[Show abstract][Hide abstract]ABSTRACT: The microbiological quality of drinking water is a concern to consumers, water suppliers, regulators, and public health authorities alike. Monitoring the microbiological quality of drinking water largely relies on the examination of indicator bacteria such as coliforms like Escherichia coli. E. coli is widely used as an indicator of fecal pollution when monitoring the microbial quality of drinking water, because it is abundant in all mammal feces and, therefore, is found in sewage and in natural waters contaminated with fecal matter, from human origin, wild animals, or derived from agricultural activity. This paper describes the development of a novel handheld fluorimeter for the rapid detection of E. coli in drinking water based on a specific cellular biomarker. The measurement system is based on a photomultiplier tube that captures the fluorescence signal produced by the cellular biomarker when it is excited by an ultraviolet LED. The cellular biomarker is also developed and it consists of a chimeric protein with a Green fluorescent protein (GFP) in the N-terminal domain and a specific amino acid sequence in the C-terminal domain (Colicin S4) that targets specifically the structure of the microorganism to be detected. The instrument is simple to use, lightweight, and can be powered by either an ac/dc power adapter or a rechargeable battery, making it an excellent choice for the rapid detection of E. coli in drinking water in field studies and laboratory measurements.
[Show abstract][Hide abstract]ABSTRACT: This paper evaluates the abilities of fast tap-changer topologies by using insulated-gate bipolar transistors to mitigate flicker generated by the ac electric arc furnaces, based on technical and economic criteria. The design problems derived from the very high powers and currents involved have been solved to a preliminary industrial level. The operation of the best resulting topology is verified on a real 80-MVA arc furnace with a dedicated graphical-mathematical multilevel simulator developed to perform short- and long-term tests. Selected pattern windows of the arc voltage, taken from exhaustive logs of electric variables of a real 80-MVA furnace during a complete meltdown process, have been loaded into the simulator. This novel simulation strategy enables the testing of the proposed compensator under reproduced “real working conditions” with several degrees of flicker severity. The simulator includes an IEC flicker meter capable of checking the flicker level online at any point in the installation. The simple open-loop and closed-loop control tests confirm the new tap changer as a fast and economical competitor to other arc furnace compensators. It manages 16% of the furnace system power at a subcycle or supercycle tap changing rate (between 0 and 10 changes per half cycle), as required. This fast switching capacity reduces the compensating time to the very limited values imposed by the L/R time constant of the furnace installation.
Article · Dec 2014 · IEEE Transactions on Power Delivery
[Show abstract][Hide abstract]ABSTRACT: Thyristor-based onload tap-changing ac voltage stabilizers can replace mechanical tap changers associated with transformers feeding medium-voltage (MV) lines (typically 69 kV primary, 34.5 kV line, 6.3-50 MVA), thus avoiding frequent contacts revision. As shown in a previous paper, the topology using a compensating transformer in the main circuit and a multiwinding coil in the commutating circuit give good technical and economical results independent of the coil operation mode (shared, nonshared, and mixed load). This second paper focuses on this topology and defines the criteria for an optimum design and the synthesis formulae that give the definition parameters of the components as a function of the equipment characteristics. Numerical results are added for a typical 10-MVA stabilizer. One of the best circuit solutions (single switch comb, mixed load, auxiliary short-circuit winding), which does not need a series association of thyristors, is developed in detail. Final synthesis formulae, effective power of the transformers and coil, and summatory of thyristors I·U products for all three operation modes are contrasted in a table as the final step of the iterative analysis and synthesis cost-comparative method followed along the research.
Article · Oct 2012 · IEEE Transactions on Power Delivery
[Show abstract][Hide abstract]ABSTRACT: Photoinduced fluorescence enhancement of colloidal quantum dots (QDs) is a hot topic addressed in many studies due to its great influence on the bioanalytical performance of such nanoparticles. However, understanding of this process is not a simple task, and it cannot be explained by a general mechanism as it greatly depends on the QDs' nature, solubilization strategies, surrounding environment, etc. In this vein, we have critically compared the behavior of CdSe QDs (widely used in bioanalytical applications) with different surface modifications (ligand exchange and polymer coating), in different controlled experimental conditions, in the presence-absence of the ZnS layer and in different media when exposed for long times to intense UV irradiation. Thus six different types of colloidal QDs were finally studied. This research was carried out from a novel perspective, based on the analysis of the dynamic behavior of the photoactivation process (of great interest for further applications of QDs as labels in biomedical applications). The results showed a different behavior of the studied colloidal QDs after UV irradiation in terms of their photoluminescence characteristics, potential toxicity due to metal release to the environment, nanoparticle stability and surface coating degradation.
Full-text available · Article · Sep 2011 · Nanotechnology
[Show abstract][Hide abstract]ABSTRACT: AC voltage and phase regulators based on tap changers implemented with silicon-controlled rectifiers and triacs are widely used due to their robustness. Tap changing is achieved under natural commutation of semiconductors during the zero crossing of current, so that the response time exceeds the half cycle of the mains. High-power transistors and gate turn-off thyristor switches make new and faster tap commutation techniques possible to achieve several tap changes in one half cycle. This paper analyzes and synthesizes a dual-tap chopping stabilizer with a compensating transformer, with a pulsewidth-modulation frequency of about 5 kHz and a new soft-switching technique achieved by two auxiliary small-power branches. Unlike other supercyclic ac soft-switching solutions, the new commutating method allows zero current turn-off, several times in a half cycle, for any sign combination of voltage and current, thus reducing the electrical stress in the switches and the electromagnetic emission. Zero-crossing current detection is not needed. A technical study and an evaluation of the power of the required components are done on the commutation techniques that extend the application field of tap changers to the reduction of the fast perturbations of the mains as flicker, voltage harmonics, voltage oscillations, etc. Experimental results with insulated-gate bipolar transistor switches are obtained in a 1 kVA prototype.
Article · Oct 2010 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract]ABSTRACT: Thyristor-based onload tap-changing AC voltage stabilizers are cheap and robust. They have replaced most mechanical tap-changers in low voltage applications from 300 VA to 300 kVA. Nevertheless, this replacement hardily applies to tap-changers associated to transformers feeding medium-voltage lines (typically 69 kV primary, 34.5 kV line, 10 MVA) which need periodical maintenance of contacts and oil. The Electric Power Research Institute (EPRI) has studied the feasibility of this replacement. It detected economical problems derived from the need for series association of thyristors to manage the high voltages involved, and from the current overload developed under line fault. The paper reviews the configurations used in that field and proposes new solutions, using a compensating transformer in the main circuit and multi-winding coils in the commutating circuit, with reduced overload effect and no series association of thyristors, drastically decreasing their number and rating. The stabilizer can be installed at any point of the line and the electronic circuit can be fixed to ground. Subsequent works study and synthesize several commutating circuits in detail.
Article · Aug 2009 · IEEE Transactions on Power Delivery
[Show abstract][Hide abstract]ABSTRACT: This paper describes the electronic design and the performance of a low-cost fiber-optic instrument for pH fluorescent measurements. The chemical sensing phase consists of an organic pH indicator (mercurochrome) immobilized in a sol-gel matrix placed at the end of a fiber optic by means of a steel grid. The active phase was excited by means of a high-intensity blue light-emitting diode. The light signal was modulated to avoid external interference. Fluorescence emission is detected by a low-cost photodiode. To avoid drifts in excitation light emission intensity, a ratiometric measurement was proposed. To perform such measurements, two fiber-optic measurement channels were used. One of them was employed to measure only the pH indicator fluorescent emission intensity. The second channel was employed to measure only the intensity of the excitation light reflected by the sensing phase. The ratio between both signals is only proportional to pH and proved to be independent of excitation light intensity. The sensor is useful over the pH range of 4-8, providing highly reliable results
Full-text available · Article · Aug 2006 · IEEE Transactions on Instrumentation and Measurement
[Show abstract][Hide abstract]ABSTRACT: Power insulated-gate bipolar transistor (IGBT) and other gate turnoff switches have allowed to analyze, in a previous paper, four new circuits for onload-tap-changing ac stabilizers that typically permit to make up to 7 or 45 (depending on the particular circuit solution) changes per half cycle of the mains voltage. This second and last paper considers the synthesis aspects of these subcyclic stabilizers giving design rules, and a synthesis calculus sheet actualized in a 100-kVA numeric example. A comparative table for the four circuit solutions, involving both technical and economical figures, is given as the final step of the iterative analysis and synthesis cost comparative method performed along the research. Preliminary experimental results are obtained from a 1-kVA prototype and a first evaluation of the possibilities of reducing voltage distortions is demonstrated in the fields of voltage low harmonics and flicker by means of a high-accuracy graphic simulator.
Article · May 2006 · IEEE Transactions on Power Delivery
[Show abstract][Hide abstract]ABSTRACT: The rate of change in classic thyristor-based onload tap-changing ac stabilizers is limited to that of the load current zero crossing (once per half cycle) due to the natural turnoff method involved. The growth of the power rate of insulated-gate bipolar transistor and other gate turnoff switches allows exploring of stabilizers that are able to change taps several times in a half cycle of the mains wave (subcyclic commutation). This paper analyzes the best four solutions for the power circuit of this new class of tap-changers in the multitap version, developed through an iterative analysis and synthesis cost comparative method that moves the tap-changing stabilizers over to the world of low-frequency voltage harmonics, oscillations, flicker, and instability phenomena attenuators. These topologies allow changing times as low as 150 μs by using a multicoil inductance to perform current limitation and voltage clamping tasks during the switching operation, as it shall be shown in a second paper dedicated to the synthesis and experimental aspects.
Article · May 2006 · IEEE Transactions on Power Delivery
[Show abstract][Hide abstract]ABSTRACT: Ongoing technological progress in electronic instrumentation triggered the development of an innovative, hands-on teaching program to help students toward a fuller understanding of recent changes in the field. This paper describes the different stages of a design project to teach electronic instrumentation to computer engineering students at the University of Oviedo, GijÓn, Spain. The project involves designing a weather station to measure the main meteorological variables and then displaying this information on a computer screen. Although this course is intended for nonspecialist students of electronics, it could easily be adapted to other syllabuses with minimum modification of the specifications. The course provides not only enhanced academic training but also increased student motivation, as students participate actively in all course activities and work in a team within which each student has specific responsibilities.
Article · Sep 2005 · IEEE Transactions on Education
[Show abstract][Hide abstract]ABSTRACT: In this paper, a relatively simple, low-cost industrial prototype
for measuring low oxygen concentrations in gaseous medium based on
phosphorescence lifetime of Al-Ferron in sol-gel probe is presented. The
main advantages over other techniques are an excellent sensitivity,
precision, selectivity, response time, and facility of maintenance.
Fiber optics is used to guide the light. This fact allows one to reach
difficult places and to make the measurements from a distance. The
design of the system and best ways to maximize the emission maximizing
the excitation light from the light source, the optimal distance from
the optical fibers to the chemical sensor, and a simple method to filter
the response are discussed and verified with the prototype developed.
The system allows the detection of oxygen concentrations of 0.005%
Article · Nov 1999 · IEEE Transactions on Instrumentation and Measurement
[Show abstract][Hide abstract]ABSTRACT: The measurement of Oxygen percentage included in fluids is an
interesting and important value. This value can not be obtained in an
easy way, so this is the reason why this article is presented. A way to
measure this value through the lifetime of phosphorescence is shown. In
order to get the lifetime, is necessary to process the signal in a
digital way, so it has been used a DSP. The phosphorescent material has
to be excited if we want to get light emitted by phosphorescence, this
is the reason for using a Xenon lamp and a chemical sensor which emits
phosphorescent light. Another important part is the transduction of
phosphorescent light to an electrical signal. This is done with a
photomultiplier tube (PMT). The signal produced by the PMT is sampled in
order to be processed with the DSP. In this way, the lifetime is
obtained and through it, the percentage of Oxygen