31,668 research outputs found
Optics robustness of the ATLAS Tile Calorimeter
TileCal, the central hadronic calorimeter of the ATLAS detector is composed
of plastic scintillators interleaved by steel plates, and wavelength shifting
optical fibres. The optical properties of these components are known to suffer
from natural ageing and degrade due to exposure to radiation. The calorimeter
was designed for 10 years of LHC operating at the design luminosity of
cms. Irradiation tests of scintillators and fibres have
shown that their light yield decrease by about 10% for the maximum dose
expected after 10 years of LHC operation. The robustness of the TileCal optics
components is evaluated using the calibration systems of the calorimeter:
Cs-137 gamma source, laser light, and integrated photomultiplier signals of
particles from proton-proton collisions. It is observed that the loss of light
yield increases with exposure to radiation as expected. The decrease in the
light yield during the years 2015-2017 corresponding to the LHC Run 2 will be
reported. The current LHC operation plan foresees a second high luminosity LHC
(HL-LHC) phase extending the experiment lifetime for 10 years more. The results
obtained in Run 2 indicate that following the light yield response of TileCal
is an essential step for predicting the calorimeter performance in future runs.
Preliminary studies attempt to extrapolate these measurements to the HL-LHC
running conditions.Comment: 8 pages, 9 figures, proceedings of CALOR 2018, Eugene, OR, USA, May
201
Bounds and extremal domains for Robin eigenvalues with negative boundary parameter
We present some new bounds for the first Robin eigenvalue with a negative
boundary parameter. These include the constant volume problem, where the bounds
are based on the shrinking coordinate method, and a proof that in the fixed
perimeter case the disk maximises the first eigenvalue for all values of the
parameter. This is in contrast with what happens in the constant area problem,
where the disk is the maximiser only for small values of the boundary
parameter. We also present sharp upper and lower bounds for the first
eigenvalue of the ball and spherical shells.
These results are complemented by the numerical optimisation of the first
four and two eigenvalues in 2 and 3 dimensions, respectively, and an evaluation
of the quality of the upper bounds obtained. We also study the bifurcations
from the ball as the boundary parameter becomes large (negative).Comment: 26 pages, 20 figure
Asymptotic behaviour and numerical approximation of optimal eigenvalues of the Robin Laplacian
We consider the problem of minimising the eigenvalue of the Robin
Laplacian in . Although for and a positive boundary
parameter it is known that the minimisers do not depend on ,
we demonstrate numerically that this will not always be the case and illustrate
how the optimiser will depend on . We derive a Wolf-Keller type result
for this problem and show that optimal eigenvalues grow at most with ,
which is in sharp contrast with the Weyl asymptotics for a fixed domain. We
further show that the gap between consecutive eigenvalues does go to zero as
goes to infinity. Numerical results then support the conjecture that for
each there exists a positive value of such that the eigenvalue is minimised by disks for all and,
combined with analytic estimates, that this value is expected to grow with
A general conservative extension theorem in process algebras with inequalities
We prove a general conservative extension theorem for transition system based process theories with easy-to-check and reasonable conditions. The core of this result is another general theorem which gives sufficient conditions for a system of operational rules and an extension of it in order to ensure conservativity, that is, provable transitions from an original term in the extension are the same as in the original system. As a simple corollary of the conservative extension theorem we prove a completeness theorem. We also prove a general theorem giving sufficient conditions to reduce the question of ground confluence modulo some equations for a large term rewriting system associated with an equational process theory to a small term rewriting system under the condition that the large system is a conservative extension of the small one. We provide many applications to show that our results are useful. The applications include (but are not limited to) various real and discrete time settings in ACP, ATP, and CCS and the notions projection, renaming, stage operator, priority, recursion, the silent step, autonomous actions, the empty process, divergence, etc
The Bragg regime of the two-particle Kapitza-Dirac effect
We analyze the Bragg regime of the two-particle Kapitza-Dirac arrangement,
completing the basic theory of this effect. We provide a detailed evaluation of
the detection probabilities for multi-mode states, showing that a complete
description must include the interaction time in addition to the usual
dimensionless parameter w. The arrangement can be used as a massive
two-particle beam splitter. In this respect, we present a comparison with
Hong-Ou-Mandel-type experiments in quantum optics. The analysis reveals the
presence of dips for massive bosons and a differentiated behavior of
distinguishable and identical particles in an unexplored scenario. We suggest
that the arrangement can provide the basis for symmetrization verification
schemes
Cosmological perturbations and the reionization epoch
We investigate the dependence of the epoch of reionization on the properties
of cosmological perturbations, in the context of cosmologies permitted by WMAP.
We compute the redshift of reionization using a simple model based on the
Press-Schechter approximation. For a power-law initial spectrum we estimate
that reionization is likely to occur at a redshift ,
consistent with the WMAP determination based on the temperature-polarization
cross power spectrum. We estimate the delay in reionization if there is a
negative running of the spectral index, as weakly indicated by WMAP. We then
investigate the dependence of the reionization redshift on the nature of the
initial perturbations. We consider chi-squared probability distribution
functions with various degrees of freedom, motivated both by non-standard
inflationary scenarios and by defect models. We find that in these models
reionization is likely occur much earlier, and to be a slower process, than in
the case of initial gaussian fluctuations. We also consider a hybrid model in
which cosmic strings make an important contribution to the seed fluctuations on
scales relevant for reionization. We find that in order for that model to agree
with the latest WMAP results, the string contribution to the matter power
spectrum on the standard scale is likely to be at most at the
level of one percent, which imposes tight constraints on the value of the
string mass per unit length.Comment: 6 pages LaTeX file with 3 figures incorporate
The Evolutionary Robustness of Forgiveness and Cooperation
We study the evolutionary robustness of strategies in infinitely repeated
prisoners' dilemma games in which players make mistakes with a small
probability and are patient. The evolutionary process we consider is given by
the replicator dynamics. We show that there are strategies with a uniformly
large basin of attraction independently of the size of the population.
Moreover, we show that those strategies forgive defections and, assuming that
they are symmetric, they cooperate
- …