1,175 research outputs found
Mid Infrared Photometry of Mass-Losing AGB Stars
We present ground-based mid-infrared imaging for 27 M-, S- and C-type
Asymptotic Giant Branch (AGB) stars. The data are compared with those of the
database available thanks to the IRAS, ISO, MSX and 2MASS catalogues. Our goal
is to establish relations between the IR colors, the effective temperature
, the luminosity and the mass loss rate , for improving
the effectiveness of AGB modelling. Bolometric (absolute) magnitudes are
obtained through distance compilations, and by applying previously-derived
bolometric corrections; the variability is also studied, using data accumulated
since the IRAS epoch. The main results are: i) Values of and for C
stars fit relations previously established by us, with Miras being on average
more evolved and mass losing than Semiregulars. ii) Moderate IR excesses (as
compared to evolutionary tracks) are found for S and M stars in our sample:
they are confirmed to originate from the dusty circumstellar environment. iii)
A larger reddening characterizes C-rich Miras and post-AGBs. In this case, part
of the excess is due to AGB models overestimating for C-stars, as a
consequence of the lack of suitable molecular opacities. This has a large
effect on the colors of C-rich sources and sometimes disentangling the
photospheric and circumstellar contributions is difficult; better model
atmospheres should be used in stellar evolutionary codes for C stars. iv) The
presence of a long-term variability at mid-IR wavelengths seems to be limited
to sources with maximum emission in the 8 -- 20 m region, usually Mira
variables (1/3 of our sample). Most Semiregular and post-AGB stars studied here
remained remarkably constant in mid-IR over the last twenty years.Comment: Accepted for publication in the Astronomical Journal - 35 pages (in
preprint), 9 figures, 5 table
Commuter aircraft aerodynamic design: wind-tunnel tests and CFD analysis
The paper presents wind-tunnel tests and CFD numerical aerodynamic analysis of Tecnam P2012 Traveller aircraft. An extensive wind tunnel tests campaign of several different modular aircraft configurations analyzed has been performed on a scaled model in order to experimentally estimate both longitudinal and lateral-directional stability, control derivatives, and to improve the aircraft aerodynamic performances. Simultaneously numerical investigations through a CFD software has been performed, both at wind-tunnel tests Reynolds number (Re=0.6millions) and at free flight Reynolds number of the full scale aircraft (Re=4 or 9 millions). Finally results are compared showing a good agreement in the lift and pitching moment coefficient both with and without control surfaces or flap deflections, and an underestimation of drag coefficient in the CFD numerical analysis. Horizontal tail positions are also tested in wind-tunnel and compared to CFD analysis highlighting how an accurate design leads to improvement both in stability and control. Results will be very useful in the final design of the aircraft and to perform dynamic simulations
Novel Cephalosporins in Septic Subjects and Severe Infections: Present Findings and Future Perspective
The challenge of perioperative pain management in opioid-tolerant patients
The increasing number of opioid users among chronic pain patients, and opioid abusers among the general population, makes perioperative pain management challenging for health care professionals. Anesthesiologists, surgeons, and nurses should be familiar with some pharmacological phenomena which are typical of opioid users and abusers, such as tolerance, physical dependence, hyperalgesia, and addiction. Inadequate pain management is very common in these patients, due to common prejudices and fears. The target of preoperative evaluation is to identify comorbidities and risk factors and recognize signs and symptoms of opioid abuse and opioid withdrawal. Clinicians are encouraged to plan perioperative pain medications and to refer these patients to psychiatrists and addiction specialists for their evaluation. The aim of this review was to give practical suggestions for perioperative management of surgical opioid-tolerant patients, together with schemes of opioid conversion for chronic pain patients assuming oral or transdermal opioids, and patients under maintenance programs with methadone, buprenorphine, or naltrexone
Design and optimization of a large turboprop aircraft
This paper proposes a feasibility study concerning a large turboprop aircraft to be used as a lower environmental impact solution to current regional jets operated on short/medium hauls. An overview of this market scenario highlights that this segment is evenly shared between regional turboprop and jet aircraft. Although regional jets ensure a large operative flexibility, they are usually not optimized for short missions with a negative effect on block fuel and environmental impact. Conversely, turboprops represent a greener solution but with reduced passenger capacity and speed. Those aspects highlight a slot for a new turboprop platform coupling higher seat capacity, cruise speed and design range with a reduced fuel consumption. This platform should operate on those ranges where neither jet aircraft nor existing turboprops are optimized. This work compares three different solutions: a highâwing layout with underâwing engines installation and both two-and threeâliftingâsurface configurations with lowâwing and tail tipsâmounted engines. For each concept, a multiâdisciplinary optimization was performed targeting the minimum block fuel on a 1600 NM mission. Optimum solutions were compared with both a regional jet such as the Airbus A220â300 operated on 1600 NM and with a jet aircraft specifically designed for this range
Carbapenem resistant Klebsiella pneumoniae in ICU-admitted COVID-19 Patients: Keep an eye on the ball
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