A review of air-fuel mixing and alternative methods in scramjets and scramjet-like engines.

This paper reviews work on two aspects of scramjet and similar ducted hypersonic propulsion. The first of these is air-fuel mixing techniques - the problem of mixing is considered the most intractable in scramjet design. The second aspect is the use of innovative techniques to supplement mixing or provide an alternative to combustion altogether. The paper outlines the mixing problem and reviews both classic treatments and newer, more innovative, work. In the light of this it also outlines conclusions and points out gaps in current knowledge and areas where more research is needed

Historic rammed earth structures in Spain : construction techniques and a preliminary classification.

Conservation and repair of historic rammed earth sites should only be undertaken if there is a good understanding of the consequences of any intervention technique. Until recently there has been little interest in the characterisation of historic rammed earth construction, yet it is only with this understanding that successful conservation strategies can be adopted. A survey of around 60 historic rammed earth sites in Spain constructed between 967AD and 1837AD has recently been undertaken. While all the sites are built primarily in rammed earth, the construction techniques and state of repair vary greatly. The high density of historic rammed earth structures in the Iberian peninsula is likely due to the Muslim presence there from the 8th century onwards. Initial expansion, a period of civil war and eventual defeat by Christians led to the construction of a large number of fortifications, many constructed in rammed earth. A famous example is the Alhambra at Granada, but there are hundreds of smaller sites throughout Spain. By the end of the 15th century Christians had replaced Muslims through most of Spain, but rammed earth continued to be used in both vernacular and monumental architecture. Examples of historic construction techniques are presented and common features of historic rammed earth construction are identified. A classification is outlined and a clear development of the rammed earth technique is observed

Analysis of Tapial structures for modern use and conservation

Tapial is an ancient form of rammed earth wall construction found in many parts of the world. In medieval Spain, Tapial was used in the construction of some large and complex structures, some many-storied. That these buildings remain standing (many remaining in use) is an indication of the durability of this form of construction, and is perhaps related to the climatic conditions found in central Spain. This paper describes an engineering study into an important structure in the Aragon region, significant parts of which are constructed in medieval Tapial, as well as other forms of construction. The aim of the study is both to improve understanding of the nature of this structure and to provide guidance on methods of preservation and new construction

The Flare-energy Distributions Generated by Kink-unstable Ensembles of Zero-net-current Coronal Loops

It has been proposed that the million degree temperature of the corona is due to the combined effect of barely-detectable energy releases, so called nanoflares, that occur throughout the solar atmosphere. Alas, the nanoflare density and brightness implied by this hypothesis means that conclusive verification is beyond present observational abilities. Nevertheless, we investigate the plausibility of the nanoflare hypothesis by constructing a magnetohydrodynamic (MHD) model that can derive the energy of a nanoflare from the nature of an ideal kink instability. The set of energy-releasing instabilities is captured by an instability threshold for linear kink modes. Each point on the threshold is associated with a unique energy release and so we can predict a distribution of nanoflare energies. When the linear instability threshold is crossed, the instability enters a nonlinear phase as it is driven by current sheet reconnection. As the ensuing flare erupts and declines, the field transitions to a lower energy state, which is modelled by relaxation theory, i.e., helicity is conserved and the ratio of current to field becomes invariant within the loop. We apply the model so that all the loops within an ensemble achieve instability followed by energy-releasing relaxation. The result is a nanoflare energy distribution. Furthermore, we produce different distributions by varying the loop aspect ratio, the nature of the path to instability taken by each loop and also the level of radial expansion that may accompany loop relaxation. The heating rate obtained is just sufficient for coronal heating. In addition, we also show that kink instability cannot be associated with a critical magnetic twist value for every point along the instability threshold

Farmers' occupational health A case of policy set-aside?

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN006433 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Historic rammed earth structures in Spain: construction techniques and a preliminary classification

Conservation and repair of historic rammed earth sites should only be undertaken if there is a good understanding of the consequences of any intervention technique. Until recently there has been little interest in the characterisation of historic rammed earth construction, yet it is only with this understanding that successful conservation strategies can be adopted. A survey of around 60 historic rammed earth sites in Spain constructed between 967AD and 1837AD has recently been undertaken. While all the sites are built primarily in rammed earth, the construction techniques and state of repair vary greatly. The high density of historic rammed earth structures in the Iberian peninsula is likely due to the Muslim presence there from the 8th century onwards. Initial expansion, a period of civil war and eventual defeat by Christians led to the construction of a large number of fortifications, many constructed in rammed earth. A famous example is the Alhambra at Granada, but there are hundreds of smaller sites throughout Spain. By the end of the 15th century Christians had replaced Muslims through most of Spain, but rammed earth continued to be used in both vernacular and monumental architecture. Examples of historic construction techniques are presented and common features of historic rammed earth construction are identified. A classification is outlined and a clear development of the rammed earth technique is observed

Analysis of Tapial structures for modern use and conservation.

Tapial is an ancient form of rammed earth wall construction found in many parts of the world. In medieval Spain, Tapial was used in the construction of some very large and complex structures, some many-storied. That these buildings remain standing (many remaining also in use) is an indication of the durability of this form of construction, and is perhaps related to the climatic conditions found in central Spain. This paper describes an engineering study into an important structure in the Aragon region, significant parts of which are constructed in medieval Tapial, as well as adobe and other forms of construction. The aim of the study is both to improve understanding of the nature of this structure and to provide guidance on methods of preservation and new construction

Analysis of historic rammed earth construction

Rammed earth is a widely used historic building material, found in Mediterranean regions, along the Silk Road, and in parts of the Himalayas. While guidelines exist for the construction of new rammed earth structures, there is very little guidance for the structural analysis of historic structures. A novel approach to the modelling of rammed earth using finite elements is presented. Each rammed earth lift is modelled as two layers, one representing the actual rammed earth and one representing the interface between each rammed earth lift. These layers are both modelled using the Mohr-Coulomb failure criteria, but different strength properties are assigned to each. A rammed earth wall is then built up using a number of these layers. These simulations have been compared with rammed earth test walls constructed in the laboratory and the above technique has been used to model these walls, with a good degree of success