Structural Test Approach for Embedded Analog Circuits Based on a Built-in Current Sensor

This paper presents a test method based on the analysis of the dynamic power supply current, both quiescent and transient, of the circuit under test. In an off-chip measurement, the global interconnect impedance associated with the chip package and the test equipment and, also, the chip input/output cells will complicate the extraction of the information provided by the current waveform of the circuit under test. Thus, the supply current is measured on-chip by a built-in current sensor integrated in the die itself. To avoid the effective reduction of the voltage supply, the measurement is performed in parallel by replicating the current that flows through selected branches of the analog circuit. With the aim of reducing the test equipment requirements, the built-in current sensor output generates digital level pulses whose width is related to the amplitude and duration of the circuit current transients. In this way the defective circuit is exposed by comparing the digital signature of the circuit under test with the expected one for the fault-free circuit. A fault evaluation has been carried out to check the efficiency of the proposed test method. It uses a fault model that considers catastrophic and parametric faults at transistor level. Two benchmark circuits have been fabricated to experimentally verify the defect detection by the built-in current sensor. One is an operational amplifier; the other is a structure of switched current cells that belongs to an analog-to-digital converter.     

Specific detection of viable Listeria monocytogenes in Spanish wastewater treatment plants by Fluorescent In Situ Hybridization and PCR

Listeria monocytogenes detection in wastewater can be difficult because of the large amount of background microbiota and the presence of viable but non-culturable forms in this environment. The aim of this study was to evaluate a Fluorescent In Situ Hybridization (FISH) assay combined with Direct Viable Count (DVC) method for detecting viable L. monocytogenes in wastewater samples, as an alternative to conventional culture methods. 16S rRNA sequence data were used to design a specific oligonucleotide probe. In order to assess the suitability of the method, the assays were performed on naturally (n = 87) and artificially (n = 14) contaminated samples and results were compared to those obtained with the isolation of cells on selective media and with a PCR method. The detection limit of FISH and PCR assays was 10⁴ cells/mL without enrichment and 10 cells/mL after enrichment. A total of 47 samples, including 3 samples from effluent sites, yielded FISH positive results for L. monocytogenes. Using DVC-FISH technique, the presence of viable L. monocytogenes cells was detected in 23 out of these 47 FISH positive wastewater samples. PCR and culture methods yielded 27 and 23 positive results, respectively. According to these results, FISH technique has the potential to be used as a sensitive method for the detection and enumeration of L. monocytogenes in environmental wastewater samples.     

Viability assessment of lactic acid bacteria in commercial dairy products stored at 4 °C using LIVE/DEAD® BacLightTM staining and conventional plate counts

The viability of lactic acid bacteria (LAB) from commercial fermented milks was studied during storage at 4 °C. The enumeration of total viable bacteria was assessed using fluorescence microscopy. Plate counting on selective media was used to enumerate LAB. Using LIVE/DEAD® BacLight^TM viability staining, it was observed that bacterial counts decreased gradually after expiry dates, the number of viable bacteria remaining above 10⁶ bacteria g^?1 for all of the products. Viable cell counts estimated by plating onto selective media were lower than those obtained by direct microscopic counting. The viability of LAB contained in acid products decreased during their storage period at 4 °C. All products contain viable LAB ranging from 10⁸ to 10⁹ bacteria g^?1 and could be considered as probiotic, given that the recommended minimum number of probiotic bacteria in such food products is approximately 10⁷ bacteria mL^?1 product. The number of bifidobacteria in commercial fermented milks declared to contain bifidobacteria varied from 10⁴ to 10⁷ bacteria mL^?1. This study confirms the usefulness of fluorescent techniques for a rapid and accurate evaluation of bacterial viability in probiotic products.     

Computational approach to the rational design of molecularly imprinted polymers for voltammetric sensing of homovanillic acid

A methodology based on density functional theory calculations for the design of molecularly imprinted polymers (MIPs) is described. The method allows the rational choice of the most suitable monomer and polymerization solvent among a set of chemicals traditionally used in MIP formulations for the molecular imprinting of a given template. It is based on the comparison of the stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of the polymerization solvent is included using the polarizable continuum model. A voltammetric sensor for homovanillic acid was constructed using different MIPs as recognition element, confirming that the solvent (toluene) and functional monomer (methacrylic acid) selected according to the theoretical predictions lead to the most efficient molecular recognition sensing phase. With the voltammetric sensor prepared using the MIP designed according to the theoretical predictions, a linear response for concentrations of homovanillic acid between 5 x 10(-8) and 1 x 10(-5) M can be obtained. The limit of detection is 7 x 10(-9) M. The selectivity obtained for homovanillic acid over other structurally related compounds buttresses the validity of this strategy of design.     

Analysis of liquid-phase chemical detection using guided shear horizontal-surface acoustic wave sensors

Direct chemical sensing in liquid environments using polymer-guided shear horizontal surface acoustic wave sensor platforms on 36 degrees rotated Y-cut LiTaO3 is investigated. Design considerations for optimizing these devices for liquid-phase detection are systematically explored. Two different sensor geometries are experimentally and theoretically analyzed. Dual delay line devices are used with a reference line coated with poly (methyl methacrylate) (PMMA) and a sensing line coated with a chemically sensitive polymer, which acts as both a guiding layer and a sensing layer or with a PMMA waveguide and a chemically sensitive polymer. Results show the three-layer model provides higher sensitivity than the four-layer model. Contributions from mass loading and coating viscoelasticity changes to the sensor response are evaluated, taking into account the added mass, swelling, and plasticization. Chemically sensitive polymers are investigated in the detection of low concentrations (1-60 ppm) of toluene, ethylbenzene, and xylenes in water. A low-ppb level detection limit is estimated from the present experimental measurements. Sensor properties are investigated by varying the sensor geometries, coating thickness combinations, coating properties, and curing temperature for operation in liquid environments. Partition coefficients for polymer-aqueous analyte pairs are used to explain the observed trend in sensitivity for the polymers PMMA, poly(isobutylene), poly(epichlorohydrin), and poly(ethyl acrylate) used in this work.     

Alternative woods for aging distillates-an insight into their phenolic profiles and antioxidant activities

Work has commenced on the study and characterization of wood native species (oak, chestnut, cherry, alder, ash, and beech), employed to a minor extent in enology, for their application in the elaboration of distillates. To this end, furanic and low molecular weight phenol compounds, total phenolic content, and antioxidant activity in alcoholic extracts by maceration of wood chips at 2 toasting levels were studied. Significant differences between samples, technologically relevant, were due both to species and toasting time. Furthermore, extracts showed interesting antioxidant activities equivalent in some cases to than those reported for alcoholic beverages aged in wood.     

Adhesion properties and competitive pathogen exclusion ability of bifidobacteria with acquired acid resistance

The adhesion properties of Bifidobacterium longum and Bifidobacterium catenulatum strains with an acquired resistance to acid and their ability to competitively exclude Salmonella enterica serovar Typhimurium, Escherichia coli, Listeria monocytogenes, Enterobacter sakazakii, and Clostridium difficile from adhering to human intestinal mucus were evaluated and compared with the results when the same experiments were run with the original acid-sensitive strains. In half of the four studied cases, the acid-resistant derivative showed a greater ability to adhere to human intestinal mucus than the original strain. The ability of bifidobacteria to inhibit pathogen adhesion to mucus was not generally improved by the acquisition of acid resistance. In contrast, three of the four acid-resistant strains showed a greater ability to displace preadhered pathogens than the original strains, especially preadhered Salmonella Typhimurium and C. difficile. Overall, the induction of acid resistance in bifidobacteria could be a strategy when selecting strains with enhanced stability and improved surface properties that favor their potential functionality as probiotics against specific pathogens.     

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