No abstract

This study analyzes the effects of COVID-19 confinement on the autonomous learning performance of students in higher education. Using a field experiment with 458 students from three different subjects at Universidad Autó noma 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 had their faceto-face activities interrupted 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 significant in activities that did not change their format when performed after the confinement. We find that this effect is significant both in subjects that increased the number of assessment activities and subjects that did not change the student workload. 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 performance.

Scanning Force Microscopy (SFM) has become a standard tool to image and manipulate surfaces with nanometer resolution. In order to minimize sample deformations due to the tip interaction, in particular when dealing with soft biological samples, the SFM images are usually taken by using different dynamic operation modes [1]. Phase contrast images, obtained by simultaneously recording the phase lag of the cantilever oscillation relative to the driving signal, often provides significantly more contrast than the topographic image. At fixed feedback amplitude, phase shift variations are directly linked to energy dissipation processes [2][3][4]. However, most of the phase and energy dissipation images are purely qualitative, mainly due to the absence of simple relationships relating phase changes and energy dissipation with specific surface properties.As a general approach, power dissipation in AM-AFM is naturally considered synonymous of energy dissipated per cycle. Assuming that the dissipation takes place in each oscillation cycle, it would be proportional to the oscillation frequency, ν 0, i.e. P dis =ΔEν 0 , being ΔE the energy dissipated in the contact process. In striking contrast to this apparently natural argument, we show that the time-averaged dissipated power is not always proportional to ΔE due to a beating phenomenon where the interaction is occasionally dissipative [5,6].In air ambient condition, the phase contrast is strongly influenced by capillary forces [5]. When the tip approaches the sample, water condensation from the humidity can induce the formation of a nanometer-sized water bridge. In this work we analyze the energy dissipation process involved in the formation and rupture of a nanometer-sized capillary-condensed water bridge (see Fig. 1). With the help of numerical simulations, dissipation contrast in AM-AFM is shown to be a result of a non-trivial interplay between the energy dissipated in each rupture process and the bi-stable motion of the cantilever. In the repulsive regime (see Fig. 2), the dissipated power is approximately constant and independent of the amplitude as expected. In contrast, in the attractive regime, after the contact process, the cantilever, which has lost energy, will not reach the same amplitude as before the contact, and the tip may not hit the sample surface during the next swings. The power dissipation is then lower than expected.In the repulsive regime, the dissipated power is a function of the tip and sample contact angles being independent of the elastic properties of the system. Working in this regime, energy dissipation images in air can be regarded as surface hydrophobicity maps.