Development of a System Model for an Indirect Passive Solar Dryer with Experimental Validation

Solar crop drying is a cheap and effective way to preserve food material, especially in developing countries where fuel and electricity are expensive or unavailable. Some tropical fruits are difficult to transport and store leading to significant spoilage. Without access to fuel and large drying systems, preserving fruits for later use is challenging or not possible for the rural farmer. Developing low-cost, easily assembled locally and low maintenance fruit drying systems would improve access to off-season and distant markets. A mathematical model of an indirect passive solar drying system was developed to design and optimize drying systems for use in developing countries and was validated through experimental testing. The prototype drying system consisted of a transpired solar absorber, drying chamber, and chimney. The transpired solar collector allows for indirect heat gain using cheap materials, specifically landscape fabric. The drying chamber houses fruit on eight screen trays and the chimney induces airflow through the system without a power source. The novel collector efficiency regularly exceeded 50% with an average temperature rise over 20oC. Bananas were dried over a two day period from an average moisture content of 73% to 8%. A total of 4kg of banana slices per square meter of absorber area were dried over the testing period. The mathematical model uses solar irradiance, ambient relative humidity, ambient temperature, and initial fruit moisture content to predict the fruit drying curves. The predicted average final moisture content of the bananas starting at 73% was 9% over the two day test period, indicating the model predicts performance reasonably well. Results from the system model highlight the need for additional experimentation to determine parameters such as the diffusivity of bananas and the mass transfer coefficient independently of experimental setup before it can be used as a tool to simulate drying performance for different environmental conditions and dryer system configurations

An optimal IV technique for identifying continuous-time transfer function model of multiple input systems

An instrumental variable method for continuous-time model identification is proposed for multiple input single output systems where the characteristic polynomials of the transfer functions associated with each input are not constrained to be identical. An associated model order determination procedure is shown to be reasonably successful. Monte Carlo simulation analyses are used to demonstrate the properties and general robustness of the model order selection and parameter estimation schemes. The results obtained to model a winding process and an industrial binary distillation column illustrate the practical applicability of the proposed identification scheme

High Power Very Low Voltage Electric Motor for Electric Vehicle

Electric vehicles are often designed in the same way as their conventional counterparts based on the internal combustion engine, they are heavy machines for comfort and safety reasons, and increasingly powerful. Under these conditions, in order to simplify the motor electrical supply system by reducing the current levels, the voltage chosen for the battery is very high and can go up to 700 V. However, for many applications where the power is relatively low (< 30 kW per motor), it can be more beneficial to size the system at very low voltage (< 60 V). This approach allows to overcome many constraining safety requirements and also to use off-the-shelf components (motor controllers, connectors, etc.) that are more easily available on the market in this voltage range. There are also many regulatory provisions that may require to stay within this voltage limit. This article presents a variety of very low voltage motorisation solutions with a required power up to 100kW. They use two complementary approaches. The first is to implement an original permanent magnet synchronous machine technology with an optimised armature winding for low voltage operation. The second is based on power splitting where the electrical machine being designed to be driven by multiple controllers. Many examples of low-voltage motorised vehicles (sporty vehicle, tractor, re-motorised automobile, etc.) are illustrated in this article

The effect of mechanical loading on osteogenesis of human dental pulp stromal cells in a novel in vitro model

Tooth loss often results in alveolar bone resorption because of lack of mechanical stimulation. Thus, the mechanism of mechanical loading on stem cell osteogenesis is crucial for alveolar bone regeneration. We have investigated the effect of mechanical loading on osteogenesis in human dental pulp stromal cells (hDPSCs) in a novel in vitro model. Briefly, 1 × 107 hDPSCs were seeded into 1 ml 3 % agarose gel in a 48-well-plate. A loading tube was then placed in the middle of the gel to mimic tooth-chewing movement (1 Hz, 3 × 30 min per day, n = 3). A non-loading group was used as a control. At various time points, the distribution of live/dead cells within the gel was confirmed by fluorescence markers and confocal microscopy. The correlation and interaction between the factors (e.g. force, time, depth and distance) were statistically analysed. The samples were processed for histology and immunohistochemistry. After 1-3 weeks of culture in the in-house-designed in vitro bioreactor, fluorescence imaging confirmed that additional mechanical loading increased the viable cell numbers over time as compared with the control. Cells of various phenotypes formed different patterns away from the reaction tube. The cells in the middle part of the gel showed enhanced alkaline phosphatase staining at week 1 but reduced staining at weeks 2 and 3. Additional loading enhanced Sirius Red and type I collagen staining compared with the control. We have thus successfully developed a novel in-house-designed in vitro bioreactor mimicking the biting force to enhance hDPSC osteogenesis in an agarose scaffold and to promote bone formation and/or prevent bone resorption

Modèles analytiques simplifiés des composants de puissance passifs et actifs pour la conception optimale de convertisseurs

Le choix d'une architecture de convertisseur puis la conception d'un prototype démonstrateur, pour répondre à une spécification donnée, reste un exercice difficile dans une jungle topologique et technologique. Le développement d'outils d'aide à la conception est donc un passage obligé pour faciliter la tâche des concepteurs mais aussi pour optimiser véritablement les solutions. La puissance sans cesse croissante des plates-formes logicielles et des ordinateurs personnels offre un potentiel largement suffisant pour atteindre des objectifs ambitieux dans cette assistance à la conception. Cela dit, de nombreux problèmes restent à résoudre et parmi eux, la synthèse de modèles réalistes et utilisables dans l'optimisation d'un système complet n'est pas le moindre. Cette contribution propose une philosophie mixant analyses physiques, formulations empiriques issues de bases de données et caractérisations expérimentales pour construire les modèles des principaux acteurs des étages de puissance que sont les composants actifs et passifs, associés selon les cas à des vecteurs de refroidissements.</p

Hospitalisation à domicile en post-partum (modalités, évaluation des pratiques, avantages et inconvénients)

NANCY1-SCD Medecine (545472101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Instrumentation virtuelle et moteur asynchrone en vitesse variable

Dans cet article, nous présentons les aspects pédagogiques et techniques d'un banc de mesure basé sur micro-ordinateur et utilisé en travaux pratiques de génie électrique. Cette instrumentation est utilisable pour de nombreuses applications. Nous nous intéresserons ici d'abord à un redresseur en pont mixte triphasé. Puis nous appliquerons ce dispositif de mesure à un entraînement à vitesse variable constitué par une machine asynchrone à cage alimentée par un variateur de vitesse industriel. Nous montrerons alors que ce type d'instrumentation peut apporter des fonctionnalités que les appareils de mesure traditionnels ne peuvent pas offrir

Simulations interactives de convertisseurs en électronique de puissance

International audienc

Caractérisation des cellules souches mésenchymateuses du sang placentaire et de la gelée de Wharton

Les cellules souches suscitent de grands espoirs pour la thérapie cellulaire et l'ingénierie tissulaire. Les CSM du tissus foetaux (sang placentaire et gelée de Wharton du cordon ombilical), à l'origine d'épiblaste embryonnaire, sont considérées comme plus primitives que les CSM provenant de sources adultes. Les conditions de culture ayant un impact sur le comportement des cellules, dans notre étude, nous avons exploré l'effet de la concentration de l'oxygène sur l'expansion, l'immunophénotypage et la différenciation de ces cellules. L'objectif de ce travail est d'identifier la méthode optimale d'isolation des CSM issues de tissus foetaux. Compte tenu du faible taux de succès dans l'isolement des CSM extraites du sang placentaire, nous nous sommes dirigés vers les CSM-GW. Nous y avons déterminé in situ, les marqueurs spécifiques exprimés dans la gelée de Wharton et à la périphérie. Des études sur la morphologie, la cinétique de croissance, et sur l'expression phénotypique des marqueurs de surface, des CSM-GW, ont été effectuées sur une longue durée (7 passages) à différentes conditions de culture. Nous avons montré que la GW est composée d'une abondante matrice extracellulaire riche en collagènes et glycosaminoglycannes et que les cellules possèdent un phénotype variable selon leur localisation dans la gelée. Ce tissu est capable de fournir une quantité importante de CSM (6,7x105 Cs/cm de cordon) qui gardent une morphologie constante. Enfin, quel que soit le passage, la concentration de l'oxygène ne semble pas avoir d'effet sur le phénotype des cellules. En revanche, une faible teneur en oxygène durant l'expansion semble diminuer le temps de doublement des cellules, favoriser la chondrogénèse et inhiber la différenciation ostéogénique. Enfin, quelles que soient les conditions de culture, la différenciation adipogénique des CSM-GW semble difficile à obtenirStem cells are the hopes for cell therapy and tissue engineering. MSCs from fetal tissue (umbilical cord blood and WJ), which are a source of embryonic epiblast grow relatively faster comparing to other adult sources. The culture condition can affect cell behavior. In our study, we explored the effect of oxygen concentration on the expansion, immunophenotyping, and differentiation of these cells. The aim of this work is to identify the optimal method for isolation of MSCs derived from fetal tissue. Given the low rate of success in the isolation of MSCs from cord blood, we headed to WJ-MSCs. We have determined in siu, the specific markers expressed in the WJ and in the perivascular region. Studies on the morphology growth kinetics, and phenotypic expression of surface makers of MSCs isolated from WJ were made over a long period (7 passages) in different culture conditions. We have shown that WJ is composed of an abundant extracellular matrix rich in collagen and glycasominoglycans and have variable phenotype depending from their localization in the jelly. This tissue is able to provide a large amount of MSCs (6.7x105 Cs/cm of cord) that maintain a constant morphology. Finally, regardless of the passage, the oxygen concentration does not effect on the phenotype of the cells. In contrast, a low oxygen concentration during expansion appears to decrease the doubling time of MSCs, promote chondrogenesis and inhibit osteogenic differentiation. Finally, whatever the culture conditions, adipogenic differentiation of WJ-MSC seems difficult to obtainMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF