The effect of lift on the wave-making resistance of multi-hull craft

A potential based panel method is presented to estimate the wave-making characteristics of multi-hull craft. In order to simulate the lifting potential flow around the sub-hulls, the method adopts mixed source/doublet distributions on the sub-hulls and their wake surface, while sources are distributed on the main hull and the free surface. In this way, the asymmetric flow characteristics of the sub-hull are properly simulated, i.e., a Kutta condition is satisfied at the trailing edge of the sub-hull. Comparison is made between the numerical and model experimental measurements, and a good correlation has been found. The wave-making characteristics and pressure distributions on the sub-hull predicted by the present method can differ from those based on a distribution of sources alone, especially the pressure distributions at the stern of the sub-hulls

A seakeeping analysis method for an air-lifted vessel

A seakeeping analysis in the frequency domain is presented to predict the motion response of an airlifted vessel (ALV) in waves. The ALV is supported by pressurised air in two separate cushion chambers; the pressure variation in the cushions has a significant effect on the motions of the vessel. The adiabatic gas law is used to couple cushion pressure and the free-surface elevation of water inside the chamber. Attention is focused on the waves generated by the pressure, and a method is presented to compute the corresponding free-surface elevation. New numerical schemes are proposed for calculating the threedimensional free-surface elevation for the four wave numbers. Numerical results of the free-surface elevation, escape area, escape volume and motion responses of the ALV are provided. & 2008 Elsevier Ltd. All rights reserved

The diatom ecology and palaeoecology of shallow lakes subject to eutrophication: three examples from the English midlands

Lowland England abounds with shallow lakes subject to different levels of eutrophication. In the absence of long-term water chemistry records, palaeolimnology provides an alternative means of assessing the onset and extent of the nutrient enrichment process at a site. The diatoms preserved in lake sediments are extremely sensitive indicators of both past nutrient levels and of eutrophication-related changes in macrophyte-phytoplankton interactions. However the success of diatom-based palaeoecology depends upon a sound knowledge of the taxonomy, environmental requirements, and taphonomy of contemporary diatom communities. This thesis has focused on aspects of the diatom ecology, taphonomy and palaeolecology of three, small (<22 ha.), shallow (<3 m), alkaline lakes of contrasting nutrient and macrophyte status in the English Midlands. These lakes, Tween and Clifton Ponds and Groby Pool, were monitored on a monthly basis (Jan-Oct) for key water chemistry parameters. At the same time samples were collected from the diatom plankton and periphyton and in turn compared with the diatom assemblages which accumulated in sediment traps and at the sediment surface. The small centric diatoms that were found in these lakes were initially difficult to identify using the light microscope (LM), and a scanning electron microscope (SEM) study of the 'problematic' forms revealed considerable ecophenotypic and life-cycle related morphological plasticity. However with careful LM analysis it was possible to confidently distinguish between the different species in the samples. The ecological studies revealed strong associations between the presence or absence of submerged macrophytes and the seasonality and relative competitiveness of planktonic and periphytic diatom species. The relationship between the present-day diatom communities and the diatoms found in the traps and surface sediments of the lakes was relatively good, although there were some problems related to the dissolution of delicate forms. The timing of surface sediment sampling was found to be a critical factor affecting the sedimentary representation of species associated with different periods of the year. The eutrophication histories of Tween Pond (approx. last 30 yrs) and Groby Pool (approx. last 250 yrs) were inferred by comparing the fossil diatom record with the available historical records of lake disturbance, changing catchment land-use and submerged plant communities. The available modern data were used to assist in this process and using a simple life-form based approach it was possible to reconstruct past changes in the relative competitiveness of phytoplankton and submerged plants in both lakes. In Tween Pond the diatom stratigraphy clearly traced the dramatic increase in nutrient loading and the loss of submerged plants from the lake following the diversion of the Erewash in 1972. Similarly, in Groby Pool it was possible to identify the much slower transition- from a mesotrophic, diverse plant dominated state to a eutrophic, tall plant dominated situation. The implications of this study are discussed in relation to modern numerical methods of reconstructing past nutrient loading

Will I? won't I? Why do men who have sex with men present for post-exposure prophylaxis for sexual exposures?

Background: Failures of post-exposure prophylaxis following sexual exposure (PEPSE) to prevent seroconversion have been reported and are often associated with ongoing risk exposure. Understanding why men who have sex with men (MSM) access PEPSE on some occasions and not others may lead to more effective health promotion and disease prevention strategies Methods: A qualitative study design using semi-structured interviews of 15 MSM within 6 months of them initiating PEPSE treatment at an HIV outpatient service in Brighton, UK. Results: PEPSE seeking was motivated by a number of factors: an episode that related to a particular sexual partner and their behaviour; the characteristics of the venue where the risk occurred; the respondent’s state of mind and influences of alcohol and recreational drug use; and their perceived beliefs on the effectiveness of PEPSE. Help was sought in the light of a “one-off” or “unusual” event. Many respondents felt they were less likely to behave in a risky manner following PEPSE. Conclusion: If PEPSE is to be effective as a public health measure, at risk individuals need to be empowered to make improved risk calculations from an increased perception that they could be exposed to HIV if they continue their current behaviour patterns. The concern is that PEPSE was sought by a low number of MSM implying that a greater number are not using the service based on failure to make accurate risk calculations or recognise high-risk scenario

The role of tree size in the leafing phenology of a seasonally dry tropical forest in Belize, Central America

Leafing phenology of two dry-forest sites on soils of different depth (S = shallow, D = deep) at Shipstern Reserve, Belize, were compared at the start of the rainy season (April-June 2000). Trees ≥ 2.5 cm dbh were recorded weekly for 8 wk in three 0.04-ha plots per site. Ten species were analysed individually for their phenological patterns, of which the three most common were Bursera simaruba, Metopium brownei and Jatropha gaumeri. Trees were divided into those in the canopy (> 10 cm dbh) and the subcanopy (≤ 10 cm dbh). Site S had larger trees on average than site D. The proportion of trees flushing leaves at any one time was generally higher in site S than in site D, for both canopy and subcanopy trees. Leaf flush started 2 wk earlier in site S than site D for subcanopy trees, but only 0.5 wk earlier for the canopy trees. Leaf flush duration was 1.5 wk longer in site S than site D. Large trees in the subcanopy flushed leaves earlier than small ones at both sites but in the canopy just at site D. Large trees flushed leaves earlier than small ones in three species and small trees flushed leaves more rapidly in two species. Bursera and Jatropha followed the general trends but Metopium, with larger trees in site D than site S, showed the converse with onset of flushing I wk earlier in site D than site S. Differences in response of the canopy and subcanopy trees on each site can be accounted for by the predominance of spring-flushing or stem-succulent species in site S and a tendency for evergreen species to occur in site D. Early flushing of relatively larger trees in site D most likely requires access to deeper soil water reserves but small and large trees utilize stored tree water in site S

Reconsidering obstetric death and female fertility in Anglo-Saxon England

Little has been written about female fertility and maternal mortality from an archaeological perspective. Typically debates focus on the physical aspects of childbirth, ignoring an obvious truth: the biggest single cause of death for women was childbirth. Whether death took place as a result of mechanical malpresentation, infection or blood loss, the root cause was undeniable. In this article we argue that post-mortem extrusion is improbable and that young infants and women found buried together are likely to have died together. However, most deaths would not have been simultaneous and so we build on demographic data to conclude that the early Anglo-Saxons engaged institutions which controlled female sexuality. Late marriage, cultural and legal taboos and an emphasis on mature fertility acted to limit the probability of death; however, the risk to the individual was real and each funerary party was the agent that constructed death ways to manage loss

Links between soil microbial communities and plant traits in a species-rich grassland under long-term climate change

Climate change can influence soil microorganisms directly by altering their growth and activity but also indirectly via effects on the vegetation, which modifies the availability of resources. Direct impacts of climate change on soil microorganisms can occur rapidly, whereas indirect effects mediated by shifts in plant community composition are not immediately apparent and likely to increase over time. We used molecular fingerprinting of bacterial and fungal communities in the soil to investigate the effects of 17 years of temperature and rainfall manipulations in a species‐rich grassland near Buxton, UK. We compared shifts in microbial community structure to changes in plant species composition and key plant traits across 78 microsites within plots subjected to winter heating, rainfall supplementation, or summer drought. We observed marked shifts in soil fungal and bacterial community structure in response to chronic summer drought. Importantly, although dominant microbial taxa were largely unaffected by drought, there were substantial changes in the abundances of subordinate fungal and bacterial taxa. In contrast to short‐term studies that report high resistance of soil fungi to drought, we observed substantial losses of fungal taxa in the summer drought treatments. There was moderate concordance between soil microbial communities and plant species composition within microsites. Vector fitting of community‐weighted mean plant traits to ordinations of soil bacterial and fungal communities showed that shifts in soil microbial community structure were related to plant traits representing the quality of resources available to soil microorganisms: the construction cost of leaf material, foliar carbon‐to‐nitrogen ratios, and leaf dry matter content. Thus, our study provides evidence that climate change could affect soil microbial communities indirectly via changes in plant inputs and highlights the importance of considering long‐term climate change effects, especially in nutrient‐poor systems with slow‐growing vegetation

Peer review and citation data in predicting university rankings, a large-scale analysis

Most Performance-based Research Funding Systems (PRFS) draw on peer review and bibliometric indicators, two different method- ologies which are sometimes combined. A common argument against the use of indicators in such research evaluation exercises is their low corre- lation at the article level with peer review judgments. In this study, we analyse 191,000 papers from 154 higher education institutes which were peer reviewed in a national research evaluation exercise. We combine these data with 6.95 million citations to the original papers. We show that when citation-based indicators are applied at the institutional or departmental level, rather than at the level of individual papers, surpris- ingly large correlations with peer review judgments can be observed, up to r <= 0.802, n = 37, p < 0.001 for some disciplines. In our evaluation of ranking prediction performance based on citation data, we show we can reduce the mean rank prediction error by 25% compared to previous work. This suggests that citation-based indicators are sufficiently aligned with peer review results at the institutional level to be used to lessen the overall burden of peer review on national evaluation exercises leading to considerable cost savings

Priorities for International Forest Research

The world is moving towards knowledge-based societies. Economies are globalizing. The global public goods value of forests is being recognised at the same time that the traditional role of state forest agencies in production forestry is being taken over by multi-national corporations. At the same time emerging technologies are greatly enhancing our ability to assess and monitor forest attributes, process and disseminate information, and enhance forest production. All of these changes will have an impact on how forest research is organized, who does it, and who pays for it. It seems inevitable that much traditional forestry research concerned with sustainability and productivity enhancement at the stand level, will be taken over by the private sector. However, there is going to be a major challenge in finding resources for research in support of the public goods values of forests at both the local, national and global levels. There is a widely held view that we are in the midst of a world forest crisis. It is not a crisis of declining production but one of erosion of public goods, environmental values of forests. So far, we have not seen a concerted scientific response to this crisis. The Inter-Governmental Panel on Forests (IPF) has given us the mandate to orchestrate such a response and the World Forestry Congress is a valuable opportunity to provide impetus to a new vision of forest science for the 21st century

Mission possible: diatoms can be used to infer past duckweed (lemnoid Araceae) dominance in ponds

Compared to larger lakes, ponds have rarely been the focus of palaeoecological studies. A common feature of ponds, especially those subject to eutrophication, is mass surface coverings of lemnoid Araceae (duckweed) which have severe implications for ecological processes in small waterbodies, in particular lowered oxygen content. To help understand the implications of duckweed dominance for the long-term ecology of ponds, and to determine the potential for palaeoecological studies in ponds more generally, we develop a new diatom-based Lemna-indicator metric. Recent studies of diatom host-plant relationships have shown significant associations between duckweed and the epiphytes Lemnicola hungarica and Sellaphora saugerresii (formally known as Sellaphora seminulum). To determine the potential of these species as palaeo-indicators of long-term duckweed dynamics in ponds, we investigated the diatom composition of surface sediment assemblages in sets of duckweed and non-duckweed-dominated ponds in Norfolk, eastern England. In addition, we undertook diatom analysis of two cores from a small farmland pond (Bodham Rail Pit) subject to a known duckweed dominance event (1999–2005). Both L. hungarica and S. saugerresii were significant predictors of past Lemna dominance in the surface sediments. Further, in the core study, both diatom species accurately and closely tracked the documented “on–off” duckweed cycle. Our study suggests huge potential for using ponds in palaeoecological studies and for diatom-based investigations of floating plant histories