Optimization by lumped control of reactors with langmuir-hinshelwood catalyst deactivation

A method is proposed for solving the problem of temperature optimal control in tubular fixed-bed reactors with reaction systems described by Langmuir-Hinshelwood-Hougen-Watson kinetic equations. The optimization problem is formulated by N state differential equations corresponding to the N differential fixed-bed reactors in which the integral reactor is divided. It is solved using the control vector parameterization computational technique. The proposed method when applied to a simple reaction system reported previously in the literature gives analogous results, and thus validates the theory. This theory is applied to the dehydrogenation of benzyl alcohol to benzaldehyde. An analysis of optimality problem shows a strong influence of the temperature dependence of the ratio of reaction rate to deactivation reaction rate on the optimal policy.     

Visitor profile, satisfaction levels and clustering of tourists for decision making in Michoacan, Mexico

The state of Michoacán, one of the states with the lowest economic development in Mexico, has been historically recognized because of its potential for tourism activities. The revenues coming from this economic sector, as well as the number of tourists who visit this state have significantly increased during the last few years. A survey was conducted on tourists who visited Michoacán, in order to determine the visitors' profile and their satisfaction levels during their visit. A cluster analysis was then used to categorize the lifestyle of these tourists into five different segments, to be able to develop the best tourism products, marketing strategies and aid the decision-making process of government and private organizations related to this sector. A regression analysis was also performed to identify the variables that determine the satisfaction of these tourists. The results are satisfactory in the sense that the actions taken, which were based on this research and led by the Ministry of Tourism of Michoacán and the Ministry of Tourism of Mexico, have attracted more national and international groups, and have also increased the revenues, profits and new investments reported by private organizations related to this economic sector.     

Evaluation of the interactivity of students in virtual learning environments using a multicriteria approach and data mining

This work seeks to provide a new multicriteria approach to evaluate and classify the level of interactivity of students in learning management systems (LMS). We describe, step by step, the complete methodological development process of the evaluation model as well as detailing the results obtained when applying it to a higher education teaching experience. This research demonstrates that the combined use of multicriteria decision methodologies and data mining prove to be particularly suitable for identifying behavioural patterns of the users through the analysis of records generated in LMS. The results reveal that the behavioural patterns in LMS offer certain indicators as to students’ academic performance, although the study does not permit to state that those students who adopt passive attitudes in these spheres may necessarily produce low academic performance.     

Vertically Aligned Hybrid Core/Shell Semiconductor Nanowires for Photonics Applications

A family of 1D organic/inorganic core/shell materials formed by an inner organic nanowire (ONW) conformally covered with an inorganic wide band gap semiconductor (ZnO or TiO₂) layer is presented. The developed procedure is a two‐steps vacuum methodology involving the formation of supported single crystal small‐molecule nanowires by physical vapor deposition and plasma enhance chemical vapor deposition (PECVD) of the inorganic shell. Critical characteristics of the last technique are the possibilities of low temperature and remote configuration deposition. Additionally, an initial step has to be included in order to create nucleation centers for the growth of the ONWs. The procedure and its general character in terms of the variability in organic core and inorganic shells composition and the applicability of the technique to different substrates are presented. The formation of the inorganic shell with no damage of the organic core single‐crystalline structure is demonstrated by high resolution transmission electron microscopy. The vertical alignment of the hybrid nanostructure is achieved thanks to the interaction of the 1D organic nanostructured surfaces and the glow discharge during the deposition of the inorganic shell by PECVD. The optical properties of these core/shell NWs are studied by fluorescence spectroscopy and microscopy, and their application as nanoscale waveguides in the 550–750 nm range addressed.     

Effects of a citrus based juice on biomarkers of oxidative stress in metabolic syndrome patients

Bioactive substances found in numerous foods can be successfully and safely used to modify various cellular functions and affect the oxidative stress. The aim of this study was to analyze the effect of a citrus-based juice (juice citrus (95%) with 5% of aronia extract (Aronia melanocarpa)) on biomarkers of oxidative stress in patients with metabolic syndrome compared with healthy individuals. The study comprised 20 healthy subjects and 33 patients with metabolic syndrome. Eighteen patients consumed daily 300 mL of a citrus-based juice during 6 months and 15 patients consumed 300 mL of a placebo beverage. The control group consumed a citrus-based juice (CJ). Before, and at sixth months after consuming of a citrus-based juice the following parameters were determined: 15-isoprostane F₂, 8-hydroxydeoxyguanosine (8-OHdG), reduced and oxidized glutathione (GSH/GSSH), carbonyl groups and oxidized LDL (ox-LDL). After consuming CJ during 6 months the values of 8-OHdG, carbonyl groups and LDL-ox decreased in both analyzed groups and the values of GSH/GSSH increased. Significant differences were observed in both groups. Thus consumption of citrus-based juice improved the biomarkers of oxidative stress in metabolic syndrome patients.     

The ALGACEA-1 method for the capacitated vehicle routing problem

We base the ALGACEA-1 method on Clarke–Wright's savings estimates, using Monte Carlo techniques for node selection. This procedure controls the assigned probabilities for node selection using a bounded Entropy function. Similarly, we have discussed the parameter tuning for this method with the purpose of obtaining a good algorithm performance. Finally, some computational results are given to show the quality of the solutions provided by ALGACEA-1 in a real case and in some benchmarking instances.     

Application-independent feature selection for texture classification

Recent developments in texture classification have shown that the proper integration of texture methods from different families leads to significant improvements in terms of classification rate compared to the use of a single family of texture methods. In order to reduce the computational burden of that integration process, a selection stage is necessary. In general, a large number of feature selection techniques have been proposed. However, a specific texture feature selection must be typically applied given a particular set of texture patterns to be classified. This paper describes a new texture feature selection algorithm that is independent of specific classification problems/applications and thus must only be run once given a set of available texture methods. The proposed application-independent selection scheme has been evaluated and compared to previous proposals on both Brodatz compositions and complex real images.     

Unstructured kinetic model for reuterin and 1,3‐propanediol production by Lactobacillus reuteri from glycerol/glucose cofermentation

BACKGROUND: Lactobacillus reuteri is unable to grow on glycerol as sole carbon and energy source hence, glycerol is used as an alternative hydrogen acceptor during growth on available carbohydrates. Thus, glycerol is converted to reuterin and 1,3‐propanediol (1,3‐PDL), both products with interesting industrial applications. These compounds are commonly produced by using resting cells in two‐step fermentation processes. RESULTS: The glycerol/glucose cofermentation by L. reuteri yields reuterin and 1,3‐PDL at a glycerol concentration higher than 100 mmol L⁻¹. An increase of glycerol concentration from 200 to 400 mmol L⁻¹ showed no additional stimulatory effect on ethanol and acetate production but consistently reduced the lactate concentration. It was also found that reuterin concentration reached a maximum value and subsequently decreased due to its conversion to 1,3‐PDL. An unstructured kinetic model was proposed to describe simultaneously microbial growth, substrates consumption and products formation. A multi‐response nonlinear regression analysis based on Marquardt algorithm combined with a Runge‐Kutta integration method was used to obtain the values of the fitting parameters. CONCLUSIONS: The optimum concentration of glycerol for maximum reuterin and 1,3‐PDL production was 200 mmol L⁻¹. The complete process was satisfactorily described by the kinetic model proposed. Copyright © 2008 Society of Chemical Industry     

Relationship between lipoprotein lipase and high density lipoprotein cholesterol in mice: modulation by cholesteryl ester transfer protein and dietary status

Plasma lipoprotein lipase (LPL) activity correlates with high density lipoprotein (HDL) cholesterol levels in humans. However, in several mouse models created either through transgenesis or targeted inactivation of LPL, no significant changes in HDL cholesterol values have been evident. One possible explanation for this species difference could be the absence of plasma cholesteryl ester transfer protein (CETP) activity in mice. To explore this possibility and further investigate interactions between LPL and CETP modulating HDL cholesterol levels in vivo, we examined the relationship between LPL activity and HDL levels in mice expressing the simian CETP transgene, compared with littermates not carrying the CETP gene. On a chow diet, increasing LPL activity was associated with a trend towards increased HDL levels (51 +/- 29 vs. 31 +/- 4 mg/dL highest vs. lowest tertiles of LPL activity, P = 0.07) in mice expressing CETP, while no such effects were seen in the absence of CETP (65 +/- 12 vs. 61 +/- 15 mg/ dL). Furthermore, in the presence of CETP, a significant positive correlation between LPL activity and HDL cholesterol was evident (r = 0.15, P = 0.006), while in the absence of CETP no such correlation was detected (r = 0.15, P = 0.36), highlighting the interactions between LPL and CETP in vivo. When mice were challenged with a high fat, high carbohydrate diet, strong correlations between LPL activity and HDL cholesterol were seen in both the presence (r = 0.45, P = 0.03) and absence (r = 0.73, P < 0.001) of CETP. Therefore, under altered metabolic contexts, such as those induced by dietary challenge, the relation between LPL activity and HDL cholesterol may also become evident. Here we have shown that both genetic and environmental factors may modulate the association between LPL activity and HDL cholesterol, and provide explanations for the absence of any changes in HDL values in mice either transgenic or with targeted disruption of the LPL gene.