Molecular Insight into the Self-Assembly Process of Cellulose Iβ Microfibril

The self-assembly process of β-D-glucose oligomers on the surface of cellulose Iβ microfibril involves crystallization, and this process is analyzed herein, in terms of the length and flexibility of the oligomer chain, by means of molecular dynamics (MD) simulations. The characterization of this process involves the structural relaxation of the oligomer, the recognition of the cellulose I microfibril, and the formation of several hydrogen bonds (HBs). This process is monitored on the basis of the changes in non-bonded energies and the interaction with hydrophilic and hydrophobic crystal faces. The oligomer length is considered a parameter for capturing insight into the energy landscape and its stability in the bound form with the cellulose I microfibril. We notice that the oligomer–microfibril complexes are more stable by increasing the number of hydrogen bond interactions, which is consistent with a gain in electrostatic energy. Our studies highlight the interaction with hydrophilic crystal planes on the microfibril and the acceptor role of the flexible oligomers in HB formation. In addition, we study by MD simulation the interaction between a protofibril and the cellulose I microfibril in solution. In this case, the main interaction consists of the formation of hydrogen bonds between hydrophilic faces, and those HBs involve donor groups in the protofibril.     

Camera characterization for improving color archaeological documentation

Determining the correct color is essential for proper cultural heritage documentation and cataloging. However, the methodology used in most cases limits the results since it is based either on perceptual procedures or on the application of color profiles in digital processing software. The objective of this study is to establish a rigorous procedure, from the colorimetric point of view, for the characterization of cameras, following different polynomial models. Once the camera is characterized, users obtain output images in the sRGB space that is independent of the sensor of the camera. In this article we report on pyColorimetry software that was developed and tested taking into account the recommendations of the Commission Internationale de l'Éclairage (CIE). This software allows users to control the entire digital image processing and the colorimetric data workflow, including the rigorous processing of raw data. We applied the methodology on a picture targeting Levantine rock art motifs in Remigia Cave (Spain) that is considered part of a UNESCO World Heritage Site. Three polynomial models were tested for the transformation between color spaces. The outcomes obtained were satisfactory and promising, especially with RAW files. The best results were obtained with a second‐order polynomial model, achieving residuals below three CIELAB units. We highlight several factors that must be taken into account, such as the geometry of the shot and the light conditions, which are determining factors for the correct characterization of a digital camera.     

Simple and highly sensitive 2-hydroxy-1,4-naphthoquinone/glassy carbon sensor for the electrochemical detection of [Ni(CN)4]2− in metallurgical industry wastewater

Journal of Applied Electrochemistry - The pollution generated by the metallurgical industry effluents represents a serious issue for human health and the environment where the presence of cyanide...     

Water slug injection containing n polymers in porous media

Injection of water containing dissolved chemicals is an efficient oil recovery technique. One of the problems of this method is the loss of the chemical components due to interactions between rock and fluid. In polymer injection, adsorption may happen and lead to low process efficiency. The interaction between rock and fluid is governed by the adsorption isotherm, which relates the polymer concentration in water with the adsorbed amount on the rock. In this paper the problem of oil displacement by a water slug containing n chemical components that may be adsorbed is analyzed. The system of conservation laws is solved and the structure of the solution for the case of Henry's adsorption isotherm is completely described. The concentration profile of each component and the chromatographic cycle is calculated through simple expressions. The complete and detailed solution for the case of slug injection containing three chemical components is presented. The general solution developed can be used to model several Enhanced Oil Recovery techniques, in which the chemical components adsorb in porous media following Henry's adsorption isotherm.     

Combined exposure to ambient UVB radiation and nitrite negatively affects survival of amphibian early life stages

Many aquatic species are sensitive to ambient levels of ultraviolet-B radiation (UVB) and chemical fertilizers. However, recent studies indicate that the interaction among multiple stressors acting simultaneously could be contributing to the population declines of some animal species. Therefore, we tested the potential synergistic effects between ambient levels of UVB and a contaminant, sodium nitrite in the larvae of two amphibian species, the common European toad Bufo bufo and the Iberian green frog Rana perezi. We studied R. perezi from both mountain and coastal populations to examine if populations of the same species varied in their response to stressors in different habitats. Both species were sensitive to the two stressors acting alone, but the interaction between the two stressors caused a multiplicative impact on tadpole survival. For B. bufo, the combination of UVB and nitrite was up to seven times more lethal than mortality for each stressor alone. In a coastal wetland, the combination of UVB and nitrite was four times more toxic for R. perezi than the sum of the effect on mortality for each stressor alone. One mg/L of nitrite killed half the population of R. perezi at Gredos Mountains at day 10 in the absence of UVB. In the presence of UVB, 50% of the tadpoles from the same experiment died at day 7. Similar toxic response were found for R. perezi in two highly contrasted environments suggesting this synergistic interaction can be a widespread phenomenon. The interaction of excess chemical fertilizers and manure with ambient UVB radiation could be contributing to the global decline of some amphibian species. We suggest that potential exposure to UVB radiation be accounted for when assessing water quality criteria regarding nitrite pollution.     

Presence of lactobacilli in the intestinal content of freshwater fish from a river and from a farm with a recirculation system

Lactobacilli are Gram-positive and catalase negative rods commonly found in lactic acid fermented foods and in the gastrointestinal tract of mammals and birds. Few studies have described lactobacilli in freshwater fish. We analysed the presence of lactobacilli in the intestines of young and adult freshwater fish inhabiting a river environment and from fish reared in an aquaculture unit with a water recirculation system. Various species of lactobacilli were present in relatively high number in the intestines of edible fresh water fish from the river, especially in the warm season but in low numbers in the cold season. Lactobacilli were scarcely found in the intestines of edible farmed fish reared in a recirculation system in warm water. Lactobacilli are reported for the first time from the intestines of wild European eel, perch, rudd, ruffe, bleak, silver bream, chub, somnul and farmed African catfish. The two first fishes, and the last one are highly valuable species for fisheries and aquaculture. Additionally, improved methods for storage and bacteriological analysis of fish intestinal content are described. The natural presence of lactic acid bacteria in fish may be of great interest in producing fermented fish products worldwide.     

Thermo and electrochemical characterization of sulfonated PEEK–WC membranes and Krytox-Si-Nafion® composite membranes

Two types of membranes, the sulfonated PEEK-WC (poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxyphenylene)(SPWC) and Krytox-Si-Nafion® (KSiN) composite membranes are proposed for DMFC applications.The properties based on water uptake, ion exchange capacity, proton conductivity, gas permeability, thermal stabilityand methanol crossover are summarized. The comparative studies on SPWC and Nafion® 117 membranes clarify us that the amorphous sulfonated PEEK-WC polymer shows thermal and mechanical stability with less methanol flux and gas permeability. The membrane also exhibits the increase in water uptake, ion exchange capacity and proton conductivity as sulfuric acid doping agent concentration was increased. The KSiN is unique in term of its miscible hybrid structure of silica particles modified with Nafion® structured Krytox 157 FSL chain (KSi) andNafion®. Based on the KSiN membranes with different KSi content, it was found that when KSi content increased, the reduction of gas permeability, methanol crossover and thermal stability are improved. The composite membrane performs the proton conductivity in the wide range of high temperature (60–130°C).     

NMR study of the lipid profile of mullet raw roe and bottarga

Samples of mullet (Mugil cephalus) roes from two different fishing areas were studied by means of ¹H, ¹³C and ³¹P NMR and GC techniques. The lipid fraction of unprocessed roes and that of the corresponding salted and dried commercial products “bottarga” were analyzed and the data compared. Roes of mullets from different origin showed different composition regarding mainly triacylglycerols, monounsaturated and n‐3 polyunsaturated fatty acids. The NMR spectra of processed roes, compared to those of the corresponding raw materials, showed a release of free fatty acids and the formation of other minor molecular components, such as free fatty alcohols, lysophospholipids, and diacylglycerols, thus indicating that hydrolytic processes were the main consequence of manufacturing. An increase of cholesterol ester concentration after processing was also detected. Through the analysis of the ³¹P NMR spectra, it was possible to follow the fate of the phospholipids and the formation of lysophospholipids induced by the salting and drying procedures.     

International convergence and local divergence

This paper presents an East–West endogenous-growth model that reproduces recent stylized facts applicable to the trade liberalization process of many developing countries: convergence with the rest of the world, higher internal divergence, increasing spatial concentration of economic activity and higher growth rates. We claim that the ongoing reduction of manufacturing trade costs may generate a net inflow of global demand towards the industrialized cores of developing countries. This will induce a reallocation of labor from traditional to modern sectors. In turn, such a sectoral shift may enlarge the catch-up (imitation) potential of developing countries and raise global growth rates, due to Grossman and Helpman’s complementarity between imitative and innovative activities. Although advanced economies may become relatively worse off, the effect on growth rates may allow them to gain in absolute terms.