930 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
Shared-care survivorship program for testicular cancer patients:safe and feasible
Background: Testicular cancer survivors are at risk for cardiovascular disease, often preceded by early development of cardiovascular risk factors due to chemotherapeutic treatment. Therefore, close collaboration between oncologists and primary care physicians (PCPs) is needed during follow-up to monitor and manage cardiovascular risk factors. We designed a shared-care survivorship program, in which testicular cancer patients visit both their oncologist and their PCP. The objective of this study was to test the safety and feasibility of shared-care follow-up after treatment for metastatic testicular cancer. Patients and methods: The study was designed as an observational cohort study with a stopping rule to check for the safety of follow-up. Safety boundaries were defined for failures in the detection of signals indicating cancer recurrence. Secondary outcomes were the proportion of carried out cardiovascular risk assessments, psychosocial status and patient preferences measured with an evaluation questionnaire. Results: One hundred and sixty-two patients were enrolled (69% of eligible testicular cancer patients). Almost all (99%, n = 150) PCPs of the enrolled patients agreed to participate in the study. In total, 364 primary care visits took place. No failures occurred in the detection of relapsed testicular cancer. Four follow-up visits were considered as failures because of organizational issues, without activation of the stopping rule. Eventually, the safe boundary was crossed indicating that this shared-care model is a safe alternative for follow-up after testicular cancer. Patients were satisfied with the knowledge level of PCPs. PCPs were willing to further extend their role in follow-up care after cancer. Conclusions: Shared-care follow-up is safe and feasible in this patient population. Patients benefit from personalized care, partly close to their home. Within shared care, PCPs can have an important role in cardiovascular risk management and psychosocial survivorship issues
Pressure Dependence of the Elastic Moduli in Aluminum Rich Al-Li Compounds
I have carried out numerical first principles calculations of the pressure
dependence of the elastic moduli for several ordered structures in the
Aluminum-Lithium system, specifically FCC Al, FCC and BCC Li, L1_2 Al_3Li, and
an ordered FCC Al_7Li supercell. The calculations were performed using the full
potential linear augmented plane wave method (LAPW) to calculate the total
energy as a function of strain, after which the data was fit to a polynomial
function of the strain to determine the modulus. A procedure for estimating the
errors in this process is also given. The predicted equilibrium lattice
parameters are slightly smaller than found experimentally, consistent with
other LDA calculations. The computed elastic moduli are within approximately
10% of the experimentally measured moduli, provided the calculations are
carried out at the experimental lattice constant. The LDA equilibrium shear
modulus C11-C12 increases from 59.3 GPa in Al, to 76.0 GPa in Al_7Li, to 106.2
GPa in Al_3Li. The modulus C_44 increases from 38.4 GPa in Al to 46.1 GPa in
Al_7Li, then falls to 40.7 GPa in Al_3Li. All of the calculated elastic moduli
increase with pressure with the exception of BCC Li, which becomes elastically
unstable at about 2 GPa, where C_11-C_12 vanishes.Comment: 17 pages (REVTEX) + 7 postscript figure
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