Material removal investigation in bonnet polishing of CoCr alloy

The manufacture of orthopaedic joint bearings surfaces requires exceptionally high levels of control of not only the surface finish but also the surface form. In the case of hip joints, the form of femoral head should be controlled to within ± 50ìm from a given diameter. It has been shown that a better form control of bearing component could enhance clearances creating the correct volume of lubrication to fill the bearing surface gap and reduce wear particle generation. This element is especially critical for the new generation non-spherical head designs. Bonnet polishing which is used successfully in the area of optics is potentially an excellent finishing process to control the form and finish of artificial joints. In the process of form control polishing an “influence function” which defines the material removal rate is of vital importance in developing a corrective polishing procedure. However, the effects of polishing parameters (such as precess angle, head speed, tool pressure and tool offset) on influence function are not very clear for CoCr alloys. These elements must be assessed if a deterministic polishing process is to be developed. Therefore, it is of paramount importance to understand the contribution of each polishing factors to influence function and consequent part polishing. This study has investigated the effects of polishing parameters on influence function, including geometric size and volumetric material removal rate (MRR). The experimental results indicate that the polishing parameter of precess angle and tool offset affect the geometric size of influence function significantly; the polishing parameter of head speed and tool pressure affect the geometric size of influence function to a lesser degree; the polishing parameter of precess angle, head speed and tool offset affect MRR greatly

Threshold Resummed and Approximate NNLO results for W+W- Pair Production at the LHC

The next-to-leading order (NLO) QCD radiative corrections to W+W- production at hadron colliders are well understood. We combine NLO perturbative QCD calculations with soft-gluon resummation of threshold logarithms to find a next-to-next-to leading logarithmic (NNLL) prediction for the total cross section and the invariant mass distribution at the LHC. We also obtain approximate next-to-next-to-leading order (NNLO) results for the total W+W- cross section at the LHC which includes all contributions from the scale dependent leading singular terms. Our result for the approximate NNLO total cross section is the most precise theoretical prediction available. Uncertainties due to scale variation are shown to be small when the threshold logarithms are included. NNLL threshold resummation increases the W+W- invariant mass distribution by ~ 3-4% in the peak region for both \sqrt{S}=8 and 14 TeV. The NNLL threshold resummed and approximate NNLO cross sections increase the NLO cross section by 0.5-3% for \sqrt{S}=7, 8, 13, and 14 TeV.Comment: 29 pages, 7 figures, 3 tables. Discussion added to introduction, references updated, and typos correcte

Emergence of highly-designable protein-backbone conformations in an off-lattice model

Despite the variety of protein sizes, shapes, and backbone configurations found in nature, the design of novel protein folds remains an open problem. Within simple lattice models it has been shown that all structures are not equally suitable for design. Rather, certain structures are distinguished by unusually high designability: the number of amino-acid sequences for which they represent the unique ground state; sequences associated with such structures possess both robustness to mutation and thermodynamic stability. Here we report that highly designable backbone conformations also emerge in a realistic off-lattice model. The highly designable conformations of a chain of 23 amino acids are identified, and found to be remarkably insensitive to model parameters. While some of these conformations correspond closely to known natural protein folds, such as the zinc finger and the helix-turn-helix motifs, others do not resemble known folds and may be candidates for novel fold design.Comment: 7 figure

Morphology and thermal conductivity of model organic aerogels

The intersection volume of two independent 2-level cut Gaussian random fields is proposed to model the open-cell microstructure of organic aerogels. The experimentally measured X-ray scattering intensity, surface area and solid thermal conductivity of both polymeric and colloidal organic aerogels can be accounted for by the model.Comment: 5 pages. RevTex with 4 encapsulated figures. Higher resolution figures have been submitted for publication. To be published in Phys. Rev. E (Rapid Comm.). email, [email protected]