1,721,052 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cryogenic machining to enhance surface finish of a biomedical grade ultra-high-molecular weight polyethylene
Full text linkIn recent years, polymeric materials are being used at an increasing rate in the biomedical industry. In particular, Ultra-High-Molecular Weight Polyethylene (UHMWPE), a thermoplastic polymer characterized by high toughness, good chemical stability and self-lubricating properties, is an ideal candidate for the manufacture of bearing implants used in hip or knee replacements. Nevertheless, it is difficult to achieve a good level of surface finish when turning it, because of its high instability at increasing temperature. In the present study, cryogenic machining was applied instead of dry cutting to machine a biomedical grade UHMWPE at different cutting speeds. The surface finish was assessed in terms of surface roughness, crystallinity degree and hardness in correspondence of the surface. To correlate machinability results with the UHMWPE mechanical behaviour, uniaxial tensile tests were performed in a wide range of temperatures. The obtained results showed that the application of cryogenic machining was an efficient mean to increase the surface finish: in fact, smoother and harder surfaces were obtained regardless of the adopted cutting parameters
On the correlation between surface quality and tool wear in micro–milling of pure copper
No full textMicro-milling is a material removal – based manufacturing technique that allows fabrication of three-dimensional features in a direct manner, unlike photolithography which relies on expensive masks to print two-dimensional features onto a substrate. However, the inadequate surface quality of micro-milled features, which could be due to improper selection of process parameters and/or tool wear, can hamper the functionality of products. This is specially critical for soft materials such as commercially pure copper. To preserve the surface integrity of such materials, this study proposes a correlation between tool wear and surface quality when micro-milling commercially pure copper. The experiments included full-immersion cutting with 200 μm micro-endmills with an axial depth of cut of 20 μm. The variation of surface roughness and burr formation with wear progression is also studied. The surface quality was investigated on the basis of the surface roughness and burrs geometrical characteristics, as well as in terms of nano-hardness. For doing that, firstly, different micro-milling parameters, namely the feed per tooth and cutting speed, were applied to manufacture a series of slots on a pure copper workpiece. Then, the best and the worst conditions in terms of surface quality were adopted for the tool wear campaign to find the correlation between the tool wear and surface quality
Wear Behavior of Ti6Al4V Surfaces Functionalized through Ultrasonic Vibration Turning
Full text linkEven if titanium alloys are widely used for biomedical applications, the tendency they show to wear is a matter of concern for their durability. In this research work, Ultrasonic Vibration Turning (UVT) was used to generate texturized surfaces on Ti6Al4V cylinders for improving their wear performances. To prove that, in vitro wear tests were performed, during which the UVT-ed Ti6Al4V cylinders were made to slide against polyethylene disks to replicate a currently used biomedical pair. It was shown that the UVT-ed Ti6Al4V cylinders were characterized by enhanced performances in terms of coefficient of friction and wear rate, which were reduced to 52 and 25%, respectively, compared to polished Ti6Al4V surfaces
Graphene nanoplatelets as additives to MQL for improving tool life in machining Inconel 718 alloy
No full textInconel 718 is widely used in the aerospace sector thanks to its excellent mechanical properties and corrosion resistance. However, these unique characteristics coupled with its low thermal conductivity make Inconel 718 a difficult-to-cut material. To limit the temperature rise within the cutting zone, flooding is conventionally used leading to health risk for operators and environmental impact. The addition of nano-sized particles to the biodegradable oil in Minimum Quantity Lubrication (MQL) to create a mixture called NanoFluid (NF) represents an alternative to flooding. In the present study, Graphene NanoPlatelets (GNPs) were chosen as additives to create NF. Turning trials were performed by spraying NF at different concentrations and flow rates. First, the NF characteristics were studied in terms of viscosity, specific heat capacity, stability and coefficient of friction. Then, the tool wear mechanisms were identified and quantified, and the machined surface finish analyzed at varying cutting length. Finally, on the basis of the experimental findings and the environmental impact of NF, the optimum combination of graphene concentration and flow rate was provided in order to simultaneously accomplish tool life increase and formation of smoother surfaces
On the corrosion, stress corrosion and cytocompatibility performances of ALD TiO2 and ZrO2 coated magnesium alloys
Full text linkMagnesium alloys are increasingly studied as materials for temporary implants. However, their high corrosion rate and susceptibility to corrosion-assisted cracking phenomena, such as stress corrosion cracking (SCC), continue to prevent their mainstream use. Recently, coatings have been considered to provide an effective solution to these issues and researchers have focused their attention on Atomic Layer Deposition (ALD). ALD stands out as a coating technology due to the outstanding film conformality and density achievable, and has shown encouraging preliminary results in terms of reduced corrosion rate and reduced SCC susceptibility. Here, we contribute to the ongoing interest in ALD-coated Mg alloys, providing a comprehensive characterisation of the effect of 100 nm thick ALD TiO2 and ZrO2 coatings on the corrosion behaviour and SCC susceptibility of AZ31 alloy. Moreover, we also investigate the effect of these coatings on the induced biological response. Our results suggest that the ALD coatings can improve the corrosion and SCC resistance of the Mg alloy, with the ZrO2 ALD coating showing the best improvements. We suggest that the different corrosion behaviours are the cause of the cytocompatibility results (only the ZrO2 ALD coating was found to meet the demands for cellular applications). Finally, we leverage on considerations about the coatings’ wettability, electrochemical stability and surface integrity to justify the different results
Libertà di scegliere e libertà di fare nell'Etica di G.E. Moore
No full textIl saggio esamina gli argomenti che G.E. Moore espone nel VI capitolo del suo Ethics a favore della libertà di scelta e ne mostra l'insufficienza, suggerendo una possibilità che Moore non ha preso in considerazione
Large Strain Extrusion Machining under Cryogenic Cooling to Enhance Corrosion Resistance of Magnesium Alloys for Biomedical Applications
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