Trajectory tracking for a quadrotor under wind perturbations: sliding mode control with state-dependent gains

The problem of position tracking of a mini drone subject to wind perturbations is investigated. The solution is based on a detailed unmanned aerial vehicle (UAV) model, with aerodynamic coefficients and external disturbance components, which is introduced in order to better represent the impact of the wind field. Then, upper bounds of wind-induced disturbances are characterized, which allow a sliding mode control (SMC) technique to be applied with guaranteed convergence properties. The peculiarity of the considered case is that the disturbance upper bounds depend on the control amplitude itself (i.e. the system is nonlinear in control), which leads to a new procedure for the control tuning presented in the paper. The last part of the paper is dedicated to the analysis and reduction of chattering effects, as well as investigation of rotor dynamics issues. Conventional SMC with constant gains, proposed first order SMC, and proposed quasi-continuous SMC are compared. Nonlinear UAV simulator, validated through in-door experiments, is used to demonstrate the effectiveness of the proposed controls.     

Perpetual Beginnings: The Role of Phenomenological Hermeneutics in Art Education

This paper reflects on the role of phenomenological hermeneutics as part of art history and theory programmes in art education. Though initially confined to Philosophy, this branch of hermeneutics can be utilised in Art Education also, as concepts explored here such as the appropriation of knowledge, interpretation, reading and understanding offer an effective tool to investigate the strength and potential of subjectivity, metaphoricity and embodiment in art practice. This paper begins with a reflection on the most effective space where theory teaching can take place and offers the concept of the hermeneutical space, where teaching is inclusive and supportive of self determined contributions to processes of theoretical reflection on art practice. A mutual learning experience is fostered in this environment, where teacher and student respect each other's readings. Finally, I put forward suggestions as to how this can be realised in an actual teaching situation by relating my own experience.     

Archaeomagnetic investigation of a metallurgical furnace in Pisa (Italy)

An archaeological excavation has been carried out at Pisa (Italy), unearthing an ancient metallurgical workshop. Since archaeological burnt materials provide important records of direction and intensity of the Earth's magnetic field in the past and they can be used to better improve geomagnetic secular variation curves (SVCs), an archaeomagnetic study has been performed. This small copper-alloy furnace presents a circular concave shape covered with a thin layer of mortar, with some traces of heated clay surrounding the feature that confirms the high temperature reached inside it. Archaeological context dating points to the last firing of the furnace between the last quarter of the 13th century and the first quarter of 14th century AD, when then the metallurgical workshop was transformed in a warehouse. Archaeomagnetic sampling has been performed using the modified Thellier method, by collecting several, large and independently oriented aliquots of heated clay, forming the bottom part of the circular wall of the structure. Laboratory treatments have been conducted at the IGG-CNR ARCHEO_LAB (Pisa, Italy) and at St. Maur Palaeomagnetic laboratory (Paris, France). Analytical measurements of the thermo-remanent magnetization index acquired from the samples have been performed using a large cell induction magnetometer for large samples, and the characteristic remanent magnetization (ChRM) has been successfully isolated after an alternate field demagnetization cleaning procedure for each sample. The final mean archaeomagnetic direction has been calculated at sampling site (D = 6.9°; I = 52.8°; N = 9; k = 305; α₉₅ = 2.6°) following the Fisher Statistics, and it exhibits a perfect agreement with some coeval already published directions obtained from Mt. Arso lava flows, these latter being an important anchor point in the preliminary Italian secular variation curve. Comparison with the preliminary Italian SVC, the French SVC and the SCHA.DIF.3K archaeomagnetic regional model have permitted to define an archaeomagnetic absolute age confirming the conventional archaeological age, underlining the importance of this result into the Italian archaeomagnetic data set.     

Attentional focus effects in balance acrobats

Performing and learning motor skills has been shown to be enhanced if the performer adopts an external relative to internal focus (or no focus) of attention (Wulf 2007). The present study examined the generalizability of this effect to top-level performers (balance acrobats). Participants performed a balance task (standing on an inflated rubber dish) under each of three attentional focus conditions: (a) external focus (i.e., minimize movements of the disk), (b) internal focus (i.e., minimize movements of the feet), and (c) control conditions (no focus instructions). While there were no differences between conditions in the amount of postural sway, the frequency of movement adjustments was higher in the control condition, relative to both external and internal focus conditions. This suggests that movement automaticity and postural stability were greatest when the balance experts were free to adopt their "normal" focus of attention. The finding implies that there may be a limit to the performance-enhancing effects of external focus instructions for top-level performers. The findings are discussed in terms of action control levels and possible changes in the optimal attentional focus with the performer's level of expertise.     

Enhanced expectancies improve movement efficiency in runners

We followed up on recent findings demonstrating that enhancing performers' expectancies can improve their performance. Specifically, we examined whether providing experienced runners with positive feedback regarding their movement efficiency would increase running efficiency. Two groups of experienced runners ran on a treadmill at 75% of their maximum oxygen consumption (VO(2max)) for 10 min. One group (enhanced expectancy) was provided with (fabricated) feedback about the efficiency of their running style every 2 min. A control group was not given feedback. Oxygen consumption decreased in the enhanced expectancy group across measurement times (every 2 min for 10 min), but remained the same in the control group. In addition, performance perceptions changed only in the enhanced expectancy group, indicating a perception of greater ease of running and reduced fatigue when assessed after compared with before running. Finally, positive affect increased from a pre- to a post-test in the enhanced expectancy group, in contrast to the control group. Our findings show that enhanced expectancies can have a positive effect on movement efficiency and running experience. They add to the accumulating evidence for the social-cognitive-affective-motor nature of motor performance.     

Feedback about more accurate versus less accurate trials: differential effects on self-confidence and activation

One purpose of the present study was to examine whether self-confidence or anxiety would be differentially affected byfeedback from more accurate rather than less accurate trials. The second purpose was to determine whether arousal variations (activation) would predict performance. On day 1, participants performed a golf putting task under one of two conditions: one group received feedback on the most accurate trials, whereas another group received feedback on the least accurate trials. On day 2, participants completed an anxiety questionnaire and performed a retention test. Shin conductance level, as a measure of arousal, was determined. The results indicated that feedback about more accurate trials resulted in more effective learning as well as increased self-confidence. Also, activation was a predictor of performance.     

Computer Self-Efficacy and Motivation to Learn in a Self-Directed Online Course

Despite the increased use of new learning technologies, there is still much to be learned about the role of learner characteristics in online learning. The purpose of this study was to examine how subjects' characteristics normally associated with effective training (i.e., initial motivation to learn and self-efficacy) related to learning in a self-directed online course. From an analysis of 190 respondents, computer and Internet usage prior to the start of class were positively related to individuals' computer self-efficacy and computer self-efficacy was positively related to learning. However, contrary to expectations, computer self-efficacy was not related to initial motivation to learn and motivation to learn was not related to learning in the class. Post hoc analysis of qualitative data enabled a rich explanation of the findings, including an evaluation of the unexpected relationships among the variables of interest and the nature of self-directed courses in virtual learning environments.     

Dealing with errors in mathematics classrooms: Structure and relevance of perceived error climate

Errors are often perceived by students as self-threatening and not as learning opportunities. The present work focuses on contextual influences on reactions to errors and learning processes. Based on prior research, a conceptualization of perceived error climate in the classroom with eight subdimensions and one superordinate uniform factor is proposed and a newly developed student questionnaire for its assessment is presented. Results of a study with N = 1116 students from 56 mathematics classrooms in German secondary schools indicated the validity of the error climate conceptualization and the suitability of the questionnaire. Moreover, the results showed that perceived error climate in the classroom predicted the adaptivity of students’ individual reactions to errors above and beyond perceived classroom goal structures and personal achievement motivation (academic self-concept, mastery goal orientation). In addition, the study provided evidence that perceived error climate affects – partially mediated through students’ individual reactions to errors – the quantity and self-regulation of students’ effort.     

The teacher work sample: A tool for scaffolding and assessing preservice teachers' early field experiences

Abstract

This article describes adapting teacher work sample methodology from the student teaching level to a 4‐week, 25‐hour field experience occurring relatively early in a teacher education program. The goals of the project were twofold: (a) to examine whether an adapted version of the teacher work sample would promote planning and reflection in preservice teachers, and (b) to explore the potential of an adapted teacher work sample as an assessment tool. Adaptations to the original, such as emphasizing formative over summative assessment, are briefly described. Survey and focus group data from a pilot combined with survey data from a semester of full implementation with 270 teacher candidates indicate the teacher work sample is useful for promoting reflection and an understanding of student assessment. The advantages of the teacher work sample are maximized when teacher candidates are engaged in whole class instruction.