4,549 research outputs found
The luminosity--volume test for cosmological Fast Radio Bursts
We perform the luminosity--volume test, also known as , to Fast Radio Bursts (FRBs). We compare the 23 FRBs,
recently discovered by ASKAP, with 20 of the FRBs found by Parkes. These
samples have different flux limits and correspond to different explored
volumes. We assume that their dispersion measure indicates their redshift and
apply the appropriate cosmological corrections to the spectrum and rate in
order to compute the for the ASKAP and Parkes
samples. For a radio spectrum of FRBs , we find
for the ASKAP sample, that includes
FRBs up to , and 0.52 for Parkes, that extends up to .
The ASKAP value suggests that the population of FRB progenitors evolves faster
than the star formation rate, while the Parkes value is consistent with it.
Even a delayed (as a power law or gaussian) star formation rate cannot
reproduce the of both samples. If FRBs do not evolve
in luminosity, the values of ASKAP and Parkes sample
are consistent with a population of progenitors whose density strongly evolves
with redshift as up to . We discuss possible
scenarios accounting for our results.Comment: 10 pages, 5 figures, 3 tables, accepted by A&A on 2019/04/0
LikeStarter: a Smart-contract based Social DAO for Crowdfunding
Crowdfunding has become a popular form of collective funding, in which small
donations or investments, made by groups of people, support the development of
new projects in exchange of free products or different types of recognition.
Social network sites, on the other hand, promote user cooperation and currently
are at the basis of any individuals cyber-interactions. In this paper, we
present LikeStarter, a blockchain-based decentralized platform that combines
social interactions with crowdfunding mechanisms, allowing any user to raise
funds while becoming popular in the social network. Being built over the
Ethereum blockchain, LikeStarter is structured as a Decentralized Autonomous
Organization (DAO), that fosters crowdfunding without the intervention of any
central authority, and recognizes the active role of donors, enabling them to
support artists or projects, while making profits.Comment: Proceedings of the 2st Workshop on Cryptocurrencies and Blockchains
for Distributed Systems (CryBlock'19). Paris, France, 29 April, 201
J-MOD: Joint Monocular Obstacle Detection and Depth Estimation
In this work, we propose an end-to-end deep architecture that jointly learns
to detect obstacles and estimate their depth for MAV flight applications. Most
of the existing approaches either rely on Visual SLAM systems or on depth
estimation models to build 3D maps and detect obstacles. However, for the task
of avoiding obstacles this level of complexity is not required. Recent works
have proposed multi task architectures to both perform scene understanding and
depth estimation. We follow their track and propose a specific architecture to
jointly estimate depth and obstacles, without the need to compute a global map,
but maintaining compatibility with a global SLAM system if needed. The network
architecture is devised to exploit the joint information of the obstacle
detection task, that produces more reliable bounding boxes, with the depth
estimation one, increasing the robustness of both to scenario changes. We call
this architecture J-MOD. We test the effectiveness of our approach with
experiments on sequences with different appearance and focal lengths and
compare it to SotA multi task methods that jointly perform semantic
segmentation and depth estimation. In addition, we show the integration in a
full system using a set of simulated navigation experiments where a MAV
explores an unknown scenario and plans safe trajectories by using our detection
model
Multicolor Photometry of the Uranus Irregular Satellites Sycorax and Caliban
We report on accurate BVRI photometry for the two Uranus irregular satellites
Sycorax and Caliban. We derive colours, showing that
Sycorax is bluer than Caliban. Our data allows us to detect a significant
variability in the Caliban's light-curve, which suggests an estimated period of
about 3 hours. Despite it is the brighter of the two bodies, Sycorax does not
display a strong statistically significant variability. However our data seem
to suggest a period of about 4 hoursComment: 17 pages, 2 eps figures, in press in Astronomical Journa
Second-Harmonic Scattering as a Probe of Structural Correlations in Liquids
Second-harmonic scattering experiments of water and other bulk molecular
liquids have long been assumed to be insensitive to interactions between the
molecules. The measured intensity is generally thought to arise from incoherent
scattering due to individual molecules. We introduce a method to compute the
second-harmonic scattering pattern of molecular liquids directly from atomistic
computer simulations, which takes into account the coherent terms. We apply
this approach to large-scale molecular dynamics simulations of liquid water,
where we show that nanosecond second-harmonic scattering experiments contain a
coherent contribution arising from radial and angular correlations on a length
scale of < 1 nm, much shorter than had been recently hypothesized (Shelton, D.
P. J. Chem. Phys. 2014, 141). By combining structural correlations from
simulations with experimental data (Shelton, D. P. J. Chem. Phys. 2014, 141),
we can also extract an effective molecular hyperpolarizability in the liquid
phase. This work demonstrates that second-harmonic scattering experiments and
atomistic simulations can be used in synergy to investigate the structure of
complex liquids, solutions, and biomembranes, including the intrinsic
intermolecular correlations
Inverse diffraction for the Atmospheric Imaging Assembly in the Solar Dynamics Observatory
The Atmospheric Imaging Assembly in the Solar Dynamics Observatory provides
full Sun images every 1 seconds in each of 7 Extreme Ultraviolet passbands.
However, for a significant amount of these images, saturation affects their
most intense core, preventing scientists from a full exploitation of their
physical meaning. In this paper we describe a mathematical and automatic
procedure for the recovery of information in the primary saturation region
based on a correlation/inversion analysis of the diffraction pattern associated
to the telescope observations. Further, we suggest an interpolation-based
method for determining the image background that allows the recovery of
information also in the region of secondary saturation (blooming)
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