Like a rolling stone: the mobility of maerl (Corallinaceae) and the neutrality of the associated assemblages

Beds of nonattached coralline algae (maerl or rhodoliths) are widespread and considered relatively species rich. This habitat is generally found in areas where there is chronic physical disturbance such that maerl thalli are frequently moved. Little is known, however, about how natural disturbance regimes affect the species associated with maerl. This study compared the richness, animal abundance, and algal biomass of maerl-associated species over a two-year period in a wave-disturbed bed and a sheltered maerl bed. Changes in associated species over time were assessed for departures from a neutral model in which the dissimilarity between samples reflects random sampling from a common species pool. Algal biomass and species richness at the wave-exposed site and on stabilized maerl at the sheltered site were reduced at times of higher wind speeds. The changes in species richness were not distinguishable from a neutral model, implying that algal species were added at random to the assemblage as the level of disturbance lessened. Results for animal species were more mixed. Although mobile species were less abundant during windy periods at the exposed site, both neutral and non-neutral patterns were evident in the assemblages. Artificial stabilization of maerl had inconsistent effects on the richness of animals but always resulted in more attached algal species. While the results show that the response of a community to disturbance can be neutral, the domain of neutral changes in communities may be relatively small. Alongside non-neutral responses to natural disturbance, artificial stabilization always resulted in an assemblage that was more distinct than would be expected under random sampling from a common pool. Community responses to stabilization treatments did not consistently follow the predictions of the dynamic equilibrium model, the intermediate disturbance model, or a facilitation model. These inconsistencies may reflect site-specific variation in both the disturbance regime and the adjacent habitats that provide source populations for many of the species found associated with maerl.

The pressure distribution along stone columns in soft clay under consolidation and foundation loading

The mechanism whereby foundation loading is transmitted through the column has received little attention from researchers. This paper reports on some interesting findings obtained from a laboratory-based model study in respect of this issue. The model tests were carried out on samples of soft clay, 300 mm in diameter and 400 mm high. The samples were reinforced with fully penetrating stone columns, of three different diameters, made of crushed basalt. Four pressure cells were located along each stone column. The 60 mm diameter footing used in the model was supported on a clay bed reinforced with a stone column and subjected to foundation loading under drained conditions. The results show that the dissipation of excess pore water pressure developed during the initial application of total stresses, when the foundation was subjected to no loading, generated considerable stresses within the column, and that this was directly attributable to the development of negative skin friction. The pressure distributions in the column during foundation loading showed some complex behaviour.

Generation and optimization of electron currents along the walls of a conical target for fast ignition

The interaction of an ultraintense laser pulse with a conical target is studied by means of numerical particle-in-cell simulations in the context of fast ignition. The divergence of the fast electron beam generated at the tip of the cone has been shown to be a crucial parameter for the efficient coupling of the ignition laser pulse to the precompressed fusion pellet. In this paper, we demonstrate that a focused hot electron beam is produced at the cone tip, provided that electron currents flowing along the surfaces of the cone sidewalls are efficiently generated. The influence of various interaction parameters over the formation of these wall currents is investigated. It is found that the strength of the electron flows is enhanced for high laser intensities, low density targets, and steep density gradients inside the cone. The hot electron energy distribution obeys a power law for energies of up to a few MeV, with the addition of a high-energy Maxwellian tail.

Near-surface temperature cycling of stone and its implications for scales of surface deterioration

Many previous studies into internal temperature gradients within stone have assumed smooth, exponential increases and decreases in sub-surface temperatures in response, for example, to diurnal patterns of heating and cooling and these have been used to explain phenomena such as large-scale contour scaling. This high-resolution experimental study, in which a porous limestone block was subjected to alternate surface heating and cooling using an infrared lamp, demonstrates that internal temperature gradients in response to short-term environmental cycles (measured in minutes) can in fact be complex and inconsistent. Results confirm the significance of very steep temperature/stress gradients within the outer 10 mm or less of exposed stone. Below this the data indicate complex patterns of temperature reversals, the amplitudes of which are attenuated with depth and which are influenced in their intensity and location by variations in the relative duration of heating and cooling phases. It is suggested that the reversals might represent ‘interference patterns’ between incoming and outgoing thermal waves, but whatever their origin they are potentially important because they occur within the zone in which many stone decay processes, especially salt weathering, operate. These processes invariably respond to temperature and moisture fluctuations, and short-term interruptions to insolation could, for example, trigger these fluctuations on numerous occasions over a day. In particular, the reversals occur at a scale that is commensurate with decay by multiple flaking and could indicate an underlying control on this previously little-researched pattern of weathering. In the context of this publication, however, the main lesson to be learned from this study is that differing scales of behaviour require different scales of enquiry.

Thin catalytic coatings on microreactor walls A way to make industrial processes more efficient

Current trends in the development of microstructured reactors with thin catalytic films (from 100 nm up to several microns) that have self-assembled nanostructures are discussed. A major technique that is used to prepare such films is sol-gel processing. This involves depositing a complex fluid on a microstructured substrate by dip, spin, or spray coating, followed by surfactant removal to form the porous nanostructures. A novel methodology has been developed by which a uniform coating containing controlled amounts of (poly) metallic nanoparticles can be obtained. This elegant strategy is based on the condensation of metal oxide species by self-assembly in the presence of metallic colloids. The potential microreactor applications brought forth by this innovative protocol are placed in perspective in the light of its versatility.

Building Clouds Drifting Walls:Year One Design Studio: A Critical Appraisal

This is a Booklet about a first year design studio in a school of architecture. It describes and reflects on changes that happened in the course over a three year period starting September 2000. The Studio is made up of students from mainstream architecture, and dual courses with landscape and engineering. The booklet is for those who are thinking of studying architecture. It might also be for those already learning and teaching architecture who want to see how other design studios work.

Determining propeller induced erosion alongside quay walls in harbours using Artificial Neural Networks

In shallow waters, such as those found close to berth structures, the wash from a manoeuvring ship’s propeller can cause erosion of the seabed. This erosion can be increased if the wash intersects a berth structure. A number of researchers have undertaken model studies and used regression analysis to develop predictive relationships for the scouring action. This paper presents an experimental investigation with Artificial Neural Networks (ANN’s), used to analyse the results. The purpose of using ANN’s was to examine the prediction accuracy of the Networks in comparison with previous regression analysis methods. ANN’s were found to provide a more accurate method of predicting propeller wash scour than the equations presented by previous investigators.

The Influence of Aspect on the Biological Colonization of Stone in Northern Ireland.

The rate and type of biological colonization of stone is influenced by a wide array of environmental factors in addition to substrate characteristics. A series of experiments was designed to compare the rate and type of biological colonization of stone at varying locations over a 21-month time period. Exposure
trials were set up at nine different sites across Northern Ireland that covered a wide variety of environmental conditions. To determine aspect-related differences in colonization, blocks of Peakmoor sandstone and Portland limestone were placed on the north- and south-facing sides of purpose-designed exposure racks. Colorimetry and visual analysis were carried out on collected samples at increasing time intervals. Results showed significantly different rates of darkening and greening over time between north-facing and south-facing blocks, for both sandstone and limestone. This difference is likely to be representative of the fact that in Northern Ireland’s wet climate and northern-latitude position, the north face of a building will receive less direct sunlight. Therefore north-facing blocks, once wet, will remain damp for much longer than blocks on other façades. This slow-drying phenomenon is much more hospitable for biological colonization and continued growth than the hostile environment of rapid wetting and drying cycles experienced on the south face.