Microthermography of diode lasers: The impact of light propagation on image formation

We analyze the effect of propagating infrared thermal radiation within a diode laser on its thermal image taken by a thermocamera. A ray-tracing analysis shows that this effect substantially influences image formation on a spatial scale of 10 mu m, i.e., in the domain of microthermography. The main parameter affecting the thermal radiation spread in the semitransparent semiconductor structure is the free carrier concentration in the substrate, governing its absorption. Two applications are presented: a quantum dot laser and a quantum-well laser, where independent thermal models are developed using the finite element method (FEM). Our ray-tracing analysis verifies the FEM simulated temperature profiles by interlinking them to experimental temperature maps obtained through microthermography. This represents a versatile experimental method for extracting reliable bulk-temperature data from diode lasers on a microscopic scale

Necrotizing vasculitis revealed in a case of multiple mononeuropathy after a 14-year course of spontaneous remissions and relapses

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Precise Temperature Mapping of GaN-Based LEDs by Quantitative Infrared Micro-Thermography

A method of measuring the precise temperature distribution of GaN-based light-emitting diodes (LEDs) by quantitative infrared micro-thermography is reported. To reduce the calibration error, the same measuring conditions were used for both calibration and thermal imaging; calibration was conducted on a highly emissive black-painted area on a dummy sapphire wafer loaded near the LED wafer on a thermoelectric cooler mount. We used infrared thermal radiation images of the black-painted area on the dummy wafer and an unbiased LED wafer at two different temperatures to determine the factors that degrade the accuracy of temperature measurement, i.e., the non-uniform response of the instrument, superimposed offset radiation, reflected radiation, and emissivity map of the LED surface. By correcting these factors from the measured infrared thermal radiation images of biased LEDs, we determined a precise absolute temperature image. Consequently, we could observe from where the local self-heat emerges and how it distributes on the emitting area of the LEDs. The experimental results demonstrated that highly localized self-heating and a remarkable temperature gradient, which are detrimental to LED performance and reliability, arise near the p-contact edge of the LED surface at high injection levels owing to the current crowding effect

The MicrOmega Investigation Onboard Hayabusa2

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Etude de l'influence de la topographie du microenvironnement sur la migration des interneurones corticaux par l'utilisation de substrats microstructurés

In the developing brain, cortical interneurons undergo a long distance migration to reach the cortex where they integrate into cortical networks and regulate their activity in the adult. Different chemical factors have been involved in the guidance of these cells, but the influence of the physical parameters of the environment in which they navigate remains unclear. It has been shown that topographical cues are able to influence and guide the migration of several cell types, a process called contact guidance. This work therefore aimed at testing and understanding the influence of the topography of the environment in the migration of cortical interneurons. By using an experimental system of microstructured substrates, we demonstrated for the first time the existence of contact guidance for these cells. By testing two types of micron-sized pillars, we showed that a change in the shape of the structures could greatly impact cell orientation, morphology, cytoskeleton organization and dynamic behavior. In particular, most interneurons migrating in between square pillars adopt an elongated, unbranched morphology associated with a slow and directed movement, whereas the majority of cells among round pillars exhibit a short and branched morphology associated with a dynamic but wandering movement. Overall, we show that micron-sized topography provides global spatial constraints promoting the establishment of different morphological and migratory states in vitro, highlighting the potential importance of these types of cues in vivo.Dans le cerveau en développement, les interneurones corticaux effectuent une longue migration avant de se positionner dans le cortex et s’intégrer dans les réseaux corticaux dont ils régulent l’activité. Différents facteurs chimiques ont été impliqués dans le guidage de ces cellules, mais l’influence des propriétés physiques de l’environnement dans lequel ils naviguent reste peu connue. Il a été montré que les indices topographiques peuvent guider le mouvement de nombreux types cellulaires, un processus appelé guidage par contact. Mes travaux de thèse ont ainsi cherché à tester et comprendre l’influence de la topographie de l’environnement sur la migration des interneurones corticaux. En utilisant un système expérimental de substrats microstructurés, nous avons mis en évidence pour la première fois l’existence du guidage par contact pour ces cellules. En testant deux types de micro-plots, nous avons établi qu’un changement de forme des structures influence de manière importante l’orientation, la morphologie, l’organisation du cytosquelette et le comportement dynamique des cellules. En particulier, les interneurones en migration entre des plots carrés adoptent majoritairement une morphologie allongée et peu branchée, associée à un mouvement lent et dirigé. A l’inverse, des cellules entre des plots ronds sont plus courtes et montrent un branchement important associé à un mouvement dynamique mais aléatoire. Plus généralement, nous montrons in vitro que la topographie génère des contraintes spatiales globales qui promeuvent la mise en place de différents états cellulaires morphologiques et dynamiques, soulignant ainsi la potentielle importance de ce type d’indices in vivo

Study of the influence of the topography of the microenvironment on cortical interneuron migration using microstructured substrates

Dans le cerveau en développement, les interneurones corticaux effectuent une longue migration avant de se positionner dans le cortex et s’intégrer dans les réseaux corticaux dont ils régulent l’activité. Différents facteurs chimiques ont été impliqués dans le guidage de ces cellules, mais l’influence des propriétés physiques de l’environnement dans lequel ils naviguent reste peu connue. Il a été montré que les indices topographiques peuvent guider le mouvement de nombreux types cellulaires, un processus appelé guidage par contact. Mes travaux de thèse ont ainsi cherché à tester et comprendre l’influence de la topographie de l’environnement sur la migration des interneurones corticaux. En utilisant un système expérimental de substrats microstructurés, nous avons mis en évidence pour la première fois l’existence du guidage par contact pour ces cellules. En testant deux types de micro-plots, nous avons établi qu’un changement de forme des structures influence de manière importante l’orientation, la morphologie, l’organisation du cytosquelette et le comportement dynamique des cellules. En particulier, les interneurones en migration entre des plots carrés adoptent majoritairement une morphologie allongée et peu branchée, associée à un mouvement lent et dirigé. A l’inverse, des cellules entre des plots ronds sont plus courtes et montrent un branchement important associé à un mouvement dynamique mais aléatoire. Plus généralement, nous montrons in vitro que la topographie génère des contraintes spatiales globales qui promeuvent la mise en place de différents états cellulaires morphologiques et dynamiques, soulignant ainsi la potentielle importance de ce type d’indices in vivo.In the developing brain, cortical interneurons undergo a long distance migration to reach the cortex where they integrate into cortical networks and regulate their activity in the adult. Different chemical factors have been involved in the guidance of these cells, but the influence of the physical parameters of the environment in which they navigate remains unclear. It has been shown that topographical cues are able to influence and guide the migration of several cell types, a process called contact guidance. This work therefore aimed at testing and understanding the influence of the topography of the environment in the migration of cortical interneurons. By using an experimental system of microstructured substrates, we demonstrated for the first time the existence of contact guidance for these cells. By testing two types of micron-sized pillars, we showed that a change in the shape of the structures could greatly impact cell orientation, morphology, cytoskeleton organization and dynamic behavior. In particular, most interneurons migrating in between square pillars adopt an elongated, unbranched morphology associated with a slow and directed movement, whereas the majority of cells among round pillars exhibit a short and branched morphology associated with a dynamic but wandering movement. Overall, we show that micron-sized topography provides global spatial constraints promoting the establishment of different morphological and migratory states in vitro, highlighting the potential importance of these types of cues in vivo

Cellular and Subcellular Contact Guidance on Microfabricated Substrates

International audienceTopography of the extracellular environment is now recognized as a major biophysical regulator of cell behavior and function. The study of the influence of patterned substrates on cells, named contact guidance, has greatly benefited from the development of micro and nano-fabrication techniques, allowing the emergence of increasingly diverse and elaborate engineered platforms. The purpose of this review is to provide a comprehensive view of the process of contact guidance from cellular to subcellular scales. We first classify and illustrate the large diversity of topographies reported in the literature by focusing on generic cellular responses to diverse topographical cues. Subsequently, and in a complementary fashion, we adopt the opposite approach and highlight cell type-specific responses to classically used topographies (arrays of pillars or grooves). Finally, we discuss recent advances on the key subcellular and molecular players involved in topographical sensing. Throughout the review, we focus particularly on neuronal cells, whose unique morphology and behavior have inspired a large body of studies in the field of topographical sensing and revealed fascinating cellular mechanisms. We conclude by using the current understanding of the cell-topography interactions at different scales as a springboard for identifying future challenges in the field of contact guidance

Is there a universal mechanism of cell alignment in response to substrate topography?

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The basement membrane as a structured surface – role in vascular health and disease

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