62 research outputs found

    Achieving carbon neutral structures through pure tension: using a fabric formwork to construct rammed earth columns and walls

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    The use of fabric to re-think conventional compressive containment for rammed earth allows the making of compressive structures through tensile means, saving weight, materials costs, and the importation of technology into ‘developing world’ situations. Fabric formwork achieves a permanent architecture that is defined with the most portable of tools. The need to develop a system that is tested and approved in the ‘developed West’ is important as a way of challenging the current stranglehold that the use of cement has on developing nations. To obtain mortgage loans in many situations cement use is a prerequisite by local funders, from urban situations in Botswana to dam relocation programmes in the Punjab, where for example displaced villages are required to build with imported concrete where earthen structures could provide secure and simple architecture that can be self built and affordable. If ‘Western’ methods are available for self-builders, then the perception of earth as ‘poor’ material can be questioned, with a chance that the cement dependent status quo can be challenged. The research programme at the University of East London School of Architecture and the Visual Arts led by Chandler and Keable has developed over 5 years a series of refinements to lighter weight, robust systems for rammed earth construction. This work has received a £10,000 grant to develop the research as a ‘Fabric earthform’ product, but also as a non-profit programme for Southern African states to promote the development of local variants of fabric formed rammed earth construction

    Structural Characterization of the P1+ Intermediate State of the P-Cluster of Nitrogenase

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    Nitrogenase is the enzyme that reduces atmospheric dinitrogen (N2) to ammonia (NH3) in biological systems. It catalyzes a series of single-electron transfers from the donor iron protein (Fe protein) to the molybdenum–iron protein (MoFe protein) that contains the iron–molybdenum cofactor (FeMo-co) sites where N2 is reduced to NH3. The P-cluster in the MoFe protein functions in nitrogenase catalysis as an intermediate electron carrier between the external electron donor, the Fe protein, and the FeMo-co sites of the MoFe protein. Previous work has revealed that the P-cluster undergoes redox-dependent structural changes and that the transition from the all-ferrous resting (PN) state to the two-electron oxidized P2+ state is accompanied by protein serine hydroxyl and backbone amide ligation to iron. In this work, the MoFe protein was poised at defined potentials with redox mediators in an electrochemical cell, and the three distinct structural states of the P-cluster (P2+, P1+, and PN) were characterized by X-ray crystallography and confirmed by computational analysis. These analyses revealed that the three oxidation states differ in coordination, implicating that the P1+ state retains the serine hydroxyl coordination but lacks the backbone amide coordination observed in the P2+ states. These results provide a complete picture of the redox-dependent ligand rearrangements of the three P-cluster redox states

    Deposition of amyloid β in the walls of human leptomeningeal arteries in relation to perivascular drainage pathways in cerebral amyloid angiopathy

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    Deposition of amyloid beta (AB) in the walls of cerebral arteries as cerebral amyloid angiopathy (CAA) suggests an age-related failure of perivascular drainage of soluble A? from the brain. As CAA is associated with Alzheimer's disease and with intracerebral haemorrhage, the present study determines the unique sequence of changes that occur as A? accumulates in artery walls. Paraffin sections of post-mortem human occipital cortex were immunostained for collagen IV, fibronectin, nidogen 2, AB and smooth muscle actin and the immunostaining was analysed using Image J and confocal microscopy. Results showed that nidogen 2 (entactin) increases with age and decreases in CAA. Confocal microscopy revealed stages in the progression of CAA: AB initially deposits in basement membranes in the tunica media, replaces first the smooth muscle cells and then the connective tissue elements to leave artery walls completely or focally replaced by AB. The pattern of development of CAA in the human brain suggests expansion of AB from the basement membranes to progressively replace all tissue elements in the artery wall. Establishing this full picture of the development of CAA is pivotal in understanding the clinical presentation of CAA and for developing therapies to prevent accumulation of AB in artery walls. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock
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