The coefficient of restitution of different representative types of granules

Gas fluidised beds have many applications in a wide range of industrial sectors and it is important to be able to predict their performance. This requires, for example, a deeper appreciation of the flow of the particles in such systems using both empirical and numerical methods. The coefficient of restitution is an important collisional parameter that is used in some granular flow models in order to predict the velocities and positions of the particles in fluidised beds. The current paper reports experimental data involving the coefficients of restitution of three different representative types of granule viz. melt, wet and binderless granules. They were measured at various impact velocities and the values were compared with those calculated from different theoretical models based on quasi-static contact mechanics. This required knowledge of the Young's moduli and yield stresses, which were measured quasi-statically using diametric compression. The results show that the current theoretical models for the coefficient of restitution explored here lead to either an over- or an under-estimation of the measured values. The melt granules exhibited the greatest values of the coefficient of restitution, Young's modulus and yield stress. The differences in these values were consistent with the nature of the interparticle bonding for each of the three granule types. A new model for the calculation of the coefficient of restitution of granular material was developed that takes account of the work hardening of the granules during impact. Generally, this model provides an improved prediction of the measured values. (c) 2006 Elsevier Ltd. All rights reserved.

THE IMPACT OF GRAZING ON COMMUNITIES OF GROUND-DWELLING SPIDERS (ARANEAE) IN UPLAND VEGETATION TYPES

Adult spider communities were sampled by pitfall trapping over a 24-month period in plots subjected to a range of grazing regimes on five vegetation types on a hill farm in County Antrim, north-east Ireland. Spider community composition was influenced by vegetation type and grazing regime. Variation in the number of individuals and species diversity was also apparent between vegetation types and grazing regime. Plots grazed by all herbivores were characterised by the predominance of species characteristic of disturbed land. Inbye land and areas where grazing had ceased had characteristic coloniser species. The spiders Erigone dentipalpis, Allomengea scopigera and Centromerita bicolor were trapped with greater success in vegetation types where grass species dominated.

Selective extracellular vesicle-mediated export of an overlapping set of microRNAs from multiple cell types

Background: MicroRNAs (miRNAs) are a class of small RNA molecules that regulate expression of specific mRNA targets. They can be released from cells, often encapsulated within extracellular vesicles (EVs), and therefore have the potential to mediate intercellular communication. It has been suggested that certain miRNAs may be selectively exported, although the mechanism has yet to be identified. Manipulation of the miRNA content of EVs will be important for future therapeutic applications. We therefore wished to assess which endogenous miRNAs are enriched in EVs and how effectively an overexpressed miRNA would be exported.

Results: Small RNA libraries from HEK293T cells and vesicles before or after transfection with a vector for miR-146a overexpression were analysed by deep sequencing. A subset of miRNAs was found to be enriched in EVs; pathway analysis of their predicted target genes suggests a potential role in regulation of endocytosis. RT-qPCR in additional cell types and analysis of publicly available data revealed that many of these miRNAs tend to be widely preferentially exported. Whilst overexpressed miR-146a was highly enriched both in transfected cells and their EVs, the cellular:EV ratios of endogenous miRNAs were not grossly altered. MiR-451 was consistently the most highly exported miRNA in many different cell types. Intriguingly, Argonaute2 (Ago2) is required for miR-451 maturation and knock out of Ago2 has been shown to decrease expression of other preferentially exported miRNAs (eg miR-150 and miR-142-3p).

Conclusion: The global expression data provided by deep sequencing confirms that specific miRNAs are enriched in EVs released by HEK293T cells. Observation of similar patterns in a range of cell types suggests that a common mechanism for selective miRNA export may exist.

Iron Age Pastoral Nomadism and Agriculture in the Eastern Eurasian Steppe: Implications from Dental Palaeopathology and Stable Carbon and Nitrogen Isotopes

Iron Age societies of the eastern Eurasian steppe are traditionally viewed as nomadic pastoralists. However, recent archaeological and anthropological research in Kazakhstan has reminded us that pastoralist economies can be highly complex and involve agriculture. This paper explores the nature of the pastoralist economies in two Early Iron Age populations from the burial grounds of Ai-Dai and Aymyrlyg in Southern Siberia. These populations represent two cultural groups of the Scythian World - the Tagar Culture of the Minusinsk Basin and the Uyuk Culture of Tuva. Analysis of dental palaeopathology and carbon and nitrogen stable isotopes suggests that domesticated cereals, particularly millet, and fish formed a major component of the diet of both groups. The findings contribute to the emerging picture of the nuances of Early Iron Age subsistence strategies on the eastern steppe.