3,199 research outputs found
A Modification of Periacetabular Osteotomy Using a Two-Incision Approach
In residual hip dysplasia periacetabular osteotomy (PAO) can improve insufficient coverage of the femoral head. It requires a broad dissection of the pelvic bones and detachment of muscle insertions, however. We have developed a modification of the Bernese periacetabular osteotomy with reduced soft tissue exposure. It uses two small skin incisions and offers therefore the perspective of nicer scars but also increases the risk of technical complications due to impaired vision. To be able to draft these risks, the clinical and radiographic results of 23 patients with PAO through the modified Smith-Petersen approach of Ganz (group A) and 24 patients with our two-incision modification (group B) have been reviewed retrospectively with an average follow-up of 19 (group A) and 12 (group B) months postoperatively
DipoleâQuadrupole and Retardation Effects in LowâEnergy AtomâAtom Scattering
Simple approximation formulas are derived for the dipoleâquadrupole and retardation effects upon the total elastic scattering cross section for atomic collisions in the thermal energy range. For a longârange potential containing both the dipoleâdipole and dipoleâquadrupole terms, i.e., V(r) = â(C(6)/r6)[1+(ÎČ/r2)], one finds ÎQ/QMMââ
Ï(ÎČ/QMM) where QMM is the MasseyâMohr cross section for an inverse sixthâpower attraction. For a longârange potential including dipoleâdipole and retardation effects, approximated by V(r) = â(C(6)/r6)[a/(a+r)], one obtains ÎQ/QMM â â(QMMÂœ)/aÎQâQMMââ(Ïâ32QMM12)âa. Since these deviations are small and opposite in sign, it is concluded that the contributions of the dipoleâquadrupole and retardation effects to the total cross sections are not sufficient to account for any significant discrepancy between theoretical and experimental Q values.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69647/2/JCPSA6-41-5-1431-1.pd
AtomicâBeam Scattering Studies on the LiâHg System: Quantum Effects and Velocity Dependence of the Cross Sections
Measurements of the velocity dependence of the angular intensity distribution of 6Li and 7Li beams scattered by a crossed Hg beam are reported. The Li beams were velocity selected, the Hg beam Maxwellian. Angular intensity distributions were measured at various relative velocities (vr) from 700â1200 m/sec, relative total cross sections (q) from vr=300 to 1350 m/sec. The differential cross sections show expected quantum interferences. Scattering patterns for 6Liâ and 7LiâHg are found to be identical at the same de Broglie wavelength. The overâall angular dependence of the scattering at low angles follows the Ξâ7/3 relationship characteristic of an râ6 longârange potential. Extrema in the total cross sections q(vr) were also observed. The experimental data were analyzed in terms of a LennardâJones (12, 6) potential, but it was not possible to determine a unique set of potential parameters. Comparison of observed and calculated results has yielded three nearly equivalent sets of Ï, Ï” lying within the ranges 2.5â€Ïâ€3.5 Ă
, 480°â€Ï”/kâ€1000°K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69950/2/JCPSA6-42-7-2295-1.pd
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Highly depleted cratonic mantle in West Greenland extending into diamond stability field in the Proterozoic
This study presents electron microprobe data for dunite xenoliths from a lamprophyre dyke located on the island of Qeqertaa, West Greenland. The minimum age of this dyke is Palaeoproterozoic and it experienced amphibolite facies metamorphism and deformation during that era. The samples consist of nearly 200 xenoliths with a size range of 0.5-8 cm. These dunite xenoliths have olivine Mg#, that range from 80.3 to 94.6 (n = 579) with a mean of 92.6. Orthopyroxene is found in three xenoliths and garnet in five others. The latter suggests the depth of the Qeqertaa xenolith suite to be near the diamond stability-field, which is substantiated by the finding of diamonds in bulk samples of the Qeqertaa dyke. This further indicates the presence of a lithospheric mantle domain dominated by high-Mg# dunite to this depth in Palaeoproterozoic time. Cr-rich spinel, in the 0.1â0.2 mm size range, is found within and between olivine grains in individual xenoliths. These Cr-spinels yield FeâMg exchange temperatures of 400â600 °C. However, the presence of intermediate spinel compositions spanning the lower temperature solvus suggests that equilibration temperatures were > 550 °C. Fe3 +#, expressed as 100 Ă Fe3 +/(Fe3 + + Al + Cr), is shown to be a useful parameter in order to screen for altered spinel (Fe3 +# > 10) with disturbed Mg# and Cr#. The screened spinel data (Fe3 +# < 10) show a distinctly different trend in terms of spinel Cr# versus Mg#, compared to unmetamorphosed xenoliths in Tertiary lavas and dikes from Ubekendt Ejland and Wiedemann Fjord, respectively, also located within the North Atlantic craton. This difference likely reflects amphibolite facies metamorphic resetting of the Qeqertaa xenolith suite by FeâMg exchange. Given the similarity of the Qeqertaa xenolith suite with the Ubekendt and Wiedemann suites, in terms of their olivine Mg# and spinel Cr# distribution, high-Mg# dunite is likely to be an important component of the subcontinental lithospheric mantle beneath the North Atlantic craton and appears to have spanned a vertical distance of at least 150 km in this region, even during the Palaeoproterozoic
Peridotite enclaves hosted by Mesoarchaean TTG-suite orthogneisses in the Fiskefjord region of southern West Greenland
AbstractThis study presents bulk-rock major, trace, and platinum-group element data, as well as mineral chemistry for peridotites which form large enclaves (up to 500Ă1000m) within Mesoarchaean orthogneisses of the Akia terrane in the Fiskefjord region, southern West Greenland. The largest peridotite body, known as Seqi, contains highly fosteritic olivine with a median Mg# of 92.6 and hosts extensive layers of chromitite, which can be traced for tens of metres with thicknesses of up to 30cm. Thinner (<100m thick), but extensive (up to 2000m long) peridotite sheets are associated with coarse norite and orthopyroxenite with distinct cumulate textures in the Amikoq complex, located a few tens of kilometres south of Seqi. Intercalated amphibolites of tholeiitic basaltic composition show complementary geochemical evolution to the peridotites, consistent with igneous crystal fractionation trends. The U-shaped trace element patterns of the peridotites may either reflect the parental melt composition from which these olivine-rich rocks were derived, or alternatively this feature may be the result of melt-rock interaction. Overall, we interpret the Fiskefjord region peridotites to have formed as ultramafic cumulates derived from Archaean high-Mg, low Ca/Al magmas, although their geodynamic setting remains to be established
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