65 research outputs found
Free energy and molecular dynamics calculations for the cubic-tetragonal phase transition in zirconia
The high-temperature cubic-tetragonal phase transition of pure stoichiometric
zirconia is studied by molecular dynamics (MD) simulations and within the
framework of the Landau theory of phase transformations. The interatomic forces
are calculated using an empirical, self-consistent, orthogonal tight-binding
(SC-TB) model, which includes atomic polarizabilities up to the quadrupolar
level. A first set of standard MD calculations shows that, on increasing
temperature, one particular vibrational frequency softens. The temperature
evolution of the free energy surfaces around the phase transition is then
studied with a second set of calculations. These combine the thermodynamic
integration technique with constrained MD simulations. The results seem to
support the thesis of a second-order phase transition but with unusual, very
anharmonic behaviour above the transition temperature
Relative energetics and structural properties of zirconia using a self-consistent tight-binding model
We describe an empirical, self-consistent, orthogonal tight-binding model for
zirconia, which allows for the polarizability of the anions at dipole and
quadrupole levels and for crystal field splitting of the cation d orbitals.
This is achieved by mixing the orbitals of different symmetry on a site with
coupling coefficients driven by the Coulomb potentials up to octapole level.
The additional forces on atoms due to the self-consistency and polarizabilities
are exactly obtained by straightforward electrostatics, by analogy with the
Hellmann-Feynman theorem as applied in first-principles calculations. The model
correctly orders the zero temperature energies of all zirconia polymorphs. The
Zr-O matrix elements of the Hamiltonian, which measure covalency, make a
greater contribution than the polarizability to the energy differences between
phases. Results for elastic constants of the cubic and tetragonal phases and
phonon frequencies of the cubic phase are also presented and compared with some
experimental data and first-principles calculations. We suggest that the model
will be useful for studying finite temperature effects by means of molecular
dynamics.Comment: to be published in Physical Review B (1 march 2000
Identifying outcomes for depression that matter to patients, informal caregivers, and health-care professionals: qualitative content analysis of a large international online survey
Background
Many clinical trials have assessed treatments for depressive disorders and bipolar depression. However, whether, and which, assessed outcome domains really matter to patients, informal caregivers, and health-care professionals remains unclear.
Methods
We did an international online survey in French, German, and English. Participants were adult patients with a history of depression, informal caregivers, and health-care professionals, recruited by purposeful sampling. To identify outcome domains, participants answered four open-ended questions about their expectations for depression treatment. We disseminated the survey without restriction via social media, patient and professional associations, and a media campaign. Four researchers independently did qualitative content analyses. We assessed data saturation using mathematical models to ensure the comprehensive identification of outcome domains.
Findings
Between April 5, 2018, and Dec 10, 2018, 1912 patients, 464 informal caregivers, and 627 health-care professionals from 52 countries provided 8183 open-ended answers. We identified 80 outcome domains related to symptoms (64 domains), such as mental pain (or psychological or psychic pain, 523 [17%] of 3003 participants) and motivation (384 [13%]), and functioning (16 domains), such as social isolation (541 [18%]). We identified 57 other outcome domains regarding safety of treatment, health care organisation, and social representation, such as stigmatisation (408 [14%]).
Interpretation
This study provides a list of outcome domains important to patients, informal caregivers, and health-care professionals. Unfortunately, many of these domains are rarely measured in clinical trials. Results from this study should set the foundation for a core outcome set for depression.
Funding
Fondation pour la Recherche Medicale and NIHR Oxford Health Biomedical Research Centre.</p
Identifying outcomes for depression that matter to patients, informal caregivers, and health-care professionals: qualitative content analysis of a large international online survey
Stress and Psychopatholog
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