2023
Authors
Wojtczak, JA; Labadie, L; Perraut, K; Tessore, B; Soulain, A; Ganci, V; Bouvier, J; Dougados, C; Alecian, E; Nowacki, H; Cozzo, G; Brandner, W; Garatti, ACO; Garcia, P; Lopez, RG; Sanchez Bermudez, J; Amorim, A; Benisty, M; Berger, JP; Bourdarot, G; Caselli, P; Clenet, Y; de Zeeuw, PT; Davies, R; Drescher, A; Duvert, G; Eckart, A; Eisenhauer, F; Eupen, F; Foerster Schreiber, NM; Gendron, E; Gillessen, S; Grant, S; Grellmann, R; Heissel, G; Henning, T; Hippler, S; Horrobin, M; Hubert, Z; Jocou, L; Kervella, P; Lacour, S; Lapeyrere, V; Le Bouquin, JB; LTna, P; Lutz, D; Mang, F; Ott, T; Paumard, T; Perrin, G; Scheithauer, S; Shangguan, J; Shimizu, T; Spezzano, S; Straub, O; Straubmeier, C; Sturm, E; van Dishoeck, E; Vincent, F; Widmann, F;
Publication
ASTRONOMY & ASTROPHYSICS
Abstract
Context. Hot atomic hydrogen emission lines in pre-main sequence stars serve as tracers for physical processes in the innermost regions of circumstellar accretion disks, where the interaction between a star and disk is the dominant influence on the formation of infalls and outflows. In the highly magnetically active T Tauri stars, this interaction region is particularly shaped by the stellar magnetic field and the associated magnetosphere, covering the inner five stellar radii around the central star. Even for the closest T Tauri stars, a region as compact as this is only observed on the sky plane at sub-mas scales. To resolve it spatially, the capabilities of optical long baseline interferometry are required.Aims. We aim to spatially and spectrally resolve the Br gamma hydrogen emission line with the methods of interferometry in order to examine the kinematics of the hydrogen gas emission region in the inner accretion disk of a sample of solar-like young stellar objects. The goal is to identify trends and categories among the sources of our sample and to discuss whether or not they can be tied to different origin mechanisms associated with Br gamma emission in T Tauri stars, chiefly and most prominently magnetospheric accretion.Methods. We observed a sample of seven T Tauri stars for the first time with VLTI GRAVITY, recording spectra and spectrally dispersed interferometric quantities across the Br gamma line at 2.16 mu m in the near-infrared K-band. We used the visibilities and differential phases to extract the size of the Br gamma emission region and the photocentre shifts on a channel-by-channel basis, probing the variation of spatial extent at different radial velocities. To assist in the interpretation, we also made use of radiative transfer models of magnetospheric accretion to establish a baseline of expected interferometric signatures if accretion is the primary driver of Br gamma emission.Results. From among our sample, we find that five of the seven T Tauri stars show an emission region with a half-flux radius in the four to seven stellar radii range that is broadly expected for magnetospheric truncation. Two of the five objects also show Br gamma emission primarily originating from within the co-rotation radius, which is an important criterion for magnetospheric accretion. Two objects exhibit extended emission on a scale beyond 10 R-(sic), one of them is even beyond the K-band continuum half-flux radius of 11.3 R-(sic). The observed photocentre shifts across the line can be either similar to what is expected for disks in rotation or show patterns of higher complexity.Conclusions. Based on the observational findings and the comparison with the radiative transfer models, we find strong evidence to suggest that for the two weakest accretors in the sample, magnetospheric accretion is the primary driver of Br gamma radiation. The results for the remaining sources imply either partial or strong contributions coming from additional, spatially extended emission components in the form of outflows, such as stellar or disk winds. We expect that in actively accreting T Tauri stars, these phenomena typically occur simultaneously on different spatial scales. Through more advanced modelling, interferometry will be a key factor in disentangling their distinct contributions to the total Br gamma flux arising from the innermost disk regions.
2023
Authors
Silva, L; Gomes, A; Borges, AR; Vasconcelos, V; Mendes, AJ;
Publication
25th International Symposium on Computers in Education, SIIE 2023
Abstract
This work focuses on the motivation levels of introductory programming students and their relationship with their learning performance. The study involved students enrolled in the Introduction to Programming (IP) course included in two slightly different Informatics Engineering degrees at the same institution. The motivation section of the Motivated Strategies for Learning Questionnaire (MSLQ) instrument includes several scales and subscales used to analyse different motivational factors.Four research questions guided the study. The first is comparing the results of the two groups of students. The second considered the student's previous programming experience and tried correlating it with motivational factors. The third is similar but separates students following IP for the first time and those who had failed it in previous years. Finally, the fourth research question examined the influence of motivational factors on students' learning performance measured by their final grades.This paper provides a detailed study description and presents and discusses its results. © 2023 IEEE.
2023
Authors
Azimian, M; Habibifar, R; Amir, V; Shirazi, E; Javadi, MS; Nezhad, AE; Mohseni, S;
Publication
IEEE ACCESS
Abstract
This paper discusses the optimal deployment of a cluster consisting of connected AC-coupled, low voltage (48 V) multi-carrier microgrids within an integrated framework. The utilization of this integrated framework proves to be an effective approach for enhancing the reliability, resiliency, and operational quality of the clustered multi-carrier microgrids. Furthermore, it enables improved utilization of distributed energy resources in both grid-connected and stand-alone scenarios. In order to address local objectives, this paper presents a hybrid approach to determine the optimal integration and size of distributed energy resources in autonomous multi-carrier microgrids. Additionally, the proposed model identifies the ideal demand response intensity for each multi-carrier microgrid, which can result in energy savings and financial profits by modifying energy demands during peak hours. The primary objective is to minimize the development cost of clustered multi-carrier microgrids while ensuring a desired level of local reliability and online reserve. To address the planning problem of the proposed integrated parallel multi-carrier microgrid network, a mixed-integer programming model is formulated. Numerical results obtained from a three-microgrid system demonstrate the effectiveness of the proposed integrated planning model, validating the economic viability of the expansion project from various financial perspectives. Finally, a practical financing strategy is proposed to facilitate the successful implementation and deployment of parallel multi-carrier microgrids, thereby contributing to the achievement of sustainable development goals. The study examines the role of governments in facilitating capital investments for clustered multi-carrier microgrid projects, aligning with sustainable development goals. It proposes a feasible financing strategy through settled billing tax rates ranging from 4% to 26% for multi-carrier microgrid customers over ten years. This strategy can assist policymakers in formulating supportive policy programs to effectively implement and promote multi-carrier microgrids in diverse premises.
2023
Authors
Soares, L; Perez Herrera, RA; Novais, S; Ferreira, A; Fraza, O; Silva, S;
Publication
OPTICAL FIBER TECHNOLOGY
Abstract
A paracetamol concentration-sensing scheme based on a linear cavity fiber laser configuration is demonstrated experimentally. The laser cavity has a fiber sensor at one end, that allows refractive index measurements. The refractometer consists of a cleaved fiber tip combined with an FBG functioning as a reflecting mirror. The combination of a fiber loop mirror at the other end allows to reflect all the light from the FBG and refractometer, forming a linear cavity. By measuring the intensity variation of the Fresnel reflection at the fiber-to-liquid interface, the measured concentration is linear and have a concentration sensitivity of [( - 8.74 & PLUSMN; 0.34) x 10-5 ] & mu;W/(g/kg), over a range of 52.61 to 219.25 g/kg, and with a resolution of 2.77 g/kg. The results obtained present high stability and prove the potential of the fiber laser system to performed realtime measurements of concentration, in a non-invasive way.
2023
Authors
Tavares, L; Lima, B; Araújo, A;
Publication
Proceedings of the 18th International Conference on Software Technologies
Abstract
2023
Authors
Moreira, C; Costa, C; Santos, AS; Bastos, JA; Varela, LR; Brito, MF;
Publication
Lecture Notes in Mechanical Engineering
Abstract
Meta-heuristics are some of the best-known techniques to approach hard optimization problems, however, there are still questions about what makes some meta-heuristics better than others in a specific problem. This paper presents an analysis of the Firefly and Cuckoo Search Algorithm, such as others meta-heuristics. In order to assess the performance of the Firefly Algorithm and the Cuckoo Search Algorithm, they were compared with other well-known optimization techniques, such as Simulated Annealing and Local Search. Both meta-heuristics analysed in an in-depth computational study, reaching the conclusion that both techniques could be useful in Scheduling Problems and lead to satisfactory solutions quickly and efficiently. Moreover, the results of the analysis show that the Firefly Algorithm, despite having a high runtime, performs better than the other techniques. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.
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