Optimization methods for Dirichlet control problems

This work was partially supported by the Spanish Ministerio de Ciencia e Innovacion [project number MTM2014-57531-P] and [project number MTM2017-83185-P]

Elicitation and representation of expert knowledge for computer aided diagnosis in mammography

To study how professional radiologists describe, interpret and make decisions about micro-calcifications in mammograms. The purpose was to develop a model of the radiologists' decision making for use in CADMIUM II, a computerized aid for mammogram interpretation that combines symbolic reasoning with image processing

Human-machine diversity in the use of computerised advisory systems: a case study

Computer-based advisory systems form with their users composite, human-machine systems. Redundancy and diversity between the human and the machine are often important for the dependability of such systems. We discuss the modelling approach we applied in a case study. The goal is to assess failure probabilities for the analysis of X-ray films for detecting cancer, performed by a person assisted by a computer-based tool. Differently from most approaches to human reliability assessment, we focus on the effects of failure diversity — or correlation — between humans and machines. We illustrate some of the modelling and prediction problems, especially those caused by the presence of the human component. We show two alternative models, with their pros and cons, and illustrate, via numerical examples and analytically, some interesting and non-intuitive answers to questions about reliability assessment and design choices for human-computer systems

Effects of Gravity and Non-Perpendicularity during Powder-Fed Directed Energy Deposition of Ni-Based Alloy 718 through Two Types of Coaxial Nozzle

The consequences of gravity and the nozzle inclination angle in the powder-fed Directed Energy Deposition (DED) process were examined in this study. We also sought to define guidelines and manufacturing strategies, depending on the DED system configuration and the nozzle type. To do so, two nozzle types were used: a continuous coaxial nozzle with a slit of 0.5 mm and a four-stream discrete coaxial nozzle. Although the main effects of the configurations and the nozzles are well-known, their effects on the clad characteristics and the deposition strategy are as yet unclear. In this paper, measurements of a single clad and the effects of different deposition strategies on cladding applications and inclined walls are presented, and the consequences for manufacturing processes are discussed. Based on a complete study of a single clad, working vertically, five different tilted deposition strategies were applied: three to a single clad and two to an inclined wall. The results for both the single clad and the inclined wall reflect a pattern of changes to height, width, area, and efficiency, at both small and large nozzle angles and deposition strategies. The inclined wall presents a maximum horizontal displacement that can be reached per layer, without geometrical distortions. The amount of material per layer has to be adapted to this limitation.This research was funded by the European Commission through the project "PARADDISE: a Productive, Affordable and Reliable solution for large scale manufacturing of metallic components by combining laser-based Additive and Subtractive processes with high Efficiency” (Grant Agreement 723440), an initiative of the Public–Private Partnership “Photonics and Factories of the Future”. This research was also funded by European Institute of Innovation & Technology (EIT), through the project "DEDALUS: Directed Energy Deposition machines with integrated process ALgorithms Under dedicated monitoring and control System” (ID 20094), and by the vice-counseling of technology, innovation and competitiveness of the Basque Government (Eusko Jaurlaritza), under the ELKARTEK Program, PROCODA project, grant number KK-2019/00004

How to discriminate between computer-aided and computer-hindered decisions: a case study in mammography

Background. Computer aids can affect decisions in complex ways, potentially even making them worse; common assessment methods may miss these effects. We developed a method for estimating the quality of decisions, as well as how computer aids affect it, and applied it to computer-aided detection (CAD) of cancer, reanalyzing data from a published study where 50 professionals (“readers”) interpreted 180 mammograms, both with and without computer support. Method. We used stepwise regression to estimate how CAD affected the probability of a reader making a correct screening decision on a patient with cancer (sensitivity), thereby taking into account the effects of the difficulty of the cancer (proportion of readers who missed it) and the reader’s discriminating ability (Youden’s determinant). Using regression estimates, we obtained thresholds for classifying a posteriori the cases (by difficulty) and the readers (by discriminating ability). Results. Use of CAD was associated with a 0.016 increase in sensitivity (95% confidence interval [CI], 0.003–0.028) for the 44 least discriminating radiologists for 45 relatively easy, mostly CAD-detected cancers. However, for the 6 most discriminating radiologists, with CAD, sensitivity decreased by 0.145 (95% CI, 0.034–0.257) for the 15 relatively difficult cancers. Conclusions. Our exploratory analysis method reveals unexpected effects. It indicates that, despite the original study detecting no significant average effect, CAD helped the less discriminating readers but hindered the more discriminating readers. Such differential effects, although subtle, may be clinically significant and important for improving both computer algorithms and protocols for their use. They should be assessed when evaluating CAD and similar warning systems

EVN observations of the farthest and brightest ULIRGs in the local Universe: the case of IRAS 23365+3604

We present high-resolution, high-sensitivity radio images of the ultra-luminous infrared galaxy (ULIRG) IRAS 23365+3604. We performed contemporaneous observations at 1.7 and 5.0 GHz, in three epochs separated by one year from each other, with the European very long baseline interferometry Network (EVN). We also present complementary Multi-Element Radio Linked Interferometry Network (MERLIN) at 1.6 and 5.0 GHz, and archival Very Large Array (VLA) data, taken at 1.4 and 4.9 GHz. We find that the emission at ~5.0 GHz remains quite compact as seen at different resolutions, whereas at ~1.7 GHz, high resolution imaging reveals some extended structure. The nuclear region has an approximate linear size of 200 pc and shows the presence of two main emission components: i) one with a composite spectrum due to ongoing non-thermal activity (probably due to recently exploded supernovae and AGN activity), ii) another one with a steep spectrum, likely dominated by an old population of radio emitters, such as supernova remnants (SNRs). Radiative losses are important, so re-acceleration or replenishment of new electrons is necessary. We estimate a magnetic field strength of 18 \mu G at galactic, and 175 \mu G at nuclear scales, which are typical for galaxies in advanced mergers.Comment: 12 pages, 4 figures and 6 tables. Accepted for publication in MNRA

Jet precession in the active nucleus of M81. Ongoing VLBI monitoring

In a recent publication, we reported results of a multi-frequency VLBI campaign of observations of the Active Galactic Nucleus (AGN) in galaxy M\,81, phase-referenced to the supernova SN\,1993J. We were able to extract precise information on the relative astrometry of the AGN radio emission at different epochs and frequencies. We found strong evidence of precession in the AGN jet (i.e., a systematic evolution in the jet inclination at each frequency) coupled to changes in the overall flux density at the different frequencies. In these proceedings, we summarise the main contents of our previous publication and we report on (preliminary) new results from our follow-up VLBI observations, now phase-referenced to the young supernova SN2008iz. We also briefly discuss how these results match the picture of our previously-reported precession model.Comment: 6 pages, 3 figures. Proceedings of EVN meeting 201