911 research outputs found
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
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
Shock Induced Order-disorder Transformation in Ni3Al
The Hugoniot of Ni3Al with L12 structure is calculated with an equation of
state (EOS) based on a cluster expansion and variation method from first
principles. It is found that an order-disorder transition occurs at a shock
pressure of 205GPa, corresponding to 3750K in temperature. On the other hand,
an unexpected high melting temperature about 6955K is obtained at the same
pressure, which is completely different from the case at ambient pressure where
the melting point is slightly lower than the order-disorder transition
temperature, implying the high pressure phase diagram has its own
characteristics. The present work also demonstrates the configurational
contribution is more important than electronic excitations in alloys and
mineral crystals within a large range of temperature, and an EOS model based on
CVM is necessary for high pressure metallurgy and theoretical Earth model.Comment: 14 pages, 5 figure
Order-disorder Effects on Equation of State in FCC Ni-Al Alloys
Order-disorder effects on equation of state (EOS) properties of
substitutional binary alloys are investigated with the cluster variation method
(CVM) based on ab initio effective cluster interactions (ECI). Calculations are
applied to the fcc based Ni-Al system. Various related quantities are shown to
vary with concentration around stoichiometry with a surprising "W shape", such
as the thermal expansion coefficient, the heat capacity and the Gruneisen
parameter, due to configurational ordering effects. Analysis shows that this
feature originates from the dominated behavior of some elements of the inverse
of Hessian matrix. For the first time we point out that the strong
compositional variation of these properties might be partially responsible for
local fractures in alloys and mineral crystals under heating, highlighting the
importance of subtle thermodynamic behavior of order-disorder systems.Comment: 17 pages, 10 figure
Is Workstyle a Mediating Factor for Pain in the Upper Extremity Over Time?
Introduction Upper extremity musculoskeletal disorders influence workers’ quality of life. Workstyle may be one factor to deal with in workers with pain in the upper extremity. The objective of this study was to determine if workstyle is a mediating factor for upper extremity pain in a changing work environment of office workers over time. Methods Office workers with upper extremity pain filled out a Workstyle questionnaire (WSF) at baseline (n = 110). After 8 and 12 months follow-up assessment took place. Participants were divided into a good and an adverse workstyle group at baseline. The presence of upper extremity pain in both groups was calculated and relative risks were determined. Chi-square tests were used. Results Eight months after baseline, 80% of the adverse and 45% of the good workstyle group reported pain. The relative risk (RR) of having upper extremity pain for the adverse compared to the good workstyle group was 1.8 (95% CI 1.08–2.86) (P = 0.055). Twelve months after baseline, upper extremity pain was more often presented in the adverse workstyle compared to the good workstyle group (RR = 3.0, (95% CI 1.76–5.11), P = 0.003). Twelve months after baseline, 100% of the adverse workstyle group and 33% of the good workstyle group reported pain in the upper extremity. Conclusion Workstyle seems to be a mediating factor for upper extremity pain in office workers in a changing work environment. It is recommended to assess workstyle among office workers with upper extremity pain, and to include workstyle behaviour in treatments
Quality of life and illness perception in working and sick-listed chronic RSI patients
OBJECTIVE: To study differences between working and sick-listed chronic repetitive strain injury (RSI) patients in the Netherlands with respect to indices of quality of life and illness perception. METHODS: In a cross-sectional design, one questionnaire was sent to all 3,250 members of the national RSI patient association. For descriptive purposes, demographics, work status and complaint-related variables such as severity, type, duration, and extent of complaints were asked for. Indices of quality of life were assessed through seven SF-36 subscales (physical (role) functioning, emotional role functioning, social functioning, pain, mental health and vitality). A work-ability estimate and VAS scales were used to assess complaint-related decrease in quality of life. Illness perception was assessed through the brief illness perception questionnaire (IPQ-B). Working patients and sick-listed patients were identified. Tests between the two independent groups were performed and P-values < 0.01 were considered significant. RESULTS: Data from 1,121 questionnaires were used. Two-thirds of the respondents worked and one-third were sick-listed. Average duration of complaints was over 5 years in both groups. The sick-listed patients reported significantly more severe and extensive complaints than did the working patients. In addition, sick-listed patients reported significantly poorer mental health, physical (role) functioning, emotional role functioning, pain, vitality, and work-ability. With respect to illness perception, both groups showed the same concerns about their complaints, but sick-listed patients had significantly more distorted perceptions in their emotional response, identity, treatment control, personal control, timeline, and life consequences. Complaint-related decrease in quality of life was 31% in the working patients and 49% in the sick-listed patients. CONCLUSION: The study found a greater number and severe complaints among sick-listed chronic RSI patients and a considerably decreased quality of life because of their complaints. These findings may allow for a better treatment focus in the futur
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