Wear Analysis of Extracted Polyethylene Acetabular Cups Using a 3D Optical Scanner

Wear analysis of total hip replacements (THRs) is considered one of the most relevant research areas helping to improve the longevity and overall design of THRs. The coordinate machine method (CMM) and Fourier profilometry are the most common methods for measuring THR wear. This article presents optical scanner digitalization as a new method for measuring the wear of polyethylene (PE) acetabular cups. The aim of this article is to explore the potential of this method for the PE wear measurements. Optical scans for the purposes of this study were produced using an ATOS Triple Scan 3D optical scanner. The optical scanner is efficient and it can measure a large number of points for polygonization and for further development of the preworn models. In this study, the scanner first generated point clouds on a sample of 13 retrieved ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups. Next, volumetric models of the cups were created by polygonizing the point clouds. Reverse engineering was used to develop models of the original acetabular cups using the geometry of the unworn parts of the retrieved cups. A comparison of the two models then showed the total volume of the PE debris. The optical scanning method was validated against the gravimetric method using three new acetabular cups that were worn out on a hip pendulum simulator. Validation shows that the optical scanning method is a valid method for wear analysis of the retrieved UHMWPE acetabular cups.     

Gas Discharge Lamps for Electrophotographic Exposure

The multitude of uses for lamps in the various steps of the xerographic process are enumerated. Particular emphasis is placed on the use of gas-discharge lamps for exposure, with their requirement of spectral control and adequate radiant power. The characteristics of various types of lamps are considered and the existence of a trouble-some ``power gap' is uncovered. The efficient performance of low-pressure arcs (such as fluorescent and low-pressure sodium lamps) is limited to low powers by electron de-excitation in the presence of self-absorption. On the other hand, high-pressure arc lamps perform efficiently at high powers, but it is difficult to operate these lamps at lower powers in the ``power gap' because of a complex set of interrelated reasons. Lamp designs which may fill this power gap are discussed. The radiant emission from various lamps is considered as well as techniques for manipulating the spectra, particularly the use of metallic halide additives. Overall, a major problem is that commercially available lamps reservice are designed for general illumination purposes while the electrophotographic requirements are different and more demanding.     

Catalytic dehydrogenation of propane over cluster-derived Ir–Sn/SiO2 catalysts

The dehydrogenation of propane was studied in gas-phase at 773 K over two series of silica-deposited Ir–Sn systems: the bimetallic catalysts obtained from Ir–Sn carbonyl clusters precursors and the ones prepared by deposition of a metallorganic Sn precursor onto preformed Ir nanoparticles. In the comparison, cluster-derived catalysts showed good propane conversion, optimal selectivity to propene and high stability under the severe reaction conditions.     

Mechanical properties-structure relationship in blends of polyamide 6 with γ-irradiated LDPE

Blends of γ-irradiated and unirradiated low density polyethylene with polyamide 6 were made in order to study possible modifications induced by this irradiation. Blends with γ-irradiated polyethylene show structure and properties significantly different with respect to blends made with the unirradiated polyethylene. In this paper data on mechanical properties (tensile and impact) of these blends are presented. Results are related to the different morphologies in the blends.     

Gas transport properties of siloxane polyurethanes

Polyurethanes (PUs) were synthesized from toluenediisocyanates (TDIs) and a polymeric diol having polydimethylsiloxane and polyoxyethylene blocks of the ABA type, ended with OH groups. Prepolymers, prepared in toluene solution using ratios [NCO]/[OH] ≥ 2, were crosslinked with triisopropanolamine (TIPA) (ratio [OH]/[NCO] = 1.1) (two-step process). PUs were also obtained with a one-step process using, contemporaneously, TDI, block copolymer, and, as crosslinking agent, TIPA or the glyceride of ε-hydroxyhexanoic acid. Polydimethylsiloxane (PDMSO) was prepared as a reference material. The course of the reaction between block copolymer and TDI was studied by differential scanning calorimetry in the absence and presence of benzoyl chloride (BzCl). Without BzCl, with ratios [NCO]/[OH] > 2, uncontrolled crosslinking side reactions occur. The properties of the PU films obtained with the two methods were studied both for the density of crosslinking and for gas transport properties. The two-step polymers are less crosslinked than the others and are characterized by higher diffusion coefficients and by higher permeability to gases. The permeability order is 10^?9 (N cm³ cm^?1 cm^?1 cm Hg^?1 s^?1) for CH₄, O₂, CO, and N₂ and is 10 times higher for CO₂. The selectivity for the couple O₂/N₂ is higher than that obtained with PDMSO films. Considerable selectivities are shown for the couples CO₂/N₂ and CO₂/CO. © 1995 John Wiley & Sons, Inc.     

Severity assessment issues for short voltage dips

This paper analyzes the impact of the systematic deviations that can be found in the measurements of voltage dips (also called sags) adopting algorithms in agreement with standards as it is commonly done by commercial instruments. This analysis is particularly interesting because the results of dip measurements are utilized for the calculation of severity levels and the assessment of site indexes that are parameters adopted in determination of the quality level of the power supply, but also to develop planning and design criteria for new electrical power grids or to select equipment with proper intrinsic immunity. The paper starts with an insight about dip phenomenon presenting the most important systematic deviations introduced by standard algorithms. Then, the remarkable effects on severity index calculations are presented with particular attention to short dip events. The conditions of non-detection, for dip shorter than 1 cycle, are analytically calculated and a great ambiguity for a dip even shorter than 2 cycles is shown.     

Conductivity and superhydrophobic effect on PFPE-modified porous carbonaceous materials

The thermal decomposition of a linear perfluoropolyether peroxide produced perfluoropolyether radicals that covalently bonded the unsaturated moieties on the surface of carbon black and carbon cloth. Measurements of contact angles demonstrated that water droplets were enduringly stable on the treated materials and that contact angle values were significantly high, exceeding the superhydrophobicity threshold. On the contrary, the droplets were adsorbed in few seconds by the native materials. Conductivity measurements showed that the covalent linkage of fluorinated chains weakly modified the electrical properties of the conductive carbonaceous materials, even if the surface properties changed so deeply. The relationship between the linkage of fluorinated chains and the variations of physical-chemical properties were studied combining X-ray photoelectron spectroscopy, resistivity measurements, scanning electron microscopy and surface area analysis. The modified carbon cloth was also tested out as gas-diffusion layer in a fuel cell and preliminary results were recorded.     

Experimental Evaluation of Conducted Emissions by Variable-Speed Drives Under Variable Operating Conditions

This paper presents an experimental study about the effects that various operating conditions have on conducted emissions by variable-speed drives. The objective of the research is to determine what quantities most significantly affect emissions so that electromagnetic compatibility test procedures can be carried out under the most appropriate conditions according to the specific destination of the equipment under test. The obtained measurements would so match the standard's requirement that they represent the worst case for the disturbance emission levels. A quantitative analysis has been made possible by introducing two indexes with values determined by emissions over the measurement band. The effects of voltage asymmetry and amplitude, motor operating frequency, and torque applied to it have been investigated. Results show a strong dependence on motor operating frequency and torque and that the fluctuations in the measured emissions largely depend on the measurement configuration adopted.     

Effect of silicates on the structure of Ni-containing catalysts obtained from hydrotalcite-type precursors

New nickel hydrotalcite-like compounds with silicates as interlayer anions used as catalyst precursors in the catalytic partial oxidation of methane were prepared by the coprecipitation method. The properties of these materials were compared with those of compounds obtained from carbonate-containing materials. The precursors and calcined samples were characterized by powder X-ray diffraction, FT-IR and Vis/UV/NIR spectroscopies, thermal analyses (DTA and TG), temperature programmed reduction (TPR) and N₂ adsorption/desorption at −196 °C. The results show that the incorporation of silicates in the lamellar compounds modifies the structural and textural properties of the precursors. After calcination, silicates – which are non-volatile anions – contribute to the final structure of the catalysts, which form a new forsterite-like phase, increasing their specific surface area but not altering the reducibility of the nickel species.     

Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)2

The organometallics chemical vapour deposition (OM-CVD) technique, using Rh(acac)(CO)₂ as a precursor, was employed for the preparation of heterogeneous Rh catalysts supported on low surface area refractory oxides (α-Al₂O₃, ZrO₂, MgO and La₂O₃). Prepared systems were tested in the methane catalytic partial oxidation (CH₄-CPO) reaction in a fixed bed reactor and compared to a reference catalyst prepared from impregnation of Rh₄(CO)₁₂.Catalysts supported on Al₂O₃, ZrO₂ and MgO show better or comparable performances with respect to the reference system.Complete decomposition of Rh precursor during formation of the metal phase under reductive conditions was investigated by TPRD and confirmed by infrared and mass spectrometry data.Supported Rh phase was characterized by CO and H₂ chemisorption, CO-DRIFT spectroscopy and HRTEM microscopy in fresh and aged selected samples. Rh(I) isolated sites and Rh(0) metal particles were found on fresh catalysts; after ageing an extensive reconstruction occurs mainly consisting in a sintering of Rh isolate sites to metal particles but without large increase in mean particles size.Catalytic performances and Rh species balance were found to be dependent on the support material.