ANN modeling of a smart MEMS-based capacitive humidity sensor

This paper presents a design of a smart humidity sensor. First we begin by the modeling of a Capacitive MEMS-based humidity sensor. Using neuronal networks and Matlab environment to accurately express the non-linearity, the hysteresis effect and the cross sensitivity of the output humidity sensor used. We have done the training to create an analytical model CHS “Capacitive Humidity Sensor”. Because our sensor is a capacitive type, the obtained model on PSPICE reflects the humidity variation by a capacity variation, which is a passive magnitude; it requires a conversion to an active magnitude, why we realize a conversion capacity/voltage using a switched capacitor circuit SCC. In a second step a linearization, by Matlab program, is applied to CHS response whose goal is to create a database for an element of correction “CORRECTOR”. After that we use the bias matrix and the weights matrix obtained by training to establish the CHS model and the CORRECTOR model on PSPICE simulator, where the output of the first is identical to the output of the CHS and the last correct its nonlinear response, and eliminate its hysteresis effect and cross sensitivity. The three blocks; CHS model, CORRECTOR model and the capacity/voltage converter, represent the smart sensor.     

Enhancement of the neural network modeling accuracy using a submodeling decomposition-based technique, application in gas sensor

This paper presents an algorithm based on the use of artificial neural networks (ANNs) in order to reduce the processing time and to improve the accuracy in ANN modeling, which can be accomplished with a division of the model to submodels by input subintervals. We apply this method with a gas sensor aiming to accurately control the small gas leaks, thus decreasing the risk of false alarms and missed detections. The sensor model accurately, especially in small concentrations, expresses the nonlinear character of the response and the dependence on temperature and relative humidity in addition to the gas nature dependency. The corrector linearizes and compensates the sensor’s responses. The results obtained show the effectiveness of the proposed technique.     

Experimental and numerical investigation of a phase change material: Thermal-energy storage and release

The application of phase change materials (PCMs) for solar thermal-energy storage capacities has received considerable attention in recent years due to their large storage capacity and isothermal nature of the storage process. This study deals with the comparison of numerical and experimental results for a PCM conditioned in a parallelepipedic polyefin envelope to be used in passive solar walls. The experimental results were obtained by use of a genuine set-up involving heat flux sensors and thermocouples mounted on two vertical aluminium exchanger plates squeezing the samples. Numerical predictions were obtained with a custom one-dimensional Fortran code and a two-dimensional use of Fluent. Both methods showed a very good agreement with experimental observations for the melting process (?5%). However during solidification, both numerical codes failed to predict the phase change process accurately, the maximal relative error was as high as 57% (with an average of 8%).     

Double-Diffusive Natural Convection in a Mixture-Filled Cavity with Walls' Opposite Temperatures and Concentrations

ABSTRACT

This paper deals with natural convection flows evolving inside an ended and differentially heated cavity, which is filled either with an air or an air–CO₂ mixture. The investigation was conducted through the laminar regime to analyze buoyancy ratio changes' effect on heat and mass transfers both in aiding and opposing flows. The thermal Rayleigh number was varied from 10³ to 10⁷. Streamlines, isotherms, iso-concentrations, and local and average Nusselt and Sherwood numbers are provided to demonstrate the convective flow induced. The governing equations are solved by finite volume method using SIMPLEC algorithm to handle the pressure–velocity coupling. The buoyancy ratio effect on dynamic, thermal, and mass fields is noteworthy, exhibiting both the competition between thermosolutal forces and fields' stratification. From the results, it turned out that, in general, when the buoyancy ratio is: (1) positive, thermosolutal buoyancy forces are cooperative, (2) nil, solutal buoyancy forces are weak and the flow is merely thermoconvective, (3) negative and greater than ?1, buoyancy effects are competing and thermal convection dominates, (4) ?1, buoyancy effects are canceled and heat and mass transfers are driven only by diffusion, and (5) less than ?1, buoyancy forces compete with a dominant solutal convection.     

Assessment of the bacteriological quality and nitrate pollution risk of Quaternary groundwater in the southern part of Abidjan District (Côte d’Ivoire)

In this study, total coliforms, thermotolerant coliforms, Escherichia coli and groundwater nitrate concentration were monitored at 127 groundwater sampling points (only 62 water points for bacteriological parameters) located in the southern part of Abidjan District. Each water sampling location was sampled in March and July 2007, representing respectively the long dry season and the long wet season. Geostatistical methods were used to analyze the spatial variability of nitrates and the groundwater nitrate pollution risk. The maximum seasonal content of total coliforms and thermotolerant coliforms ranged from 400 to 1000 CFU/100 mL and from 200 to 500 CFU/100 mL respectively. Moreover, 94% of these locations presented traces of bacteriological contamination. This contamination was mainly recorded during the rainy period. The degree of correlation between bacterial abundance and chemical parameters is variable. Nitrites, ammonium and potassium favoured coliform abundance. In the 127 water points, groundwater nitrate concentrations ranged from 4 to 198 mg L^?1 and were log-normally distributed in the study area. The groundwater contamination risk map indicated that the strongly urbanized west side of the site presented a high probability of exceeding the WHO drinking water standard (50 mg L^?1NO₃^?).     

Extracting parameters of OFET before and after threshold voltage using genetic algorithms

This paper presents a compact analytical model for the organic field-effect transistors(OFETs), which describes two main aspects, the first one is related to the behavior in above threshold regime, while the other corresponds to the below threshold regime.The total drain current in the OFET device is calculated as the sum of two components, with the inclusion of a smooth transition function in order to take into account both regions using a single expression. A genetic algorithm based approach(GA) is investigated as a parameter extraction tool in the case of the compact OFET model to find the parameters values from experimental data such as:mobility enhancement factor γ, threshold voltage VT h, subthreshold swing S, channel length modulation λ, and knee region sharpness m. The comparison of the developed current model with the experimental data shows a good agreement in terms of the transfer and the output characteristics. Therefore, the GA based approach can be considered as a competitive candidate compared to the direct method.     

A two-dimensional analytical subthreshold behavior analysis including hot-carrier effect for nanoscale Gate Stack Gate All Around (GASGAA) MOSFETs

The Gate All Around (GAA) MOSFET is considered as one of the most promising devices for downscaling below 50?nm. By surrounding the channel completely, the gate gains increased electrostatic control of the channel and short-channel-effects (SCEs) can be drastically suppressed. However, challenges still remain to resolve the important issues particularly concerning hot-carrier reliability and accurate device models for nanoscale circuit designs. Hot-carrier effects have been the major issues in the long-term stability of subthreshold performances in a nanoscale MOS transistor. In this paper we present a two-dimensional analytical analysis of the subthreshold behavior, subthreshold current and subthreshold swing, including the interfacial hot-carrier effects. The calculated results of the proposed approach match well with those of the 2-D numerical device simulator. The present work provides valuable design insights in the performance of nanoscale CMOS-based devices including hot-carrier degradation effects.     

A Novel Technique for Experimental Thermophysical Characterization of Phase-Change Materials

The major objective of this project is to use phase-change materials (PCMs) as integrated components in passive solar heat recovery systems. The suggested approach involves experimental investigations and characterization of the global behavior of a parallelepiped “material wrap” filled with the PCM. The experimental apparatus permits simultaneous measurements of heat fluxes and temperatures. It also allows imposing and measuring temperatures variations with respect to selected time scales between the two predominant faces of the sample. The instantaneous heat flux measurements allow the determination of the “apparent” or overall heat storage capacities and thermal conductivities of the PCM—in the solid and liquid states—and that of the latent heat of melting. Results were found to be very satisfactory.     

Modeling of a Smart Nano Force Sensor Using Finite Elements and Neural Networks

Machine Intelligence Research - The aim of this work is to model and analyze the behavior of a new smart nano force sensor. To do so, the carbon nanotube has been used as a suspended gate of a...