19 research outputs found
The Formation of the First Massive Black Holes
Supermassive black holes (SMBHs) are common in local galactic nuclei, and
SMBHs as massive as several billion solar masses already exist at redshift z=6.
These earliest SMBHs may grow by the combination of radiation-pressure-limited
accretion and mergers of stellar-mass seed BHs, left behind by the first
generation of metal-free stars, or may be formed by more rapid direct collapse
of gas in rare special environments where dense gas can accumulate without
first fragmenting into stars. This chapter offers a review of these two
competing scenarios, as well as some more exotic alternative ideas. It also
briefly discusses how the different models may be distinguished in the future
by observations with JWST, (e)LISA and other instruments.Comment: 47 pages with 306 references; this review is a chapter in "The First
Galaxies - Theoretical Predictions and Observational Clues", Springer
Astrophysics and Space Science Library, Eds. T. Wiklind, V. Bromm & B.
Mobasher, in pres
Appropriateness of treatment recommendations for PPI in hospital discharge letters
International audienc
Flows of X-ray gas reveal the disruption of a star by a massive black hole
Tidal forces close to massive black holes can violently disrupt stars that make a close approach. These extreme events are discovered via bright X-ray and optical/ultraviolet flares in galactic centres. Prior studies based on modelling decaying flux trends have been able to estimate broad properties, such as the mass accretion rate. Here we report the detection of flows of hot, ionized gas in high-resolution X-ray spectra of a nearby tidal disruption event, ASASSN-14li in the galaxy PGC 043234. Variability within the absorption-dominated spectra indicates that the gas is relatively close to the black hole. Narrow linewidths indicate that the gas does not stretch over a large range of radii, giving a low volume filling factor. Modest outflow speeds of a few hundred kilometres per second are observed; these are below the escape speed from the radius set by variability. The gas flow is consistent with a rotating wind from the inner, super-Eddington region of a nascent accretion disk, or with a filament of disrupted stellar gas near to the apocentre of an elliptical orbit. Flows of this sort are predicted by fundamental analytical theory and more recent numerical simulations
Tonometers and infectious risk: myth or reality? Efficacy of different disinfection regimens on tonometer tips.
Purpose To evaluate the adequacy of
common disinfection regimens for disposable
tonometer tips and assess if disinfection of
reusable prisms or the use of disposable tips is
preferable.
Methods We used disposable tonometer tips,
using the same material and tip diameter of
standard Goldmann tonometer prism. Strains
of Pseudomonas aeruginosa, Staphylococcus
aureus, Bacillus subtilis and Candida albicans
were tested according to the European
standard guidelines for disinfectants test.
Antimicrobial effectiveness of the following
disinfection practices has been assessed:
dry wipe, Minuten wipes (Alpros), soaking
in 3% hydrogen peroxide, 0.5% benzalkonium
chloride, and 0.5% Pantasepts for 1, 5, and
15 min. All tests have been performed
three times and all conditions tested in
duplicate.
Results Dry wiping and 1 min soak in 3%
hydrogen peroxide were ineffective on all
microrganisms. Minuten wipes, 1 min soak in
0.5% benzalkonium chloride or 3% hydrogen
peroxide were ineffective on B. subtilis. 0.5%
Pantasepts soak was effective in 1 min for all
microrganisms tested, whereas 3% hydrogen
peroxide and 0.5% benzalkonium chloride
soaks were effective when performed for at
least 5 min. B. subtilis was the most resistant
organism to disinfectant regimes at 1 min time.
Conclusions Results of our study
demonstrate a relative disinfection efficacy for
the different evaluated regimens, provided
that correct exposure times are adopted for the
chosen disinfectants, a condition difficult to
ensure in a busy clinic setting. We conclude
that disposable prism tonometry provides a
safe alternative to Goldmann tonometry