64 research outputs found
Testing the weak equivalence principle
AbstractThe discovery of Dark Energy and the fact that only about 5% of the mass of the universe can be explained on the basis of the current laws of physics have led to a serious impasse. Based on past history, physics might indeed be on the verge of major discoveries; but the challenge is enormous. The way to tackle it is twofold. On one side, scientists try to perform large scale direct observations and measurements â mostly from space. On the other, they multiply their efforts to put to the most stringent tests ever the physical theories underlying the current view of the physical world, from the very small to the very large. On the extremely small scale very exciting results are expected from one of the most impressive experiments in the history of mankind: the Large Hadron Collider. On the very large scale, the universe is dominated by gravity and the present impasse undoubtedly calls for more powerful tests of General Relativity â the best theory of gravity to date. Experiments testing the Weak Equivalence Principle, on which General Relativity ultimately lies, have the strongest probing power of them all; a breakthrough in sensitivity is possible with the "Galileo Galilei" (GG) satellite experiment to fly in low Earth orbit
Acute Alitasic Cholecystitis
Acute acalculous cholecystitis (AAC) is the inflammatory disease of the gallbladder in the absence of gallstones. Typically affects critically ill patients. Diagnosis is not straightforward as Murphyâs sign is difficult to detect in critically ill and many imaging findings are numb or nonspecific. Acalculous cholecystitis is a life-threatening disorder that has a high risk of perforation and necrosis compared to the more typical calculous disease. Management involves a percutaneous cholecystostomy, a surgical cholecystectomy, or, more recently, a metal stent placed endoscopically through the gastrointestinal tract into the gallbladder. Acalculous cholecystitis is a serious illness that has high morbidity and mortality. The reported mortality of the condition varies from 30 to 50% depending on the age of the patient. Even those who survive have a long recovery that can take months
Be X-ray binaries in the SMC as indicators of mass transfer efficiency
Be X-ray binaries (BeXRBs) consist of rapidly rotating Be stars with neutron
star companions accreting from the circumstellar emission disk. We compare the
observed population of BeXRBs in the Small Magellanic Cloud with simulated
populations of BeXRB-like systems produced with the COMPAS population synthesis
code. We focus on the apparently higher minimal mass of Be stars in BeXRBs than
in the Be population at large. Assuming that BeXRBs experienced only
dynamically stable mass transfer, their mass distribution suggests that at
least 30% of the mass donated by the progenitor of the neutron star is
typically accreted by the B-star companion. We expect these results to affect
predictions for the population of double compact object mergers. A convolution
of the simulated BeXRB population with the star formation history of the Small
Magellanic Cloud shows that the excess of BeXRBs is most likely explained by
this galaxy's burst of star formation around 20--40 Myr ago
Key Science Goals for the Next Generation Very Large Array (ngVLA): Report from the ngVLA Science Advisory Council
This document describes some of the fundamental astrophysical problems that
require observing capabilities at millimeter- and centimeter wavelengths well
beyond those of existing, or already planned, telescopes. The results
summarized in this report follow a solicitation from the National Radio
Astronomy Observatory to develop key science cases for a future U. S.-led radio
telescope, the "next generation Very Large Array" (ngVLA). The ngVLA will have
roughly 10 times the collecting area of the Jansky VLA, operate at frequencies
from 1 GHz to 116 GHz with up to 20 GHz of bandwidth, possess a compact core
for high surface-brightness sensitivity, and extended baselines of at least
hundreds of kilometers and ultimately across the continent to provide
high-resolution imaging. The ngVLA builds on the scientific and technical
legacy of the Jansky VLA and ALMA, and will be designed to provide the next
leap forward in our understanding of planets, galaxies, and black holes.Comment: ngVLA memo 1
The relative growth of Optical and Radio Quasars in SDSS
We cross-correlate the SDSS DR3 quasar sample with FIRST and the Vestergaard
et al. black hole (BH) mass sample to compare the mean accretion histories of
optical and radio quasars. We find significant statistical evidence that radio
quasars have a higher mean Eddington ratio Lambda at z > 2 with respect to
optical quasars, while the situation is clearly reverse at z 2
radio quasars happen to be less massive than optical quasars; however, as
redshift decreases radio quasars appear in increasingly more massive BHs with
respect to optical quasars. These two trends imply that radio sources are not a
mere random subsample of optical quasars. No clear correlation between radio
activity and BH mass and/or accretion rate is evident from our data, pointing
to other BH properties, possibly the spin, as the driver of radio activity. We
have checked that our main results do not depend on any evident bias. We
perform detailed modelling of reasonable accretion histories for optical and
radio quasars, finding that radio quasars grow by a factor of a few, at the
most, since z ~ 4. The comparison between the predicted mass function of active
radio quasars and the observed optical luminosity function of radio quasars,
implies a significantly lower probability for lower mass BHs to be radio loud
at all epochs, in agreement with what is observed in the local universe.Comment: 15 pages, 8 Figures. Accepted by MNRA
The innovative Cherenkov camera based on SiPM sensors of the ASTRI-Horn telescope: from the T/M and electrical design to the full assembly and testing in a harsh environment
ASTRI-Horn is a prototypal telescope of an imaging atmospheric Cherenkov telescope developed by the Italian National Institute of Astrophysics (INAF), proposed for the Cherenkov Telescope Array (CTA) Observatory. The CTA Observatory represents the next generation of imaging atmospheric Cherenkov telescopes and will explore the very highenergy domain from a few tens of GeV up to few hundreds of TeV. It will be composed of large-, medium-, and small sized telescopes; ASTRI-Horn is an end-to-end prototype proposed for the Small Sized array. The main scientific instrument of the ASTRI-Horn telescope is an innovative and compact Camera with Silicon- Photomultiplier based detectors and a specifically designed fast read-out electronics based on a custom peak-detector mode. The thermo-mechanical assembly is designed to host both the entire electronics chain, from the sensors to the raw data transmission system and the calibration system, and the complete thermoregulation system. This contribution gives a high level description of the T/M and electrical design of the Cherenkov Camera, it describes the assembling procedure of its different subsystems and their integration into the complete camera system. A discussion about possible design improvements coming from the problems/difficulties encountered during assembly is also presented. Finally, results from engineering tests conducted in-field are also presented
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