9,782 research outputs found
Asymptotic normalization of mirror states and the effect of couplings
Assuming that the ratio between asymptotic normalization coefficients of
mirror states is model independent, charge symmetry can be used to indirectly
extract astrophysically relevant proton capture reactions on proton-rich nuclei
based on information on stable isotopes. The assumption has been tested for
light nuclei within the microscopic cluster model. In this work we explore the
Hamiltonian independence of the ratio between asymptotic normalization
coefficients of mirror states when deformation and core excitation is
introduced in the system. For this purpose we consider a phenomenological rotor
+ N model where the valence nucleon is subject to a deformed mean field and the
core is allowed to excite. We apply the model to 8Li/8B, 13C/13N, 17O/17F,
23Ne/23Al, and 27Mg/27P. Our results show that for most studied cases, the
ratio between asymptotic normalization coefficients of mirror states is
independent of the strength and multipolarity of the couplings induced. The
exception is for cases in which there is an s-wave coupled to the ground state
of the core, the proton system is loosely bound, and the states have large
admixture with other configurations. We discuss the implications of our results
for novae.Comment: 8 pages, 2 figures, submitted to PR
Energy dependence of non-local potentials
Recently a variety of studies have shown the importance of including
non-locality in the description of reactions. The goal of this work is to
revisit the phenomenological approach to determining non-local optical
potentials from elastic scattering. We perform a analysis of neutron
elastic scattering data off Ca, Zr and Pb at energies MeV, assuming a Perey and Buck or Tian, Pang, and Ma non-local
form for the optical potential. We introduce energy and asymmetry dependencies
in the imaginary part of the potential and refit the data to obtain a global
parameterization. Independently of the starting point in the minimization
procedure, an energy dependence in the imaginary depth is required for a good
description of the data across the included energy range. We present two
parameterizations, both of which represent an improvement over the original
potentials for the fitted nuclei as well as for other nuclei not included in
our fit. Our results show that, even when including the standard Gaussian
non-locality in optical potentials, a significant energy dependence is required
to describe elastic-scattering data.Comment: 6 pages, 3 figures, accepted by Phys. Rev. C Rapid Communicatio
Hierarchical reinforcement learning using path clustering
In this paper we intend to study the possibility to improve the performance of the Q-Learning algorithm, by automatically finding subgoals and making better use of the acquired knowledge. This research explores a method that allows an agent to gather information about sequences of states that lead to a goal, detect classes of common sequences and introduce the states at the end of these sequences as subgoals. We use the taxiproblem (a standard in Hierarchical Reinforcement Learning literature) and conclude that, even though this problem's scale is relatively small, in most of the cases subgoals do improve the learning speed, achieving relatively good results faster than standard Q-Learning. We propose a specific iteration interval as the most appropriate to insert subgoals in the learning process. We also found that early adoption of subgoals may lead to suboptimal learning. The extension to more challenging problems is an interesting subject for future work.info:eu-repo/semantics/acceptedVersio
Temperature dependence of the coercive field in single-domain particle systems
The magnetic properties of Cu97Co3 and Cu90Co10 granular alloys were measured
over a wide temperature range (2 to 300K). The measurements show an unusual
temperature dependence of the coercive field. A generalized model is proposed
and explains well the experimental behavior over a wide temperature range. The
coexistence of blocked and unblocked particles for a given temperature rises
difficulties that are solved here by introducing a temperature dependent
blocking temperature. An empirical factor gamma arise from the model and is
directly related to the particle interactions. The proposed generalized model
describes well the experimental results and can be applied to other
single-domain particle system.Comment: 7 pages, 8 figures, revised version, accepted to Physical Review B on
29/04/200
Development of a laboratorial robotized filament winding equipment
Filament winding is the mostly suitable technology to produce at large volume scale structural composite parts presenting revolution form, such as pressure and non-pressure vessels, tanks and pipes, aircraft fuselage, helicopter blades, etc. [1, 2]. Such process allows optimising the deposition and orientation of continuous reinforced fibres in order to manufacture the best performance and customised composite part for each specific application. Another advantage of this technological processing method is the possibility it gives of using almost all continuous reinforcing fibres (carbon, glass, aramid) and plastic matrices (both thermosetting and/or thermoplastic). As the investment for acquiring a filament winding equipment was too much high, the Pole for Innovation in Polymer Engineering (PIEP) decided to use its proper know-how to self-develop an own robotised filament winding equipment for laboratorial use. The aim of such equipment is to support R&D projects with industrial companies concerning the production of filament wound scaled prototype parts for testing, optimising and improving fibre deposition trajectories, study the complex shape manufacturing, testing the application of new fibres and matrices, etc. This paper will present the developed and built robotised filament winding equipment and will discuss its major possibilities, trajectories and software data acquisition capabilities and the results obtained on composite parts manufactured by it.FCT projeto SFRH/BD/60852/200
Statistical Process Control automation in the final inspection process: an industrial case study
This case study arises from the need to make more robust and effective quality assurance procedures of the products by automating the final inspection process. The case study explains how the automation of the inspection process was performed in a company from the automotive sector. Knowledge, involvement and commitment of operators and respective managers should not be neglected because their reaction against the change procedures influence the success of any automation performed. The successful introduction of automation contributed to a more efficient process and from the pilot station to the remaining stations problem solving and continuous improvement was evidenced.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT - Fundacao para a Ciencia e Tecnologia within the Project Scope: UID/CEC/00319/2013.info:eu-repo/semantics/publishedVersio
Light field coding with field of view scalability and exemplar-based inter-layer prediction
Light field imaging based on microlens arrays—a.k.a. holoscopic, plenoptic, and integral imaging—has currently risen up as a feasible and prospective technology for future image and video applications. However, deploying actual light field applications will require identifying more powerful representations and coding solutions that support arising new manipulation and interaction functionalities. In this context, this paper proposes a novel scalable coding solution that supports a new type of scalability, referred to as field-of-view scalability. The proposed scalable coding solution comprises a base layer compliant with the High Efficiency Video Coding (HEVC) standard, complemented by one or more enhancement layers that progressively allow richer versions of the same light field content in terms of content manipulation and interaction possibilities. In addition, to achieve high-compression performance in the enhancement layers, novel exemplar-based interlayer coding tools are also
proposed, namely: 1) a direct prediction based on exemplar texture samples from lower layers and 2) an interlayer compensated prediction using a reference picture that is built relying on an exemplar-based algorithm for texture synthesis. Experimental results demonstrate the advantages of the proposed scalable coding solution to cater to users with different preferences/requirements in terms of interaction functionalities, while providing better rate-
distortion performance (independently of the optical setup used for acquisition) compared to HEVC and other scalable light field coding solutions in the literature.info:eu-repo/semantics/acceptedVersio
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