1,395 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
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
iPINNs: Incremental learning for Physics-informed neural networks
Physics-informed neural networks (PINNs) have recently become a powerful tool
for solving partial differential equations (PDEs). However, finding a set of
neural network parameters that lead to fulfilling a PDE can be challenging and
non-unique due to the complexity of the loss landscape that needs to be
traversed. Although a variety of multi-task learning and transfer learning
approaches have been proposed to overcome these issues, there is no incremental
training procedure for PINNs that can effectively mitigate such training
challenges. We propose incremental PINNs (iPINNs) that can learn multiple tasks
(equations) sequentially without additional parameters for new tasks and
improve performance for every equation in the sequence. Our approach learns
multiple PDEs starting from the simplest one by creating its own subnetwork for
each PDE and allowing each subnetwork to overlap with previously learned
subnetworks. We demonstrate that previous subnetworks are a good initialization
for a new equation if PDEs share similarities. We also show that iPINNs achieve
lower prediction error than regular PINNs for two different scenarios: (1)
learning a family of equations (e.g., 1-D convection PDE); and (2) learning
PDEs resulting from a combination of processes (e.g., 1-D reaction-diffusion
PDE). The ability to learn all problems with a single network together with
learning more complex PDEs with better generalization than regular PINNs will
open new avenues in this field
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