1,036 research outputs found
Vacuum moulding of a superplastic
The objective of this research is to develop a model for simulating the super-plastic forming process and for predicting the thickness distribution as well the minimum radius of curvature when the material has to fill a sharp corner. Other questions of interest are the deflection of the sheet as a function of pressure for a given mould opening, and the deflection as a function of mould diameter for a given pressure. Modeling based on shell theory is carried out for cylindrical, spherical and arbitrary-shape shells of uniform as well as non-uniform thick- nesses
Full characterisation of a focussed extreme ultraviolet beam using a non-redundant array of apertures
This paper presents a novel technique for characterising wavefront curvature and M2, by utilising a non-redundant array (NRA) of apertures to define the plane of investigation through an experimental extreme ultraviolet (EUV) focus. Appropriately sampled, far-field EUV scattering from this NRA is captured on a CCD as the NRA is scanned along the beam axis through the focus. By taking the inverse Fourier transform (IFT), it is possible obtain the spatial autocorrelation functions, via the Wiener-Khinchin theorem, of the exit wave field. By observing the position of the first-order peaks in the autocorrelation as a function of grid translation, both the real and imaginary parts of the complex beam parameter can be determined and the M2 calculated, yielding full characterisation of the embedded Gaussian. Since the periodicity of the grid is known, the planar pixel resolution can be calculated, also allowing the translations movement to be confirmed due to the change in angular acceptance of the fixed CCD. This makes the technique self-calibrating. A high impact, easy to use, cross field technique for full profiling of the embedded Gaussian of probe beams using a non-redundant array of apertures is presented. The technique is experimentally verified in the highly absorbing EUV spectral regime, and is expected to play a significant role in other regimes, where experimental issues prevent the use of existing techniques
Recommended from our members
Radar studies of the vertical distribution of insects migrating over southern Britain: the influence of temperature inversions on nocturnal layer concentrations
Insects migrating over two sites in southern UK (Malvern in Worcestershire, and Harpenden in Hertfordshire) have been monitored continuously with nutating vertical-looking radars (VLRs) equipped with powerful control and analysis software. These observations make possible, for the first time, a systematic investigation of the vertical distribution of insect aerial density in the atmosphere, over temporal scales ranging from the short (instantaneous vertical profiles updated every 15 min) to the very long (profiles aggregated over whole seasons or even years). In the present paper, an outline is given of some general features of insect stratification as revealed by the radars, followed by a description of occasions during warm nights in the summer months when intense insect layers developed. Some of these nocturnal layers were due to the insects flying preferentially at the top of strong surface temperature inversions, and in other cases, layering was associated with higher-altitude temperature maxima, such as those due to subsidence inversions. The layers were formed from insects of a great variety of sizes, but peaks in the mass distributions pointed to a preponderance of medium-sized noctuid moths on certain occasions
Cyanobacterial Abundance and Microcystin Profiles in Two Southern British Lakes: The Importance of Abiotic and Biotic Interactions.
Freshwater cyanobacteria blooms represent a risk to ecological and human health through induction of anoxia and release of potent toxins; both conditions require water management to mitigate risks. Many cyanobacteria taxa may produce microcystins, a group of toxic cyclic heptapeptides. Understanding the relationships between the abiotic drivers of microcystins and their occurrence would assist in the implementation of targeted, cost-effective solutions to maintain safe drinking and recreational waters. Cyanobacteria and microcystins were measured by flow cytometry and liquid chromatography coupled to tandem mass spectrometry in two interconnected reservoirs varying in age and management regimes, in southern Britain over a 12-month period. Microcystins were detected in both reservoirs, with significantly higher concentrations in the southern lake (maximum concentration >7 µg L-1). Elevated microcystin concentrations were not positively correlated with numbers of cyanobacterial cells, but multiple linear regression analysis suggested temperature and dissolved oxygen explained a significant amount of the variability in microcystin across both reservoirs. The presence of a managed fishery in one lake was associated with decreased microcystin levels, suggestive of top down control on cyanobacterial populations. This study supports the need to develop inclusive, multifactor holistic water management strategies to control cyanobacterial risks in freshwater bodies
Void elimination in screen printed thick film dielectric pastes
The problem is to understand the mechanisms for the formation and evolution of defects in wet screen printed layers. The primary objective is to know how best to alter the properties of the paste (rather than the geometry of the screen printing process itself) in order to eliminate the defects.
With these goals in mind the work done during the Study Group reported here was as follows; to describe a simple model for the closure of craters, a model for the partial closure of vias, a possible mechanism for the formation of pinholes and finally a more detailed consideration of the screen printing process
Self-organised criticality in base-pair breathing in DNA with a defect
We analyse base-pair breathing in a DNA sequence of 12 base-pairs with a
defective base at its centre. We use both all-atom molecular dynamics (MD)
simulations and a system of stochastic differential equations (SDE). In both
cases, Fourier analysis of the trajectories reveals self-organised critical
behaviour in the breathing of base-pairs. The Fourier Transforms (FT) of the
interbase distances show power-law behaviour with gradients close to -1. The
scale-invariant behaviour we have found provides evidence for the view that
base-pair breathing corresponds to the nucleation stage of large-scale DNA
opening (or 'melting') and that this process is a (second-order) phase
transition. Although the random forces in our SDE system were introduced as
white noise, FTs of the displacements exhibit pink noise, as do the
displacements in the AMBER/MD simulations.Comment: 18 pages, 8 figure
Towards a collaborative, global infrastructure for biodiversity assessment
Biodiversity data are rapidly becoming available over the Internet in common formats that promote sharing and exchange. Currently, these data are somewhat problematic, primarily with regard to geographic and taxonomic accuracy, for use in ecological research, natural resources management and conservation decision-making. However, web-based georeferencing tools that utilize best practices and gazetteer databases can be employed to improve geographic data. Taxonomic data quality can be improved through web-enabled valid taxon names databases and services, as well as more efficient mechanisms to return systematic research results and taxonomic misidentification rates back to the biodiversity community. Both of these are under construction. A separate but related challenge will be developing web-based visualization and analysis tools for tracking biodiversity change. Our aim was to discuss how such tools, combined with data of enhanced quality, will help transform today's portals to raw biodiversity data into nexuses of collaborative creation and sharing of biodiversity knowledge
- …