130,715 research outputs found
Neutron diffraction and symmetry analysis of the martensitic transformation in Co-doped Ni2MnGa
No full textMartensitic transformations are strain driven displacive transitions governing the mechanical and physical properties in intermetallic materials. This is the case in Ni2MnGa, where the martensite transition is at the heart of the striking magnetic shape memory and magnetocaloric properties. Interestingly, the martensitic transformation is preceded by a premartensite phase, and the role of this precursor and its influence on the martensitic transition and properties is still a matter of debate. In this work we report on the influence of Co doping (Ni50-xCoxMn25Ga25 with x=3 and 5) on the martensitic transformation path in stoichiometric Ni2MnGa by neutron diffraction. The use of the superspace formalism to describe the crystal structure of the modulated martensitic phases, joined with a group theoretical analysis, allows unfolding the different distortions featuring the structural transitions. Finally, a general Landau thermodynamic potential of the martensitic transformation, based on the symmetry analysis, is outlined. The combined use of phenomenological and crystallographic studies highlights the close relationship between the lattice distortions at the core of the Ni2MnGa physical properties and, more in general, on the properties of the martensitic transformations in the Ni-Mn based Heusler systems
Long-range antiferromagnetic interactions in Ni-Co-Mn-Ga metamagnetic Heusler alloys: A two-step ordering studied by neutron diffraction
No full textWe report on the experimental observation of a long-range antiferromagnetic structure in the metamagnetic Ni-Co-Mn-Ga Heusler alloys. The accurate magnetic symmetry analysis based on experimental neutron diffraction data, exploiting the Shubnikov theory, allows the determination of the correct magnetic space group of the system. A two-step process, featuring the ordering of the Ni and Mn sublattices at different temperatures, leads to the antiferromagnetic structure in martensite. A perfect, constrained by the symmetry, antiferromagnetic ordering of the Ni sublattice in the "paramagnetic gap" is observed, followed by the ordering of the Mn sublattice at lower temperatures. The observation of such antiferromagnetic structure clarifies the current debate on the presence of antiferromagnetic interactions in the (Ni,Co)-Mn-X (X=Ga, Sn, Sb, and In) ferromagnetic shape memory alloys and yields new insights in understanding the magnetostructural properties of this relevant class of materials
Evolution of Magneto-Orbital order Upon B -Site Electron Doping in Na1-xCaxMn7 O12 Quadruple Perovskite Manganites
No full textWe present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the well-known pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic, and orbital ordering across a wide range of compounds
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Scholarly Communication and Publishing Lunch and Learn Talk #11: The ULS Open Access Author Fee Fund
No full textAt the May 2014 talk, you will learn about the ULS Open Access Author Fee Fund--what it is, why we do it, how it works, and how the program is going so far
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