Analysis of the boundary conditions for the simulation of the pressure equalization step in PSA cycles

In this work, the physical validity of Danckwerts boundary conditions (original and modified) for simulating the connection of two beds in the pressure equalization step of a PSA cycle with a dynamic model including axial dispersion is analyzed. A model of this kind has been employed to simulate the separation of a carbon dioxide/methane mixture with silicalite as the adsorbent using a Skarstrom PSA cycle including a pressure equalization step before the pressurization step of each bed. It is demonstrated that both kinds of boundary conditions can lead to unrealistic results (either mass and heat flux are not conserved or molar fraction and temperature are not continuous in both beds) if the contribution of dispersion to axial mass flow is important, which occurs for long equalization times. To overcome these problems, the continuity of both dependent variables and fluxes as boundary conditions is proposed, which lead to the expected results for very long equalization times (the flux of each component is conserved and flat and continuous spatial profiles of all the dependent variables are obtained in both beds). These boundary conditions, unlike the ones proposed in the literature, can be the same regardless of the direction of flow. The impact of the different kind of boundary conditions on the performance results of the selected PSA process at the cyclic steady state is also analyzed.     

Subtraction of edge-diffracted fields in antenna radiation patterns for simulation of infinite ground plane

A measurement technique is introduced to simulate the radiation pattern of an antenna mounted on an infinite sized ground plane. The edge diffracted fields from a finite ground plane are measured and then subtracted from the total field to yield only the direct radiation from the antenna that would be present if the antenna were mounted on an infinitely large ground plane. Comparisons with theory are also presented.<>     

Instructed smoking expectancy modulates cue-elicited neural activity: a preliminary study.

In recent years, research applying functional neuroimaging to the study of cue-elicited drug craving has emerged. This research has begun to identify a distributed system of brain activity during drug craving. A review of this literature suggested that expectations regarding the opportunity to use a drug affected the pattern of neural responses elicited by drug cues. Using functional magnetic resonance imaging (fMRI), we examined the effects of smoking expectancy on the neural response to neutral (e.g., roll of tape) and smoking-related (a cigarette) stimuli in male cigarette smokers deprived of nicotine for 8 hr. As predicted, several brain regions (e.g., the anterior cingulate cortex) exhibited differential activation during cigarette versus neutral cue exposure. Moreover, we found that subregions of the prefrontal cortex (i.e., ventromedial, ventrolateral, and dorsolateral prefrontal cortices) showed cue-elicited activation that was modulated by smoking expectancy. These results highlight the importance of perceived drug use opportunity in the neurobiological response to drug cues.     

Occurrence of acetic acid and formic acid in breakfast cereals

Breakfast cereals are usually manufactured by extrusion followed by drying and toasting steps in which thermal treatments are applied. In addition, owing to the low water activity and the content in cereals of proteins and carbohydrates, precursors of the Maillard reaction, this reaction and degradation of sugars are favoured during processing. Acetic and formic acids have been identified as final products of Maillard reaction (MR) and sugar caramelisation. Acetic and formic acid contents have been determined by ion exchange high‐performance liquid chromatography in 56 commercial breakfast cereals. Results were evaluated taking into account the sample formulation. Acetic and formic acids were detected in all samples, and significant variations were observed for acetic acid depending on the protein and fibre content. Acetic acid, originating from 1‐deoxyglucosone cleavage during MR, proved to be a good indicator of processing in cereals enriched with or based on wheat flour because of their high protein content. Fibre addition increased acetic acid concentration. The application of acetic acid as a chemical marker of processing in breakfast cereals and its possible generation pathways are discussed. Copyright © 2006 Society of Chemical Industry     

Scavenger effect of a mango (Mangifera indica L.) food supplement’s active ingredient on free radicals produced by human polymorphonuclear cells and hypoxanthine–xanthine oxidase chemiluminescence systems

The in vitro antioxidant and free radical scavenging properties of a stem bark aqueous extract of mango tree (Mangifera indica L.), whose formulations are used in Cuba as food supplements under the brand name of Vimang^®, were studied. Luminol-enhanced chemiluminescence was used to elucidate the effect of this extract on the generation of reactive oxygen species in PMA- or zymosan-stimulated human polymorphonuclear leukocytes and on superoxide radicals generated in the hypoxanthine–xanthine oxidase reaction. Chemiluminescence was reduced in a dose-dependent manner at extract concentrations from 5 to 100 μg/ml, most probably by inhibiting the superoxide generation reaction. Part of this M. indica extract antioxidant activity could be ascribed to the presence of mangiferin as its main component.     

Modeling Lightning Impact Thermo-Mechanical Damage on Composite Materials

Carbon fiber-reinforced polymers, used in primary structures for aircraft due to an excellent strength-to-weight ratio when compared with conventional aluminium alloy counterparts, may nowadays be considered as mature structural materials. Their use has been extended in recent decades, with several aircraft manufacturers delivering fuselages entirely manufactured with carbon composites and using advanced processing technologies. However, one of the main drawbacks of using such composites entails their poor electrical conductivity when compared with aluminium alloy competitors that leads to lightning strikes being considered a significant threat during the service life of the aircraft. Traditionally, this problem was overcome with the use of a protective copper/bronze mesh that added additional weight and reduced the effectiveness of use of the material. Moreover, this traditional sizing method is based on vast experimental campaigns carried out by subjecting composite panels to simulated lightning strike events. While this method has proven its validity, and is necessary for certification of the structure, it may be optimized with the aid provided by physically based numerical models. This paper presents a model based on the finite element method that includes the sources of damage observed in a lightning strike, such as thermal damage caused by Joule overheating and electromagnetic/acoustic pressures induced by the arc around the attachment points. The results of the model are compared with lightning strike experiments carried out in a carbon woven composite.     

Free fatty acids and oxidative changes of a raw goat milk cheese through maturation

Free fatty acids (FFA) and lipid and protein oxidation changes were studied throughout maturation process of a raw goat milk cheese with protected designation of origin. Cheeses were analyzed at 4 different times of maturation, at 1, 30, 60, and 90 d. All FFA significantly increased during maturation and the relative increase was higher for long-chain than medium- or short-chain FFA. At the end of maturation, oleic (C18:1 n9), butyric (C4:0), and palmitic (C16:0) acids were the most abundant. The higher levels of short-chain fatty acids (SCFA) regarding total FFA obtained at the end of Ibores cheese ripening compared with other raw goat milk cheeses, highlight the notable role of SCFA on the flavor of this cheese owing to their low-odor thresholds. Lipid oxidation values significantly increased during maturation process but low levels of malondialdehyde were reported; however, protein oxidation did not significantly change during ripening.     

Undoped tin oxide thin films obtained by the sol gel technique,starting from a simple precursor solution

In this work, we report the synthesis and the structural, optical and electrical properties of undoped tin oxide thin films obtained by the sol–gel technique. The films have been prepared from a simpler precursor solution than other ones reported; it is based on stannous chloride (SnCl₂·2H₂O), ethanol, glycerol and triethylamine. The films are deposited on glass slide substrates and sintered at temperatures in the 300–550 °C range, in an open atmosphere. A second thermal treatment in vacuum is made in order to decrease the resistivity of the films. The X-ray diffraction patterns show the tetragonal phase of SnO₂ with a small preferential orientation in the (110) plane. All films show high optical transmission (~85%) and a direct band gap value around of 3.8 eV. The minimum resistivity value, 2 × 10⁻¹ Ohm-cm, is obtained for the films sintered at 300 and 350 °C and thermal treated in vacuum at 500 °C for 1 h. The decrease of the resistivity with the thermal treatment in vacuum is associated with an increase in the oxygen vacancies concentration.     

Crystal Size,Morphology, and Growth Mechanism in Bio‐Inspired Apatite Nanocrystals

Bio‐inspired apatite nanoparticles precipitated in the presence of citrate ions at increasing maturation times are characterized in terms of structure, size, morphology, and composition through advanced X‐ray total scattering techniques. The origin of the platy crystal morphology, breaking the hexagonal symmetry, and the role of citrate ions is explored. By cross‐coupling the size and shape information of crystal domains with those obtained by atomic force microscopy on multidomain nanoparticles, a plausible mechanism underlying the amorphous‐to‐crystal transformation is reconstructed. In the present study, citrate plays the distinct roles of inducing the platy morphology of the amorphous precursor and controlling the thickness of the Ca‐deficient apatite nanocrystals. These findings can open new scenarios also in bone mineralization, where citrate might have a broader role to play than has been thought to date.     

Compliance with hypertension treatment: 10 years of publications in Spain

INTRODUCTION: Ten years of publications (1984-1993) about drug compliance in spanish hypertensive patients are presented. MATERIAL AND METHODS: A bibliography search of Medline (EBSCO CD-ROM ver 104.1, act Jul 1995), Indice Médico Espa?ol (CSIC CD-ROM, act Oct 1993) and other sources has been made. RESULTS: 39 articles have been located and 23 investigational publications have been analysed. All the publications, but one, have evaluated the compliance by an indirect method, mainly patient selfdeclaration. The degree of patient compliance determined by interviews, questionnaires or inquiries is 55.5% (IC 95%: 52.7-58.3). The patient compliance in the publications that use methods based in pill counts is 46.4% (IC 95%: 41.6-51.2). The treatment dropout is present in the 18.5% of the patients (IC 95%: 20.5-16.5). CONCLUSIONS: The drug compliance degree in Spanish patients with hypertension is low.