1,406 research outputs found
Using bond-length dependent transferable force constants to predict vibrational entropies in Au-Cu, Au-Pd, and Cu-Pd alloys
A model is tested to rapidly evaluate the vibrational properties of alloys
with site disorder. It is shown that length-dependent transferable force
constants exist, and can be used to accurately predict the vibrational entropy
of substitutionally ordered and disordered structures in Au-Cu, Au-Pd, and
Cu-Pd. For each relevant force constant, a length- dependent function is
determined and fitted to force constants obtained from first-principles
pseudopotential calculations. We show that these transferable force constants
can accurately predict vibrational entropies of L1-ordered and disordered
phases in CuAu, AuPd, PdAu, CuPd, and PdAu. In
addition, we calculate the vibrational entropy difference between
L1-ordered and disordered phases of AuCu and CuPt.Comment: 9 pages, 6 figures, 3 table
The prevalence and incidence of musculoskeletal symptoms among hospital physicians: a systematic review
Physicians are exposed to a range of work-related risk factors that may result in occupational diseases. This systematic review aims at shedding light on the prevalence and incidence of musculoskeletal complaints among hospital physicians. A systematic literature search was performed in Pubmed and EMBASE (1990-2010), and methodological quality criteria were applied. A search was done for musculoskeletal complaints. Five medium-quality studies and three high-quality studies were included in this review. The definitions and assessment used in the studies for musculoskeletal complaints were different. In short, the frequently reported prevalence for hand and wrist pain was 8-33 and 0%, 17% for shoulder pain, and 9-28% for neck pain. Moreover, the annual prevalence of low back pain was between 33 and 68%. The limited number of studies makes it difficult to draw conclusions, and the results should be intepreted with care. In conclusion, musculoskeletal complaints may be work-related complaints in hospital physicians, which need future attentio
Hybrid expansions for local structural relaxations
A model is constructed in which pair potentials are combined with the cluster
expansion method in order to better describe the energetics of structurally
relaxed substitutional alloys. The effect of structural relaxations away from
the ideal crystal positions, and the effect of ordering is described by
interatomic-distance dependent pair potentials, while more subtle
configurational aspects associated with correlations of three- and more sites
are described purely within the cluster expansion formalism. Implementation of
such a hybrid expansion in the context of the cluster variation method or Monte
Carlo method gives improved ability to model phase stability in alloys from
first-principles.Comment: 8 pages, 1 figur
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Theoretical investigation of phase stability in non-magnetic Fe-V substitutional alloys
The assessed phase diagram of Fe-V exhibits a continuous high temperature bcc solid solution intersected at lower temperatures by a complex sigma phase centered around equiatomic composition. Slow kinetics of the bcc to sigma transformation make it possible to retain the bcc solid solution at low temperature. It has been observed that this metastable solid solution has a tendency to order with a CsCl type structure (B2) below 970 K. As a first attempt to describe this behavior from an electronic structure approach, this paper will study the phase stability on the bcc lattice using a realistic tight-binding Hamiltonian. Main features are as follows: Element and structure specific Slater-Koster parameters are used and lattice parameter effects are incorporated through scaling. Charge transfer is set to zero by rigidly shifting the onsite energies of one constituent. The Coherent Potential Approximation (CPA) is invoked with four levels corresponding to states with s, p, t{sub 2g} and e{sub g} like symmetry. Effects of off-diagonal disorder (ODD) have not been included, instead, an average alloy Hamiltonian was defined using the Slater-Koster parameters of the components weighted by concentration. At equiatomic composition the effect of this approximation has been evaluated by repeating the electronic structure calculation with inclusion of ODD effects. Effective pair interactions, as defined within the Generalized Perturbation Method (GPM), have been computed and have been used to evaluate the ground states of configurational order on the bcc lattice in the Fe-V system. Furthermore, the theoretically derived energetic properties have been used to determine the phase diagram pertaining to the (metastable) bcc lattice with the Cluster Variation Method (CVM) in the tetrahedron approximation. 11 refs., 4 figs., 1 tab
First-principles equation of state and phase stability for the Ni-Al system under high pressures
The equation of state (EOS) of alloys at high pressures is generalized with
the cluster expansion method. It is shown that this provides a more accurate
description. The low temperature EOSs of Ni-Al alloys on FCC and BCC lattices
are obtained with density functional calculations, and the results are in good
agreement with experiments. The merits of the generalized EOS model are
confirmed by comparison with the mixing model. In addition, the FCC phase
diagram of the Ni-Al system is calculated by cluster variation method (CVM)
with both spin-polarized and non-spin-polarized effective cluster interactions
(ECI). The influence of magnetic energy on the phase stability is analyzed. A
long-standing discrepancy between ab initio formation enthalpies and
experimental data is addressed by defining a better reference state. This aids
both evaluation of an ab initio phase diagram and understanding the
thermodynamic behaviors of alloys and compounds. For the first time the
high-pressure behavior of order-disorder transition is investigated by ab
initio calculations. It is found that order-disorder temperatures follow the
Simon melting equation. This may be instructive for experimental and
theoretical research on the effect of an order-disorder transition on shock
Hugoniots.Comment: 27 pages, 12 figure
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