Complementary Speckle Patterns : deterministic interchange of intrinsic vortices and maxima through Scattering Media

Intensity minima and maxima of speckle patterns obtained behind a diffuser are experimentally interchanged by applying a spiral phase delay of charge $\pm 1$ to the impinging coherent beam. This transform arises from the intuitive expectation that a tightly focused beam is so-changed into a vortex beam and vice-versa. The statistics of extrema locations and the intensity distribution of the so-generated "complementary" patterns are characterized by numerical simulations. It is demonstrated experimentally that the incoherent superposition of the three "complementary speckle patterns" yield a synthetic speckle grain size enlarged by a factor $\sqrt{3}$. A cyclic permutation of optical vortices and maxima is unexpectedly observed and discussed.Comment: 9 pages, 9 figure

Topological transformations of speckles

Deterministic control of coherent random light is highly important for information transmission through complex media. However, only a few simple speckle transformations can be achieved through diffusers without prior characterization. As recently shown, spiral wavefront modulation of the impinging beam allows permuting intensity maxima and intrinsic $\pm 1$-charged optical vortices. Here, we study this cyclic-group algebra when combining spiral phase transforms of charge $n$, with $D_3$- and $D_4$-point-group symmetry star-like amplitude modulations. This combination allows statistical strengthening of permutations and controlling the period to be 3 and 4, respectively. Phase saddle-points are shown to complete the cycle. These results offer new tools to manipulate critical points in speckles.Comment: 14 pages, 10 figures, 4 table

Essais précoces en cancérologie, éthique et justice

National audienceC'est dans le cadre d'un programme de recherche sur l'égalité d'accès aux essais cliniques de cancérologie ("EgaliCan") que le symposium "Essais précoces en cancérologie : quelles définitions, quelle justice ?" s'est tenu au Collège de France le 24 mai dernier 2012. Ce symposium avait pour objet de contribuer à la réflexion sur la définition des essais précoces en cancérologie et sur les questions nouvelles de justice et d'éthique qu'ils posent

TinyTerp: A FULLY AUTONOMOUS MOBILE SMART CENTI-ROBOT

A fully autonomous modular 8 cm3 robot is presented using commercially available off-the-shelf (COTS) components. The robot introduced is called Tiny Terrestrial Robotic Platform (TinyTeRP) which provides an inexpensive, easily assembled, small robotic platform for researchers to study swarm behavior. TinyTeRP can be assembled in 30 minutes and costs $51.50. TinyTeRP is fully autonomous, with approximately 10 minutes of run time, and the ability to travel over 20 cm/s with DC motors and wheels. Communication to other TinyTeRP robots and stationary sensors is performed using a 2.4 GHz IEEE 802.15.4 radio. TinyTeRP has the ability to interface with additional sensors modules and locomotion actuators, including a wheeled locomotion and inertial measurement unit (IMU) module. An additional legged platform module that uses thermally actuated polymer legs with a silver composite acrylic is discussed. Finally, TinyTeRP demonstrates the use of two control algorithms to interact with a fixed beacon using received signal strength indicator (RSSI)

Optical-resolution photoacoustic imaging through thick tissue with a thin capillary as a dual optical-in acoustic-out waveguide

We demonstrate the ability to guide high-frequency photoacoustic waves through thick tissue with a water-filled silica-capillary (150 \mu m inner diameter and 30 mm long). An optical-resolution photoacoustic image of a 30 \mu m diameter absorbing nylon thread was obtained by guiding the acoustic waves in the capillary through a 3 cm thick fat layer. The transmission loss through the capillary was about -20 dB, much lower than the -120 dB acoustic attenuation through the fat layer. The overwhelming acoustic attenuation of high-frequency acoustic waves by biological tissue can therefore be avoided by the use of a small footprint capillary acoustic waveguide for remote detection. We finally demonstrate that the capillary can be used as a dual optical-in acoustic-out waveguide, paving the way for the development of minimally invasive optical-resolution photoacoustic endoscopes free of any acoustic or optical elements at their imaging tip

Pré-dimensionnement de convertisseur de très forte puissance pour une application à la propulsion aéronautique hybride

Dans le cadre de l’étude sur l’intérêt de l’hybridation électrique de la propulsion des futurs aéronefs, le travail réalisé consiste à proposer des structures de conversion de puissance et à pré-dimensionner une chaîne électrique forte puissance intégrant un bus continu haute tension, son câblage et l’électronique de puissance interfaçant le bus et la motorisation électrique. La première étape de cette étude consiste à déterminer la tension du bus DC en prenant en compte la problématique des décharges partielles qui limite la possibilité de l’augmentation du niveau de tension au niveau des conducteurs placés en zone non pressurisée. Pour choisir une plage de tension optimale, il est nécessaire d’étudier le rendement de plusieurs topologies multiniveaux mais cela est rendu difficile par la discrétisation des calibres en tension disponibles sur le marché des semi-conducteurs de puissance. Pour pallier à ce problème, une base de données de composants continue qui s’adapte à la tension de calibre souhaitée est créée en extrapolant les familles de composants existants

In silico vs. Over the Clouds: On-the-Fly Mental State Estimation of Aircraft Pilots, Using a Functional Near Infrared Spectroscopy Based Passive-BCI

There is growing interest for implementing tools to monitor cognitive performance in naturalistic work and everyday life settings. The emerging field of research, known as neuroergonomics, promotes the use of wearable and portable brain monitoring sensors such as functional near infrared spectroscopy (fNIRS) to investigate cortical activity in a variety of human tasks out of the laboratory. The objective of this study was to implement an on-line passive fNIRS-based brain computer interface to discriminate two levels of working memory load during highly ecological aircraft piloting tasks. Twenty eight recruited pilots were equally split into two groups (flight simulator vs. real aircraft). In both cases, identical approaches and experimental stimuli were used (serial memorization task, consisting in repeating series of pre-recorded air traffic control instructions, easy vs. hard). The results show pilots in the real flight condition committed more errors and had higher anterior prefrontal cortex activation than pilots in the simulator, when completing cognitively demanding tasks. Nevertheless, evaluation of single trial working memory load classification showed high accuracy (>76%) across both experimental conditions. The contributions here are two-fold. First, we demonstrate the feasibility of passively monitoring cognitive load in a realistic and complex situation (live piloting of an aircraft). In addition, the differences in performance and brain activity between the two experimental conditions underscore the need for ecologically-valid investigations