1,720,972 research outputs found
Thermoelectric Properties of the XCoSb (X: Ti,Zr,Hf) Half-Heusler Alloys
No full textWe investigate the thermoelectric properties of the half-Heusler alloys XCoSb (X: Ti,Zr,Hf) by solving Boltzmann transport equations and discuss them in terms of the electronic band structure. The rigid band approximation is employed to address the effects of doping. While many half-Heuser alloys show excellent thermoelectric performance, the materials under study are special by supporting both n- and p-doping. We identify the reasons for this balanced thermoelectric transport and explain why experimentally p-doping is superior to n-doping. We also determine the spectrum of phonon mean free paths to guide grain refinement methods to enhance the thermoelectric figure of merit.The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). For computer time, this research used the resources of the Supercomputing Laboratory at KAUST
Electron dominated thermoelectric response in MNiSn (M: Ti, Zr, Hf) half-Heusler alloys
No full textWe solve the transport equations of the electrons and phonons to understand the thermoelectric behaviour of the technologically important half-Heusler alloys MNiSn (M: Ti, Zr, Hf). Doping is simulated within the rigid band approximation. We clarify the origin of the electron dominated thermoelectric response and determine the carrier concentrations with maximal figures of merit. The phonon mean free path is studied to calculate the grain size below which grain refinement methods can enforce ballistic heat conduction to enhance the figure of merit. © The Owner Societies 2016.The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). Computational resources were provided by the Supercomputing Laboratory of KAUST
Martensitic transformation in TiNi based shape memory alloys – a first principles study
Get PDFThe martensitic transformation in TiNi-based shape memory alloys
has been investigated using various theoretical methods. The direct
method for ab initio lattice dynamics is used for calculating phonon
dispersion relations in austenite (B2) and martensites (B19, B19′).
Normal mode symmetries in a B2 crystal are determined. Vibrational
modes in the B2 crystal are labelled according to symmetry
properties of their polarisation vector. Normal modes with imaginary
frequencies are observed at the locations of experimentally observed
soft modes. While labelling normal modes, the published mode symmetry
label of a soft transverse acoustic (TA2) mode with a [Mathematical formula appears here. To view, please open pdf attachment]
polarisation at [Mathematical formula appears here. To view, please open pdf attachment] is corrected to Σ2. Irreducible representations
of the soft modes are used for determining the order parameters
for various martensitic transformation paths experimentally observed
using group theoretical methods. Accuracy of the interpolated frequencies
in the phonon dispersion relations is assessed by using three
different supercell sizes and by calculating the elastic constants from
the slopes of the acoustic branches at the Brillouin zone.
Born et al. derived a relation between the force constants and
elastic constants for a general crystal. Further simplification of this
relation is possible for a B2 crystal because of its symmetry. This
simplification is derived by applying elementary group theory. Elastic
constants calculated with the simplified relation are in agreement
with the elastic constants calculated from the slopes of the dispersion
relations.
The self-consistent ab initio lattice dynamics (SCAILD) formulation
is derived for an ordered compound. Precautions that need to be
taken while practically implementing this formulation are discussed.
The effect of Hf or Zr addition to a binary Ti-Ni system is studied
by considering one configuration at each of five compositions from 0
to 25 at.% Hf or Zr. Elastic constants are calculated following a
homogeneous deformation method. Selected normal mode frequencies
are calculated using the direct method
Thermal conductivity of bulk and monolayer MoS2
No full text© Copyright EPLA, 2016. We show that the lattice contribution to the thermal conductivity of MoS2 strongly dominates the carrier contribution in a broad temperature range from 300 to 800 K. Since theoretical insight into the lattice contribution is largely missing, though it would be essential for materials design, we solve the Boltzmann transport equation for the phonons self-consistently in order to evaluate the phonon lifetimes. In addition, the length scale for transition between diffusive and ballistic transport is determined. The low out-of-plane thermal conductivity of bulk MoS2 (2.3 Wm-1K-1 at 300 K) is useful for thermoelectric applications. On the other hand, the thermal conductivity of monolayer MoS2 (131 Wm-1K-1 at 300 K) is comparable to that of Si.The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). Computational resources were provided by the Supercomputing Laboratory of KAUST
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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