Dynamic block GMRES: an iterative method for block linear systems

We present variants of the block-GMRES() algorithms due to Vital and the block-LGMRES(,) by Baker, Dennis and Jessup, obtained with replacing the standard QR factorization by a rank-revealing QR factorization in the Arnoldi process. The resulting algorithm allows for dynamic block deflation whenever there is a linear dependency between the Krylov vectors or the convergence of a right-hand-side occurs. implementations of the algorithms were tested on a number of test matrices and the results show that in some cases a substantial reduction of the execution time is obtained. Also a parallel implementation of our variant of the block-GMRES() algorithm, using and was tested on parallel computer, showing good parallel efficiency. This work was carried out while the author was at IM/UFRGS.     

Topochemical acetylation of cellulose nanopaper structures for biocomposites: mechanisms for reduced water vapour sorption

Moisture sorption decreases dimensional stability and mechanical properties of polymer matrix biocomposites based on plant fibers. Cellulose nanofiber reinforcement may offer advantages in this respect. Here, wood-based nanofibrillated cellulose (NFC) and bacterial cellulose (BC) nanopaper structures, with different specific surface area (SSA), ranging from 0.03 to 173.3 m²/g, were topochemically acetylated and characterized by ATR-FTIR, XRD, solid-state CP/MAS ¹³C-NMR and moisture sorption studies. Polymer matrix nanocomposites based on NFC were also prepared as demonstrators. The surface degree of substitution (surface-DS) of the acetylated cellulose nanofibers is a key parameter, which increased with increasing SSA. Successful topochemical acetylation was confirmed and significantly reduced the moisture sorption in nanopaper structures, especially at RH = 53 %. BC nanopaper sorbed less moisture than the NFC counterpart, and mechanisms are discussed. Topochemical NFC nanopaper acetylation can be used to prepare moisture-stable nanocellulose biocomposites.     

Quantum Vacuum Fluctuations in a Chromomagnetic-Like Background

In this paper, we study the effects associated to quantum vacuum fluctuations of vectorial perturbations of the Abelian SU(2) Yang-Mills field in a static and homogeneous chromomagnetic-like background field, at zero temperature. We use periodic and antiperiodic boundary conditions in order to calculate the Casimir energy by means of the frequency sum technique and of the regularization method based on zeta functions, analyzing its behavior in the weak and strong coupling regimes. We compare the obtained results with the similar ones found for scalar and spinor fields placed in an ordinary magnetic field background. We show that only in the weak coupling regime the non-trivial topology of the system encoded in the antiperiodic boundary conditions changes the nature of the Casimir force with respect to the periodic ones. Considering the weak coupling scenario, we show that the introduction of a third polarization state in the perturbations makes manifest the effects on the Casimir energy due to the coupling with the chromomagnetic-like background field, for both the boundary conditions. Finally, in the strong coupling regime, in which the quantum vacuum is not stable due to the Nielsen-Olesen instabilities, we evaluate the effects of a compact extra dimension on its stabilization.     

RP-HPLC method for estimation of sesamin in two Zanthoxylum species

Zanthoxylum naranjillo and Z. tingoassuiba (Rutaceae) are traditional herbal medicines with various biological activities including anti-inflammatory, analgesic, and antimalarial action. In this work, we have developed a simple HPLC-DAD method to quantify sesamin, a bioactive lignan present in Z. naranjillo and Z. tingoassuiba; egonol was the internal standard. According to the developed method, 11.07 ± 1.66, 8.69 ± 0.95, and 15.11 ± 0.72 µg/mL sesamin was present in the ethanol extract of Z. naranjillo leaves, in the methanol extract of Z. naranjillo leaves, and in the methanol extract of Z. tingoassuiba bark, respectively. The limits of detection and quantification were 0.32 and 1.06 µg/mL, respectively. The developed method can be easily applied during routine analysis of sesamin in these medicinal plants.