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

Analysis of the 3C445 Soft X-ray Spectrum as Observed by Chandra high-energy gratings

We present a detailed analysis of the soft X-ray emission of 3C445 using an archival Chandra HETG spectrum. Highly-ionized H- and He-like Mg, Si and S lines, as well as a resolved low-ionized Si K$\alpha$ line, are detected in the high resolution spectrum. The He-like triplets of Mg and Si are resolved into individual lines, and the calculated R ratios indicate a high density for the emitter. The low values of the G ratios indicate the lines originate from collisionally ionized plasmas. However, the detection of a resolved narrow Ne X RRC feature in the spectrum seems to prefer to a photoionized environment. The spectrum is subsequently modelled with a photoionization model, and the results are compared with that of a collisional model. Through a detailed analysis on the spectrum, we exclude a collisional origin for these emission lines. A one-component photoionization model provides a great fit to the emission features. The best-fit parameters are log$\xi$ = $3.3^{+0.4}_{-0.3}$ erg cm s$^{-1}$, $n_{H}$ = $5^{+15}_{-4.5}\times10^{10}$ cm$^{-3}$ and $N_{H}$ = $2.5^{+3.8}_{-1.7}\times10^{20}$ cm$^{-2}$. According to the calculated high density for the emitter, the measured velocity widths of the emission lines and the inferred the radial distance (6 $\times$ $10^{14}$ - 8 $\times$ $10^{15}$ cm), we suggest the emission lines originating from matter locate in the broad line region (BLR)

Electrostatic patch effects in Casimir force experiments performed in the sphere-plane geometry

Patch potentials arising from the polycrystalline structure of material samples may contribute significantly to measured signals in Casimir force experiments. Most of these experiments are performed in the sphere-plane geometry, yet, up to now all analysis of patch effects has been taken into account using the proximity force approximation which, in essence, treats the sphere as a plane. In this paper we present the exact solution for the electrostatic patch interaction energy in the sphere- plane geometry, and derive exact analytical formulas for the electrostatic patch force and minimizing potential. We perform numerical simulations to analyze the distance dependence of the minimizing potential as a function of patch size, and quantify the sphere-plane patch force for a particular patch layout. Once the patch potentials on both surfaces are measured by dedicated experiments our formulas can be used to exactly quantify the sphere-plane patch force in the particular experimental situation.Comment: 13 pages, 4 figure