Abstract

Abstract
Crowdsourcing has become an essential source of information for tourists and tourism industry. Every day, large volumes of data are exchanged among stakeholders in the form of searches, posts, shares, reviews or ratings. Specifically, this paper explores inter-guest trust and similarity post-filtering, using crowdsourced ratings collected from the Expedia and TripAdvisor platforms, to improve hotel recommendations generated by incremental collaborative filtering. First, the profiles of hotels and guests are created using multi-criteria ratings and inter-guest trust and similarity. Next, incremental model-based collaborative filtering is adopted to predict unknown hotel ratings based on the multi-criteria ratings and, finally, post-recommendation filtering sorts the generated predictions based on the inter-guest trust and similarity. The proposed method was tested both off-line (post-processing) and on-line (real time processing) for performance comparison. The results highlight: (i) the increase of the quality of recommendations with the inter-guest trust and similarity; and (ii) the decrease of the predictive errors with the on-line incremental collaborative filtering. Thus, this work contributes with a novel method, integrating incremental collaborative filtering and inter-guest trust and similarity post-filtering, for on-line hotel recommendation based on multi-criteria crowdsourced rating streams. © 2019, Springer Nature Switzerland AG.

Abstract
Optical waveguides were fabricated in alkaline earth boro-aluminosilicate glass, by femtosecond laser direct writing, with varying pulse energy and scan velocity. A spectral characterization, from 500 nm to 1700 nm, was made in order to determine their losses and understand its dependence on the processing parameters. Three major loss mechanisms were identified. At longer wavelengths, loss is mainly due to weak coupling. On the other hand, the behavior at shorter wavelengths is governed by propagation loss due to Rayleigh scattering, which was shown to be practically eliminated (& x003C; 0.05 dB $\cdot$ cm $<^>{-1} {\cdot }\,\,\mu \text{m}<^>{4}$ ) at higher scan velocities. Bulk absorption was also found to have an influence in the propagation losses at higher wavelengths. The combination of intermediate pulse energies (between 125-250 nJ) and high scan velocities (above 6 cm/s) allowed the fabrication of optical waveguides offering low losses across the entire range of wavelengths tested, facilitating applications that require larger wavelength working bands. Furthermore, since optimal fabrication conditions are achieved at higher scanning velocities, mass production with reduced fabrication times can be achieved.

Abstract
Nowadays statistics plays a major role either in society or in the research fields, with a particular emphasis in decision-making, therefore the importance of statistical inference. Statistical inference teaching is a new chapter, so this is an innovative study in Angola, since the scientific council of Polytechnic School of Malanje (PSM, Angola) had to agree to change the course syllabus in order to include the topics of statistical inference, in which confidence intervals (CI) and hypothesis testing were proposed by the first time in Angolan higher education. This work is part of a broader research that has adopted the theoretical framework of the Ontosemiotic Approach (OSA) since we are trying to overcome the error and difficulties of the students, using the semiotic conflict concept. Those conflicts are of two kinds: conflicts in using the new concepts of CI and conflicts that arise by the use of the spreadsheet. In this smaller work, we focus on the teaching of confidence intervals using the spreadsheet, in the course of Probabilities and Statistics in the PSM (Angola) during the academic year 2017/2018. The statistical inference through teaching confidence intervals in the course of Probability and Statistics of PSM was taught for the first time, as well as the a technologic tool, the spreadsheet. In this paper, our main goal is to present the classes planning of this module and it is qualitative and descriptive work. After the planning stage, we describe what the students were asked to do with the spreadsheet after completing the suggested problems using paper and pencil. The spreadsheet was selected since all students have it in their laptop and they may easily use it. During this first implementation of the CI classes, students did find the difficulties and made some of the errors described in the literature. Nevertheless, we noticed a great satisfaction from the students and they were motivated with this theme, and were very enthusiastic by the use of the spreadsheet and hopefully other topics in this Probabilities and Statistics course will also use it.

Abstract
An online data-based methodology for early damage detection and localisation under the effects of environmental and operational variations (EOVs) is proposed. The methodology is described in detail and implemented in a large prestressed concrete cable-stayed bridge of which 3.5 years of data are available. The effects of EOVs are suppressed by the combined application of two well-established multivariate data analysis methods: multiple linear regression and principal component analysis. Criteria for the systematic choice of the predictor variables and the number of principal components to retain are proposed. Because the bridge is new and sound, the experimental time series are corrupted with numerically simulated damage scenarios in order to evaluate the damage detection ability. It is demonstrated that the sensitivity to damage is increased when daily, 2-day, or 3-day averaged data are used instead of hourly data. The effectiveness of the proposed methodology is also demonstrated with the detection of a real, small, and temporary sensor anomaly. The implemented methodology has revealed to be robust and efficient, presenting a contribution to the transition of structural health monitoring from academia to industry.

Abstract
During its orbit around the four million solar mass black hole Sagittarius A* the star S2 experiences significant changes in gravitational potential. We use this change of potential to test one part of the Einstein equivalence principle: the local position invariance (LPI). We study the dependency of different atomic transitions on the gravitational potential to give an upper limit on violations of the LPI. This is done by separately measuring the redshift from hydrogen and helium absorption lines in the stellar spectrum during its closest approach to the black hole. For this measurement we use radial velocity data from 2015 to 2018 and combine it with the gravitational potential at the position of S2, which is calculated from the precisely known orbit of S2 around the black hole. This results in a limit on a violation of the LPI of vertical bar beta(He) - beta(H)vertical bar = (2.4 +/- 5.1) x 10(-2). The variation in potential that we probe with this measurement is six magnitudes larger than possible for measurements on Earth, and a factor of 10 larger than in experiments using white dwarfs. We are therefore testing the LPI in a regime where it has not been tested before.