Preparation and characterization of transition metal-modified lacunary Keggin 11-tungstophosphates supported on carbon

Transition metal-modified lacunary Keggin heteropolycompounds [PW₁₁O₃₉M]⁵⁻, with M = Ni²⁺, Co²⁺, Cu²⁺, or Zn²⁺, were synthesized and characterized. These heteropolycompounds were used to prepare the carbon-supported catalysts. Both the heteropolycompounds and the carbon-supported catalysts showed FT-IR spectra with the characteristic bands of these compounds and provided an indirect measure of the interaction strength between M and the oxygen of the central tetrahedron group of the Keggin structure. The anion decomposition of the modified compounds takes place at equal or lower temperature than that of the bulk and supported parent lacunary [PW₁₁O₃₉]⁷⁻ anion. The species present on the support surface may be highly dispersed as a non-crystalline form, as a result of the interaction with the support surface groups. The activity of the synthesized catalysts in isopropanol dehydration, reflecting their acidity, increases as the reduction temperature of the decomposition products of the heteropolycompounds decreases. It may be assumed that the generation of acid sites is a result of the interaction of hydrogen, donated by isopropanol during its decomposition, with the M cation, leading to M reduction and protons.     

Moisture absorption effects on the thermal and mechanical properties of wood flour/linseed oil resin composites

The thermal and mechanical behavior of new natural polymeric composite materials after exposure to humid environments must be well known and understood in order to predict their performance in final applications. For this reason, composites made from unsaturated polyesters based on linseed oil and filled with wood flour were exposed to environments of different relative humidities and their final properties were measured. In general, the equilibrium moisture content increased as the wood flour percentage increased. Dynamic mechanical tests performed in temperature scan mode were carried out in order to monitor the changes resulting from moisture absorption on the main transition temperature of the matrix (T_α). The temperature of this transition decreased as the amount of absorbed water increased, but the effect was partially reversible by re‐drying the samples. The mechanical properties were also strongly affected by moisture. The flexural modulus and ultimate stress of the composites decreased after equilibration in humid environments. Copyright © 2006 Society of Chemical Industry     

Desaturation of fatty acids inTrypanosoma cruzi

Uptake and metabolism of saturated (16∶0, 18∶0) and unsaturated [18∶1(n−9), 18∶2(n−6), 18∶3(n−3)] fatty acids by cultured epimastigotes ofTrypanosoma cruzi were studied. Between 17.5 and 33.5% of the total radioactivity of [1-¹⁴C]labeled fatty acids initially added to the culture medium was incorporated into the lipids ofT. cruzi and mostly choline and ethanolamine phospholipids. As demonstrated by argentation thin layer chromatography, gas liquid chromatography and ozonolysis of the fatty acids synthesized, exogenous palmitic acid was elongated to stearic acid, and the latter was desaturated to oleic acid and 18∶2 fatty acid. The 18∶2 fatty acid was tentatively identified as linoleic acid with the first bond in the Δ9 position and the second bond toward the terminal methyl end. Exogenous stearic acid was also desaturated to oleic and 18∶2 fatty acid, while oleic acid was only converted into 18∶2. All of the saturated and unsaturated fatty acids investigated were also converted to a small extent (2–4%) into polyunsaturated fatty acids. No radioactive aldehyde methyl ester fragments of less than nine carbon atoms were detected after ozonolysis of any of the fatty acids studied. These results demonstrate the existence of Δ9 and either Δ12 or Δ15 desaturases, or both, inT. cruzi and suggest that Δ6 desaturase or other desaturases of the animal type are likely absent in cultured forms of this organism.     

Hierarchical Learning in Polynomial Support Vector Machines

We study the typical properties of polynomial Support Vector Machines within a Statistical Mechanics approach that takes into account the number of high order features relative to the input space dimension. We analyze the effect of different features' normalizations on the generalization error, for different kinds of learning tasks. If the normalization is adequately selected, hierarchical learning of features of increasing order takes place as a function of the training set size. Otherwise, the performance worsens, and there is no hierarchical learning at all.     

Effect of impregnation on the degree of polymerization of cellulose during bleaching of sodapulped sugar cane bagasse

Samples of sugar cane bagasse pulps, digested at different times without and with previous impregnation, have been bleached and the bleached materials submitted to a detailed study of their degree of polymerization (DP) and the corresponding distributions. The respective results turn out that like in the case of the effect of impregnation on the digestion process, impregnation affects also the bleaching reaction of the digested samples, causing a further remarkable decrease of the degree of polymerization of the cellulose molecules and a deviation of its distribution from the character of a most probable one. The impregnated bleached materials show in addition to the decrease of their DP a certain, albeit slight, diminution in their tensile strength.     

Estimation of potentially available protein in infant starting formulas for term and preterm neonates

Sixteen milk-based starting formulas were analyzed with the aim of calculating their "true protein" content and assessing "in vitro" protein digestibility, in order to estimate levels of potentially available protein. Ten of them were designed for term infants: 7 had a casein:whey protein ratio 40:60 (adapted formulas) and 3 a ratio 80:20 (non-adapted); the 6 remaining formulas (all adapted) were for preterm infants. Nitrogen was determined by the Kjeldahl method. True protein was calculated as (total N--non-protein N) x 6.25. NPN was determined in the soluble fraction, after protein precipitation with 24% trichloroacetic acid and centrifugation. Digestibility was assessed by digestion with pepsin and pancreatin, and defined as the increase in non-protein N after enzymatic digestion. Values for true protein were from 1.3 to 2.3 g/dL and for non protein N, from 4.5 to 13.7%. Digestibility values varied between 59.0 and 92.5%; an inverse trend was observed between protein digestibility and protein content. Considering both the "true protein" levels and their digested proportions, all preterm and 60% of the term formulas would present potentially available amounts below those recommended. These observations constitute an alert, even though this method of assessing "in vitro" protein digestibility represents only an approximation to physiological processes; however, it could be useful in order to evaluate the intensity of the heat treatments to which these formulas were subjected. On the other hand, since NPN allows the estimation of the true protein provided by the formulas, either its percentage or the true protein content could be included on the label.     

Characterization of the Sonar Signals Benchmark

We study the classification of sonar targets first introduced by Gorman & Sejnowski (1988). We discovered that not only the training set and the test set of this benchmark are both linearly separable, although by different hyperplanes, but that the complete set of patterns, training and test patterns together, is also linearly separable. The distances of the patterns to the separating hyperplane determined by learning with the training set alone, and to the one determined by learning the complete data set, are presented.     

Waterborne polyurethane nanocomposites based on vegetable oil and microfibrillated cellulose

This work analyzes the differences in the final properties of two waterborne polyurethanes (WBPU) prepared with two macrodiols of different chemical structure, but similar molecular weight, as well as the variations caused by incorporating low percentages of microfibrillated cellulose nanocrystals. One of the polyurethanes was based on a synthetic but biodegradable precursor (polycaprolactone diol, PCL) and a second one based on a bio‐based macrodiol derived from castor oil (CO1). The bio‐based material presented higher mechanical properties at room temperature than the synthetic one, with the Young's modulus (MPa) ranging from 2.23 ± 0.09 to 84.88 ± 0.96 for the PCL and bio‐based WBPUs, respectively. Additionally, the PCL‐based WBPU showed to be more sensitive to the incorporation of cellulose than the bio‐based WBPU, and it also suffered changes during time due to delayed crystallization. The behavior of the two systems were compared and related to the different structure of the macrodiols that led to different interfacial interactions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44207.     

On the existence of the nonlinear weighted least squares estimate for a three-parameter Weibull distribution

The problem of nonlinear weighted least squares fitting of the three-parameter Weibull distribution to the given data (w_i,t_i,y_i), i=1,…,n, is considered. The part w_i>0 of the data stands for the data weights. It is shown that the best least squares estimate exists provided that the data satisfy just the following two natural conditions: (i) 0<t₁<t₂<?<t_n and (ii) 0<y₁<y₂<?<y_n<1. To support this, an illustrative numerical example is given.