Properties and applications of supports for enzyme‐mediated transformations in solid phase synthesis

With the increasing interest in automated synthesis and screening protocols, solid supported chemistry and biochemistry have become attractive technologies. Furthermore, the use of enzymes in solid phase synthesis has opened the route to selective and mild processes. The efficiency of enzymes in transforming substrates that are bound on solid supports is strictly related to the availability of polymers endowed with specific properties, above all permeability to enzymes. This review describes how the recent developments of this rapidly evolving area have made possible novel challenging applications of enzymes in solid phase synthesis. Copyright © 2006 Society of Chemical Industry     

An enhanced beam-theory model of the asymmetric double cantilever beam (ADCB) test for composite laminates

The paper introduces a mechanical model of the asymmetric double cantilever beam (ADCB) test, usable to assess the mixed-mode interlaminar fracture toughness of composite laminates. The laminated specimen is represented as an assembly of sublaminates, each of which is modelled as an elastic beam partly connected to the other by a deformable interface, in turn considered to be a continuous distribution of elastic-brittle springs. Based on Timoshenko’s beam theory, a set of six differential equations, accompanied by suitable boundary conditions, governs the problem. By adopting the interfacial stresses as the main unknowns, the differential problem is solved analytically, and the contributions of the opening and sliding fracture modes are evaluated directly. Moreover, explicit expressions are determined for the interfacial stresses, internal forces, and displacements, as well as for the compliance, energy release rate, and mode-mixity angle. The predictions of the model are to some extent similar to those of analogous mechanical models in the literature and appear in good agreement with both numerical and experimental results.     

The <Emphasis Type="Italic">POINT</Emphasis> approach to represent <Emphasis Type="Italic">now</Emphasis> in bitemporal databases

Most modern database applications involve a significant amount of time dependent data and a significant portion of this data is now-relative. Now-relative data are a natural and meaningful part of every temporal database as well as being the focus of most queries. Previous studies indicate that the choice of the representation of now significantly influences the efficiency of accessing bitemporal data. In this paper we propose and experimentally evaluate a novel approach to represent now that we termed the POINT approach, in which now-relative facts are represented as points on the transaction-time and/or valid-time line. Furthermore, in the POINT approach we propose a logical query transformation that relies on the above representation and on the geometry features of spatial access methods. Such a logical query transformation enables off-the-shelf spatial indexes to be used. We empirically prove that the POINT approach is efficient on now-relative bitemporal data, outperforming the maximum timestamp approach that has been proven to the best approach to now-relative data in the literature, independently of the indexing methodology (B ⁺- tree vs R ^*- tree) being used. Specifically, if spatial indexing is used, the POINT approach outperforms the maximum timestamp approach to the extent of factor more than 10, both in number of disk accesses and CPU usage.     

The Tyndall decarbonisation scenarios—Part I: Development of a backcasting methodology with stakeholder participation

The Tyndall decarbonisation scenarios project has outlined alternative pathways whereby a 60% reduction in CO₂ emissions from 1990 levels by 2050, a goal adopted by the UK Government, can be achieved. This paper, Part I of a two part paper, describes the methodology used to develop the scenarios and outlines the motivations for the project. The study utilised a backcasting approach, applied in three phases. In phase one, a set of credible and consistent end-points that described a substantially decarbonised energy system in 2050 were generated and reviewed by stakeholders. In phase two, pathways were developed to achieve the transition to the desired end-point. The impacts of the scenarios were assessed in phase three, by means of a deliberative multi-criteria assessment framework. The scenarios to emerge from this process are elaborated in Part II, and conclusions drawn in relation to the feasibility of achieving the 60% target.     

Three-reactors chemical looping process for hydrogen production

This paper analyzes a novel process for producing hydrogen from natural gas, based on chemical looping (CL) techniques, allowing for intrinsic capture of carbon dioxide. The core of the process consists of a three-reactors CL system, where iron oxide particles are circulated to: (i) oxidize natural gas (thus providing, after cooling and water condensation, a CO₂ stream ready for sequestration), (ii) reduce steam, to produce hydrogen as the final product of the process, (iii) consume oxygen from an air stream, to sustain the thermal balance of the system.

The process is intrinsically very attractive, because it directly produces hydrogen and CO₂ from natural gas, by means of a process simpler than the conventional technologies with CO₂ capture capabilities. Hence, a significant potential for investment cost reduction can be anticipated.

However, to fully exploit the system potential, an efficient energy recovery from the gaseous streams exiting the reactors must be arranged, taking into account power and steam production needed to support internal consumptions. Therefore, after an introduction clarifying the concept and the scope of the system, as well as its basic chemistry, this paper presents a discussion of two plant configurations, including different integration levels with power production (fired gas turbine (GT) vs. unfired turbocharger) and/or heat recovery steam production methods (also considering steam compression devices). A comparison with “proven technology” plants, based on steam reforming, is also carried out. Due to the lack of reliable estimates of the investment costs for components to be developed from scratch (CL reactors), the analysis is limited to the thermodynamic and technological aspects. Results show, however, that an impressive potential exists for CL systems for hydrogen production, thus deserving substantial R&D activities in the near future.     

Strengthening of Brick Masonry Arches with Externally Bonded Steel Reinforced Composites

The objective of this study is to investigate the efficiency of an innovative technique for strengthening masonry arches, based on the use of high strength steel cords embedded in either an epoxy (steel reinforced polymer) or mortar matrix (steel reinforced grout). Ten prototypes of brickwork arches strengthened by composite laminates were tested under a monotonic vertical load applied at the quarter-span. Load tests were performed to compare the behavior up to collapse of strengthened masonry arches; the influence of the types of reinforcement (steel and carbon fibers) and matrices (epoxy and cementitious), as well as location of the strengthening layer (intrados, extrados, and both) and the presence of anchorage systems has been investigated. The experimental results highlight the enhanced strength of the arches reinforced with steel cords, as well as the role of the mechanical anchoring with regard to the resulting final strength.