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This paper is dedicated to the problem of stable model reduction for partial differential equations (PDEs). We propose to use proper orthogonal decomposition (POD) method to project the PDE model into a lower dimensional given by an ordinary differential equation (ODE) model. We then stabilize this model, following the closure model approach, by proposing to use reinforcement learning (RL) to learn an optimal closure model term. We analyze the stability of the proposed RL closure model and show its performance on the coupled Burgers equation.

Approximate controllability of systems of coupled parabolic partial differential equations has been of interest for a few decades, where the existence of open-loop control laws performing approximate state transitions within a finite time is studied. In this work, we specialize to systems of reaction-diffusion equations where the connectivity structure is triangular in the reaction parameters and the controls appear at the boundary. We first generate controllers by combining a decoupling backstepping approach with differential flatness that allow us to generate admissible trajectories for system outputs from a given initial condition. As a byproduct of our approach, we achieve approximate state transitioning for the system within a finite terminal time. We enhance our control law by introducing time-varying error feedback controllers which reject variations in initial conditions within the terminal time. The resulting control law not only performs the approximate control task but also output trajectory tracking, all within the terminal time which can be prescribed independently of initial conditions.

In this paper we propose a new family of continuous-time optimization algorithms based on discontinuous second order gradient optimization flows, with finite-time convergence guarantees to local optima, for locally strongly convex time-varying cost functions. To analyze our flows, we first extend a well-know Lyapunov inequality condition for finite-time stability, to the case of time-varying differential inclusions. We then prove the convergence of these second-order flows in finite-time. We show the performance of these flows on a time-varying quadratic cost and on the nonlinear time-varying Rosenbrock function.

The increasing availability of information-rich data sets offers an invaluable opportunity to complement and improve the performance of existing model-based feedback algorithms. Following this principle, in this paper we present a novel class of Data-Enabled Extremum Seeking (DEES) algorithms for static maps, which make use of current and recorded data in order to solve a convex optimization problem characterized by a variational inequality. The optimization dynamics synergistically combine ideas from concurrent learning and classic neuro-adaptive extremum seeking in order to dispense with the assumption of requiring a persistence of excitation condition in the closed-loop system. Using analytical tools for nonlinear systems we show that for a general class of optimization dynamics it is possible to tune the parameters of the controller to guarantee convergence in finite time to an arbitrarily small neighborhood of the set of optimizers. The results are illustrated in a scalar constrained minimization problem.

The present research aimed to study the combined effects of natural pozzolana and curing on the compressive and flexural strengths of mortars; it also investigated the chloride permeability of concrete. To do that, Ordinary Portland cement (CEMI) was used and three concrete preparations were made by incorporating natural pozzolana at a rate of 10, 20 and 30% by weight of CEMI. Moreover, three curing methods were employed. The first one is a standard curing method, at temperature 20 °C, and 2 other thermo-activation methods at the temperatures of 40 °C and 70 °C, for a setting time of 4 h. The thermo-activation methods were used to accelerate the initial hydration, for the purpose of improving the strength of the prepared mortars and concretes at the early age. The results obtained indicate that, substituting natural pozzolana for CEMI with a level below 20% gives strengths comparable to those obtained with CEMI alone. The curing methods at 40 °C and 70 °C allowed increasing mortar and concrete strengths at the early age; however, it was found that the temperature of 70 °C reduces strengths, at later age. Natural pozzolana limits the penetration of chlorides. Keywords: CEMI, Pozzolana, Hydration, Strength, Temperature, Chlorides

Expanded polyvinyl chloride (PVC) or “FOREX” is widely used in advertising and signage boards, shop fittings and shop window decorations. This article attempts to study the physico-mechanical and thermal properties of lightweight composite mortars based on expanded polyvinyl chloride (LMEPVC), in which the natural sand are replaced by lightweight aggregates from expanded PVC sheets, with different volume proportions (0, 15, 25, 50 and 75%v). The consistency, density, porosity accessible to water, mechanical strengths (compressive and flexural tests), ultrasonic pulse velocity (UPV), dynamic modulus of elasticity (Ed), and thermal conductivity are measured on various LMEPVC samples. Scanning electron microscopy (SEM) for microstructural analysis is performed to elucidate the mechanism of strength development. The results obtained showed that reduce the specific weight of the LMEPVC composites and improve their thermal insulation, particularly the composite LMEPVC75 (λ = 0.760 W/m.K). On the other hand, the dynamic modulus of elasticity (Ed) of that same composite was found to decrease by about 66% as compared to that of the reference mortar.

Today, a large number of research projects are concerned with the recycling of plastic waste to be reused in the field of construction. This work, which is part of a research programme, focuses on the valorization of plastic waste from high density polyethylene (HDPE) pipes, to be used as aggregates. The HDPE aggregates were used as partial replacements of natural sand at 0, 15, 30, 45 and 60%, for the same volume. Only one particle size of the HDPE aggregates was used in each composition of the lightweight composite mortars (LWCM). Prismatic specimens 4 × 4 × 16 cm3 were prepared with a ratio W/C = 0.5. The density of the composite mortars was measured in the fresh and cured states. The compressive and flexural strengths, the thermo-physical characteristics as well as the ultrasonic pulse velocity (UPV) and the dynamic modulus of elasticity (Ed) were also investigated. In addition, composite mortars were analysed using a Scanning Electronic Microscope (SEM). Laboratory tests revealed encouraging results. Compared to the normal composite mortar (NMC), outcomes showed that composite mortar with 60% HDPE aggregates (LWCM60) increased ductility and reduced by 73% the dynamic modulus of elasticity. Analyses using SEM indicated that HDPE aggregates exhibited low adhesion to the cementitious matrix and mortars with higher HDPE rates improved the energy performance of composite mortars (LWCM).

To find a seemly solution to the problems of efficiency dependency of the hybrid PV/TE devices, on important factors like “high-absorbance with high-ZT materials” and improving the performance of existing devices, are essential research topics nowadays. In this regard, we report here optical coating, and thermoelectric features of the kesterite-structured Ag2CdSnS4 and Ag2CdSnSe4 compounds. These investigations are performed at the level of “full-potential linearized augmented plane wave plus local orbital method, FP-L(APW + lo)” framed within the “density functional theory (DFT)” method comprised with relativistic effects. Our study of the optical coating shows that both the investigated materials have a good level of absorbance (A), approximately 80% in the visible part of the spectra. Further, we found that the magnitude of reflectance (R) of the Ag2CdSnX4 (X = S, Se) thin films increase with increasing film thickness, while the response of the transmittance (T) spectra is reverse to it. These results are corroborated by the study of the transport properties by employing the Boltztrap code, and correspondingly electrical conductivity, Seebeck coefficient, electronic thermal conductivity as well as the figure of merit parameters were evaluated and analyzed as a function of the chemical potential for both investigated compounds at five values of the temperatures. Hence our obtained results show that both the investigated semiconductor materials exhibit strong potential for the application of hybrid PV/TE systems.

Background Salvage transjugular intrahepatic portosystemic shunts (TIPS) are associated with poor prognosis, especially in patients with Child-Pugh C cirrhosis. Since preemptive TIPS improved prophylaxis of variceal bleeding in those patients, recourse to salvage TIPS may now affect patients with a better prognosis. Aim To assess the impact of the preemptive TIPS policy on outcomes after salvage TIPS placement. Methods We conducted a retrospective monocentric study on cirrhotic patients undergoing salvage TIPS with polytetrafluoroethylene-covered stents from 2002 to 2017 (period 1 until February 2011; period 2 after the preemptive TIPS policy in March 2011). The primary endpoint was one-year transplant-free survival. Results We included 106 patients (period 1/2 = 53/53 patients, male gender 82%, age 54 ± 9 years, alcoholic cirrhosis 70%, Child-Pugh score B/C 94%). One-year transplant-free survival was 46.0% during period 1 compared to 40.2% during period 2 (p = 0.65). Amongst 61 patients with history of variceal bleeding, 32 (52.5%) had an inadequate secondary prophylaxis, including 19 (59.4%) with a previous indication of preemptive TIPS. One-year transplant-free survival was 33.2% if inadequate secondary prophylaxis vs 65.2% if adequate (p = 0.008). Independent factors associated with survival were a lower Child-Pugh or MELD score, infection, failure to control bleeding, and hepatic encephalopathy after TIPS. Conclusion Prognosis after salvage TIPS remained poor in our series. Optimizing secondary prophylaxis, including preemptive TIPS placement, should be the main concern to improve prognosis.

We present some results on the stabilization of reduced-order models (ROMs) for thermal fluids. The stabilization is achieved using robust Lyapunov control theory to design a new closure model that is robust to parametric uncertainties. Furthermore, the free parameters in the proposed ROM stabilization method are optimized using a data-driven multi-parametric extremum seeking (MES) algorithm. The 2D and 3D Boussinesq equations provide challenging numerical test cases that are used to demonstrate the advantages of the proposed method.

This paper studies the problem of averaging-based extremum seeking in dynamical multi-agent systems with time-varying communication graphs. We consider a distributed consensus-optimization problem where the plants and the controllers of the agents share information via time-varying graphs, and where the cost function to be minimized corresponds to the summation of the individual response maps generated by the agents. Although the problem of averaging-based extremum seeking control in multi-agent dynamical systems with time-invariant graphs has been extensively studied, the case where the graph is time-varying remains unexplored. In this paper we address this problem by making use of recent results for generalized set-valued hybrid extremum seeking controllers, and the framework of switched differential inclusions and common Lyapunov functions. For the particular consensus-optimization problem considered in this paper, a semi-global practical stability result is established. A numerical example in the context of dynamic electricity markets illustrates the results.

In this paper we present some results on parametric identification for dynamical systems. More specifically, we consider the general case of dynamics described by partial differential equations (PDEs), which includes the special case of ordinary differential equations (ODEs). We follow a stochastic approach and formulate the identification problem as a Gaussian process optimization with respect to the unknown parameters of the PDE. We use proper orthogonal decomposition (POD) model reduction theory together with a data-driven Gaussian Process Upper Confidence Bound (GP-UCB), to solve the identification problem. The proposed approach is validated on the coupled Burgers’ equation benchmark.

We present here some preliminary results on the problem of estimating pedestrian crowds from limited measurements. More specifically, we focus on a data-driven operator-based approach. We use the Koopman operator and its approximation with the kernel dynamic mode decomposition kDMD, to design a dynamical observer, which allows us to estimate the full crowd flow, based on a partial-view of a sensing camera. We explain the dynamical observer design, discuss its limitations, and propose some numerical simulations to validate the proposed approach.

The structural, electronic and optical properties of pure ZnO and Er-doped ZnO are investigated by density functional theory (DFT) with generalized gradient approximation plus modified Becke-Johnson exchange potential (GGA + mBJ). The obtained results of electronic and optical properties were improved. Good agreement with the experimental and theoretical studies is obtained for pure ZnO since the results of Er-doped ZnO in zinc blend structure are considered as new predictions. The energy gap value of Er-doped ZnO is found to increase with Erbium incorporation, affecting the absorption coefficients in all spectra regions. Red shift is also achieved under Er doping indicating the importance of its 4f donor occupied states. Similar behavior is observed in the literature for Er-doped ZnO in wurtzite structure.

In this work, we explored the possibility of using aggregates of shredded polyethylene terephthalate strapping bands (SPETSB) in mortar. A survey was carried out to assess the feasibility of recycling this plastic waste to be used in the manufacture of environmentally-friendly lightweight mortars through partial replacement of silica-calcareous sand with lighter SPETSB aggregates, by volume at 0, 15, 30, 45 and 60 %. A scanning electron microscopy analysis along with a study of the alkali – silica reaction was conducted; the density, mechanical and thermal properties were assessed for evaluating the properties of lightweight mortar containing SPETSB aggregates (LWMSB). Laboratory tests revealed encouraging results and confirmed the feasibility of manufacturing lightweight aggregate mortar with a density between 1620 and 1944 Kg/m3, a compressive strength equal to 28.8 MPa and thermal conductivity of 0.75 W/m.K, at 28 days, for 60% of SPETSB. The flexural strength, ultrasonic pulse velocity (UPV) and dynamic elastic modulus (Ed) were lower by 46%, 25% and 56%, respectively, compared to the values of normal weight mortar (NWM). This study also allowed deducing that the expansion due to the alkali–silica reaction decreases for all LWMSB types, when the substitution rate of SPETSB increases; this makes it possible to obtain a non-reactive mortar. Therefore, these findings suggest that using LWMSB composite mortars in building applications is possible.

A robust, low-order POD-based state estimator, also known as an observer, for the challenging fluid-dynamics test-case of uncertain 2D Boussinesq equations is presented in this paper. The observer design is based on the methodology recently introduced by the authors 1 , which incorporates robustness to bounded model uncertainties, and data-driven auto-tuning of the observer gains. An extensive numerical study on the 2D Boussinesq equations with parametric uncertainties demonstrates the performance of our observer. The reported numerical results show that the proposed observer allows estimation of the complete temperature and velocity fields from a reduced number of measurements. It is also shown that the proposed observer is robust to changes or errors in the value of the Reynolds number. In other words, we show that we can design the observer based on an assumed uncertain value for the Reynolds number, and be able to estimate the temperature and velocity solutions corresponding to actual Reynolds number.

The self-consistent electron densities and the corresponding positron states are calculated for the zinc chalcogenides, ZnS, ZnSe and ZnTe, in the local-density approximation of the density-functional formalism. The calculations are performed with the full-potential linearized augmented plane-wave (FP-LAPW) method. The emphasis of this work is on the energy levels of the delocalized positron and the electron chemical potential. These energies determine quantities such as the positron and positronium work functions and the deformation potentials which are important parameters in slow-positron-beam experiments.

Resume Nous rapportons le cas clinique d’un melanome pulmonaire dans sa forme achromique, decouvert chez un patient de 52 ans par l’etude anatomopathologique d’une lobectomie inferieure droite. La recherche d’un eventuel primitif est restee negative. Nous rappelons par ailleurs les modalites diagnostiques, therapeutiques et evolutives de ce type histologique de cancer pulmonaire.

We study in this paper the problem of adaptive trajectory tracking control for a class of nonlinear systems with parametric uncertainties. We propose to use a modular adaptive approach, where we first design a robust nonlinear state feedback which renders the closed loop input-to-state stable (ISS). The input is considered to be the estimation error of the uncertain parameters, and the state is considered to be the closed-loop output tracking error. We augment this robust ISS controller with a model-free learning algorithm to estimate the model uncertainties. We implement this method with a Bayesian optimization-based method called Gaussian Process Upper Confidence Bound (GP-UCB). The combination of the ISS feedback and the learning algorithms gives a learning-based modular indirect adaptive controller. We test the efficiency of this approach on a two-link robot manipulator example, under noisy measurements conditions.

In this paper we present some results on partial differential equations (PDEs) parametric identification. We follow a deterministic approach and formulate the identification problem as an optimization with respect to unknown parameters of the PDE. We use proper orthogonal decomposition (POD) model reduction theory together with a model free multi-parametric extremum seeking (MES) approach, to solve the identification problem. Finally, the well known Burgers’ equation test-bed is used to validate our approach.

International audience; Two retinal implants have recently received the CE mark and one has obtained FDA approval for the restoration of useful vision in blind patients. Since the spatial resolution of current vision prostheses is not sufficient for most patients to detect faces or perform activities of daily living, more electrodes with less crosstalk are needed to transfer complex images to the retina. In this study, we modelled planar and three-dimensional (3D) implants with a distant ground or a ground grid, to demonstrate greater spatial resolution with 3D structures. Using such flexible 3D implant prototypes, we showed that the degenerated retina could mould itself to the inside of the wells, thereby isolating bipolar neurons for specific, independent stimulation. To investigate the in vivo biocompatibility of diamond as an electrode or an isolating material, we developed a procedure for depositing diamond onto flexible 3D retinal implants. Taking polyimide 3D implants as a reference, we compared the number of neurones integrating the 3D diamond structures and their ratio to the numbers of all cells, including glial cells. Bipolar neurones were increased whereas there was no increase even a decrease in the total cell number. SEM examinations of implants confirmed the stability of the diamond after its implantation in vivo. This study further demonstrates the potential of 3D designs for increasing the resolution of retinal implants and validates the safety of diamond materials for retinal implants and neuroprostheses in general.

Introduction La mediastinite fibreuse chronique est un desordre benin rare, resultant d’un processus sclereux du tissu mediastinal avec survenue de compression, d’obstruction, voir une infiltration des organes mediastinaux, il constitue la premiere etiologie benigne du syndrome cave superieur (SCS). Methodes Il s’agit d’une etude retrospective, realisee au service de pneumologie du centre hospitalier universitaire Ibn-Sina, sur une periode de 4 ans, s’etalant de janvier 2016 a juin 2019 incluant 3 patients hospitalises pour sd cave sup et diagnostiques mediastinite fibreuse. Resultats Trois patients, 2 femmes et 1 homme, l’âge moyen est de 40 ans, un antecedent de diabete a ete retrouve chez (1 cas), une thyroidectomie totale chez (1 cas), ils etaient admis pour bilan de magmas d’ADP mediastinale chez (2 patients) et masse mediastinales chez (1 cas), le delai moyen d’apparition des signes est de 1 an, a type de dyspnee (3 cas), toux seche (3 cas), hemoptysie (1 cas), l’examen physique note un syndrome cave superieur (3 cas), La Rx de thorax a montre un elargissement mediastinale chez les 3 cas, la TDM thoracique met en evidence une masse mediastinale tissulaire heterogene avec calcifications chez (1 cas), magmas d’ADP mediastinales chez (2 cas), l’endoscopie bronchique est normale. Une mediastinoscopie a ete realisee dans (3 cas), les biopsies sont revenues en faveur de mediastinite fibreuse chronique. Le traitement medical par corticotherapie orale est indique chez (2 cas), la corticotherapie et le traitement antibacillaire chez une patiente. La mediastinite fibrosante est une affection rare provoquee par une proliferation fibro-inflammatoire due probablement a une reponse immunologique anormale d’origine le plus souvent infectieuse (tuberculose, histoplasmose) entrainant un engainement avec envahissement et compression des structures de basse pression : VCS, veines pulmonaires, arteres pulmonaires. Conclusion La mediastinite fibreuse chronique est une affection rare, l’imagerie grâce a la TDM et IRM permet une approche diagnostique, celui-ci reste histologique afin d’eliminer toute cause neoplasique.

L’observance therapeutique est largement sous-estimee en psychiatrie comme l’ensemble des disciplines medicales, pourtant le phenomene devrait etre considere comme un probleme de sante publique. La mauvaise observance therapeutique est un phenomene frequent dans les troubles bipolaires, elle est associee a un risque accru de rechutes, une augmentation du cout des soins et a une majoration de la souffrance aussi bien pour les patients que leurs proches, notre travail avait pour objectif principal l’identification des causes les plus frequentes de l’abandon du traitement pharmacologique au moyen d’une etude transversale descriptive menee aupres de 48 patients atteints de troubles bipolaires type I selon les criteres DSM-IV TR, les donnees sociodemographiques, cliniques et therapeutiques ont ete recueillis aupres des patients eux-memes et de leurs dossiers medicaux, l’observance ayant ete evaluee grâce a l’echelle Medication Adherence Rating Scale (MARS) de Thompson. Notre echantillon comportait deux fois plus d’hommes que de femmes leur âge moyen etait de 33,9 ans, la plupart des patients etaient celibataires et vivaient avec leurs familles 77 %, la mauvaise observance therapeutique ete identifie chez 60 % des patients et les facteurs qui ont ete associes a cette derniere etaient : la consommation de toxique, le manque de consideration par rapport a la maladie, la relation medecin malade, les effets secondaires dues au traitement et la complexite des prescriptions, aussi le manque d’information sur la maladie et le traitement, ainsi que le faible niveau d’instruction et un niveau de vie bas. L’observance therapeutique est un phenomene complexe et dynamique dont les facteurs sont nombreux, interagissent entre eux et peuvent evoluer dans le temps chez un meme patient. En conclusion l’amelioration de cette derniere chez les patients bipolaires doit etre axee sur la bonne information des patients concernant leur maladie et la prise du traitement, avec simplification des prescriptions en veillant a les adapter a chaque patient tout en tenant compte des facteurs de risque de non-observance qu’il presente.

Resume Le chylothorax spontane est une entite rare, la tuberculose ganglionnaire en est une etiologie exceptionnelle. Nous rapportons une observation exceptionnelle d’un patient porteur d’une tuberculose ganglionnaire abdominale et mediastinale revelee par un chylothorax spontane bilateral qui repond rapidement au traitement medical symptomatique et aux anti-bacillaires.

SummaryWe present a method to label and trace the lineage of multiple neural progenitors simultaneously in vertebrate animals via multiaddressable genome-integrative color (MAGIC) markers. We achieve permanent expression of combinatorial labels from new Brainbow transgenes introduced in embryonic neural progenitors with electroporation of transposon vectors. In the mouse forebrain and chicken spinal cord, this approach allows us to track neural progenitor’s descent during pre- and postnatal neurogenesis or perinatal gliogenesis in long-term experiments. Color labels delineate cytoarchitecture, resolve spatially intermixed clones, and specify the lineage of astroglial subtypes and adult neural stem cells. Combining colors and subcellular locations provides an expanded marker palette to individualize clones. We show that this approach is also applicable to modulate specific signaling pathways in a mosaic manner while color-coding the status of individual cells regarding induced molecular perturbations. This method opens new avenues for clonal and functional analysis in varied experimental models and contexts.

In this work we study the problem of rope sway dynamics control for elevator systems, with time-varying rope lengths. We formulate this problem as a nonlinear control problem and propose nonlinear controllers based on Lyapunov theory for time-varying systems. We study the stability of the proposed controllers, and test their performances on a numerical example.

We present in this paper a preliminary result on extremum seeking (ES)-based adaptive trajectory tracking control for nonlinear systems. We propose, for the class of nonlinear systems with parametric uncertainties which can be rendered integral Input-to-State stable (iISS) w.r.t. the parameter estimation errors input, that it is possible to merge together the integral Input-to-State stabilizing feedback controller and a model-free extremum seeking algorithm to realize a learning-based indirect adaptive controller. We show the efficiency of this approach on a mechatronic example.

Resume Introduction La tuberculose pulmonaire multiresistante (MDR-TB) est un probleme de sante mondial. La chirurgie est souvent utilisee comme un adjuvant therapeutique aux antibacillaires. Le but de ce travail est de presenter nos resultats des resections pulmonaires dans le traitement de la MDR-TB. Patients et methodes Nous avons mene une etude retrospective monocentrique incluant 29 patients operes entre 1995 et 2010 pour MDR-TB. Resultats La tuberculose evoluait depuis 9 a 108 mois avec une duree mediane de 34,77 ± 19,88 mois. Le nombre moyen des rechutes tuberculeuses etait de 2,73 rechutes par patient. Tous les patients avaient un parenchyme detruit et/ou cavitaire et 17 avaient un examen direct des prelevements respiratoires positif au moment de l’intervention. Les lobectomies (51,17 %) et les pneumonectomies (41,37 %) etaient les principaux gestes realises. La mortalite operatoire etait de 3,44 %. Des problemes de bullage prolonge et de pyothorax survenaient chez 9 patients. Le taux de conversion microbiologique postoperatoire etait de 88,23 %. Un patient a presente une rechute 5 mois apres la chirurgie. Conclusion La chirurgie associee au traitement medical permet d’obtenir un taux eleve de guerison au detriment d’une morbi-mortalite acceptable.

This paper presents the results of an experimental program devoted to the study of Polymer Modified Mortars’ (PMM) thermal conductivity, thermal diffusivity and calorific capacity at different temperatures and compressive and flexural strengths at room-temperature. For this purpose, Ordinary Mortar (OM) and PMM samples with different contents and through partial substitution of Portland cement were prepared. A real improvement of the PMM thermal properties was observed in comparison with those of OM despite the decrease of mechanical strength. X-rays Diffract Meter (XDM), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscope (SEM) were also conducted to show the interaction of the polymer material considered.

Blindness affects tens of million people worldwide and its prevalence constantly increases along with population aging. In some pathologies leading to vision loss, prosthetic approaches are currently the only hope for the patient to recover some visual perception. Here, we review the latest advances in visual prosthetic strategies with their respective strength and weakness. The principle is to electrically stimulate neurons along the visual pathway. Ocular approaches target the remaining retinal cells whereas brain stimulation aims at stimulating higher visual structures directly. Even though ocular approaches are less invasive and easier to implement, brain stimulation can be applied to diseases where the connection between the retina and the brain is lost such as in glaucoma and could therefore benefit to patients with different pathologies. Today, numbers of groups are investigating these strategies and the first devices start being commercialized. However, critical bottlenecks still impair our scientific efforts towards efficient visual implants. These challenges include electrode miniaturization, material optimization, multiplexing of stimulation channels and encoding of visual information into electrical stimuli.