1,721,056 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
Corrosione galvanica di diversi tipi di amalgami in contatto con una lega aurea
No full textIl contatto galvanico tra due metalli dove il catodo è più grande dell'anodo porta ad un incremento della corrosione di quest'ultimo. In questo lavoro si presentano gli andamenti delle correnti galvaniche generate da amalgami e leghe auree per protesi posti a contatto per lunghi periodi in saliva artificial
Dental casting alloys : in vitro tarnish and corrosion
No full textFive dental alloys of various noble metal concentrations and one Pd-Cu alloy were examined for corrosion and tarnish resistance by means of anodic polarization curves in artificial saliva containing increasing amounts of sulphide. The electrochemical data were compared with the results obtained from immersion experiments in sulphide-rich solutions. Good agreement between the two kinds of measurement was found. Emphasis is given to the use of electrochemical tests (rapidly performed) in predicting the behaviour of dental alloys in aggressive solutions
In vitro corrosion of dental amalgams
No full textA series of dental alloys were characterized with respect to chemical composition, microstructure and corrosion resistance in artificial saliva. The following types of amalgams were studied: conventional and high copper dispersed phase dental alloys. Anodic polarization curves were recorded on these samples and periodic polarization resistance measurements were performed during a test of immersion in artificial saliva. The results are in accordance with extensive clinical findings, which attribute a greater corrosion resistance to the dispersion phase alloys. Examination by scanning electron microscopy and electron probe microanalysis allowed the identification of the various phases present on the amalgams and of the main corrosion products
In vitro corrosion of some Co-Cr and Ni-Cr alloys used for removable partial dentures: influence of heat treatments
No full textThe influence of heat treatments on the corrosion resistance of some base-metal alloys currently used in dentistry as a base for porcelain substrate systems has been investigated. Four Co-Cr alloys (Wironit, Wironit extra hard, Wirobond and Wirolloy) and two Ni-Cr alloys (Wiron 88 and Wirolloy) were submitted to heat treatments for 30 min at 880, 980, 1080 °C for 30 min, and slowly cooled in air. The electrochemical characterization was performed by means of anodic polarization curves in Ringer's solution and artificial saliva at 37 °C. In both solutions it was found that ageing at 880 °C detrimentally affects the corrosion resistance of Co-Cr alloys; the passive zone is narrow and shows rather high current densities. On the contrary, the samples annealed at 1080 °C display a superior corrosion resistance. With Wiron 88 the effect is opposite, but the electrochemical behaviour of Wirolloy, is not affected by heat treatments; although it does have a more negative transpassive potential in artificial saliva and cannot be passivated in Ringer's solution. The SEM examination of the alloys evinces the microstructural modifications induced by heat treatments responsible for changes in the corrosion behaviour of the base-metal alloys
High copper dental amalgams: comparative study of the structure and the in vitro corrosion resistance
No full textA dental amalgam made from a lathe-cut powder with a high copper content was characterized with respect to its microstructure by means of scanning electron microscopy techniques. A comparison was made between the in vitro corrosion resistance of this relatively new high copper amalgam, a dispersion-type amalgam and a ‘single composition alloy' amalgam. The effect of toothbrushing was included to avoid the superficial accumulation of corrosion products. Electrochemical data on the behaviour of the three types of high copper amalgams examined were collected by tracing anodic polarization curves and by measuring the polarization resistance. After immersion in synthetic saliva for 30 days, the amalgam made from the lathe-cut powder with high copper content and the dispersion-type amalgam showed preferential attack on the copper-rich phases, while the γ1 phase appeared only slightly altered; corrosion products rich in tin and chlorine were detected. The ‘single composition alloy' corroded to a lesser extent
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