Selective Laser Sintering Preparation and Tribological Testing of Nanostructured Tungsten Carbide-Cobalt Composites

This paper describes the results to date ofresearch done to compare and contrast the tribological properties ofnanostructured tungsten carbide-cobalt composites consolidated by selective laser sintering (SLS) and conventional grain size composites ofthe same chemical composition consolidated by conventional commercial methods. The powder preprocessing and selective laser sintering methods will briefly be described. The tribological testing methods will be discussed, and the tribological properties ofthe selective laser sintered and commercially consolidated materials will be compared. It will be seen that the nanosized WC-Co composites have far superior harness and wear resistance compared to their microsized counterparts.Mechanical Engineerin

Selective Area Laser Deposition - A Method of Solid Freeform Fabrication

Mechanical Engineerin

Recruitment of ethnic minority patients to a cardiac rehabilitation trial: The Birmingham Rehabilitation Uptake Maximisation (BRUM) study [ISRCTN72884263]

Background: Concerns have been raised about low participation rates of people from minority ethnic groups in clinical trials. However, the evidence is unclear as many studies do not report the ethnicity of participants and there is insufficient information about the reasons for ineligibility by ethnic group. Where there are data, there remains the key question as to whether ethnic minorities more likely to be ineligible (e.g. due to language) or decline to participate. We have addressed these questions in relation to the Birmingham Rehabilitation Uptake Maximisation (BRUM) study, a randomized controlled trial (RCT) comparing a home-based with a hospital-based cardiac rehabilitation programme in a multi-ethnic population in the UK. Methods: Analysis of the ethnicity, age and sex of presenting and recruited subjects for a trial of cardiac rehabilitation in the West-Midlands, UK. Participants: 1997 patients presenting post-myocardial infarction, percutaneous transluminal coronary angioplasty or coronary artery bypass graft surgery. Data collected: exclusion rates, reasons for exclusion and reasons for declining to participate in the trial by ethnic group. Results: Significantly more patients of South Asian ethnicity were excluded (52% of 'South Asian' v 36% 'White European' and 36% 'Other', p < 0.001). This difference in eligibility was primarily due to exclusion on the basis of language (i.e. the inability to speak English or Punjabi). Of those eligible, similar proportions were recruited from the different ethnic groups (white, South Asian and other). There was a marked difference in eligibility between people of Indian, Pakistani or Bangladeshi origin

Measurement of ϒ production in pp collisions at √s = 2.76 TeV

The production of ϒ(1S), ϒ(2S) and ϒ(3S) mesons decaying into the dimuon final state is studied with the LHCb detector using a data sample corresponding to an integrated luminosity of 3.3 pb−1 collected in proton–proton collisions at a centre-of-mass energy of √s = 2.76 TeV. The differential production cross-sections times dimuon branching fractions are measured as functions of the ϒ transverse momentum and rapidity, over the ranges pT &#60; 15 GeV/c and 2.0 &#60; y &#60; 4.5. The total cross-sections in this kinematic region, assuming unpolarised production, are measured to be σ (pp → ϒ(1S)X) × B ϒ(1S)→μ+μ− = 1.111 ± 0.043 ± 0.044 nb, σ (pp → ϒ(2S)X) × B ϒ(2S)→μ+μ− = 0.264 ± 0.023 ± 0.011 nb, σ (pp → ϒ(3S)X) × B ϒ(3S)→μ+μ− = 0.159 ± 0.020 ± 0.007 nb, where the first uncertainty is statistical and the second systematic

Laser-based solid freeform fabrication techniques for the direct production of ceramic and metal/ceramic shapes

Materials Science and Engineerin

Embracing the Lag: Real-Time Challenges in Multi-Agent Systems

In this paper, we discuss the interplay between distributed multi-agent systems and the concept of "lag." We introduce a new representation of these systems to more clearly include time and the effects of latency. We also present real-world situations where communication delays can mean the difference between success and failure, between order and chaotic disarray

Joining ceramics and attaching fasteners to ceramics by gas phase selective beam deposition

A process for joining solid compositions, comprising placing a first solid composition having a first joining zone and a second solid composition having a second joining zone in a chamber; positioning a first gas phase, which comprises a substance that decomposes to a material that adheres to the first and second solid compositions during the process, proximate the target area; directing an energy beam to the first and second joining zones to selectively deposit material from the first gas phase on the first joining zone and the second joining zone until a joint is formed between the first and second solid compositions wherein the joint adheres to the first and second compositions at the first and second joining zones. A process useful for attaching a solid fastener to a solid composition, comprising: placing the solid composition in a chamber; positioning a first gas phase, which comprises a substance that decomposes to a material that adheres to the solid composition during the process, proximate the solid composition; directing at least one energy beam to the solid composition to selectively deposit material from the first gas phase on the solid composition to form the solid fastener attached to the solid composition. The invention can also be used to repair solid compositions which contain defects such as chips or cracks or to modify the preexisting shape by localized addition of material from the gas phase.Board of Regents, University of Texas Syste

Method and apparatus for direct use of low pressure vapor from liquid or solid precursors for selected area laser deposition

Methods and apparatus for selectively depositing a layer of material from a gas phase to produce a part comprising a plurality of deposited layers. The apparatus includes a computer controlling a directed energy beam, such as a laser, to direct the laser energy into an unheated chamber substantially containing the gas phase to preferably produce photodecomposition or thermal decomposition of the gas phase and selectively deposit material within the boundaries of the desired cross-sectional regions of the part. At least one component of the gas phase is a vapor which condenses at a temperature above the ambient temperature of the chamber. Each such component can exist at a partial pressure no higher than its equilibrium vapor pressure at the chamber ambient temperature. For each cross section, the aim of the laser beam is scanned over a target area and the beam is switched on to deposit material within the boundaries of the cross-section. Each subsequent layer is joined to the immediately preceding layer to produce a part comprising a plurality of joined layers. A catalytic environment can be created proximate or upon the target area to ensure that initial nucleation and renucleation layers are receptive to substantially rapid and uniform growth of decomposed gas phase material at the target location. The catalyst can be placed on the initial substrate layer and/or upon successive layers as the layers are being deposited on the outer surface of the evolving part.Board of Regents, University of Texas Syste

Synthesis, Selective Laser Sintering and Infiltration of High Super Tc Dual Phase Ag-YBa2Cu307-x Superconductor Composites

Fine, homogeneous dual phase Ag-YBa2Cu307-x composite powders were prepared by a simple colloidal sol-gel co-precipitation technique. Silver did not react with or degrade YBa2Cu307-x. Bulk porous samples of pure YBa2Cu307-x and Ag-YBa2Cu307-x were made from powders by Selective Laser Sintering. The porous parts were further densified by infiltrating silver into pores, resulting in a dense, structurally sound dual phase superconducting composite. Laser processing parameters were varied to obtain optimum microstructure. The laser sintered parts required oxygen annealing after infiltration to restore the orthorhombic, superconducting structure. X-ray diffraction and Tc measurements indicate some impurity phases present in samples processed under aggressive laser conditions.Mechanical Engineerin

NMR/SAXS study of SDS/DDAO dish liquid

NMR/SAXS study of SDS/DDAO dish liqui