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Eight ring-ditches and several stretches of pit alignment have been excavated between 1981 and 1985, as part of the investigation of an extensive cropmark complex on a gravel terrace in the Upper Severn valley at Four Crosses, northern Powys. Excavation of the ring-ditches, which form part of a more scattered barrow cemetery, has revealed a long and complex pattern of development of barrow types and burial forms in the period between the Middle Neolithic and the Middle Bronze Age. This is compared with the recently published sequence from the neighbouring upland barrow cemetery at Trelystan, and subdivided into four hypothetical phases. There is evidence of activity in the vicinity of some of the sites in the Iron Age, Romano-British, and possibly the early post-Roman period.

Glass bangles are found in southern England and Wales from the mid-first century ad and become common in the north of England and southern Scotland in the late first century, before their numbers decline a century later. British bangles develop at a time of change, as Roman glassmaking practices were introduced across large areas of Britain, and as blown, transparent, colourless and naturally-coloured glassware became increasingly popular. In many communities, however, there was still a demand for strongly coloured opaque glass, including for bangles, and glassworkers devised ways of extending their supplies of opaque coloured glass. This study is based on over one hundred and fifty analyses of bangle fragments from sites in Wales, northern England and southern Scotland, spanning this transitional period. The bangle makers recycled coloured glass from imported vessels, and probably beads and bangle-making waste, to supplement supplies of fresh coloured glass. The novel methods used to modify and extend the coloured glass may derive from pre-Roman bead-making industries, and made use of widely available materials, including smithing hammerscale and possibly plant ashes. The results show the shifting balance of indigenous and Roman influences on different bangle types, depending on when and where they were made, and by whom.

As part of a long-term research project on prehistoric and medieval iron-working sites in northwest Wales, a technique has been developed for processing magnetic survey data to improve the presentation and recognition of the high-amplitude dipolar signals that are characteristic of ironsmelting furnaces. This technique has now been used successfully on some 37 British iron-working sites. High-resolution surveys, on a 10-cm grid, have been made both by caesium magnetometer and fluxgate gradiometer over four prehistoric furnaces and one medieval furnace giving detailed maps of their magnetic signals. Mathematical models of these maps, using multiple dipoles, has given estimates of the directions of total magnetization of the furnaces. Three of the furnaces were also surveyed at subsequent stages of excavation and after the removal of the furnace, giving the background signal. The background signals can then be subtracted from the survey data to give clean residual maps. These are easier to model, giving more reliable results, and they give useful information on the contribution of the different furnace materials to the overall magnetic signals. The corrections required for the influence of induced magnetism and for viscous remanent magnetism are examined. The results are compared with the British archaeomagnetic curve, and with the archaeomagnetic date estimates from three of the furnaces, to assess the value of the modelling technique in giving usable estimates of the date of last firing of the furnaces.

Abstract:The most widely employed industrial process for producing alumina (Bayer process) involves the dissolution of available aluminium hydroxide minerals present in raw bauxite into high temperature sodium hydroxide solutions. On cooling of the solution, or liquor in the industrial vernacular, Al is precipitated from solution in the form of gibbsite (Al(OH) 3 ). In order to optimise the process, a detailed knowledge of factors influencing gibbsite solubility is required, a problem that is confounded by the presence of liquor impurities. In this paper, the use of the Group Method of Data Handling (GMDH) polynomial neural network for developing a gibbsite equilibrium solubility model for Bayer process liquors is discussed. The resulting predictive model appears to correctly incorporate the effects of liquor impurities and is found to offer a level of performance comparable to the most sophisticated phenomenological model presented to date.

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