992 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
2,2-Dibromo-N-(4-fluorophenyl)acetamide
In the crystal structure of the title compound, C8H6Br2FNO, C—H⋯O and N—H⋯O hydrogen bonding results in six-membered rings and links the molecules into chains running parallel to the c axis. The dihedral angle between the fluorophenyl ring and the acetamide group is 29.5 (5)°
Thermal conductivity of deformed carbon nanotubes
We investigate the thermal conductivity of four types of deformed carbon
nanotubes by using the nonequilibrium molecular dynamics method. It is reported
that various deformations have different influence on the thermal properties of
carbon nanotubes. For the bending carbon nanotubes, the thermal conductivity is
independent on the bending angle. However, the thermal conductivity increases
lightly with XY-distortion and decreases rapidly with Z-distortion. The thermal
conductivity does not change with the screw ratio before the breaking of carbon
nanotubes but decreases sharply after the critical screw ratio.Comment: 6figure
First-principles calculations of phase transition, low elastic modulus, and superconductivity for zirconium
The elasticity, dynamic properties, and superconductivity of ,
, and Zr are investigated by using first-principles methods.
Our calculated elastic constants, elastic moduli, and Debye temperatures of
and phases are in excellent agreement with experiments.
Electron-phonon coupling constant and electronic density of states at
the Fermi level (\emph{E}) are found to increase with pressure
for these two hexagonal structures. For cubic phase, the critical
pressure for mechanical stability is predicted to be 3.13 GPa and at \emph{P}=4
GPa the low elastic modulus (=31.97 GPa) can be obtained. Besides, the
critical pressure for dynamic stability of phase is achieved by phonon
dispersion calculations to be 26 GPa. Over this pressure,
and (\emph{E}) of phase decrease upon further
compression. Our calculations show that the large value of superconducting
transition temperature \emph{T}_{\rm{c}} at 30 GPa for Zr is mainly
due to the TA1 soft mode. Under further compression, the soft vibrational mode
will gradually fade away.Comment: 15 pages, 5 figure
Effect of temperature on microstructure and deformation mechanism of Fe-30Mn-3Si-4Al TWIP steel at strain rate of 700 s-1
As twinning-induced plasticity (TWIP) steel is one potential material for shaped charge liner due to the combination of high strength and high plasticity, deformation mechanism at high strain rate and high temperature is required to study. Compression experiments of Fe-30Mn-3Si-4Al TWIP steel were conducted using a Gleeble-1500 thermal simulation machine and a split-Hopkinson pressure bar (SHPB) between 298 and 1073 K at strain rates of 10-3 and 700 s-1, respectively. Microstructures were observed using optical microscopy (OM) and transmission electron microscopy (TEM). Results show that flow stress and densities of deformation twins and dislocations decrease with increasing deformation temperature at strain rates of 10-3 and 700 s-1. The stack fault energy (SFE) values (Γ) of Fe-30Mn-3Si-4Al TWIP steel at different temperatures were calculated using thermodynamic data. Based on corresponding microstructures, it can be inferred that at 700 s-1, twinning is the main deformation mechanism at 298-573 K for 30 mJ/m2≤Γ≤63 mJ/m, while dislocation gliding is the main deformation mechanism above 1073 K for Γ≥ 145 mJ/m2. In addition, with increasing strain rate from 10-3 to 700 s-1, the SFE range of twinning is enlarged and the SEF value of twinning becomes higher
Earthquake-Induced Lateral Displacement of a Landfill
In the wake of stability failure of the Kettleman Hills Waste Repository on March 19, 1988, the stability of landfill mass in earthquake-prone areas has become an important issue in the community. Based on a proposed landfill site in the Memphis, Tennessee area, this paper studies behaviors of landfills under various landfill and earthquake conditions (height and slope angle of the landfill, average unit weight of the landfill refuse, and peak acceleration and time duration of bedrock motion) by calculating lateral displacements induced by a design earthquake. Results indicate that lateral displacement of a landfill is proportional to the slope angle of the landfill, peak acceleration and time duration of bedrock motion, and is inversely proportional to the average unit weight of the landfill refuse. The slope angle of a landfill and the peak acceleration of bedrock motion have significant influence on the lateral displacement of a landfill compared with landfill height, average unit weight of landfill refuse and time duration of bedrock motion. Results also indicate that some landfill heights should be avoided to diminish landfill resonance, and the maximum slope angle of a landfill under certain seismic conditions depends on the internal friction angle of the landfill refuse. In addition, the lateral displacements calculated from actual and pseudo-accelerations are compared and discussed
Molecular cloning of dihydroflavonol 4-reductase gene from grape berry and preparation of an anti-DFR polyclonal antibody
Dihydroflavonol 4-reductase (DFR, EC 1.1.1.219) is a key enzyme of the flavonoid pathway, which synthesizes numerous secondary metabolites to determine the quality of grape berry and wine. The full-length dfr cDNA with 1014 bp was cloned from grape berry, and then introduced into an expressed plasmid pET-30a (+) vector at the EcoR I and Xho I restriction sites. With induction of the isopropyl-β-D-thiogalactoside (IPTG), the pET-dfr was highly expressed in Escherichia coli BL21 (DE3) pLysS cells. A fusion protein with the His-Tag was purified through Ni-NTA His Bind Resin and then used as the antigen to immunize a New Zealand rabbit. The resulting antiserum was further purified precipitated by 50 % saturated ammonium sulfate and DEAE-Sepharose FF chromatography to obtain the immunoglobulin G (IgG) fraction. The resulting polyclonal antibody was found capable of immuno-recognizing the DFR of the crude protein extracts from grape berry. This work undoubtedly provides the possibility for further studies on biological regulation of DFR activity in grape berry.
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