938 research outputs found
Finite volume corrections to pi-pi scattering
Lattice QCD studies of hadron-hadron interactions are performed by computing
the energy levels of the system in a finite box. The shifts in energy levels
proportional to inverse powers of the volume are related to scattering
parameters in a model independent way. In addition, there are non-universal
exponentially suppressed corrections that distort this relation. These terms
are proportional to exp(-m_pi L) and become relevant as the chiral limit is
approached. In this paper we report on a one-loop chiral perturbation theory
calculation of the leading exponential corrections in the case of I=2 pi-pi
scattering near threshold.Comment: 17 pages, 2 figures, 1 table. Version published in PR
Policy gradients using variational quantum circuits
Variational quantum circuits are being used as versatile quantum machine learning models. Some empirical results exhibit an advantage in supervised and generative learning tasks. However, when applied to reinforcement learning, less is known. In this work, we considered a variational quantum circuit composed of a low-depth hardware-efficient ansatz as the parameterized policy of a reinforcement learning agent. We show that an epsilon-approximation of the policy gradient can be obtained using a logarithmic number of samples concerning the total number of parameters. We empirically verify that such quantum models behave similarly to typical classical neural networks used in standard benchmarking environments and quantum control, using only a fraction of the parameters. Moreover, we study the barren plateau phenomenon in quantum policy gradients using the Fisher information matrix spectrum.Open access funding provided by FCT-FCCN (b-on). This work is financed by National Funds through the Portuguese funding agency, FCT - Fundacao para a Ciencia e a Tecnologia, within grants LA/P/0063/2020, UI/BD/152698/2022 and project IBEX, with reference PTDC/CCI-COM/4280/2021
Automatic allocation of safety requirements to components of a software product line
Safety critical systems developed as part of a product line must still comply with safety standards. Standards use the concept of Safety Integrity Levels (SILs) to drive the assignment of system safety requirements to components of a system under design. However, for a Software Product Line (SPL), the safety requirements that need to be allocated to a component may vary in different products. Variation in design can indeed change the possible hazards incurred in each product, their causes, and can alter the safety requirements placed on individual components in different SPL products. Establishing common SILs for components of a large scale SPL by considering all possible usage scenarios, is desirable for economies of scale, but it also poses challenges to the safety engineering process. In this paper, we propose a method for automatic allocation of SILs to components of a product line. The approach is applied to a Hybrid Braking System SPL design
Generalised quantum tree search
This extended abstract reports on on-going research on quantum algorithmic approaches to the problem of generalised tree search that may exhibit effective quantum speedup, even in the presence of non-constant branching factors. Two strategies are briefly summarised and current work outlined.This research is financed by the ERDF through the Opera tional Programme for Competitiveness and Internationalisation - COMPETE 2020 Programme and by National Funds through the Portuguese funding agency, FCT, within project POCI-01- 0145-FEDER-03094
Enhancement of optical absorption by modulation of the oxygen flow of TiO2 films deposited by reactive sputtering
Oxygen-deficient TiO2
films with enhanced visible and near-infrared optical absorption have been
deposited by reactive sputtering using a planar diode radio frequency magnetron configuration. It is
observed that the increase in the absorption coefficient is more effective when the O2 gas supply is
periodically interrupted rather than by a decrease of the partial O2 gas pressure in the deposition
plasma. The optical absorption coefficient at 1.5 eV increases from about 1 102
cm 1
to more than
4 103
cm 1
as a result of the gas flow discontinuity. A red-shift of 0.24 eV in the optical
absorption edge is also observed. High resolution transmission electron microscopy with
composition analysis shows that the films present a dense columnar morphology, with estimated
mean column width of 40 nm. Moreover, the interruptions of the O2 gas flow do not produce
detectable variations in the film composition along its growing direction. X-ray diffraction and
micro-Raman experiments indicate the presence of the TiO2
anatase, rutile, and brookite phases.
The anatase phase is dominant, with a slight increment of the rutile and brookite phases in films
deposited under discontinued O2 gas flow. The increase of optical absorption in the visible and
near-infrared regions has been attributed to a high density of defects in the TiO2
films, which is
consistent with density functional theory calculations that place oxygen-related vacancy states in the
upper third of the optical bandgap. The electronic structure calculation results, along with the
adopted deposition method and experimental data, have been used to propose a mechanism to
explain the formation of the observed oxygen-related defects in TiO2 thin films. The observed
increase in sub-bandgap absorption and the modeling of the corresponding changes in the electronic
structure are potentially useful concerning the optimization of efficiency of the photocatalytic
activity and the magnetic doping of TiO2
films
Microstructure identification via detrended fluctuation analysis of ultrasound signals
We describe an algorithm for simulating ultrasound propagation in random
one-dimensional media, mimicking different microstructures by choosing physical
properties such as domain sizes and mass densities from probability
distributions. By combining a detrended fluctuation analysis (DFA) of the
simulated ultrasound signals with tools from the pattern-recognition
literature, we build a Gaussian classifier which is able to associate each
ultrasound signal with its corresponding microstructure with a very high
success rate. Furthermore, we also show that DFA data can be used to train a
multilayer perceptron which estimates numerical values of physical properties
associated with distinct microstructures.Comment: Submitted to Phys. Rev.
The use of vasopressors during anaesthesia for caesarean section: a retrospective observational study
info:eu-repo/semantics/publishedVersio
Epidural top-up for caesarean section: a retrospective observational study
info:eu-repo/semantics/publishedVersio
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