Systematic study of effect of cross-drafts and nozzle diameter on shield gas coverage

A shield gas flow rate of 15–20 L min21 is typically specified in metal inert gas welding, but is often adjusted to as high as 36 L min21 by welders in practice. Not only is this overuse of shield gas wasteful, but uncontrolled high gas flows can lead to significant turbulence induced porosity in the final weld. There is therefore a need to understand and control the minimum shield gas flow rate used in practical welding where cross-drafts may affect the coverage. Very low gas coverage or no shielding leads to porosity and spatter development in the weld region. A systematic study is reported of the weld quality achieved for a range of shield gas flow rates, cross-draft speeds and nozzle diameters using optical visualisation and numerical modelling to determine the shield gas coverage. As a consequence of the study, the shield gas flow has been reduced to 12 L min21 in production welding, representing a significant process cost saving and reduced environmental impact with no compromise to the final weld quality

The Bright and the Dark Side of Malin 1

Malin 1 has long been considered a prototype giant, dark matter dominated Low Surface Brightness galaxy. Two recent studies, one based on a re-analysis of VLA HI observations and the other on an archival Hubble I-band image, throw a new light on this enigmatic galaxy and on its dark/luminous matter properties.Comment: 4 pages, 3 figures, to appear in the Proceedings of the 41st ESLAB Symposium "The Impact of HST on European Astronomy", 29 May to 1 June 2007, ESTEC, Noordwijk, N

MIG gas shielding : Economic savings without detriment to quality

Over the years a number of claims have been made related to potential savings of the shielding gas used in the MIG process. A number of work streams have been set up to consider such areas from a technical and economic standpoint. The use of small helium additions has particular benefits and despite an increase in unit cost, the overriding benefits are achieved in reduced manhour cost. A similar situation has been established when using a high frequency process to switch shielding gases during welding. The outcome from this was very similar to that already described. Overlaid on these has been the increasing use of a technique that visualises actual gas flow during welding by the use of laser backlighting. Some preliminary work in this area is described particularly related to the effect of drafts on the gas distribution. A recent development on the market place is a piece of equipment, which regulates the gas flow automatically and synchronously with the welding current. Gas savings in the region of 50-60% have been obtained. Data has been produced to illustrate these benefits. The potential benefit of developing a computational fluid dynamic model of the gas flow is also described, and early development stages of the model shown. However, there will always exist the very basic management need to minimise leaks from the gas delivery systems

Cross-modality in multi-channel acousmatic music: the physical and virtual in music where there is ‘nothing to see’

Acousmatic music asks for very active listening and is often quite challenging. Allowing for cross-modality enables strong, often physical associations to emerge and potentially affords greater understanding during the work and greater recollection of the work. Composers of acousmatic music are often aware of the need to engage the listener at numerous levels of experience and understanding, creating sounds that tend both towards the superficial and the structural. Acousmatic music in multi-channel formats affords certain degrees of freedom, allowing the listener to more easily prioritise their listening. This freedom potentially affords a more immersive experience making cross-modality easier through the acceptance of a plausible sonic reality no matter how foreign the sound-world

Time dependent neutrino billiards

Quantum dynamica of a massless Dirac particle in time-dependent 1D box and circular billiard with time-dependent radius is studied. An exact analytical wave functions and eigenvalues are obtained for the case of linear time-dependence of the boundary position

Visualisation of alternating shielding gas flow in GTAW

The alternating shielding gas technique is a method of achieving transient arc characteristics during arc welding; however the complex flow that occurs through its use has not been investigated previously. A schlieren system was used to image density gradients that arise when alternating argon and helium shield gases, under varying flow parameters, with gas tungsten arc welding (GTAW). A theoretical analysis was carried out to determine the conditions under which the technique facilitates arc pulsing, in particular to avoid mixing the shield gases in the delivery pipe prior to the welding nozzle. At appropriate pulsing frequency and flow rates, a stable horizontal region of helium was obseved in the weld region, maintained in position by the denser argon from the preceding pulse. This higher than average mass fraction of helium when applying the shielding gases alternately, compare to a premixed gas with the same volume of argon and helium, increased the weld penetration by 13% on average, suggesting a modest improvement in heat transfer

What is the origin of the Scottish populations of the European endemic Cherleria sedoides (Caryophyllaceae)?

Cherleria sedoides L. (Minuartia sedoides (L.) Hiern) is a montane perennial which, with some species in Minuartia sect. Spectabiles, is more closely related to Scleranthus than to other Minuartia species and is therefore best restored to the reinstated and redefined genus Cherleria. Reconstruction of the ancestral area of the clade containing C. sedoides suggests that it evolved in the Alps or the Balkan peninsula. The species now has an unusual distribution, being present in the mountains of southern Europe and Scotland but absent from the Arctic. Three historical scenarios that might have led to the presence of the species in Scotland are outlined and tested by a molecular analysis comparing Scottish populations with populations from the Pyrenees and the Alps. The sampled populations show little variation in internal transcribed spacer (ITS)/external transcribed spacer (ETS) but much more in cpDNA. The latter reveals a major division between some Alpine material and the other Alpine, Pyrenean and Scottish plants. Once the anomalous Alpine haplotypes are excluded, Scottish populations are at least as variable as those from the Alps and Pyrenees, and are closely related to both. We conclude that they have not undergone a long period of isolation, nor have they originated by recent, long-distance dispersal from the Alps or Pyrenees. They appear to be derived from a metapopulation that was probably widespread at the last glacial maximum (LGM) and gave rise to the Alpine, Pyrenean and Scottish plants

Gnathostomiasis: An Emerging Imported Disease

As the scope of international travel expands, an increasing number of travelers are coming into contact with helminthic parasites rarely seen outside the tropics. As a result, the occurrence of Gnathostoma spinigerum infection leading to the clinical syndrome gnathostomiasis is increasing. In areas where Gnathostoma is not endemic, few clinicians are familiar with this disease. To highlight this underdiagnosed parasitic infection, we describe a case series of patients with gnathostomiasis who were treated during a 12-month period at the Hospital for Tropical Diseases, London