1,720,996 research outputs found
Micro and sub-micron surface structuring of AZ31 by laser re-melting and dimpling
Full text linkn this work, the use of ns-pulsed fibre laser for surface structuring of AZ31 Mg alloy is investigated. Surface re-melting was employed to change surface morphology, especially in terms of surface roughness. Dimpling by percussion microdrilling was investigated to control the hole geometry.. With surface remelting mono-directional and homogeneous surfaces were obtained with F-l < 500 J/cm(2). Above 500 J/cm(2) particle generation was observed, which induced sub-micron structure growth with nanofibrous features. Moreover, surface roughness could be controlled below the initial value and much higher. With dimpling, transformation from gentle to strong ablation was observed at F-0=10.3 J/cm(2). XRD analysis was employed to link oxide growth to the surface morphology. Tensile tests were carried out to assess the damage on the mechanical properties after surface structuring. (C) 2015 Elsevier Ltd. All rights reserved
Surface structuring of AZ31 Mg alloy with a laser beam for biodegradable stent applications
No full textIn biomedical applications functional surfaces are becoming accepted due to the advancements and availability of the new manufacturing methods in the industry. Among other methods, the use of a laser beam to structure surfaces is highly advantageous for industrial applications, since it is a highly flexible process generating both deterministic or stochastic patterns. In the case of biomedical applications, surface modifications can be exploited for the control of wetting behaviour, surface passivation and corrosion resistance, as well as control of the surface roughness for improved biocompatibility [1,2]. The proposed study investigates the use of a pulsed laser source operating in ns regime for the structuring of AZ31 Mg alloy, destined to be used on a biodegradable stent platform [3]
Surface structuring of AZ31 Mg alloy with a laser beam for biodegradable stent applications
No full textIn biomedical applications functional surfaces are becoming accepted due to the advancements and availability of the new manufacturing methods in the industry. Among other methods, the use of a laser beam to structure surfaces is highly advantageous for industrial applications, since it is a highly flexible process generating both deterministic or stochastic patterns. In the case of biomedical applications, surface modifications can be exploited for the control of wetting behaviour, surface passivation and corrosion resistance, as well as control of the surface roughness for improved biocompatibility [1,2]. The proposed study investigates the use of a pulsed laser source operating in ns regime for the structuring of AZ31 Mg alloy, destined to be used on a biodegradable stent platform [3]
Laser micro-polishing of stainless steel for antibacterial surface applications
Full text linkIn this work laser micro polishing (LMP) of cold rolled 0.3 mm thick 304 stainless steel with a pulsed fibre laser is studied, for applications
where antibacterial properties are required. Due to its production method, the initial surface roughness of the tested material was considerably
low (Sa=85.3±2.8 μm), rendering a demanding case for the laser polishing process. Accordingly, process feasibility under three different
atmospheric conditions, namely ambient, Ar and N2 atmosphere, was investigated. A large set of process parameter combinations was tested
and initial analysis was carried out to identify the polishing feasibility by inspection under an optical microscope. Once the feasibility window
was determined, a primary characterization was made on selected surfaces for roughness and waviness. Results show that in some process
conditions belonging to the explored feasibility range, surface roughness could be decreased by 50%
VEGF concentrations levels in bovine ovulatori follicles after prostaglandin treatment
No full textThe aim of this study was to evaluate variations in the bovine follicular VEGF concentrations 72 hours after a double prostaglandin synchronisation treatment The experiment was performed on 17 multiparous Italian Friesian dairy cows which were at least 90 days post-calving. The follicular fluid was collected from the dominant follicles under ultrasound guidance. The ratio between the progesterone and estrogen follicular fluid concentrations were used to allow into active and nonactive estrogen follicles. The average VEGF follicular concentrations were significantly different (P<0.05) between the two groups. Moreover, the follicular NEFA levels increased significantly (P<0.01) in the nonestrogen active group, while its IGF-I concentrations were significantly lower (P<0.05). Our data suggest that follicular VEGF and NEFA, as well as IGF-I, may play a key role in bovine follicle growth and could be valuable biochemical markers of oocyte maturation
Interplay between powder catchment efficiency and layer height in self-stabilized laser metal deposition
Full text linkIn laser metal deposition (LMD) the height of the deposited track can vary within and between layers, causing significant deviations during the process evolution. Previous works have shown that in certain conditions a self-stabilizing mechanism occurs, maintaining a regular height growth and a constant standoff distance between the part and the deposition nozzle. Here we analyze the link between the powder catchment efficiency and the deposition height stability. To this purpose, a monitoring system was developed to study the deposition in different process conditions, using inline measurements of the specimen weight in combination with the layer height information obatined with coaxial optical triangulation. An analytical model was used to estimate the deposition efficiency in real-time from the height monitoring and the process parameters, which was verified by the direct mass measurements. The results show that the track height stabilization is associated to a reduction of the powder catchment efficiency, which is governed by the melt pool relative position with respect to the powder cone and the laser beam. For a given set of parameters, the standoff distance can be estimated to achieve the highest powder catchment efficiency and a regular height through the build direction
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
Prototyping of biodegradable flat stents in pure zinc by laser microcutting and chemical etching
Full text linkCardiovascular stents are biomedical devices, which restore normal blood flow in the case of coronary artery obstructions. Biodegradable metals provide the possibility of a less-invasive treatment, where the stent is dissolved in body fluids after remodelling of the artery. Compared to Mg-and Fe-alloys, Zn and its alloys provide optimal corrosion rates as a more recent option. New Zn-alloys are under development and often need to be tested for corrosion and biological properties. However, Zn and its alloys still require further investigation in terms of the production routes involved for stent manufacturing. Especially at a prototyping stage, the extrusion of thin biodegradable tubes is an expensive and difficult process. This work investigates a novel manufacturing route consisting of laser microcutting and chemical etching of pure Zn sheets to develop inflatable devices that can take a tubular form. Initially, laser microcutting parameters were studied to understand the dross formation on a low melting point material. Chemical etching of the material with low corrosion resistance was investigated for the dross removal. Prototype flat stents were produced and expanded using a medical catheter
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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