Linear force and moment equations for an annular smooth shaft seal perturbed both angularly and laterally

Coefficients are derived for equations expressing the lateral force and pitching moments associated with both planar translation and angular perturbations from a nominally centered rotating shaft with respect to a stationary seal. The coefficients for the lowest order and first derivative terms emerge as being significant and are of approximately the same order of magnitude as the fundamental coefficients derived by means of Black's equations. Second derivative, shear perturbation, and entrance coefficient variation effects are adjudged to be small

About the screening of the charge of a proton migrating in a metal

The amount of screening of a proton in a metal, migrating under the influence of an applied electric field, is calculated using different theoretical formulations. First the lowest order screening expression derived by Sham (1975) is evaluated. In addition 'exact' expressions are evaluated which were derived according to different approaches. For a proton in a metal modeled as a jellium the screening appears to be 15 +/- 10 %, which is neither negligible not reconcilable with the controversial full-screening point of view of Bosvieux and Friedel (1962). In reconsidering the theory of electromigration, a new simplified linear-response expression for the driving force is shown to lead to essentially the same result as found by Sorbello (1985), who has used a rather complicated technique. The expressions allow for a reduction such that only the scattering phase shifts of the migrating impurity are required. Finally it is shown that the starting formula for the driving force of Bosvieux and Friedel leads exactly to the zero-temperature limit of well-established linear response descriptions, by which the sting of the controversy has been removed.Comment: 14 pages, 5 figure

Iterative maximum-likelihood reconstruction in quantum homodyne tomography

I propose an iterative expectation maximization algorithm for reconstructing a quantum optical ensemble from a set of balanced homodyne measurements performed on an optical state. The algorithm applies directly to the acquired data, bypassing the intermediate step of calculating marginal distributions. The advantages of the new method are made manifest by comparing it with the traditional inverse Radon transformation technique

Atomic level micromagnetic model of recording media switching at elevated temperatures

An atomic level micromagnetic model of granular recording media is developed and applied to examine external field-induced grain switching at elevated temperatures which captures non-uniform reversal modes. The results are compared with traditional methods which employ the Landau-Lifshitz-Gilbert equations based on uniformly magnetized grains with assigned intrinsic temperature profiles for $M(T)$ and $K(T)$. Using nominal parameters corresponding to high-anisotropy FePt-type media envisioned for Energy Assisted Magnetic Recording, our results demonstrate that atomic-level reversal slightly reduces the field required to switch grains at elevated temperatures, but results in larger fluctuations, when compared to a uniformly magnetized grain model.Comment: 4 pages, 5 figure

Resistivity due to low-symmetrical defects in metals

The impurity resistivity, also known as the residual resistivity, is calculated ab initio using multiple-scattering theory. The mean-free path is calculated by solving the Boltzmann equation iteratively. The resistivity due to low-symmetrical defects, such as an impurity-vacancy pair, is calculated for the FCC host metals Al and Ag and the BCC transition metal V. Commonly, 1/f noise is attributed to the motion of such defects in a diffusion process.Comment: 24 pages in REVTEX-preprint format, 10 Postscript figures. Phys. Rev. B, vol. 57 (1998), accepted for publicatio

Impact of Gold Mining on Soil and some Staple Foods Collected from Selected mining communities in and around Tarkwa-Prestea Area

The principle of neutron activation was used to investigate the presence of toxic elements and possible heavy metals in samples of cassava, plantain and soil from the mining communities in and around Tarkwa in the Western Region of Ghana. The results showed that the maximum concentrations of the respective metals in cassava: plantain: soil samples were arsenic (As = 0.7 ƒÊg/g:0.25 ƒÊg/g:14.35 ƒÊg/g), mercury (Hg = 0.25 ƒÊg/g:0.52 ƒÊg/g:0.09 ƒÊg/g), antimony (Sb = 0.03 ƒÊg/g: 0.03 ƒÊg/g: 2.98 ƒÊg/g ), chromium (Cr = 0.72 ƒÊg/g:3.42 ƒÊg/g:40.35 ƒÊg/g ), vanadium (V = 0.8 ƒÊg/g:0.76 ƒÊg/g:188.40 ƒÊg/g ), zinc (Zn = 38.42 ƒÊg/g:24.92 ƒÊg/g:42.36 ƒÊg/g), and copper (Cu = 66.39 ƒÊg/g: 8.74 ƒÊg/g: 53.46 ƒÊg/g). The concentrations in cassava and plantain were higher than the values proposed by the FAO, the Expert Committee on Food Additives of the WHO and the Agency for Toxic Substance and Disease Registry (ATSDR). The concentrations of Hg (0,09 ƒÊg/g) in soil at Teberebie and of V (188.40ig/g) at the University of Mines and Technology (UMaT) in soil were above the permitted concentrations of 5 ƒÊg/g and 90 ƒÊg/g, respectively. Samples from communities further away from the centres of mine drainages (mile 8., mile 10.) had smaller values of element concentrations. An enrichment factor (EF) analysis for both cassava and plantain were Zn (7%) and Hg (90%). The remaining elements together add up to 3%. The enrichment factor analysis for plantain is greater than that for cassava. Mercury is the element that is chiefly enriched in both cassava and plantain. The second predominant element enriched in cassava and plantain is zinc

Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media

The results of micromagnetic simulations are presented which examine the impact of thermal fluctuations on sweep rate dependent coercivities of both single-layer and exchange-coupled-composite (ECC) perpendicular magnetic recording media. M-H loops are calculated at four temperatures and sweep rates spanning five decades with fields applied normal to the plane and at 45 degrees. The impact of interactions between grains is evaluated. The results indicate a significantly weaker sweep-rate dependence for ECC media suggesting more robustness to long-term thermal effects. Fitting the modeled results to Sharrock-like scaling proposed by Feng and Visscher [J. Appl. Phys. 95, 7043 (2004)] is successful only in the case of single-layer media with the field normal to the plane.Comment: 7 pages, 14 figure