Magnetic energy harvesting and concentration at distance by transformation optics

Magnetic energy is one the main agents powering our society: generating energy in power plants, keeping information in magnetic memories, moving our devices with motors. All of these applications require a certain spatial distribution of magnetic energy, for example concentrating it in a transformer core or in a magnetic sensor. We introduce in this work a way to collect magnetic energy and distribute it in space with unprecedented efficiency and flexibility, allowing very large concentration of magnetic energy in a free space region, an enhanced magnetic coupling between two magnetic sources, and the transfer of magnetic energy from a source to a given distant point separated by empty space. All these features are achieved with a single device, a magnetic shell designed by transformation optics.Comment: 15 pages, 5 figure

Attention training through gaze-contingent feedback: effects on reappraisal and negative emotions

Reappraisal is central to emotion regulation but its mechanisms are unclear. This study tested the theoretical prediction that emotional attention bias is linked to reappraisal of negative emotion-eliciting stimuli and subsequent emotional responding using a novel attentional control training. Thirty-six undergraduates were randomly assigned to either the control or the attention training condition and were provided with different task instructions while they performed an interpretation task. Whereas control participants freely created interpretations, participants in the training condition were instructed to allocate attention toward positive words to efficiently create positive interpretations (i.e., recruiting attentional control) while they were provided with gaze-contingent feedback on their viewing behavior. Transfer to attention bias and reappraisal success was evaluated using a dot-probe task and an emotion regulation task which were administered before and after the training. The training condition was effective at increasing attentional control and resulted in beneficial effects on the transfer tasks. Analyses supported a serial indirect effect with larger attentional control acquisition in the training condition leading to negative attention bias reduction, in turn predicting greater reappraisal success which reduced negative emotions. Our results indicate that attentional mechanisms influence the use of reappraisal strategies and its impact on negative emotions. The novel attention training highlights the importance of tailored feedback to train attentional control. The findings provide an important step toward personalized delivery of attention training

Older adults' attentional deployment : differential gaze patterns for different negative mood states

Background and objectives: Older adults are characterized by an attentional preference for positive over negative information. Since this positivity effect is considered to be an emotion regulation strategy, it should be more pronounced when emotion regulation is needed. In contrast to previous studies that focused on the effects of sad mood on attention, we used a stressor to activate emotion regulation and evaluate the effects of different types of mood state changes. Moreover, we evaluated mood effects on attentional processes using a paradigm that allows disentangling between different attentional engagement and disengagement processes. Methods: Sixty older adults were randomly assigned to receive a stressor or a control task. Before and after this manipulation, mood state levels (happy, sad, nervous, calm) were assessed. Next, attentional processing of happy, sad, and angry faces was investigated using an eye-tracking paradigm in which participants had to either engage their attention towards or disengage their attention away from emotional stimuli. Results: Changes in different mood state levels were associated with different attentional disengagement strategies. As expected, older adults who increased in sad mood level showed a larger positivity effect as evidenced by a longer time to disengage attention from happy faces. However, older adults who received the tension induction and who decreased in calm mood level were characterized by longer times to disengage attention from sad faces. Limitations: The stressor was only partially effective as it led to changes in calm mood, but not in nervous mood. Conclusions: These results suggest that older adults may deploy a positivity effect in attention (i.e., longer times to disengage from positive information) in order to regulate sad mood, but that this effect may be hampered during the confrontation with stressors. (C) 2016 Elsevier Ltd. All rights reserved

Depression-related difficulties disengaging from negative faces are associated with sustained attention to negative feedback during social evaluation and predict stress recovery

The present study aimed to clarify: 1) the presence of depression-related attention bias related to a social stressor, 2) its association with depression-related attention biases as measured under standard conditions, and 3) their association with impaired stress recovery in depression. A sample of 39 participants reporting a broad range of depression levels completed a standard eye-tracking paradigm in which they had to engage/disengage their gaze with/from emotional faces. Participants then underwent a stress induction (i.e., giving a speech), in which their eye movements to false emotional feedback were measured, and stress reactivity and recovery were assessed. Depression level was associated with longer times to engage/disengage attention with/from negative faces under standard conditions and with sustained attention to negative feedback during the speech. These depression-related biases were associated and mediated the association between depression level and self-reported stress recovery, predicting lower recovery from stress after giving the speech

Ultrafast measurements using x-ray free-electron lasers

X-ray free-electron lasers (XFELs) are unique tools for ultrafast science, allowing one to generate tunable pairs of few-fs x-ray pulses with photon energies between ~10 eV and ~10 keV. XFEL machines are however much larger and much more complex than table-top optical lasers, spanning from several hundreds of metres in length up to a few kilometres. This increased size and complexity makes them very prone to fluctuations and single-shot jitter in the parameters of the generated x-ray pulses such as photon energy, intensity and time delay, of up to ~1%, ~100% and ~15 fs, respectively. Using data from different experiments carried out at the Linac Coherent Light Source (LCLS) and the SPring-8 Angstrom Compact Free Electron Laser (SACLA), the author will show examples of the influence that these fluctuations can have on the experimental signals, proposing solutions to separate this influence from actual meaningful experimental results. The thesis starts with a brief introduction to x-ray science and the working principles of XFELs followed by an extensive description of the common configurations that allow generating pairs of pulses for time-resolved experiments. The first experimental results are then presented for two successful experiments measuring nuclear dynamics in the 10-100 fs timescales in the acetylene and C60 molecules. While successful, these experiments already show the effects of the fluctuations, effects that, as shown in the following chapter, are amplified when attempting to use few-fs pulses to measure few-fs dynamics. Although the presence of the fluctuations may be unavoidable, this thesis shows, using data from three additional ultrafast experiments, that the fluctuations can be circumvented by performing a full single-shot characterization of all x-ray pulses and implementing sophisticated data analysis techniques to sort the experimental data. Finally, having exposed the importance of single-shot x-ray characterization, the author proposes and demonstrates a technique based on machine learning to enable such full x-ray characterization at the next generation of high-repetition-rate XFELs.Open Acces