1,721,152 research outputs found
The formation volume in rare earth intermetallic systems: A representation by means of atomic physical quantities
No full textThe formation of the intermetallic phases is often accompanied by large volume effects, and several interpretations of this phenomenon have been proposed following different approaches, either from a simply empirical or purely theoretical point of view. In his pioneering work, Biltz (Biltz 1934) employed the experimental density values to list the molar volumes of the elements and of numerous inorganic and organic solids, including intermetallic phases. The systematic analysis of the data allowed the scientist to estimate the effective volumes of the atoms within the compounds, making possible the application of the volume additivity. Machlin studied the effects of electronegativity on energy and volume of formation, assuming that the volume corrections depend on the Gordy electronegativity difference (Machlin 1980). Watson and Bennett obtained 82a good correlation between the volume effects shown by the phases of the transition elements and a scale resembling the Gordy electronegativity, while a cellular method was applied to estimate the volume changes in phases with alkaline and alkaline earth metals (Watson and Bennett 1982, 1984). Alonso showed that a model of a disordered binary alloy of nontransition metals explains the tendency to a negative deviation from Vegard’s law as this lowers the energy of formation (Alonso et al. 1984). In the Miedema model (Miedema and Niessen 1982), the volume contraction in metallic systems can be ascribed to a charge transfer effect, described mainly by the differences both in an electronegativity-like scale (F*) and in the electron density parameter (nWS). Moreover, in systems with atoms of different radius, a further volume contraction may arise from elastic size mismatch energy. The differences in electronegativity are ignored in the Hafner approach, based on the lowest-order pseudopotential perturbation theory (Hafner 1985). This method provides good results for extended solid solutions of homovalent systems (intra-alkaline and intra-alkaline-earth alloys) and for some intermetallics of the cited elements. A phenomenological approach was used to describe the volume effects displayed by the intermetallic compounds formed by alkaline earths (Ca, Sr, Ba) and divalent rare earths (Eu, Yb) (Merlo 1988) and by the trivalent rare earths (Merlo and Fornasini 1993), introducing a charge transfer atomic parameter, correlated with Pauling’s electronegativity. More recently, the volume contractions of the binary phases of Ca, Sr, Ba, Eu and Yb were represented by a simple equation containing the electronegativity, the compressibility and the group number (Fornasini and Merlo 2006). The most advanced method is based on the calculation of partial atomic volumes and charges as a function of composition (Baranov et al. 2007)
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
Eco-programming of industrial robots for sustainable manufacturing via dynamic time scaling of trajectories
No full textNowadays, Industrial Robots (IRs) have become widespread in many manufacturing industries. Medium and high payload IRs cover a significant percentage of the overall factory Energy Consumption (EC). This article focuses on the IRs eco-programming to minimize the EC of a robot, being energy efficiency one of the fundamental aims of sustainable manufacturing. By leveraging well-known trajectory scaling methods, this research develops a novel, versatile, fast, and efficient process to define the IR optimal velocity/acceleration profile in time, keeping the geometry of the trajectory fixed. A complete IR system model that founds application in various types of 6 degrees of freedom articulated manipulators has been developed by considering electrical motors, actuator drive systems, and controller cabinet losses. A new optimization technique based on Dynamic Time Scaling of trajectories is presented, and the obtained results are compared with other methods used in the scientific literature. When performing critical path analysis, the EC of the robot system is estimated to be cut down, being the robot motion time fixed, by about 13% through this novel approach. The model has been validated through commercial software, and the proposed optimization algorithm has been implemented in a user-friendly interface tool
Sample treatment for the determination of steroid hormone contaminants in water samples: Analytical greenness assessment
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An effective recommender system for highly dynamic and large web sites
No full textIn this demo we show a recommender system, called SUGGEST, that dynamically generates links to pages that have not yet been visited by a user and might be of his potential interest. Usually other recommender systems exploit a kind of two-phase architecture composed by an off-line component that analyzes Web server access logs and generates information used by a successive online component that generates recommendations. SUGGEST collapse the two-phase into a single on-line Apache module. The component is able to manage very large Web sites made up of dinamically generated pages by means of an efficient LRU-based database management strategy. The demo will show the way SUGGEST is able to anticipate users' requests that will be made farther in the future, introducing a limited overhead on the Web server activity1. © Springer-Verlag Berlin Heidelberg 2004
Structural anomaly in GdNiAl: a crystallographic, electric and magnetic investigation
No full textLow temperature electrical resistivity and X-ray powder diffraction measurements showed a transformation paint at about 200 K, attributed to a transition between two slightly different crystallographic forms of the ZrNiAl type. A corresponding anomaly was observed in the thermal behaviour of the magnetic susceptibility, and the results were analyzed in the framework of the RKKY theory. Ferromagnetic ordering occurs at 57 K, and two other transition temperatures, 30 and 14 K, were detected: these points, as already observed for TbNiAl, DyNiAl and HoNiAl may be imputed to order-order magnetic transitions
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