Real time frequency domain fiberoptic temperature sensor

The excited state phosphorescence lifetime of alexandrite crystals is used to monitor temperature in the physiological range from 15-45°C with precision and accuracy of 0.2°C. A 500-μm cubic alexandrite crystal bounded to the distal end of an optical fiber of similar core dimensions is excited with pulsed Ne-He laser light. This apparatus uses a sampler for data acquisition and frequency domain methods for data fitting. The instrument amplifies the AC components of the detector output and band limits the signal to 12.5 kHz. The fundamental frequency of the excitation is set to 195.13 Hz to obtain 64 harmonics. This band limited signal is sampled and averaged over few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. Five to 50 values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited state lifetimes from subpicowatt luminescent signals in plastic optical fibers. A least squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation seen by the photodetector leaking through optical interference filters. The phosphorescence lifetimes measured reproducibly to about three parts in a thousand are used to monitor physiological temperature. Temperatures are computed employing empirical polynomials. The system drift is negligible over 15 h of continuous operation. The instrumentation and methods allow 1.3-s update times and 30-s full response times     

A Multiobjective Evolutionary Approach to Concurrently Learn Rule and Data Bases of Linguistic Fuzzy-Rule-Based Systems

In this paper, we propose the use of a multiobjective evolutionary approach to generate a set of linguistic fuzzy-rule-based systems with different tradeoffs between accuracy and interpretability in regression problems. Accuracy and interpretability are measured in terms of approximation error and rule base (RB) complexity, respectively. The proposed approach is based on concurrently learning RBs and parameters of the membership functions of the associated linguistic labels. To manage the size of the search space, we have integrated the linguistic two-tuple representation model, which allows the symbolic translation of a label by only considering one parameter, with an efficient modification of the well known (2 + 2) Pareto archived evolution strategy (PAES). We tested our approach on nine real world datasets of different sizes and with different numbers of variables. Besides the (2 + 2)PAES, we have also used the well known nondominated sorting genetic algorithm (NSGA-II) and an accuracy-driven single-objective evolutionary algorithm (EA). We employed these optimization techniques both to concurrently learn rules and parameters and to learn only rules. We compared the different approaches by applying a nonparametric statistical test for pairwise comparisons, thus taking into consideration three representative points from the obtained Pareto fronts in the case of the multiobjective EAs. Finally, a data complexity measure, which is typically used in pattern recognition to evaluate the data density in terms of average number of patterns per variable, has been introduced to characterize regression problems. Results confirm the effectiveness of our approach, particularly for (possibly high dimensional) datasets with high values of the complexity metric.     

Hot metal pretreatment by powder injection of lime‐based reagents

A mathematical model earlier proposed has been improved to predict the kinetics of multicomponent reactions in the hot metal pretreatment through the injection of reactive fluxes. It is assumed that there are two reaction zones along the flux injection operation: a transitory reaction between the rising particles and the bulk metal, and the permanent reaction between the metal and the top slag. A criterion to estimate the fraction of solids which will react with molten iron in a three‐phase jet (gas‐solid‐liquid) was considered; this fraction of solids carries out the transitory reaction. The model also takes into account the thermodynamic changes produced in the metal and slag due to the chemical reactions. Calculated results of the model are in good agreement with experimental results for the desulfurization of hot metal through the injection of CaO‐SiO₂‐CaF₂‐FeO‐Na₂O reagents at 1400 ‐ 1450 °C. Two kinds of hot metal were tested, one with a low carbon mass content of 3 % and the other with a high carbon mass content of 4.5 %.     

Anodic oxidation of Ta/Fe alloys

The behaviour of iron during anodizing of sputter-deposited Ta/Fe alloys in ammonium pentaborate electrolyte has been examined by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Anodic films on Ta/1.5 at.% Fe, Ta/3 at.% Fe and Ta/7 at.% Fe alloys are amorphous and featureless and develop at high current efficiency with respective formation ratios of 1.67, 1.60 and 1.55 nm V⁻¹. Anodic oxidation of the alloys proceeds without significant enrichment of iron in the alloy in the vicinity of the alloy/film interface and without oxygen generation during film growth, unlike the behaviour of Al/Fe alloys containing similar concentrations of iron. The higher migration rate of iron species relative to that of tantalum ions leads to the formation of an outer iron-rich layer at the film surface.     

High-quality output PWM AC voltage regulator based on Cuk converter

This paper describes the design of an AC–AC converter capable of generating a high-quality output. It is based on the Cuk configuration, with the transistors replaced by bidirectional switches. Since there are no transformers in the configuration, the converter lends itself to a compact and lightweight implementation. The design process is aimed at using, as much as possible, the tools and devices already developed for DC–DC applications. This approach greatly simplifies the design and implementation of the converter. An integrated circuit, developed for DC–DC applications, is used to control the converter. Both the set-point and the feedback signal are rectified in order to fit the input range of the controller. Tests performed show that the output exhibits a maximum total harmonic distortion of 3% (resistive load). The efficiency is slightly higher than 89%, and the average output regulation is 0.3%. The converter is capable of correcting voltage sags down to 60% and voltage swells up to 30%, with the output returning to its nominal value within one mains cycle. The results show that the converter is suitable for energizing information-processing equipment.     

Mechanochemical synthesis of vanadium nitride

Vanadium nitride (VN) has been prepared by mechanosynthesis from vanadium metal under a pressurized nitrogen atmosphere in a short milling time. The characterization of the final product by X-ray diffraction, scanning electron microscopy, electron energy loss (EELS), and X-ray absorption spectroscopy (XAS) is presented. The final product, VN with 96% of purity, is obtained at room temperature with nanometric particle size and a very high microhardness after sintering. A relationship between microstructure and microhardness as well as a comparison between the VN obtained mechanical and thermal method is also presented.     

A Multifrequency Phase Fluorometer Using the Harmonic Content of a Mode-Locked Laser

ABSTRACT

We describe the construction and operation of a cross-correlation phase and modulation fluorometer which uses the harmonic content of a high repetition rate mode-locked laser as the excitation source.

A mode-locked argon ion laser is used to synchronously pump a dye laser. The pulse train output from the dye laser is amplitude modulated by an acousto-optic modulator and then frequency doubled with an angle tuned frequency doubler. With the particular dye utilized in these studies, the ultraviolet light obtained was continuously tunable over the range 280-310 nm. In the frequency domain the high repetition rate pulsed source gives a large series of equally spaced harmonic frequencies. The frequency spacing of the harmonics is determined by the repetition frequency of the laser. Amplitude modulation of the pulse train permits variation of the frequency quasi-continuously from a few hertz to gigahertz. Use of cross-correlation techniques permits precise isolation of individual frequencies. The cross-correlation frequency required for the analysis of the phase delay and modulation ratio is obtained using coupled frequency synthesizers. In the present instrument three synthesizers are used. One drives the pump mode-locker head, a second drives the acousto-optic modulator and the third is used to modulate the response of the photomultiplier tubes which detect the signal. The accuracy, reproducibility and sensitivity of the instrumentation have been determined. Experimental data are provided to show use of this high frequency cross-correlation phase-modulation fluorometer for the determination of fluorescence lifetimes and rotational motions of tryptophan in solution and in proteins.     

Reconstruction-based contribution for process monitoring

This paper presents a new method to perform fault diagnosis for data-correlation based process monitoring. As an alternative to the traditional contribution plot method, a reconstruction-based contribution for fault diagnosis is proposed based on monitored indices, SPE, T² and a combined index φ. Analysis of the diagnosability of the traditional contributions and the reconstruction-based contributions is performed. The lack of diagnosability of traditional contributions is analyzed for the case of single sensor faults with large fault magnitudes, whereas for the same case the proposed reconstruction-based contributions guarantee correct diagnosis. Monte Carlo simulation results are provided for the case of modest fault magnitudes by randomly assigning fault sensors and fault magnitudes.