Dolbeault Cohomology for G2-Manifolds

Cocalibrated G₂-manifolds are seven-dimensional Riemannian manifolds with a distinguished 3-form which is coclosed. For such a manifold M, S. Salamon in Riemannian Geometry and Holonomy Groups (Longman, 1989) defined a differential complex related with the G₂-structure of M.In this paper we study the cohomology of this complex;it is treated as an analogue of a Dolbeault cohomologyof complex manifolds. For compact G₂-manifoldswhose holonomy group is a subgroup of G₂ special propertiesare proved. The cohomology of any cocalibrated G₂-nilmanifold \K is also studied.     

Serine versus threonine glycosylation: the methyl group causes a drastic alteration on the carbohydrate orientation and on the surrounding water shell

Different behavior has been observed for the psi torsion angle of the glycosidic linkages of D-GalNAc-Ser and D-GalNAc-Thr motifs, allowing the carbohydrate moiety to adopt a completely different orientation. In addition, the fact that the water pockets found in alpha-D-GalNAc-Thr differ from those obtained for its serine analogue could be related to the different capability that the two model glycopeptides have to structure the surrounding water. This fact could have important biological inferences (i.e., antifreeze activity).     

Organometal additions to alpha-iminoesters: N-alkylation via umpolung

Alpha-iminoesters are useful precursors to substituted alpha-amino acid derivatives and are utilized in a number of organic transformations. As a consequence of the adjacent ester functionality, these imines are more reactive relative to other types of imines. While a significant body of work has focused on nucleophilic additions to the imine carbon (C-alkylation), a second pathway that involves nucleophilic reaction at the nitrogen (N-alkylation) is much less explored. This tutorial review highlights work that has exploited this unusual alpha-iminoester reactivity mode.     

On MDS convolutional codes over $${\mathbb {Z}}_{p^{r}}$$

Maximum distance separable (MDS) convolutional codes are characterized through the property that the free distance meets the generalized Singleton bound. The existence of free MDS convolutional codes over \({\mathbb {Z}}_{p^{r}}\) was recently discovered in Oued and Sole (IEEE Trans Inf Theory 59(11):7305–7313, 2013) via the Hensel lift of a cyclic code. In this paper we further investigate this important class of convolutional codes over \({\mathbb {Z}}_{p^{r}}\) from a new perspective. We introduce the notions of p-standard form and r-optimal parameters to derive a novel upper bound of Singleton type on the free distance. Moreover, we present a constructive method for building general (non necessarily free) MDS convolutional codes over \({\mathbb {Z}}_{p^{r}}\) for any given set of parameters.     

Thermal characterization of anaerobic sludges from wastewater treatments applied to biological generation of H<Subscript>2</Subscript>

A wide variety of organic residues may be used as energy source such as anaerobic sludge from wastewater treatment systems. However, due to inherent differences in composition, the proper characterization of these biomasses is essential to support their reuse through any conversion process. The aim of this study was the employment of thermal analysis techniques (TG/DTG and DTA) to perform the characterization of anaerobic sludges from different wastewater treatment plants (industrial and municipal), which were further applied for biological production of H₂. The different profiles observed through thermal characterization support the application of these residues as inocula, confirming their potential for H₂ production, while demonstrating the main causes for the different yields obtained (mol H₂ mol^?1 sucrose): 0.9 from sludge of brewery industry and 2.0 from sludge of municipal wastewater treatment plant, corresponding to the overall yields of 10.8 and 25%, respectively. These results confirm the versatility of thermal analysis techniques for biomass characterization, focused on its application for power generation. It is urgent to adopt more sustainable and cost-effective solutions for their management, considering a large amount of residues daily generated in both treatment processes addressed; therefore, biohydrogen production by anaerobic digestion may be a promising alternative for the reuse of both residues as it promotes their transformation from costly and potentially polluting waste into clean and renewable energy sources. The development of this anaerobic process is even more attractive in countries as Brazil, where the weather conditions are naturally favorable.     

Biomimetic construction of the tetracyclic ring system of ngouniensine

2-Cyanotetrahydropyridine 9, bearing an indole-2-acetate moiety, was envisaged as a model synthetic equivalent of the dihydropyridinium cations A, which have been proposed as common biogenetic intermediates to both ngouniensine and Strychnos indole alkaloids. Lewis acid-promoted cyclization of the O-silyl ketene acetal derived from 9 led to the ngouniensine-type derivative 11.     

Synthesis and Characterization of Dendronized Polymers

Summary: This research aims at the synthesis of several dendrons with different functional groups on their surface, and their use as functionalizing agents of synthetic polymers. Two principal products were synthesized and characterized: dendronized MDI oligomers and dendronized PMMI. The results of the characterization studies of dendronized polymers demonstrated the influence of the polarity of dendrons and the dendronization pathway on the properties of the final products.