3,690 research outputs found
First-principles calculations of phase transition, elasticity, and thermodynamic properties for TiZr alloy
tructural transformation, pressure dependent elasticity behaviors, phonon,
and thermodynamic properties of the equiatomic TiZr alloy are investigated by
using first-principles density-functional theory. Our calculated lattice
parameters and equation of state for and phases as well as
the phase transition sequence of
are
consistent well with experiments. Elastic constants of and
phases indicate that they are mechanically stable. For cubic phase,
however, it is mechanically unstable at zero pressure and the critical pressure
for its mechanical stability is predicted to equal to 2.19 GPa. We find that
the moduli, elastic sound velocities, and Debye temperature all increase with
pressure for three phases of TiZr alloy. The relatively large values
illustrate that the TiZr alloy is rather ductile and its ductility is more
predominant than that of element Zr, especially in phase. Elastic wave
velocities and Debye temperature have abrupt increase behaviors upon the
transition at around 10 GPa and exhibit
abrupt decrease feature upon the
transition at higher pressure. Through Mulliken population analysis, we
illustrate that the increase of the \emph{d}-band occupancy will stabilize the
cubic phase. Phonon dispersions for three phases of TiZr alloy are
firstly presented and the phase phonons clearly indicate its
dynamically unstable nature under ambient condition. Thermodynamics of Gibbs
free energy, entropy, and heat capacity are obtained by quasiharmonic
approximation and Debye model.Comment: 9 pages, 10 figure
The Applications and Obstacles of Metabonomics in Traditional Chinese Medicine
In the recent years, a wide range of metabonomic technologies are widely used in the modern research of traditional chinese medicine (TCM). At present, the most prevailing methods for TCM research are mainly nuclear magnetic resonance (NMR), gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-mass spectrometry (LC-MS). With these techniques, metabonomics will help to understand syndromes, efficacy and toxicity of TCM. However, every analytical technique has its advantages and drawbacks, and there exist some obstacles of its applications on TCM. So, we discuss metabonomics in TCM and analyze some problems of its applications to study TCM in recent years. We believe that with the further development of metabonomic analytical technology, especially multianalysed techniques, metabonomics will greatly promote TCM research and be beneficial to the modernization of TCM
Electronic, mechanical, and thermodynamic properties of americium dioxide
By performing density functional theory (DFT) + calculations, we
systematically study the electronic, mechanical, tensile, and thermodynamic
properties of AmO. The experimentally observed antiferromagnetic
insulating feature [J. Chem. Phys. 63, 3174 (1975)] is successfully reproduced.
It is found that the chemical bonding character in AmO is similar to that
in PuO, with smaller charge transfer and stronger covalent interactions
between americium and oxygen atoms. The valence band maximum and conduction
band minimum are contributed by 2 hybridized and 5 electronic states
respectively. The elastic constants and various moduli are calculated, which
show that AmO is less stable against shear forces than PuO. The
stress-strain relationship of AmO is examined along the three low-index
directions by employing the first-principles computational tensile test method.
It is found that similar to PuO, the [100] and [111] directions are the
strongest and weakest tensile directions, respectively, but the theoretical
tensile strengths of AmO are smaller than those of PuO. The phonon
dispersion curves of AmO are calculated and the heat capacities as well
as lattice expansion curve are subsequently determined. The lattice thermal
conductance of AmO is further evaluated and compared with attainable
experiments. Our present work integrally reveals various physical properties of
AmO and can be referenced for technological applications of AmO
based materials.Comment: 23 pages, 8 figure
Ideal strengths and bonding properties of PuO2 under tension
We perform a first-principles computational tensile test on PuO based
on density-functional theory within local density approximation (LDA)+\emph{U}
formalism to investigate its structural, mechanical, magnetic, and intrinsic
bonding properties in the four representative directions: [001], [100], [110],
and [111]. The stress-strain relations show that the ideal tensile strengths in
the four directions are 81.2, 80.5, 28.3, and 16.8 GPa at strains of 0.36,
0.36, 0.22, and 0.18, respectively. The [001] and [100] directions are
prominently stronger than other two directions since that more PuO bonds
participate in the pulling process. Through charge and density of states
analysis along the [001] direction, we find that the strong mixed
ionic/covalent character of PuO bond is weakened by tensile strain and
PuO will exhibit an insulator-to-metal transition after tensile stress
exceeds about 79 GPa.Comment: 11 pages, 6 figure
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