Sporopollenin, the least known yet toughest natural biopolymer

© 2015 Mackenzie, Boa, Diego-Taboada, Atkin and Sathyapalan. Sporopollenin is highly cross-linked polymer composed of carbon, hydrogen, and oxygen that is extraordinarily stable and has been found chemically intact in sedimentary rocks some 500 million years old. It makes up the outer shell (exine) of plant spores and pollen and when extracted it is in the form of an empty exine or microcapsule. The exines resemble the spores and pollen from which they are extracted, in size and morphology. Also, from any one plant such characteristics are incredible uniform. The exines can be used as microcapsules or simply as micron-sized particles due to the variety of functional groups on their surfaces. The loading of a material into the chamber of the exine microcapsule is via multi-directional nano-diameter sized channels. The exines can be filled with a variety of polar and non-polar materials. Enzymes can be encapsulated within the shells and still remain active. In vivo studies in humans have shown that an encapsulated active substance can have a substantially increased bioavailability than if it is taken alone. The sporopollenin exine surface possesses phenolic, alkane, alkene, ketone, lactone, and carboxylic acid groups. Therefore, it can be derivatized in a number of ways, which has given rise to applications in areas, such as solid supported for peptide synthesis, catalysis, and ion-exchange chromatography. Also, the presence of the phenolic groups on sporopollenin endows it with antioxidant activity

A low-order mixed finite element method for a class of quasi-Newtonian Stokes flows. Part I: a priori error analysis

[Abstract] We present a mixed finite element method for a class of non-linear Stokes models arising in quasi-Newtonian fluids. Our results include, as a by-product, a new mixed scheme for the linear Stokes equation. The approach is based on the introduction of both the flux and the tensor gradient of the velocity as further unknowns, which yields a twofold saddle point operator equation as the resulting variational formulation. We prove that the continuous and discrete formulations are well posed, and derive the associated a priori error analysis. The corresponding Galerkin scheme is defined by using piecewise constant functions and Raviart–Thomas spaces of lowest order

A mixed finite element method for the generalized Stokes problem

[Abstract] We present and analyse a new mixed finite element method for the generalized Stokes problem. The approach, which is a natural extension of a previous procedure applied to quasi-Newtonian Stokes flows, is based on the introduction of the flux and the tensor gradient of the velocity as further unknowns. This yields a two-fold saddle point operator equation as the resulting variational formulation. Then, applying a slight generalization of the well known Babuška–Brezzi theory, we prove that the continuous and discrete formulations are well posed, and derive the associated a priori error analysis. In particular, the finite element subspaces providing stability coincide with those employed for the usual Stokes flows except for one of them that needs to be suitably enriched. We also develop an a posteriori error estimate (based on local problems) and propose the associated adaptive algorithm to compute the finite element solutions. Several numerical results illustrate the performance of the method and its capability to localize boundary layers, inner layers, and singularities

Sulfonated sporopollenin as an efficient and recyclable heterogeneous catalyst for dehydration of D-xylose and xylan into furfural

The natural acidity of sporopollenin, the biopolymer coating the outer walls of pollen grains, was enhanced by the sulfonation of its surface. Modified sporopollenin displaying sulfonic acid groups has been prepared, characterized by elemental analysis, SEM, EDX, FTIR and XPS and tested as a heterogeneous catalyst in the dehydration of D-xylose and xylan to produce furfural. The optimal reaction conditions involve 10 wt % of sulfonated sporopollenin in the presence of 1.5 mmol of NaCl in a biphasic water-CPME system. When heated at 190 °C, the reaction affords furfural in a yield of 69% after 40 min under microwave irradiation. The time dependence of the dehydration and influence of temperature, pentose loading and positive effect of chloride ions on the reaction rate are reported. It was found that the catalytic system, recharged with the pentose and solvent, could be recycled ten times without loss of performance. The transformation of xylan into furfural at 190 °C for 50 min gave furfural in a yield of 37%

El jarro de agua o Las gallinas de la tía Marcela : zarzuela para niñas solas, en un acto y en verso

Sólo contiene la letraCopia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

Effect of deforestation and subsequent land use management on soil carbon stocks in the South American Chaco

The subhumid Chaco region of Argentina, originally covered by dry sclerophyll forest, has been subjected to clearing since the end of the 1970s and replacement of the forest by no-till farming. Land use changes produced a decrease in aboveground carbon (C) stored in forests, but little is known about the impact on soil organic C stocks. The aim of this study was to evaluate soil C stocks and C fractions up to 1&thinsp;m depth in soils under different land use:  &lt; 10-year continuous cropping,  &gt; 20-year continuous cropping, warm-season grass pasture and native forest in 32 sites distributed over the Chaco region. The organic C stock content up to 1&thinsp;m depth expressed as equivalent mass varied as follows: forest (119.3&thinsp;Mg&thinsp;ha−1)&thinsp; &gt; &thinsp;pasture (87.9&thinsp;Mg&thinsp;ha−1)&thinsp; &gt; &thinsp;continuous cropping (71.9 and 77.3&thinsp;Mg&thinsp;ha−1), with no impact of the number of years under cropping. The coarse particle fraction (2000–212&thinsp;µm) at 0–5 and 5–20&thinsp;cm depth layers was the most sensitive organic carbon fraction to land use change. Resistant carbon ( &lt; 53&thinsp;µm) was the main organic matter fraction in all sample categories except in the forest. Organic C stock, its quality and its distribution in the profile were responsive to land use change. The conversion of the Chaco forest to crops was associated with a decrease of organic C stock up to 1&thinsp;m depth and with the decrease of the labile fraction. The permanent pastures of warm-season grasses allowed higher C stocks to be sustained than cropping systems and so could be considered a sustainable land use system in terms of soil C preservation. As soil organic C losses were not restricted to the first few centimetres of the soil, the development of models that would allow the estimation of soil organic C changes in depth would be useful to evaluate the impact of land use change on C stocks with greater precision.</p

First record of Biremis circumtexta (Bacillariophyceae) for Tucumán, Argentina

En el presente trabajo se da a conocer el primer registro de Biremis circumtexta (Bacillariophyceae) para Tucumán, Argentina y de datos fisicoquímicos del ambiente lótico estudiado. Se amplía el área de distribución de esta especie para Argentina.This paper presents the first record of Biremis circumtexta (Bacillariophyceae) for Tucumán, Argentina, and the physicochemical data of the studied lotic environment. The range of this species is extended for new areas in Argentina.Fil: Taboada, María de Los Ángeles. Fundacion Miguel Lillo. Direccion de Botanica. Instituto de Ficologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Martínez de Marco, Silvia N.. Fundacion Miguel Lillo. Direccion de Botanica. Instituto de Ficologia; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Instituto de Limnología del Noroeste Argentino; ArgentinaFil: Tracanna, Beatriz Concepcion. Fundacion Miguel Lillo. Direccion de Botanica. Instituto de Ficologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Emissões de N2o de um chernossolo cultivado : o tempo ideal do dia para amostragem e papel da temperatura do solo

1814-1819The correct use of closed field chambers to determine N2O emissions requires defining the time of day that best represents the daily mean N2O flux. A short-term field experiment was carried out on a Mollisol soil, on which annual crops were grown under no-till management in the Pampa Ondulada of Argentina. The N2O emission rates were measured every 3 h for three consecutive days. Fluxes ranged from 62.58 to 145.99 ug N-N2O m-2 h-1 (average of five field chambers) and were negatively related (R2 equal 0.34, p less than 0.01) to topsoil temperature (14 - 20 oC). N2O emission rates measured between 9:00 and 12:00 am presented a high relationship to daily mean N2O flux (R2 equal 0.87, p less than 0.01), showing that, in the study region, sampling in the mornings is preferable for GHG