24,443 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
Cosmic reionization constraints on the nature of cosmological perturbations
We study the reionization history of the Universe in cosmological models with non-Gaussian density fluctuations, taking them to have a renormalized probability distribution function parametrized by the number of degrees of freedom, . We compute the ionization history using a simple semi-analytical model, considering various possibilities for the astrophysics of reionization. In all our models we require that reionization is completed prior to , as required by the measurement of the Gunn--Peterson optical depth from the spectra of high-redshift quasars. We confirm previous results demonstrating that such a non-Gaussian distribution leads to a slower reionization as compared to the Gaussian case. We further show that the recent WMAP three-year measurement of the optical depth due to electron scattering, , weakly constrains the allowed deviations from Gaussianity on the small scales relevant to reionization if a constant spectral index is assumed. We also confirm the need for a significant suppression of star formation in mini-halos, which increases dramatically as we decrease
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