Phase Behavior and Structure of Systems Based on Mixtures of n‐Hentriacontane and Melissic Acid

Candelilla wax (CW) organogelation is a promising method for providing structure to solid‐like fat‐based foods, cosmetics, and drug delivery systems. The main component, n‐hentriacontane (C31), defines, to a large extent, the thermal properties of CW. CW is a complex mixture of n‐alkanes, fatty acids, triterpenic alcohols, and fatty alcohols. In this initial examination of the role of CW components on the phase behavior and structure, CW and binary mixtures of C31 and melissic acid (C30) were studied in bulk and in solutions of vegetable oil. Binary mixtures of C31 and C30 presented a predominantly monotectic phase behavior in which the melting temperature of C31 remained constant independently of the mixture composition. Crystal packing of the pure components and mixtures had an orthorhombic subcell, and the microstructures of the mixtures were extremely different from that of the pure components. In solutions with less than 50 % C31, the order–disorder transition observed in bulk C31 was absent. Organogels of C31, C30, or the mixture were softer than those of CW. The increased strength of CW organogels is associated with the relatively small crystal size of this system.     

Fluorescence from the maillard reaction and its potential applications in food science

The chemistry of the Maillard reaction involves a complex set of steps, and its interpretation represents a challenge in basic and applied aspects of Food Science. Fluorescent compounds have been recognized as important early markers of the reaction in food products since 1942. However, the recent advances in the characterization of fluorophores' development were observed in biological and biomedical areas. The in vivo non-enzymatic glycosylation of proteins produces biological effects, promoting health deterioration. The characteristic fluorescence of advanced glycosylation end products (AGEs) is similar to that of Maillard food products and represents an indicator of the level of AGE-modified proteins, but the structure of the fluorescent groups is, typically, unknown. Application of fluorescence measurement is considered a potential tool for addressing key problems of food deterioration as an early marker or index of the damage of biomolecules. Fluorophores may be precursors of the brown pigments and/or end products. A general scheme of the Maillard reaction is proposed in this article, incorporating the pool concept. A correct interpretation of the effect of environmental and compositional conditions and their influences on the reaction kinetics may help to define the meaning of fluorescence development for each particular system.     

Iron(II)-catalyzed oxidation of arsenic(III) in a sediment column

Arsenic contamination in aquatic systems is a worldwide concern. Understanding the redox cycling of arsenic in sediments is critical in evaluating the fate of arsenic in aquatic environments and in developing sediment quality guidelines. The direct oxidation of inorganic trivalent arsenic, As(III), by dissolved molecular oxygen has been studied and found to be quite slow. A chemical pathway for As(III) oxidation has been proposed recently in which a radical species, Fe(IV), produced during the oxidation of divalent iron, Fe(II), facilitates the oxidation of As(III). Rapid oxidation of As(III) was observed (on a time scale of hours) in batch systems at pH 7 and 7.5, but the extent of As(III) oxidation was limited. The Fe(II)-catalyzed oxidation of As(III) is examined in a sediment column using both computational and experimental studies. A reactive-transport model is constructed that incorporates the complex kinetics of radical species generation and Fe(II) and As(III) oxidation that have been developed previously. The model is applied to experimental column data. Results indicate that the proposed chemical pathway can explain As(III) oxidation in sediments and that transport in sediments plays a vital role in increasing the extent of As(III) oxidation and efficiency of the Fe(II) catalysis.     

Ultrasonic propagation in high-concentration TiO2 slurries for photocatalytic reactors

This work reports measurements of the speed of sound and ultrasonic attenuation in high concentration (up to 3 g · L⁻¹) aqueous TiO₂ slurries close to neutral pH. Measurements were made at frequencies of 1675, 5545, and 9340 kHz using ultrasonic transducers submerged in the slurry. The experimental setup may be applied to slurries in practical reactors while in operation. Within an experimental uncertainty of ±0.5 m · s⁻¹, the speed of sound in the slurry was the same as in pure water, at all the studied catalyst concentrations and frequencies. The excess ultrasonic attenuation with respect to pure water increases linearly with the catalyst concentration and is inversely proportional to the square of the excitation frequency. This indicates that viscous and thermal acoustic losses predominate over scattering. For TiO₂ concentrations in the range of 0.15–3 g · L⁻¹, the catalyst concentration in the slurry may be estimated as a linear function of the excess ultrasonic attenuation, with an uncertainty of 0.1 g · L⁻¹.     

Autonomous detection and loading of ore piles with load–haul–dump machines in Room & Pillar mines

Automation of machines in underground mines is a topic with increasing interest, both for research and industrial applications. Autonomous load–haul–dump (LHD) machines need to load material successfully before dumping it into a crusher or an ore pass. The autonomous loading method must be robust to enable reliable operation of the LHD during long periods of time. In this work, a method to perform autonomous loading in Room & Pillar mines is presented. It is based on detecting all ore piles in real-time, and then computing attack poses in each pile. Then, a positioning process is performed to get the machine in front of the selected ore pile, and an excavation algorithm is executed for loading until the bucket is filled. The proposed method is able to detect multiple ore piles, with different slopes and sizes, and to consider different possible trajectories for attacking and loading the most feasible pile. The method was tested in the Werra Potash Mine, under real operational conditions. The results show that the method can load about 80% of the material that an experienced operator can load. Also, the success rate of the autonomous loading process is very high, being able to load enough material in all trials, and performing successfully the full procedure in 88% of the cases. Thus, the proposed autonomous loading method is a suitable alternative to be used in Room & Pillar mines.     

An order‐based algorithm for implementing multiparty synchronization

Multiparty interactions are a powerful mechanism for coordinating several entities that need to cooperate in order to achieve a common goal. In this paper, we present an algorithm for implementing them that improves on previous results in that it does not require the whole set of entities or interactions to be known at compile‐ or run‐time, and it can deal with both terminating and non‐terminating systems. We also present a comprehensive simulation analysis that shows how sensitive to changes our algorithm is, and compare the results with well‐known proposals by other authors. This study proves that our algorithm still performs comparably to other proposals in which the set of entities and interactions is known beforehand, but outperforms them in some situations that are clearly identified. In addition, these results prove that our algorithm can be combined with a technique called synchrony loosening without having an effect on efficiency. Copyright © 2004 John Wiley & Sons, Ltd.