6,137 research outputs found
Short gamma-ray bursts within 200 Mpc
We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14 yr of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance ≲100 Mpc and four plausible candidates in the range 100 Mpc ≲ D ≲ 200 Mpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses (≲10−3M⊙) of lanthanide-poor ejecta or unfavorable orientations (θ_(obs) ≳ 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is 1.3^(+1.7)_(−0.8) yr⁻¹ (68 per cent confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of ≲2.0 yr⁻¹ (90 per cent confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi
The Físchlár digital video system: a digital library of broadcast TV programmes
Físchlár is a system for recording, indexing, browsing and playback of broadcast TV programmes which has been operational on our University campus for almost 18 months. In this paper we give a brief overview of how the system operates, how TV programmes are organised for browse/playback and a short report on the system usage by over 900 users in our University
Localization of Eigenfunctions in the Stadium Billiard
We present a systematic survey of scarring and symmetry effects in the
stadium billiard. The localization of individual eigenfunctions in Husimi phase
space is studied first, and it is demonstrated that on average there is more
localization than can be accounted for on the basis of random-matrix theory,
even after removal of bouncing-ball states and visible scars. A major point of
the paper is that symmetry considerations, including parity and time-reversal
symmetries, enter to influence the total amount of localization. The properties
of the local density of states spectrum are also investigated, as a function of
phase space location. Aside from the bouncing-ball region of phase space,
excess localization of the spectrum is found on short periodic orbits and along
certain symmetry-related lines; the origin of all these sources of localization
is discussed quantitatively and comparison is made with analytical predictions.
Scarring is observed to be present in all the energy ranges considered. In
light of these results the excess localization in individual eigenstates is
interpreted as being primarily due to symmetry effects; another source of
excess localization, scarring by multiple unstable periodic orbits, is smaller
by a factor of .Comment: 31 pages, including 10 figure
Brownian motion meets Riemann curvature
The general covariance of the diffusion equation is exploited in order to
explore the curvature effects appearing on brownian motion over a d-dimensional
curved manifold. We use the local frame defined by the so called Riemann normal
coordinates to derive a general formula for the mean-square geodesic distance
(MSD) at the short-time regime. This formula is written in terms of
invariants that depend on the Riemann curvature tensor. We study the
n-dimensional sphere case to validate these results. We also show that the
diffusion for positive constant curvature is slower than the diffusion in a
plane space, while the diffusion for negative constant curvature turns out to
be faster. Finally the two-dimensional case is emphasized, as it is relevant
for the single particle diffusion on biomembranes.Comment: 16 pages and 3 figure
Lifetime Measurement of the 6s Level of Rubidium
We present a lifetime measurements of the 6s level of rubidium. We use a
time-correlated single-photon counting technique on two different samples of
rubidium atoms. A vapor cell with variable rubidium density and a sample of
atoms confined and cooled in a magneto-optical trap. The 5P_{1/2} level serves
as the resonant intermediate step for the two step excitation to the 6s level.
We detect the decay of the 6s level through the cascade fluorescence of the
5P_{3/2} level at 780 nm. The two samples have different systematic effects,
but we obtain consistent results that averaged give a lifetime of 45.57 +- 0.17
ns.Comment: 10 pages, 9 figure
Correlated Gravitational Wave and Neutrino Signals from General-Relativistic Rapidly Rotating Iron Core Collapse
We present results from a new set of 3D general-relativistic hydrodynamic
simulations of rotating iron core collapse. We assume octant symmetry and focus
on axisymmetric collapse, bounce, the early postbounce evolution, and the
associated gravitational wave (GW) and neutrino signals. We employ a
finite-temperature nuclear equation of state, parameterized electron capture in
the collapse phase, and a multi-species neutrino leakage scheme after bounce.
The latter captures the important effects of deleptonization, neutrino cooling
and heating and enables approximate predictions for the neutrino luminosities
in the early evolution after core bounce. We consider 12-solar-mass and
40-solar-mass presupernova models and systematically study the effects of (i)
rotation, (ii) progenitor structure, and (iii) postbounce neutrino leakage on
dynamics, GW, and, neutrino signals. We demonstrate, that the GW signal of
rapidly rotating core collapse is practically independent of progenitor mass
and precollapse structure. Moreover, we show that the effects of neutrino
leakage on the GW signal are strong only in nonrotating or slowly rotating
models in which GW emission is not dominated by inner core dynamics. In rapidly
rotating cores, core bounce of the centrifugally-deformed inner core excites
the fundamental quadrupole pulsation mode of the nascent protoneutron star. The
ensuing global oscillations (f~700-800 Hz) lead to pronounced oscillations in
the GW signal and correlated strong variations in the rising luminosities of
antineutrino and heavy-lepton neutrinos. We find these features in cores that
collapse to protoneutron stars with spin periods <~ 2.5 ms and rotational
energies sufficient to drive hyper-energetic core-collapse supernova
explosions. Hence, joint GW + neutrino observations of a core collapse event
could deliver strong evidence for or against rapid core rotation. [abridged]Comment: 29 pages, 14 figures. Replaced with version matching published
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Thermo-visual feature fusion for object tracking using multiple spatiogram trackers
In this paper, we propose a framework that can efficiently combine features for robust tracking based on fusing the outputs of multiple spatiogram trackers. This is achieved without the exponential increase in storage and processing that other multimodal tracking approaches suffer from. The framework allows the features to be split arbitrarily between the trackers, as well as providing the flexibility to add, remove or dynamically weight features. We derive a mean-shift type algorithm for the framework that allows efficient object tracking with very low computational overhead. We especially target the fusion of thermal infrared and visible spectrum features as the most useful features for automated surveillance applications. Results are shown on multimodal video sequences clearly illustrating the benefits of combining multiple features using our framework
Analysis of the Bronze Age Heslington Brain by FTIR Imaging and Hierarchical Cluster Analysis
Working with and for social enterprises: the role of the volunteer ethnographer
Purpose – This paper considers the specific opportunities and challenges of engaging in ethnographic research with organisations in which the researcher participates as a volunteer ethnographer. Design/methodology/approach – The findings in this paper are based on four years of ethnographic research within a social enterprise. Findings – This paper finds that there are significant benefits of the role of the volunteer ethnographer and suggests ways to address some of the challenges. Research limitations/implications – As the field of social enterprise and ethnography grows and researchers engage with methodological discussions about participant observation, the authors suggest that attention should also be paid to the specifics of the role of the volunteer ethnographer. Originality/value – There is growing interest in the use of ethnography in social enterprises. This paper offers unique insight into how this methodology has been applied in the context of self-reliant groups and the importance of the engaging with discussion about the specific role of the volunteer ethnographer
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