Tight-Binding Molecular Dynamics Simulations on Point Defects Diffusion and Interactions in Crystalline Silicon

Tight-binding molecular dynamics (TBMD) simulations are performed (i) to evaluate the formation and binding energies of point defects and defect clusters, (ii) to compute the diffusivity of self-interstitial and vacancy in crystalline silicon, and (iii) to characterize the diffusion path and mechanism at the atomistic level. In addition, the interaction between individual defects and their clustering is investigated

Adaptive Interpolatory MOR by Learning the Error Estimator in the Parameter Domain

Interpolatory methods offer a powerful framework for generating reduced-order models (ROMs) for non-parametric or parametric systems with time-varying inputs. Choosing the interpolation points adaptively remains an area of active interest. A greedy framework has been introduced in Feng et al. [ESAIM: Math. Model. Numer. Anal. 51(6), 2017] and in Feng and Benner [IEEE Trans. Microw. Theory Techn. 67(12), 2019] to choose interpolation points automatically using a posteriori error estimators. Nevertheless, when the parameter range is large or if the parameter space dimension is larger than two, the greedy algorithm may take considerable time, since the training set needs to include a considerable number of parameters. As a remedy, we introduce an adaptive training technique by learning an efficient a posteriori error estimator over the parameter domain. A fast learning process is created by interpolating the error estimator using radial basis functions (RBF) over a fine parameter training set, representing the whole parameter domain. The error estimator is evaluated only on a coarse training set including a few parameter samples. The algorithm is an extension of the work in Chellappa et al. [arXiv e-prints 1910.00298] to interpolatory model order reduction (MOR) in frequency domain. Beyond this work, we use a newly proposed inf-sup-constant-free error estimator in the frequency domain, which is often much tighter than the error estimator using the inf-sup constant.Comment: 21 pages, 6 figures, 3 tables. Submitted to the proceedings of MODRED 201

Fast A Posteriori State Error Estimation for Reliable Frequency Sweeping in Microwave Circuits via the Reduced-Basis Method

We develop a compact, reliable model order reduction approach for fast frequency sweeps in microwave circuits by means of the reduced-basis method. Contrary to what has been previously done, special emphasis is placed on certifying the accuracy of the reduced-order model with respect to the original full-order model in an effective and efficient way. Previous works on model order reduction accuracy certification rely on costly $\textit{a posteriori}$ error estimators, which typically require expensive $\textit{inf-sup}$ constant evaluations of the underlying full-order model. This scenario is often too time-consuming and unaffordable in electromagnetic applications. As a result, less expensive and heuristic error estimators are commonly used instead. Very often, one is interested in knowing about the full state vector, instead of just some output quantities derived from the full state. Therefore, error estimators for the full state vector become relevant. In this work, we detail the frequency behavior of both the electric field and the state error when an approximation to the electric field solution is carried out. Both field quantities share the same frequency behavior. Based on this observation, we focus on the efficient estimation of the electric field state error and propose a fast evaluation of the reduced-order model state error in the frequency band of analysis, minimizing the number of full-order model evaluations. This methodology is of paramount importance to carry out a reliable fast frequency sweep in microwave circuits. Finally, real-life applications will illustrate the capabilities and efficiency of the proposed approach.Comment: 24 pages, 13 Figures, 6 Table

Influence of COVID-19 confinement in students’ performance in higher education

Documento procedente de EdArXiv Preprints , se deposita en Biblos-e Archivo versión 2 de 7 Mayo de 2020This study explores the effects of COVID-19 confinement in the students’ performance in higher education. Using a field experiment of 458 students from three different subjects in Universidad Autónoma de Madrid (Spain), we study the differences in assessments by dividing students into two groups. The first group (control) corresponds to academic years 2017/2018 and 2018/2019. The second group (experimental) corresponds to students from 2019/2020, which is the group of students that interrupted their face-to-face activities because of the confinement. The results show that there is a significant positive effect of the COVID-19 confinement on students’ performance. This effect is also significative in activities that did not change their format when performed after the confinement. We find that this effect is significative both in subjects that increased the number of assessment activities and subjects that did not change the workload of students. Additionally, an analysis of students’ learning strategies before confinement shows that students did not study on a continuous basis. Based on these results, we conclude that COVID-19 confinement changed students’ learning strategies to a more continuous habit, improving their efficiency. For these reasons, better scores in students’ assessment are expected due to COVID-19 confinement that can be explained by an improvement in their learning performanceThis work has been financed by the project Erasmus+ 2017-1-ES01-KA203-038266 Project of the European Union: “Advanced Design of e-Learning Applications Personalizing Teaching to Improve Virtual Education

Striking Increase in Hole Mobility upon Metal Coordination to Triphenylene Schiff Base Semiconducting Multicolumnar Mesophases

Producción CientíficaThis paper reports the synthesis, liquid-crystal behavior, and charge-transport properties in the mesophase of triphenylene Schiff bases and their copper(II), nickel(II), and oxovanadium(IV) complexes. The thermal and electronic properties of the Schiff bases are modulated by coordination to the corresponding metal moieties, which have the ability to self-assemble into linear structures and help the alignment of the triphenylene columns. This produces two kinds of electronically nonconnected columnar regions, one purely organic and one more inorganic. The most remarkable effect is a striking charge mobility enhancement in the metal-containing mesophases, due to the contribution of the more inorganic columns: in comparison to values of hole mobility along the columnar stacking for the purely organic columnar mesophases, on the order of 10–7 cm2 V–1 s–1, these values jump to 1–10 cm2 V–1 s–1 in these hybrid inorganic/organic columnar materials.Ministerio de Ciencia, Innovación y Universidades (Project CTQ2017-89217-P)Junta de Castilla y León (Project VA038G18)Universidad del País Vasco / EHU (ProjectGIU18/146

Secondary School Students' Knowledge and Opinions on Astrobiology Topics and Related Social Issues

Astrobiology is the study of the origin of life on Earth and the distribution of life in the Universe. Its multidisciplinary approach, social and philosophical implications, and appeal within the discipline and beyond make astrobiology a uniquely qualified subject for general science education. In this study, student knowledge and opinions on astrobiology topics were investigated. Eighty-nine students in their last year of compulsory education (age 15) completed a written questionnaire that consisted of 10 open questions on the topic of astrobiology. The results indicate that students have significant difficulties understanding the origin of life on Earth, despite exposure to the topic by way of the assigned textbooks. The students were often unaware of past or present achievements in the search for life within the Solar System and beyond, topics that are far less commonly seen in textbooks. Student questionnaire answers also indicated that students had problems in reasoning and critical thinking when asked for their opinions on issues such as the potential for life beyond Earth, the question of whether UFOs exist, or what our place is in the Universe. Astrobiology might help initiate student awareness as to current thinking on these matters and should be considered for general science educatio

Synchronization of fluctuating delay-coupled chaotic networks

We study the synchronization of chaotic units connected through time-delayed fluctuating interactions. Focusing on small-world networks of Bernoulli and Logistic units with a fixed chiral backbone, we compare the synchronization properties of static and fluctuating networks in the regime of large delays. We find that random network switching may enhance the stability of synchronized states. Synchronization appears to be maximally stable when fluctuations are much faster than the time-delay, whereas it disappears for very slow fluctuations. For fluctuation time scales of the order of the time-delay, we report a resynchronizing effect in finite-size networks. Moreover, we observe characteristic oscillations in all regimes, with a periodicity related to the time-delay, as the system approaches or drifts away from the synchronized state

Seasons and Other Factors Affecting the Quality of Life of Asthmatic Children

[email protected]: To study the effect of seasons on the health-related quality of life (HRQL) of asthmatic children. Methods: Four groups of asthmatic children 7 to 14 years old were recruited by pediatricians during each season of the year. Their HRQL was assessed by means of the Paediatric Asthma Quality of Life Questionnaire (PAQLQ). Other factors surveyed were asthma severity, atopy, medical treatment, immunotherapy, obesity, parental smoking, and anti-allergic measures. Results: The mean (SD) overall PAQLQ score was highest in summer at 6.2 (1.0) and lowest in autumn at 5.5 (1.2). The same trend was found for domains in summer and autumn, respectively: symptoms, 6.2 (1.0) vs 5.4 (1.4); emotions, 6.5 (0.8) vs 6.0 (1.0); and activities, 5.9 (1.4) vs 5.0 (1.5). Factors such as male gender (odds ratio [OR], 0.60; 95% confi dence interval [CI], 0.41–0.87), being on immunotherapy (OR, 0.59; 95% CI, 0.38–0.92), living in an urban environment (OR, 0.56; 0.33–0.93), and residing on the northern coast of Spain along the Bay of Biscay (OR, 0.56; 0.36-0.89) were independent protective factors against having a total PAQLQ score in the lower tertile. Conversely, being recruited in a primary care setting (OR, 1.55; 1.01–2.38) and having more severe asthma were risks for being in the lower tertile. Conclusions: Irrespective of the severity of the disease, season has a significant influence on the HRQL of asthmatic [email protected]