805 research outputs found
Intermediate-pressure phases of cerium studied by an LDA + Gutzwiller method
The thermodynamic stable phase of cerium metal in the intermediate pressure
regime (5.0--13.0 GPa) is studied in detail by the newly developed
local-density approximation (LDA)+ Gutzwiller method, which can include the
strong correlation effect among the 4\textit{f} electrons in cerium metal
properly. Our numerical results show that the phase, which has the
distorted body-centered-tetragonal structure, is the thermodynamic stable phase
in the intermediate pressure regime and all the other phases including the
phase (-U structure), phase (fcc structure), and bct
phases are either metastable or unstable. Our results are quite consistent with
the most recent experimental data.Comment: 17 pages, 7 figure
LDA+Gutzwiller Method for Correlated Electron Systems: Formalism and Its Applications
We introduce in detail our newly developed \textit{ab initio} LDA+Gutzwiller
method, in which the Gutzwiller variational approach is naturally incorporated
with the density functional theory (DFT) through the "Gutzwiller density
functional theory (GDFT)" (which is a generalization of original Kohn-Sham
formalism). This method can be used for ground state determination of electron
systems ranging from weakly correlated metal to strongly correlated insulators
with long-range ordering. We will show that its quality for ground state is as
high as that by dynamic mean field theory (DMFT), and yet it is computationally
much cheaper. In additions, the method is fully variational, the charge-density
self-consistency can be naturally achieved, and the quantities, such as total
energy, linear response, can be accurately obtained similar to LDA-type
calculations. Applications on several typical systems are presented, and the
characteristic aspects of this new method are clarified. The obtained results
using LDA+Gutzwiller are in better agreement with existing experiments,
suggesting significant improvements over LDA or LDA+U.Comment: 20 pages, 11 figure
The Application of Exemplarist Moral Theory and Problem-Based Learning in the Course of Structural Mechanics
Structural mechanics is an important basic course for undergraduates majoring in civil engineering. However, due to the difficulty and extent of the content, students are often not able to master the course. Problem-based learning is an excellent way of teaching engineering, and character education can improve students’ performance. This study explores the combined application of problem-based learning and exemplarist moral theory. In this model, students analyze the structure and force of buildings, and they learn about the historical stories behind them. In this way, students improve their morality, civility, performance, and intellect. In character education, the use of case studies and examples can increase students’ interest in the course, improve classroom participation, enrich teaching connotations, and strengthen students’ understanding of basic concepts and their ability to memorize them
Localization, phases and transitions in the three-dimensional extended Lieb lattices
We study the localization properties and the Anderson transition in the 3D Lieb lattice L3(1) and its extensions L3(n) in the presence of disorder. We compute the positions of the flat bands, the disorder-broadened density of states and the energy-disorder phase diagrams for up n = 4. Via finite-size scaling, we obtain the critical properties such as critical disorders and energies as well as the universal localization lengths exponent ν. We find that the critical disorder Wc decreases from ∼ 16.5 for the cubic lattice, to ∼ 8.6 for L3(1), ∼ 5.9 for L3(2) and ∼ 4.8 for L3(3). Nevertheless, the value of the critical exponent ν for all Lieb lattices studied here and across various disorder and energy transitions agrees within error bars with the generally accepted universal value ν = 1.590 (1.579, 1.602)
A novel method for estimating myocardial strain: assessment of deformation tracking against reference magnetic resonance methods in healthy volunteers
We developed a novel method for tracking myocardial deformation using cardiac magnetic resonance (CMR) cine imaging. We hypothesised that circumferential strain using deformation-tracking has comparable diagnostic performance to a validated method (Displacement Encoding with Stimulated Echoes- DENSE) and potentially diagnostically superior to an established cine-strain method (feature-tracking).
81 healthy adults (44.6 ± 17.7 years old, 47% male), without any history of cardiovascular disease, underwent CMR at 1.5T including cine, DENSE, and late gadolinium enhancement in subjects >45 years. Acquisitions were divided into 6 segments, and global and segmental peak circumferential strain were derived and analysed by age and sex.
Peak circumferential strain differed between the 3 groups (DENSE: -19.4 ± 4.8 %; deformation-tracking: -16.8 ± 2.4 %; feature-tracking: -28.7 ± 4.8%) (ANOVA with Tukey post-hoc, F-value 279.93, p<0.01). DENSE and deformation-tracking had better reproducibility than feature-tracking. Intra-class correlation co-efficient was >0.90. Larger magnitudes of strain were detected in women using deformation-tracking and DENSE, but not feature-tracking.
Compared with a reference method (DENSE), deformation-tracking using cine imaging has similar diagnostic performance for circumferential strain assessment in healthy individuals. Deformation-tracking could potentially obviate the need for bespoke strain sequences, reducing scanning time and is more reproducible than feature-tracking
Cerebral vasomotor reactivity predicts the development of acute stroke in patients with internal carotid artery stenosis
Objective
To investigate the relationship between cerebral vasomotor reactivity (VMR) and acute stroke in patients with internal carotid artery stenosis.
Methods
54 patients with internal carotid artery stenosis were enrolled. VMR was calculated by transcranial Doppler monitoring of the velocity of blood flow. 3-Dimensional dynamic contrast enhanced magnetic resonance angiography was used to detect stenosis, and diffusion weighted imaging was used to detect infarction.
Results
VMR value was significantly lower in patients with carotid artery stenosis than in control group (T=3.112, P=0.002), and significantly lower in patients with aortic atherosclerotic stroke than in non-infarct group (T=10.930, P=0.000). However, VMR value was significantly higher in patients with new-onset small-artery occlusion stroke than in non-infarction group (T=−2.538, P=0.013). Scatter plots showed that aortic atherosclerotic stroke occurred mainly in patients with severe internal carotid artery stenosis, and VMR value in cerebral artery significantly decreased.
Conclusion
Decreased VMR value is an important prognostic factor for the occurrence of aortic atherosclerotic stroke, and can be used as a reference for preoperative hemodynamic evaluation in patients with internal carotid artery stenosis
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