Gain scheduled controllers for dynamic systems using sector nonlinearities

In this work we explore the use of gain scheduling for the control of nonlinear systems. The nonlinear system is represented locally by uncertain linear models using sector nonlinearities representation. The uncertain linear models are then used to design a family of robust controllers. We propose a gain scheduling procedure for the problem of guaranteed transition from an actual operating condition to a desired one by constructing a pre-specified path in the state space for the system operating points. As far as we know this problem has not been addressed before. The gain scheduling control procedure given is illustrated in the context of the regulator problem with state feedback.     

Communication Response Time in P-NET Networks: Worst-Case Analysis Considering the Actual Token Utilization

Fieldbus networks aim at the interconnection of field devices such as sensors, actuators and small controllers. Therefore, they are an effective technology upon which distributed computer-controlled systems (DCCS) can be built. DCCS impose strict timeliness requirements to the communication network. In essence, by timeliness requirements we mean that traffic must be sent and received within a bounded interval, otherwise a timing fault is said to occur. P-NET is a multi-master fieldbus standard based on a virtual token passing scheme. In P-NET each master is allowed to transmit only one message per token visit, which means that in the worst-case the communication response time could be derived considering that the token is fully utilized by all stations. However, such analysis can be proved to be quite pessimistic. In this paper, we propose a more sophisticated P-NET timing analysis model, which considers the actual token utilization by different masters. The major contribution of this model is to provide a less pessimistic, and thus more accurate, analysis for the evaluation of the worst-case communication response time in P-NET fieldbus networks.     

Presence of Clostridium perfringens in meat-based preparations in public food services in central San Jose, Costa Rica

In Costa Rica there are a large number of public food services distributed along the country, where a considerable number of people eat daily. Clostridium perfringens is a bacteria associated with foodborne illness related, especially, to meat products kept for long time at temperatures under 70 degrees C. The aim of this study was to evaluate the public food services that use water baths for keeping food hot in order to establish the presence of C. perfringens in cooked bovine meat dishes and to evaluate the enterotoxigenic capacity of the strains isolated. 81 samples of cooked bovine meat plates coming from 27 public food services, located in the Central County of San José were analyzed. The methodology described by Labbe & Harmon for the isolation of C. perfringens was used in 10 g of sample. Also, the enterotoxigenic capacity of the strains was evaluated using the passive-reverse-latex-agglutination assay from Oxoid. From the 27 public food services analyzed, eight (30%) were positive in the three samplings done, nine (33%) were positive in one or two occasions, and ten (37%) were negative all times. This implies that in 17 (63%) of the establishments studied, the bacteria was isolated at least once. From the 81 preparations studied, 37 (46%) were positive for the bacteria. The temperatures at which food was kept varied from 56 to 82 degrees C, with an average of 68.7 degrees C. From the 37 strains identified as C. perfringens, 12 (32%) were positive for enterotoxin. In conclusion, the presence of C. perfringens in bovine meat dishes, maintained in water baths, represents an important risk for public health, and the temperature at which the preparation is kept is critical for the multiplication of the bacteria.     

Insights into the selective sensing mechanism of a luminescent Cd(II)-based MOF chemosensor toward NACs: roles of the host–guest interactions and PET processes

Journal of Materials Science - The structural and photophysical properties of the [Cd2(H2L)2(H2O)5].5H2O (where H4L is the ligand 5,5'-((thiophene-2,5-dicarbonyl)bis(azanediyl))diisophthalic...     

An Independent Component Analysis Approach for Wide-Area Monitoring of Power System Disturbances

Abstract

Wide-area power system monitoring based on phasor measurement units allows collecting a set of physical variables for evaluating the system security and stability, as well as for detecting power system disturbances. However, trends, noise and non-Gaussian distribution in measurements are important challenges for carrying out the detection, localization and visualization of power system disturbances. In this paper, a methodology that combines independent component analysis with statistical indices for detecting and visualizing anomalous dynamic events from wide-area measurements is proposed. From the statistical indices, two charts are also proposed to provide a better understanding of the system disturbances. Finally, a set of simulated data obtained from a transient stability model of the New England/New York test system is used to demonstrate the effectiveness of the proposed technique.     

Phthalocyanine–Virus Nanofibers as Heterogeneous Catalysts for Continuous‐Flow Photo‐Oxidation Processes

The generation of highly reactive oxygen species (ROS) at room temperature for application in organic synthesis and wastewater treatment represents a great challenge of the current chemical industry. In fact, the development of biodegradable scaffolds to support ROS‐generating active sites is an important prerequisite for the production of environmentally benign catalysts. Herein, the electrostatic cocrystallization of a cationic phthalocyanine (Pc) and negatively charged tobacco mosaic virus (TMV) is described, together with the capacity of the resulting crystals to photogenerate ROS. To this end, a novel peripherally crowded zinc Pc (1) is synthesized. With 16 positive charges, this photosensitizer shows no aqueous aggregation, and is able to act as a molecular glue in the unidimensional assembly of TMV. A step‐wise decrease of ionic strength in mixtures of both components results in exceptionally long fibers, constituted by hexagonally bundled viruses thoroughly characterized by electron and confocal microscopy. The fibers are able to produce ROS in a proof‐of‐concept microfluidic device, where they are immobilized and irradiated in several cycles, showing a resilient performance. The bottom‐up approach also enables the light‐triggered disassembly of fibers after use. This work represents an important example of a biohybrid material with projected application in light‐mediated heterogeneous catalysis.     

Fatigue crack growth analysis of different adhesive systems: Effects of mode mixity and load level

The aim of this paper is to investigate the fatigue fracture behavior of three different adhesive systems (epoxy‐based, acrylic, and a rubber‐like adhesive). To achieve this, double cantilever beam specimens were manufactured with different adhesives and tested under several mode mixities and different load levels. Fatigue crack growth rate was evaluated through a Paris law equation. For postprocessing, the compliance‐based beam method was used. Results showed that the variation of the threshold energy with load level is more pronounced for the epoxy‐based adhesive. The crack propagation life is higher for the acrylic adhesive. Although, for pure mode I conditions, the normalized threshold of the rubber‐like adhesive is lower, for pure mode II, it was higher than the epoxy‐based adhesive. Due to the normalization by the static fracture energy, the slope of the Paris law was approximately constant for all the adhesive systems.     

Photoprocesses in microaggregates

Despite the potential complexity of microaggregate-containing systems, photophysical probe techniques have made important fundamental contributions to our understanding of the structure and properties of the aggregates and of the dynamics and reactivity of small molecules added to the system. By appropriate choice of the probe and quencher, one can often reduce the behavior of such microheterogeneous systems to that of a simple pseudophase system, amenable to study by steady-state fluorescence techniques. Rather general photophysical probe-based methods are now available for measuring equilibrium constants for solute incorporation and exchange selectivity coefficients for counterion binding to various types of microaggregates, including micelles, vesicles, and reverse micelles.     

Efficacy of a national program to promote breast feeding: Chile 1993-2002

Promotion of breast feeding is a priority in Chilean health's policies. The aim of the study was to evaluate the tendency of breastfeeding (exclusive, continued, partial), in children less than 18 months old, controlled in the Chilean public health system, based in four national surveys. Through a 24 h food intake recall (breastfeeding, water, juice, infant formula, solids) food patterns were explored every 3 years, as well as maternal participation in jobs located away from home. the sample consisted of approximately 10 thousand children, less than 18 months old of the 28 health services throughout the country. The prevalence of children with exclusive breastfeeding, predominant (breastfeeding, water or juice), complemented (breastfeeding plus solids) or any other way of feeding for each month of age in each survey, and changes in period studied, was determined. Between 1993 and 2002, exclusive breastfeeding for 6 months increased from 16 to 43.1% (p<0.001) and predominant breastfeeding from 25.4 to 57.4%. at the same time, complemented breastfeeding at 12 months increased from 10.7 to 21.3%, and partial or complemented breastfeeding in 12 to 18 month old children went from 24.1 to 46.7%. Maternal work located away from home was inversely associated with the prevalence of exclusive and complemented breastfeeding during the first year (p<0.001). There has been a significant increase of maternal breastfeeding in the period analyzed. The negative effects of maternal labor on breastfeeding suggests to explore more effective forms of social support to the working mother.     

Recovery of phytosterols from sunflower oil deodorizer distillates

Phytosterols are usually recovered by crystallization from the deodorizer distillate (DD) of vegetable oils. In this work, the impact of the principal process variables (viz., solvents and cosolvents, cooling rate, crystallization temperature, and ripening time) on the quality and yield of the recovered phytosterols was studied by using a sunflower oil DD “enriched” (i.e., preconcentrated) via transesterification with ethanol (EDD) as a feedstock and commercial hexane as solvent (S), with S/EDD mass ratios of 3 to 5. Water (0 to 4.5 wt%) and ethanol (0 to 10 wt%) were used as cosovents, with crystallization temperatures between 0 and −20°C and crystallization times from 4 to 96 h. The cooling rate was either −20°C/h or “brisk chilling” from 40 to −5°C. The nature and composition of the EDD solvent and cosolvent composite arose as the most important process variable, strongly influencing both the percentage of sterol yield and the purity of the crystals, as well as their filterability and washability. Water-saturated hexane sufficed to give good crystallization, yet the beneficial effect of adding water as the single cosolvent was enhanced by adding small and precise amounts of ethanol. A recovery of sterols as high as 84% (with 36% purity) was achieved by using a single-stage batch crystallization of the S/EDD mixture (S/EDD=mass ratio 4).