Colloidal CdSe quantum dots (QDs) are suitable as electron acceptors in polymer/nanoparticle bulk heterojunction hybrid solar cells. For this application, a thick organic ligand shell which is typically surrounding the QDs after synthesis needs to be removed. Ligand exchange with pyridine is the most widely used method for this purpose. Although this approach is already 15 years old, detailed studies on the effectiveness of ligand exchange with pyridine for solar cell applications are still missing. In the present work hybrid solar cells were prepared from CdSe QDs initially capped with oleic acid (OA), and the impact of single and multiple pyridine treatment was thoroughly investigated. NMR was applied to determine the composition of the ligand shell as well as to distinguish the bound and free ligands before and after ligand exchange. It is shown that after a single pyridine treatment some amount of OA is still present in the samples. By using thermal gravimetric analysis (TGA) we could obtain also quantitative information about the effectiveness of subsequent pyridine treatments. In a series of one-, two-, and threefold ligand exchange, the estimated surface coverage by OA decreased from 26% to 12%, whereas that of pyridine increased from 54% to 80%. Laboratory solar cells with pyridine-capped CdSe QDs and poly(3-hexylthiophene) (P3HT) were characterized by current-voltage (I-V) measurements, and in order to get deeper insight into charge carrier generation and recombination processes, CdSe/P3HT blends were studied by light-induced electron spin resonance (l-ESR). Although repeated pyridine treatment was found to have a beneficial effect in the sense that more complete ligand exchange was achieved, which in turn enabled more efficient charge transfer, the performance of the solar cells was found to be reduced. This fact correlates with increased aggregation tendency of repeatedly pyridine-treated particles, negatively influencing the morphology of the blends, as well as with a larger amount of surface defects in particles stabilized by the weak pyridine ligand shell.

Wear of the modular taper between head and shaft has been related to clinical failure resulting from adverse reactions to metallic debris. The problem has become pronounced in large metal-on-metal bearings, but the mechanism has not yet been fully understood. We analyzed retrieved components from five patients revised with various diagnoses. Two distinct wear patterns were observed for the head tapers. Three samples demonstrated "asymmetric" wear towards the inner end of the head taper. The other two showed "axisymmetric" radial wear (up to 65 mm) presenting the largest wear volumes (up to 20 mm 3 ). Stem tapers demonstrated relatively little wear, and the fine thread on the stem taper surface was observed to be imprinted on the taper inside of the head. Our findings demonstrate that the cobalt-chrome head wears preferentially to the titanium stem taper. "asymmetric" wear suggests toggling due to the offset of the joint force vector from the taper. In contrast, samples with "axisymmetric" radial wear and a threaded imprint suggested that corrosion led to head subsidence onto the stem taper with gradual rotation. The clinical failure of metal-on-metal hip joint replacements has become a major public issue since national registries indicated revision rates more than double those for other bearing material pairs.1 Revisions have been related to metallic debris, which causes a severe soft tissue reaction that can be painful and destructive.2 Such problems first became an issue for resurfacing bearings, where the head was found to wear against the edge of the cup.3-5 Following the introduction of resurfacing components, large modular metal heads were introduced with a taper connection to standard femoral stem implants to provide a revision option after resurfacing failure, leaving the cup in situ. Clinical revision rates for these modular designs were found to be greater than for resurfacing systems. Revision rates at 7 years for resurfacing are 11.8% (95% confidence: 10.8-12.9%) versus 13.6% (95% confidence: 10.9-17.0%) for metal-on-metal in the British Joint Registry,6 suggesting that the taper-lock between head and stem might be the problem.7 Furthermore, higher metal ion levels measured for modular systems than for similar resurfacing systems have been reported 8 and taper corrosion and metallic debris surrounding the taper have been observed during revision procedures. 9,10

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Evaporated films may have different thermal expansion coefficients from their substrates. When the temperature of such a combination is changed, thermal strains are introduced into the film. Calculations of the thermal strains and strain energies for the differently oriented grains in a polycrystalline sample were made. The theoretical results were checked by x-ray diffractometry, using thick gold and copper films bonded to glass substrates by means of thin chromium films. The calculations are useful in investigations of x-ray line shifts, elastic constants, adhesion, and relative grain growth in polycrystalline films formed on cold substrates and annealed.

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