrograph South (GMOS-S) are most
similar to the average spectrum of S- and Sq-type asteroids. The most
diagnostic feature is the 151 silicate absorption feature at
0.9-1.0~micron. Small S- and Sq-type asteroids have moderately high
albedos ranging from 0.17-0.35. Using this albedo range for Dinkinesh in
combination with measured absolute magnitude, it is possible to derive an
effective diameter and surface brightness for this body. The albedo, size and
surface brightness are important inputs required for planning a successful
encounter by the Lucy spacecraft.Comment: 7 pages, 1 figure. Under review in Icaru
Coronary covered stents
Covered stents offer an effective bail-out strategy in vessel perforations, are an alternative to surgery for the exclusion of coronary aneurysms, and have a potential role in the treatment of friable embolisation-prone plaques. The aim of this manuscript is to offer an overview of currently available platforms and to report results obtained in prior studies
An Extremely Massive White Dwarf Escaped from the Hyades Star Cluster
We searched the Gaia DR3 database for ultramassive white dwarfs with kinematics consistent with having escaped the nearby Hyades open cluster, identifying three such candidates. Two of these candidates have masses estimated from Gaia photometry of approximately 1.1 solar masses; their status as products of single-stellar evolution that have escaped the cluster was deemed too questionable for immediate follow-up analysis. The remaining candidate has an expected mass >1.3 solar masses, significantly reducing the probability of it being an interloper. Analysis of follow-up Gemini GMOS spectroscopy for this source reveals a nonmagnetized hydrogen atmosphere white dwarf with a mass and age consistent with having formed from a single star. Assuming a single-stellar-evolution formation channel, we estimate a 97.8% chance that the candidate is a true escapee from the Hyades. With a determined mass of 1.317 solar masses, this is potentially the most massive known single-evolution white dwarf and is by far the most massive with a strong association with an open cluster
Absorb bioresorbable vascular scaffold: What have we learned after 5 years of clinical experience?
Bioresorbable scaffolds have the potential to introduce a paradigm shift in interventional cardiology, a true anatomical and functional "vascular restoration" instead of an artificial stiff tube encased by persistent metallic foreign body. Early clinical studies using the first commercially available drug-eluting bioresorbable vascular scaffold (BVS) reported very promising safety and efficacy outcomes, comparable to best-in-class second-generation drug-eluting metal stent. To date, more than 60,000 Absorb BVSs have been implanted with only the interim analysis of one randomized trial (ABSORB II RCT) available. Recent registries have challenged the initial claim that BVS is immune from Scaffold Thrombosis (ST). However, suboptimal device expansion and insufficient intracoronary imaging guidance can explain higher than expected ST, especially in complex lesions. The aim of this review article is to critically evaluate the results of the available Absorb BVS studies and discuss the lessons learned to optimize lesion selection and implantation technique of such devices
Near-infrared spectroscopy-intravascular ultrasound: Scientific basis and clinical applications
Coronary angiography underestimates the magnitude of the atherosclerotic burden and cannot detect the presence of disease in the early phases. Recognition of these inherent limitations of angiography has been an impetus for the development of other coronary imaging techniques. The novel near-infrared spectroscopy-intravascular ultrasound (NIRS-IVUS) catheters can detect and quantify the presence of lipid core in the atherosclerotic plaque and associate it with other features such as lumen size and plaque architecture. Lipid-rich plaques are known to pose a higher risk of distal embolization during interventions and plaque disruption. The aim of this manuscript is the review of the potential clinical and research applications of this technology as highlighted by recent studies
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