P. R. Hernández

Determination of Ammonium Ion Employing an Electronic Tongue Based on Potentiometric Sensors

Abstract A method for determining ammonium ion concentration from complex aqueous samples is presented in this work. It does not need to eliminate chemical interferences, mainly sodium and potassium, because an array of potentiometric sensors with intrinsic responses is used. The measurements taken from the array are processed with a multicomponent data treatment. This approach is already known as electronic tongue. Multivariable calibration was implemented with an artificial neural network, trained under the rules of the Bayesian regularization. The developed system has been applied to water samples from rivers and wastewaters with ammonium content in the range 1 × 10−4–5 × 10−2 mol L−1. Results are similar to those obtained with other reference methods.

Data Compression for a Voltammetric Electronic Tongue Modelled with Artificial Neural Networks

Abstract In the study of voltammetric electronic tongues, a key point is the preprocessing of the departure information, the voltammograms which form the response of the sensor array, prior to classification or modeling with advanced chemometric tools. This work demonstrates the use of the discrete wavelet transform (DWT) for compacting these voltammograms prior to modeling. After compression, a system based on artificial neural networks (ANNs) was used for the quantification of the electroactive substances present, using the obtained wavelet decomposition coefficients as their inputs. The Daubechies wavelet of fourth order permitted an effective compression up to 16 coefficients, reducing the original dimension by ca. 10 times. The case studied is a mixture of three oxidizable amino acids:tryptophan, cysteine, and tyrosine. With the reduced information, one ANN per specie was trained using the Bayesian regularization algorithm. The proposed procedure was compared with the more conventional treatments of downsampling the voltammogram, or its feature extraction employing principal component analysis prior to ANNs.

Remote environmental monitoring employing a potentiometric electronic tongue

This work investigates the use of electronic tongues for environmental monitoring. Electronic tongues were based on arrays of potentiometric sensors plus a complex data processing by artificial neural networks and data transmission by radiofrequency. A first application, intended for a system simulating real conditions in surface water, performed a simultaneous monitoring of ammonium, potassium, sodium, chloride, and nitrate ions. The proposed system allowed us to assess the effect of natural biodegradation stages for these species. A second application was used to monitor concentrations of ammonium, potassium, and sodium in the ‘Ignacio Ramírez’ dam (Mexico). The electronic tongue used here allowed us to determine the content of the three cations in real water samples, although a high matrix effect was encountered for sodium determination. The implemented radio transmission worked robustly during all the experiments, thus demonstrating the viability of the proposed systems for automated remote applications.

Multivariate Calibration Model for a Voltammetric Electronic Tongue Based on a Multiple Output Wavelet Neural Network

Electronic tongues are bioinspired sensing schemes that employ an array of sensors for analysis, recognition or identification in liquid media. An especially complex case happens when the sensors used are of the voltammetric type, as each sensor in the array yields a 1-dimensional data vector. This work presents the use of a Wavelet Neural Network (WNN) with multiple outputs to model multianalyte quantification from an overlapped voltammetric signal. WNN is implemented with a feedforward multilayer perceptron architecture, whose activation functions in its hidden layer neurons are wavelet functions, in our case, the first derivative of a Gaussian function. The neural network is trained using a backpropagation algorithm, adjusting the connection weights along with the network parameters. The principle is applied to the simultaneous quantification of the oxidizable aminoacids tryptophan, cysteine and tyrosine, from its differential-pulse voltammetric signal. WNN generalization ability was validated with training processes of k-fold cross validation with random selection of the testing set.

Monitoring of environmental systems using electronic tongues as sensor networks

This paper introduces Electronic Tongues (ETs) for remote environmental monitoring applications. ETs are bio-inspired systems that employ an array of sensors for analysis, recognition or identification in liquid media. In this work it will be used as node sensor network for monitoring of heavy metals (Cu2+, Pb2+, Zn2+ and Cd2+) in open air waste streams and rivers heading down the Gulf of Mexico. The proposed arrays were formed by potentiometric sensors based on polymeric membranes (PVC) and the subsequent cross-response processing was based on a multilayer Artificial Neural Network (ANN) model. Analytical measures were performed using a laboratory-made electronic system which includes data transmission by radiofrequency, in order to demonstrate system viability for automated remote applications.

Electrical stimulator for surface nerve stimulation by using modulated pulses

This work presents the design of an electrical stimulator based on modulated pulses. A reduction of the electrical impedance of the skin is pursued in order to facilitate the nerve stimulation with lower intensities of current and for reducing burning and painful effects as well. The stimulator is controlled by a PC through a graphic interface under the LabVIEW platform. Two outputs are available: a) monophasic rectangular pulses with programmable facilities in amplitude, frequency, and pulse width, which are used as the envelope; b) monophasic rectangular pulses with amplitude modulation and pulse width, amplitude and frequency of the carrier, all three adjustable.

Experimental Gastric Stimulator for Refractory Obesity Treatment

Morbid obesity and overweight have alarmingly increased their incidence around the world. They have become a disabling disease with major repercussions. A new and promising method to treat refractory cases of obesity has emerged in the last years. It uses electrical stimulation on vagus nerves to diminish gastric motility producing an early satiety sensation. In this work an experimental gastric stimulator is presented, intended to determine optimal values of intensity, and pulse width as well as better sites of stimulation and electrode-nerve attaching techniques. This device was designed considering a wide range in values to test the feasibility of the technique in vivo and in situ conditions. The device was submitted to a laboratory evaluation, as a first phase, but an implantable gastric pacemaker is pretended

Development of a system for measuring and controlling environmental parameters in an chamber for in vitro cell cultures experimentation

Cell cultures are essential in research. They need to be under appropriate conditions of temperature, humidity, and carbon dioxide to promote their growth. A system for monitoring and controlling the CO2 concentration, as well as for measuring and recording both temperature and humidity parameters inside of a conditioned chamber for experimentation with magnetic fields and recording the Transepithelial Electrical Impedance of cells, has been developed in this work. This system was designed to support the development of healthy growth of monolayer cultures and their survival. The system was based on the device K-33 BLG for CO2 concentration measurements and the sensor DHT22 for monitoring temperature and relative humidity. A graphical interface was developed for the control and monitoring of CO2, the exhibition of temperature and relative humidity values, the definition of set points parameter, and for alerting when thresholds are exceeded. The system is autonomous and can be adapted to several types of incubators. The validation was performed using three commercial incubators as a reference, and according to the performance results, this system can be used in experimental procedures.

A muscle fatigue monitor based on the surface electromyography signals and frequency analysis

People with lower-limb movement disorders often receive physical therapies for recovery. These procedures can cause muscle fatigue and pain without the patient noticing it. In this work the development of a system to monitor muscle fatigue is presented. It is based on the measurement of the median frequency shifting in the power spectrum density generated by surface electromyography recordings, as well as the Borg scale criteria related to pain, eventually caused by fatigue in healthy subjects. Electromyography signal processing was performed using non-parametric methods to determine the median frequency shifting, whereas the root mean square value in time domain, as indicators of muscle fatigue. Measurements were performed in rectus femoris and lateral gastrocnemius muscles of 16 healthy subjects when they were submitted to physical performance tests. Results showed fatigue in rectus femoris in 12% of cases when Welch method was applied, in contrast with 18% of cases of lateral gastrocnemius recordings when periodogram method was used.

Pressure distribution analysis of focused shock wave by using finite element method

The aim of this study is to analyze the generated pressure by the focusing of a shock wave and to verify that the focal point has the smallest width of the wavefront and the maximum pressure value. The study was achieved by simulation using the finite element method because it allows us to obtain a numerical solution at any point in the considered domain. It was necessary to consider a specific geometry to achieve the focusing of a shock wave; in this case a semi-ellipse was used. When a shock wave is generated in a semi-ellipse, a part of the wave is transmitted and the remaining wave is reflected. The part of the wave that is reflected on the surface of the semi-ellipse focuses later at a focal point while the width of its waveform is reduced and its pressure increases. The non-reflected wave, looses pressure and scatters as it travels away from the semi-ellipse. Furthermore, the pressure obtained during the trajectory of the non-reflected wave is not zero and may damage surrounding materials, like organs in a lithotripsy treatment, by the focal point.