Stable Light‐Emitting Diodes Using Phase‐Pure Ruddlesden–Popper Layered Perovskites

State‐of‐the‐art light‐emitting diodes (LEDs) are made from high‐purity alloys of III–V semiconductors, but high fabrication cost has limited their widespread use for large area solid‐state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase‐pure 2D Ruddlesden–Popper (RP) halide perovskites with a formula (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_n?1Pb_nI_3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr^?1 cm^?2 at 744 nm with an ultralow turn‐on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase‐pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm^?2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.     

Microneedles for the Noninvasive Structural and Functional Assessment of Dermal Lymphatic Vessels

The medical and scientific communities' interest in the lymphatic system has been growing rapidly in recent years. It has become evident that the lymphatic system is much more than simply a homeostasis controller and that it plays key roles in several pathological conditions. This work describes the identification of the optimal combination of poly(N‐vinylpyrrolidone) and a near‐infrared dye (indocyanine green) for the manufacturing of soluble microneedles and their application to the imaging of the lymphatic system. Upon application to the skin, the microneedle‐bearing indocyanine green is delivered in the dermal layer, where the lymphatic vessels are abundant. The draining lymphatics can then be visualized and the clearance kinetics from the administration site simply determined using a near‐infrared camera. This painless functional “tattooing” procedure can be used for quantitative assessment of the dermal lymphatic function in several dermal conditions and treatment‐response evaluations. The two components of these microneedles are extensively used in routine medical care, potentially leading to rapid clinical translation. Moreover, this procedure may have a significant impact on preclinical lymphatic studies.     

Contribution à la modélisation de lignes hyperfréquences supraconductrices à haute température critique par la méthode FDTD

The purpose of this study is to determine the electrical behaviour of high-Tc superconductor microstrip lines. TheFdtd method is used to put into discrete terms Maxwell’s equations. The two-fluid model has been chosen to describe the behaviour of the superconductor. The variation of electrical parameters such as surface resistance as a function of frequency up to 60 GHz is presented.     

Gallium nitride MEMS resonators: how residual stress impacts design and performances

Microsystem Technologies - Starting from Gallium Nitride epitaxially grown on silicon, pre-stressed micro-resonators with integrated piezoelectric transducers have been designed, fabricated, and...     

Automated architecture synthesis for parallel programs on FPGA multiprocessor systems

This paper presents a concept for automated architecture synthesis for adaptive multiprocessors on chip, in particular for Field-Programmable Gate-Array (FPGA) devices. Given a parallel program, the intent is to simultaneously allocate processor resources and the corresponding communication network, and at the same time, to map the parallel application to get an optimum application-specific architecture. This approach builds up on a previously proposed design platform that automates system integration and FPGA synthesis for such architectures. As a result, the overall concept offers an automated design approach from application mapping to system and FPGA configuration. The automated synthesis is based on combinatorial optimization. Automation is possible because a solvable Integer Linear Programming (ILP) model that captures all necessary design trade-off parameters of such systems has been found. Experimental results to study the feasibility of the automated synthesis indicate that problems with sizes that can be encountered in the embedded domain can be readily solved. Results obtained underscore the need for an automated synthesis for design space exploration.     

Missing data mask estimation with frequency and temporal dependencies

Automatic speech recognition (ASR) has reached a very high level of performance in controlled situations. However, the performance degrades drastically when environmental noise occurs during recognition. Nowadays, the major challenge is to reach a good robustness to adverse conditions. Missing data recognition has been developed to deal with this challenge. Unlike other denoising methods, missing data recognition does not match the whole data with the acoustic models, but instead considers part of the signal as missing, i.e. corrupted by noise. The main challenge of this approach is to identify accurately missing parts (also called masks). The work reported here focuses on this issue. We start from developing Bayesian models of the masks, where every spectral feature is classified as reliable or masked, and is assumed independent of the rest of the signal. This classification strategy results in sparse and isolated masked features, like the squares of a chess-board, while oracle reliable and unreliable features tend to be clustered into consistent time–frequency blocks. We then propose to take into account frequency and temporal dependencies in order to improve the masks’ estimation accuracy. Integrating such dependencies leads to a new architecture of a missing data mask estimator. The proposed classifier has been evaluated on the noisy Aurora2 (digits recognition) and Aurora4 (continuous speech) databases. Experimental results show a significant improvement of recognition accuracy when these dependencies are considered.     

A Metric Approach to nD Images Edge Detection with Clifford Algebras

The aim of this paper is to perform edge detection in color-infrared images from the point of view of Clifford algebras. The main idea is that such an image can be seen as a section of a Clifford bundle associated to the RGBT-space (Red, Green, Blue, Temperature) of acquisition. Dealing with geometric calculus and covariant derivatives of appropriate sections with respect to well-chosen connections allows to get various color and temperature information needed for the segmentation. We show in particular how to recover the first fundamental form of the image embedded in a LSHT-space (Luminance, Saturation, Hue, Temperature) equipped with a metric tensor. We propose applications to color edge detection with some constraints on colors and to edge detection in color-infrared images with constraints on both colors and temperature. Other applications related to different choices of connections, sections and embedding spaces for nD images may be considered from this general theoretical framework.

Calibration and validation of hyperspectral indices for the estimation of broadleaved forest leaf chlorophyll content,leaf mass per area,leaf area index and leaf canopy biomass

This article aims at finding efficient hyperspectral indices for the estimation of forest sun leaf chlorophyll content (CHL, µg cm_leaf^? 2), sun leaf mass per area (LMA, g_{dry matter} m_leaf^? 2), canopy leaf area index (LAI, m²_leaf m_soil^? 2) and leaf canopy biomass (B_leaf, g_{dry matter} m_soil^? 2). These parameters are useful inputs for forest ecosystem simulations at landscape scale. The method is based on the determination of the best vegetation indices (index form and wavelengths) using the radiative transfer model PROSAIL (formed by the newly-calibrated leaf reflectance model PROSPECT coupled with the multi-layer version of the canopy radiative transfer model SAIL). The results are tested on experimental measurements at both leaf and canopy scales. At the leaf scale, it is possible to estimate CHL with high precision using a two wavelength vegetation index after a simulation based calibration. At the leaf scale, the LMA is more difficult to estimate with indices. At the canopy scale, efficient indices were determined on a generic simulated database to estimate CHL, LMA, LAI and Bleaf in a general way. These indices were then applied to two Hyperion images (50 plots) on the Fontainebleau and Fougères forests and portable spectroradiometer measurements. They showed good results with an RMSE of 8.2 µg cm^? 2 for CHL, 9.1 g m^? 2 for LMA, 1.7 m² m^? 2 for LAI and 50.6 g m^? 2 for Bleaf. However, at the canopy scale, even if the wavelengths of the calibrated indices were accurately determined with the simulated database, the regressions between the indices and the biophysical characteristics still had to be calibrated on measurements. At the canopy scale, the best indices were: for leaf chlorophyll content: ND_chl = (ρ₉₂₅ ? ρ₇₁₀)/(ρ₉₂₅ + ρ₇₁₀), for leaf mass per area: ND_LMA = (ρ₂₂₆₀ ? ρ₁₄₉₀)/(ρ₂₂₆₀ + ρ₁₄₉₀), for leaf area index: D_LAI = ρ₁₇₂₅ ? ρ₉₇₀, and for canopy leaf biomass: ND_Bleaf = (ρ₂₁₆₀ ? ρ₁₅₄₀)/(ρ₂₁₆₀ + ρ₁₅₄₀).     

A palindromization map for the free group

We define a self-map Pal:_F2→_F2$Pal:F_2\to F_2$ of the free group on two generators a,b$a,b$, using automorphisms of _F2$F_2$ that form a group isomorphic to the braid group _B3$B_3$. The map Pal$Pal$ restricts to de Luca’s right iterated palindromic closure on the submonoid generated by a,b$a,b$. We show that Pal$Pal$ is continuous for the profinite topology on _F2$F_2$; it is the unique continuous extension of de Luca’s right iterated palindromic closure to _F2$F_2$. The values of Pal$Pal$ are palindromes and coincide with the elements g∈_F2$g\in F_2$ such that abg$abg$ and bag$bag$ are conjugate.     

Piezo-tunneling strain sensors integrated on plastic by combining vacuum thin film coatings and 3D printing technologies

There is a growing demand for the integration of sensor functions on flexible substrates for wearable electronics, robotics or medical monitoring. For this, it is necessary to develop strain gauges both sensitive and integrable at low cost with a low thermal budget. The gauge factor of metal/insulator/metal piezo-tunneling strain sensors is first measured as a function of applied current and polarity, for different electrode materials (Al, Pt or Pd) and insulator (Al₂O₃) thicknesses. A maximum gauge factor of 90 is obtained with an Al/Al₂O₃ (10 nm)/Al junction and top electrode injection. Results are discussed based on the Fowler–Nordheim model and it is shown that the electron effective mass in Al₂O₃ most likely plays a major role in the observed mechano-sensitivity. Next, the feasibility of a low-pressure sensor demonstrator based on a 3D-printing process on a polymer substrate is shown with a sensitivity of 0.19 bar⁻¹ in the 0–450 mbar range.