Dislocation dynamics simulations with climb: kinetics of dislocation loop coarsening controlled by bulk diffusion

Dislocation climb mobilities, assuming vacancy bulk diffusion, are derived and implemented in dislocation dynamics simulations to study the coarsening of vacancy prismatic loops in fcc metals. When loops cannot glide, the comparison of the simulations with a coarsening model based on the line tension approximation shows a good agreement. Dislocation dynamics simulations with both glide and climb are then performed. Allowing for glide of the loops along their prismatic cylinders leads to faster coarsening kinetics, as direct coalescence of the loops is now possible

Croissance et spectroscopie de boîtes quantiques diluées d'InAs/InP(001) pour des applications nanophotoniques à 1,55 [micro]m

This thesis focus on the epitaxial growth and optical characterization of diluted InAs/InP(001) quantum dots for the realisation of new nanophotonic devices emitting at 1.55 [micro]m. The structural and optical properties of the quantum islands are correlated to different growth parameters of a solid source molecular beam epitaxy system. Our results highlight the influence of InAs surface reconstructions on the island shape. Dots rather than elongated dashes usually observed can be directly formed by adequate growth conditions. Dash to dot shape transition is also demonstrated by post-growth treatments. Low dot densities are obtained for small InAs deposited thickness. Their emission wavelength is easily tuned to 1.55 [micro]m using the"double cap" procedure for the growth of the InP capping layer. Optical properties of such single InAs/InP quantum dots are then evaluated. Micro-photoluminescence studies reveal sharp and well separated emission lines near 1.55 [micro]m from single dots confirming their atom-like properties. Last, we propose for the first time a high spatial resolution method to study the carrier transport in the vicinity of a single quantum dot using a low-voltage cathodoluminescence technique. A direct measurement of the carrier diffusion length before capture into one dot has been obtained. These results open the way to the integration of these single dots into optical micro-cavities for the realisation of quantum light sources at 1.55 [micro]m

Dielectric GaAs Antenna Ensuring an Efficient Broadband Coupling between an InAs Quantum Dot and a Gaussian Optical Beam

We introduce the photonic trumpet, a dielectric structure which ensures a nearly perfect coupling between an embedded quantum light source and a Gaussian free-space beam. A photonic trumpet exploits both the broadband spontaneous emission control provided by a single-mode photonic wire and the adiabatic expansion of this mode within a conical taper. Numerical simulations highlight the outstanding performance and robustness of this concept. As a first application in the field of quantum optics, we report the realisation of an ultra-bright single-photon source. The device, a GaAs photonic trumpet containing few InAs quantum dots, demonstrates a first-lens external efficiency of $0.75 \pm 0.1$

A longitudinal study of mental health before and during COVID-19 lockdown in the French population

BACKGROUND: The impact of general population lockdown implemented in the face of the COVID-19 epidemic needs to be evaluated. We describe here a longitudinal study on the mental health of adults in France. METHODS: We did a secondary analysis of a web-based cohort, initially set up to study home and leisure injuries, in order to measure the consequences of the national lockdown implemented in France from 17 March 2020 to 11 May 2020, and to assess potential vulnerability and resilience factors. Eligible participants were invited to answer an online questionnaire designed to assess their living conditions and health during lockdown. Comparisons were done with answers provided 4.8 years earlier on average. RESULTS: On 15th April 2020, we sent email invitations to 9598 participants recruited between November 2014 and December 2019 and 1237 volunteers took part in the study by completing the online questionnaire. The proportion of those with anxiety symptoms markedly increased from 17.3 to 20.1%. The average self-rated level of mental health decreased from 7.77 to 7.58. Women, the elderly and the youngest appeared to be more vulnerable. A small living space (less than 30 m(2)) was associated with an increase in depression symptoms (PHQ-9 score), and poorer self-rated physical health at recruitment was associated with an increase in anxiety symptoms (GAD-7 score). On the contrary, the average self-rated level of physical health markedly increased from 7.44 to 7.94 between recruitment and lockdown, and the proportion of those who reported a level of 9 or 10 jumped from 25.7% at recruitment to 43.1% during lockdown. CONCLUSIONS: Mental health deteriorated during lockdown in France during the 2020 COVID-19 crisis. Overall, self-rated physical health improved but those who experienced a worse physical health were more likely to report anxiety symptoms

Surface effects in a semiconductor photonic nanowire and spectral stability of an embedded single quantum dot

We evidence the influence of surface effects for InAs quantum dots embedded into GaAs photonic nanowires used as efficient single photon sources. We observe a continuous temporal drift of the emission energy that is an obstacle to resonant quantum optics experiments at the single photon level. We attribute the drift to the sticking of oxygen molecules onto the wire, which modifies the surface charge and hence the electric field seen by the quantum dot. The influence of temperature and excitation laser power on this phenomenon is studied. Most importantly, we demonstrate a proper treatment of the nanowire surface to suppress the drift

Evaluation of a virtual agent to train medical students conducting psychiatric interviews for diagnosing major depressive disorders

Background: A psychiatric diagnosis involves the physician's ability to create an empathic interaction with the patient in order to accurately extract semiology (i.e., clinical manifestations). Virtual patients (VPs) can be used to train these skills but need to be evaluated in terms of accuracy, and to be perceived positively by users. Methods: We recruited 35 medical students who interacted in a 35-min psychiatric interview with a VP simulating major depressive disorders. Semiology extraction, verbal and non-verbal empathy were measured objectively during the interaction. The students were then debriefed to collect their experience with the VP. Results: The VP was able to simulate the conduction of a psychiatric interview realistically, and was effective to discriminate students depending on their psychiatric knowledge. Results suggest that students managed to keep an emotional distance during the interview and show the added value of emotion recognition software to measure empathy in psychiatry training. Students provided positive feedback regarding pedagogic usefulness, realism and enjoyment in the interaction. Limitations: Our sample was relatively small. As a first prototype, the measures taken by the VP would need improvement (subtler empathic questions, levels of difficulty). The face-tracking technique might induce errors in detecting non-verbal empathy. Conclusion: This study is the first to simulate a realistic psychiatric interview and to measure both skills needed by future psychiatrists: semiology extraction and empathic communication. Results provide evidence that VPs are acceptable by medical students, and highlight their relevance to complement existing training and evaluation tools in the field of affective disorders.Bordeaux Region Aquitaine Initiative for NeurosciencePhénotypage humain et réalité virtuelleInitiative d'excellence de l'Université de Bordeau