211 research outputs found
Constraints on extragalactic transmitters via Breakthrough Listen
The Breakthrough Listen Initiative has embarked on a comprehensive SETI
survey of nearby stars in the Milky Way that is vastly superior to previous
efforts as measured by a wide range of different metrics. SETI surveys
traditionally ignore the fact that they are sensitive to many background
objects, in addition to the foreground target star. In order to better
appreciate and exploit the presence of extragalactic objects in the field of
view, the Aladin sky atlas and NED were employed to make a rudimentary census
of extragalactic objects that were serendipitously observed with the 100-m
Greenbank telescope observing at 1.1-1.9 GHz. For 469 target fields (assuming a
FWHM radial field-of-view of 4.2 arcminutes), NED identified a grand total of
143024 extragalactic objects, including various astrophysical exotica e.g. AGN
of various types, radio galaxies, interacting galaxies, and one confirmed
gravitational lens system. Several nearby galaxies, galaxy groups and galaxy
clusters are identified, permitting the parameter space probed by SETI surveys
to be significantly extended. Constraints are placed on the luminosity function
of potential extraterrestrial transmitters assuming it follows a simple power
law and limits on the prevalence of very powerful extraterrestrial transmitters
associated with these vast stellar systems are also determined. It is
demonstrated that the recent Breakthrough Listen Initiative, and indeed many
previous SETI radio surveys, place stronger limits on the prevalence of
extraterrestrial intelligence in the distant Universe than is often fully
appreciated.Comment: 9 Pages, 5 figures, accepted by MNRA
Extending the Breakthrough Listen nearby star survey to other stellar objects in the field
We extend the source sample recently observed by the Breakthrough Listen
Initiative by including additional stars (with parallaxes measured by Gaia)
that also reside within the FWHM of the GBT and Parkes radio telescope target
fields. These stars have estimated distances as listed in the extensions of the
Gaia DR2 catalogue. Enlarging the sample from 1327 to 288315 stellar objects
permits us to achieve substantially better Continuous Waveform Transmitter Rate
Figures of Merit (CWTFM) than any previous analysis, and allows us to place the
tightest limits yet on the prevalence of nearby high-duty-cycle
extraterrestrial transmitters. The results suggest % of stellar systems within 50 pc host such
transmitters (assuming an EIRP W) and % within 200 pc (assuming an EIRP W). We further extend our analysis to much greater distances, though
we caution that the detection of narrow-band signals beyond a few hundred pc
may be affected by interstellar scintillation. The extended sample also permits
us to place new constraints on the prevalence of extraterrestrial transmitters
by stellar type and spectral class. Our results suggest targeted analyses of
SETI radio data can benefit from taking into account the fact that in addition
to the target at the field centre, many other cosmic objects reside within the
primary beam response of a parabolic radio telescope. These include foreground
and background galactic stars, but also extragalactic systems. With distances
measured by Gaia, these additional sources can be used to place improved limits
on the prevalence of extraterrestrial transmitters, and extend the analysis to
a wide range of cosmic objects.Comment: 10 pages, 5 figures, 3 tables. Accepted by MNRA
A Millisecond Interferometric Search for Fast Radio Bursts with the Very Large Array
We report on the first millisecond timescale radio interferometric search for
the new class of transient known as fast radio bursts (FRBs). We used the Very
Large Array (VLA) for a 166-hour, millisecond imaging campaign to detect and
precisely localize an FRB. We observed at 1.4 GHz and produced visibilities
with 5 ms time resolution over 256 MHz of bandwidth. Dedispersed images were
searched for transients with dispersion measures from 0 to 3000 pc/cm3. No
transients were detected in observations of high Galactic latitude fields taken
from September 2013 though October 2014. Observations of a known pulsar show
that images typically had a thermal-noise limited sensitivity of 120 mJy/beam
(8 sigma; Stokes I) in 5 ms and could detect and localize transients over a
wide field of view. Our nondetection limits the FRB rate to less than
7e4/sky/day (95% confidence) above a fluence limit of 1.2 Jy-ms. Assuming a
Euclidean flux distribution, the VLA rate limit is inconsistent with the
published rate of Thornton et al. We recalculate previously published rates
with a homogeneous consideration of the effects of primary beam attenuation,
dispersion, pulse width, and sky brightness. This revises the FRB rate downward
and shows that the VLA observations had a roughly 60% chance of detecting a
typical FRB and that a 95% confidence constraint would require roughly 500
hours of similar VLA observing. Our survey also limits the repetition rate of
an FRB to 2 times less than any known repeating millisecond radio transient.Comment: Submitted to ApJ. 13 pages, 9 figure
Rehospitalizacje w niewydolności serca z upośledzoną funkcją lewej komory — strategie zapobiegania
Niewydolność serca (HF) w krajach rozwiniętych dotyczy ponad 10% populacji powyżej 70. roku życia, stanowiąc tym samym ważny problem zarówno zdrowotny, społeczny, jak i ekonomiczny. Szacuje się, że obecnie w Polsce na HF cierpi 600 000–700 000 osób. Mimo postępu, jaki się dokonał w ostatnich 30 latach w zakresie farmakoterapii niewydolności serca z istotnie upośledzoną funkcją skurczową lewej komory (HFrEF) (wdrożenie inhibitorów konwertazy angiotensyny [ACEI], blokerów receptora angiotensyny II [ARB], antagonistów receptora mineralokortykoidowgo [MRA] oraz iwabradyny) rokowanie pacjentów z tej grupy pozostaje niekorzystne. Jednym z głównych czynników istotnie zwiększających współczynnik śmiertelności w tej grupie chorych jest wysoki odsetek ponownych hospitalizacji (w ciągu roku dla ostrej HF — 43,9%; dla przewlekłej HF — 31,9%). Tym samym HF stanowi również wiodącą przyczynę rehospitalizacji pacjentów powyżej 65. roku życia. W sytuacji nadmiernego obciążenia oddziałów kardiologicznych i niedostatecznego finansowania hospitalizacji pacjentów z HF istnieje bardzo duże niebezpieczeństwo skracania okresu pobytu w szpitalu poniżej bezpiecznego minimum. Przy czym powszechny i wczesny dostęp do kardiologa wciąż stanowi problem dla wielu pacjentów z HF. W efekcie wczesne rehospitalizacje są w wielu przypadkach wynikiem nieoptymalnego wyrównania w trakcie hospitalizacji, utrudnionego wczesnego dostępu do specjalisty po wypisaniu ze szpitala, a także braku sprecyzowanego planu dalszej opieki ambulatoryjnej zarówno w zakresie terminu najbliższej wizyty, jak i eskalacji farmakoterapii. Świadomość problemów codziennej opieki nad pacjentem z HFrEF oraz czynników ryzyka rehospitalizacji i gorszego rokowania może stanowić nieocenioną pomoc w wyłonieniu z szerokiej grupy chorych z HFrEF tych, którzy wymagają wzmożonej czujności i częstszych kontroli w poradni specjalistycznej
Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses
Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens
Panoramic optical and near-infrared SETI instrument: prototype design and testing
The Pulsed All-sky Near-infrared Optical Search for ExtraTerrestrial
Intelligence (PANOSETI) is an instrument program that aims to search for fast
transient signals (nano-second to seconds) of artificial or astrophysical
origin. The PANOSETI instrument objective is to sample the entire observable
sky during all observable time at optical and near-infrared wavelengths over
300 - 1650 nm. The PANOSETI instrument is designed with a number of modular
telescope units using Fresnel lenses (0.5m) arranged on two geodesic
domes in order to maximize sky coverage. We present the prototype design
and tests of these modular Fresnel telescope units. This consists of the design
of mechanical components such as the lens mounting and module frame. One of the
most important goals of the modules is to maintain the characteristics of the
Fresnel lens under a variety of operating conditions. We discuss how we account
for a range of operating temperatures, humidity, and module orientations in our
design in order to minimize undesirable changes to our focal length or angular
resolution.Comment: 12 pages, 8 figures, 1 tabl
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