104,846 research outputs found

    Micro milling performance assessment of diamond-like carbon coatings on a micro-end mill

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    This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2013 Institution of Mechanical Engineers.In micro milling, unpredictable tool life and premature tool failures are the major constraints for its industrial applications, and prolongation of the tool life so as to enhance the tooling performance presents great challenges. Appropriate coating techniques potentially offer a feasible and promising solution. In this study, diamond-like carbon films are deposited on a Ø500 ”m diameter tungsten carbide (WC) micro-end mill by the plasma-enhanced chemical vapour deposition process. Coating characterisation has been undertaken and the diamond-like carbon coatings are found in good coverage on the tool except for a slight delaminating on the edge corners. Besides, the surface of the amorphous coatings is much smoother than that of WC. In addition, comprehensive cutting performance of the diamond-like carbon coated tool in dry slot milling of Al 6061-T6 has been compared with those of uncoated tools in both dry and wet conditions. It is observed that the use of diamond-like carbon coatings can reduce the cutting forces, lessen the tool wear, improves the surface roughness and minimise the micro-burr formation as compared to the corresponding performance of an uncoated tool in dry cutting. However, the performance improvement is still unreachable to those resulting from the cutting fluid influence.UK Technology Strategy Board and Kistler UK Ltd

    Collapsing strange quark matter in Vaidya geometry

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    Exact solutions of the gravitational field equations for a mixture of a null charged strange quark fluid and radiation are obtained in a Vaidya space-time. The conditions for the formation of a naked singularity are analyzed by considering the behavior of radial geodesics originating from the central singularity.Comment: 6 pages, no figure

    Constraints on extra-dimensions and variable constants from cosmological gamma ray bursts

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    The observation of the time delay between the soft emission and the high-energy radiation from cosmological gamma ray bursts can be used as an important observational test of multi-dimensional physical theories. The main source of the time delay is the variation of the electromagnetic coupling, due to dimensional reduction, which induces an energy dependence of the speed of light. For photons with energies around 1 TeV, the time delay could range from a few seconds in the case of Kaluza-Klein models to a few days for models with large extra-dimensions. Based on these results we suggest that the detection of the 18-GeV photon ∌ \sim 4500 s after the keV/MeV burst in GRB 940217 provides a strong evidence for the existence of extra-dimensions. The time delay of photons, if observed by the next generation of high energy detectors, like, for example, the SWIFT and GLAST satellite based detectors, or the VERITAS ground-based TeV gamma-ray instrument, could differentiate between the different models with extra-dimensions.Comment: 8 pages, 4 figures, contribution to the proceedings of the II Workshop on Unidentified Gamma-Ray Sources, Hong Kong, June 1-4, 200

    Calculation of Radiative Corrections to E1 matrix elements in the Neutral Alkalis

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    Radiative corrections to E1 matrix elements for ns-np transitions in the alkali metal atoms lithium through francium are evaluated. They are found to be small for the lighter alkalis but significantly larger for the heavier alkalis, and in the case of cesium much larger than the experimental accuracy. The relation of the matrix element calculation to a recent decay rate calculation for hydrogenic ions is discussed, and application of the method to parity nonconservation in cesium is described