The effects of compression on single and multiphase flow in a model polymer electrolyte membrane fuel cell gas diffusion layer

A two-dimensional study of an idealised fibrous medium representing the gas diffusion layer of a PEMFC is conducted using computational fluid dynamics. Beginning with an isotropic case the medium is compressed uni-directionally to observe the effects on single and multiphase flow. Relations between the compression ratio and the permeability of the medium are deduced and key parameters dictating the changes in flow are elucidated. The main conclusions are that whilst compression reduces the absolute permeability of an isotropic medium, the creation of anisotropic geometry results in preferential liquid water pathways. The most important parameter for capillary flow, in uniformly hydrophobic media, is the minimum fibre spacing normal to the flow path. The effect is less pronounced with decreasing contact angle and non-existent for neutrally wettable media

C-3 branched δ-3,5-cis- and trans-THF sugar amino acids: synthesis of the first generation of branched homooligomers.

This article describes the efficient synthesis of the first generation of branched sugar amino acid (SAA) oligomers in solution phase via two main routes: by the use of a standard coupling reagent and via the use of active ester intermediates. Benzyl-protected dimeric carbopeptoid and methyl-protected dimeric and tetrameric, hexameric and octameric carbopeptoids were obtained from a branched δ-3,5-trans-tetrahydrofuran (THF) SAA and methyl-protected dimeric and tetrameric carbopeptoids were synthesised from a branched δ-3,5-cis-THF SAA. These systems are of interest because of their potential to display foldameric properties reminiscent of those observed in α-peptides and proteins. Amongst their many uses, foldamers provide simpler models in the study of the factors which induce the folding and unfolding of proteins and, ultimately, potential insights into their functioning

Carbon-branched delta-tetrahydrofuran sugar amino acids (SAAs) as dipeptide isostere scaffolds

The synthesis of the first branched sugar amino acid (SAA) scaffolds [methyl (3R,4R,5R)-5-azidomethyl-3,4-dihydroxy-tetrahydrofuran-3-carboxylate and methyl (3R,4R,5S)-5-azidomethyl-3,4-dihydroxy-tetrahydrofuran-3-carboxylate] by an efficient intramolecular displacement of a highly hindered neopentyl triflate allows access to enantiopure THF derivatives which have carbon substituents. © 2008 Elsevier Ltd. All rights reserved

Secondary structure in oligomers of carbohydrate amino acids

Short oligomeric chains of tetrahydrofuran amino acids exhibit a novel repeating β-turn type secondary structure in solution stabilised by hydrogen bonds and provide clear evidence that carbopeptoids will allow control of conformation in peptidomimetics

Isopropyl 6-amino-2,5-anhydro-6-N-(2,5anhydro-6-azido-3,6-dideoxy-L-lyxo-hexonyl)-3,6-dideoxy-L-lyxo-hexonate 2.5-hydrate

The title compound, C15H24N4O7·2.5H2O, was crystallized with great difficulty from an aqueous solution after several months at 278 K. The crystal structure contains two independent mol-ecules in the asymmetric unit, together with five mol-ecules of water. The independent mol-ecules, which have a very similar geometry, are related by a non-crystallographic pseudo-twofold rotation axis approximately perpendicular to the bc plane. Some intra-molecular hydrogen bonds are present in both of the independent mol-ecules. Moreover, the water mol-ecules play a key role in the formation of a hydrogen-bond network. © International Union of Crystallography 2007

Evaluating the likelihood of the adoption of an animal welfare assessment system in European agri-food supply chains

Purpose – The purpose of this paper is to analyse the likelihood of adoption of a recently designed Welfare Assessment System in agri-food supply chains and the factors affecting the adoption decision. The application is carried out for pig and poultry chains. Design/methodology/approach – This research consisted of two main components: interviews with retailers in pig and poultry supply chains in eight different EU countries to explore their perceptions towards the adoption possibilities of the welfare assessment system; and a conjoint analysis designed to evaluate the perceived adoption likelihood of the assessment system by different Standards Formulating Organisations (SFOs). Findings – Stakeholders were found to be especially concerned about the costs of implementation of the system and how it could, or should, be merged with existing assurance schemes. Another conclusion of the study is that the presence of a strong third independent party supporting the implementation of the welfare assessment system would be the most important influence on the decision whether, or not, to adopt it. Originality/value – This research evaluates the adoption possibilities of a novel Welfare Assessment System and presents the views of different supply chain stakeholders on an adoption of such a system. The main factors affecting the adoption decision are identified and analysed. Contrary to expectations, the costs of adoption of a new welfare assessment system were not considered to be the most important factor affecting the decision of supply chain stakeholders about the adoption of this new welfare system