The importance of inversion disorder in the visible light induced persistent luminescence in Cr3+^{3+} doped AB2_2O4_4 (A = Zn or Mg and B = Ga or Al)

Cr$^{3+}$ doped spinel compounds AB$_2$O$_4$ with A=Zn, Mg and B=Ga, Al exhibit a long near infrared persistent luminescence when excited with UV or X-rays. In addition, persistent luminescence of ZnGa$_2$O$_4$ and to a lesser extent MgGa$_2$O$_4$, can also be induced by visible light excitation via $^4$A$_2$ $\rightarrow$ $^4$T$_2$ transition of Cr$^{3+}$, which makes these compounds suitable as biomarkers for in vivo optical imaging of small animals. We correlate this peculiar optical property with the presence of antisite defects, which are present in ZnGa$_2$O$_4$ and MgGa$_2$O$_4$. By using X-ray absorption fine structure (XAFS) spectroscopy, associated with electron paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown that an increase in antisite defects concentration results in a decrease in the Cr-O bond length and the octahedral crystal field energy. A part of the defects are in the close environment of Cr$^{3+}$ ions, as shown by the increasing strain broadening of EPR and XAFS peaks observed upon increasing antisite disorder. It appears that ZnAl$_2$O$_4$, which exhibits the largest crystal field splitting of Cr$^{3+}$ and the smallest antisite disorder, does not show considerable persistent luminescence upon visible light excitation as compared to ZnGa$_2$O$_4$ and MgGa$_2$O$_4$. These results highlight the importance of Cr$^{3+}$ ions with neighboring antisite defects in the mechanism of persistent luminescence exhibited by Cr$^{3+}$ doped AB$_2$O$_4$ spinel compounds.Comment: 10 pages + supplementary (available on request

RÉVOLUTION ET UTOPIE DANS LE ROMAN LE SIÈCLE DES LUMIÈRES D'ALEJO CARPENTIER (1958) : LES ITINÉRAIRES D'UN DÉSENCHANTEMENT

Des répercussions de la Révolution française aux Caraïbes – abolition et restauration de l'esclavage – à la terreur de la France en révolution et à l'Espagne occupée par les troupes de Napoléon le couple de jumeaux que constituent Sofia et Esteban parcourt une à une les étapes d'une désillusion et d'un dépouillement absolus avant de disparaître à Madrid dans les hécatombes du Tres de Mayo dont Goya – constamment cité dans le roman – a été le grand témoin. Les chemins de l'utopie de la jeunesse et de l'espoir débouchent ainsi sur une apocalypse. En nous appuyant notamment sur les travaux de l'historien des imaginaires sociaux Bronislaw Baczko et en analysant plus précisément les mutations des personnages dans leur confrontation aux événements successifs, nous nous proposons de mettre en lumière cette dynamique de la désillusion

Contribution à l'étude de la cycloalcoylation d'alcenylthiophènes alcenylbenzo [b] thiophènes et alcenyldibenzothiophènes : application à la synthèse d'hétérocycles aromatiques sulfurés catacondensés polysubstitués

Montréal Trigonix inc. 201

Pedestrian Detection with Wearable Cameras for the Blind: A Two-way Perspective

Blind people have limited access to information about their surroundings, which is important for ensuring one's safety, managing social interactions, and identifying approaching pedestrians. With advances in computer vision, wearable cameras can provide equitable access to such information. However, the always-on nature of these assistive technologies poses privacy concerns for parties that may get recorded. We explore this tension from both perspectives, those of sighted passersby and blind users, taking into account camera visibility, in-person versus remote experience, and extracted visual information. We conduct two studies: an online survey with MTurkers (N=206) and an in-person experience study between pairs of blind (N=10) and sighted (N=40) participants, where blind participants wear a working prototype for pedestrian detection and pass by sighted participants. Our results suggest that both of the perspectives of users and bystanders and the several factors mentioned above need to be carefully considered to mitigate potential social tensions.Comment: The 2020 ACM CHI Conference on Human Factors in Computing Systems (CHI 2020

A specific flagellum beating mode for inducing fusion in mammalian fertilization and kinetics of sperm internalization

International audienceThe salient phases of fertilization are gamete adhesion, membrane fusion, and internalization of the spermatozoon into the oocyte but the precise timeline and the molecular, membrane and cell mechanisms underlying these highly dynamical events are far from being established. The high motility of the spermatozoa and the unpredictable location of sperm/egg fusion dramatically hinder the use of real time imaging optical techniques that should directly provide the dynamics of cell events. Using an approach based on microfluidics technology, the sperm/egg interaction zone was imaged with the best front view, and the timeline of the fertilization events was established with an unparalleled temporal accuracy from the onset of gamete contact to full sperm DNA decondensation. It reveals that a key element of the adhesion phase to initiate fusion is the oscillatory motion of the sperm head on the oocyte plasma membrane generated by a specific flagellum-beating mode. It also shows that the incorporation of the spermatozoon head is a two steps process that includes simultaneous diving, tilt, and plasma membrane degradation of the sperm head into the oocyte and subsequent DNA decondensation