3,997 research outputs found
Investigation of the Influence of Nanodispersed Compositions Obtained by Plasmochemical Synthesis on the Crystallization Processes of Structural Alloys
The state of the problem of stabilizing the structure, improving the quality and properties of structural alloys is studied. To solve the problem, it is proposed to modify melts of low–alloyed alloys with nanodispersed compositions obtained by plasma–chemical synthesis. Process technological parameters are developed. Nanopowders of carbide and carbonitride class SiC and Ti (C, N) with a size of 50 ... 100 nm are obtained. The crystallographic parameters of the nanocompositions and the specific surface are determined, and the dependency curves are plotted. The macro– and microstructure of structural steels and alloys was studied before and after the modification. A significant (in 2 ... 3.5 times) grain refinement and stabilization of the alloy structure as a result of nanopowder modification of titanium carbonitride have been achieved. Thermodynamic calculations of the dimensions of crystalline seeds during the crystallization of steels and alloys are carried out. A complex criterial estimation of the efficiency of nanodispersed compositions in a steel melt is proposed. The features of crystallization and structure formation of modified structural steels are studied. The obtained results are of theoretical and practical importance for production of critical parts from structural steels and high–quality alloys
Probing the role of single defects on the thermodynamics of electric-field induced phase transitions
The kinetics and thermodynamics of first order transitions is universally
controlled by defects that act as nucleation sites and pinning centers. Here we
demonstrate that defect-domain interactions during polarization reversal
processes in ferroelectric materials result in a pronounced fine structure in
electromechanical hysteresis loops. Spatially-resolved imaging of a single
defect center in multiferroic BiFeO3 thin film is achieved, and the defect size
and built-in field are determined self-consistently from the single-point
spectroscopic measurements and spatially-resolved images. This methodology is
universal and can be applied to other reversible bias-induced transitions
including electrochemical reactions.Comment: 34 pages,4 figures, high quality figures are available upon request,
submitted to Phys. Rev. Let
The 2mrad horizontal crossing angle IR layout for a TeV ILC
The current status of the 2mrad crossing angle layout for the ILC is
reviewed. The scheme developed in the UK and France is described and the
performance discussed for a TeV machine. Secondly, the scheme developed at SLAC
and BNL is then studied and modified for a TeV machine. We find that both
schemes can handle the higher energy beam with modifications, and share many
common features.Comment: The proceedings of the 2005 International Linear Collider Workshop,
March 2005. 4 pages, 5 figure
Finite size and intrinsic field effect on the polar-active properties of the ferroelectric-semiconductor heterostructures
Using Landau-Ginzburg-Devonshire approach we calculated the equilibrium
distributions of electric field, polarization and space charge in the
ferroelectric-semiconductor heterostructures containing proper or incipient
ferroelectric thin films. The role of the polarization gradient and intrinsic
surface energy, interface dipoles and free charges on polarization dynamics are
specifically explored. The intrinsic field effects, which originated at the
ferroelectric-semiconductor interface, lead to the surface band bending and
result into the formation of depletion space-charge layer near the
semiconductor surface. During the local polarization reversal (caused by the
inhomogeneous electric field induced by the nanosized tip of the Scanning Probe
Microscope (SPM) probe) the thickness and charge of the interface layer
drastically changes, it particular the sign of the screening carriers is
determined by the polarization direction. Obtained analytical solutions could
be extended to analyze polarization-mediated electronic transport.Comment: 35 pages, 12 figures, 1 table, 2 appendices, to be submitted to Phys.
Rev.
Analysis of phase distributions in the Li\u3csub\u3e2\u3c/sub\u3eO–Nb\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e5\u3c/sub\u3e–TiO\u3csub\u3e2\u3c/sub\u3e system by piezoresponse imaging
The M-phase solid solutions Li1+x-yNb1-x-3yTix+4yO3) (0.1 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.175) in the Li2O–Nb2O5–TiO2 system have promising microwave dielectric properties. However, these compounds can contain small quantities of ferroelectric impurities that affect the polarization response of the material. Due to their low concentration and their chemical similarity to the host material, the impurities cannot be detected by x-ray diffraction or local elemental analysis. Scanning surface potential microscopy and piezoresponse imaging were used to analyze phase compositions in this system. Piezoresponse imaging demonstrated the presence of thin (\u3c200–300 nm) ferroelectric layers on the grain boundaries oriented along the c-axis of the M-phase. Differences between the surface potential and the piezoresponse of ferroelectric multicomponent systems are discussed
Suppression of Octahedral Tilts and Associated Changes of Electronic Properties at Epitaxial Oxide Heterostructure Interfaces
Epitaxial oxide interfaces with broken translational symmetry have emerged as
a central paradigm behind the novel behaviors of oxide superlattices. Here, we
use scanning transmission electron microscopy to demonstrate a direct,
quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen
octahedral rotations across the BiFeO3-La0.7Sr0.3MnO3 interface to elucidate
how the change of crystal symmetry is accommodated. Combined with low-loss
electron energy loss spectroscopy imaging, we demonstrate a mesoscopic
antiferrodistortive phase transition and elucidate associated changes in
electronic properties in a thin layer directly adjacent to the interface
Use of computer simulation to establish parameters of steel structure strengthening elements
The article presents the results of computer simulation related to establishing the parameters of mine hoisting machine steel structure strengthening elements. The simulation was performed using the ANSYS computer program. The basis of this program is the finite element method therefore, selecting the type and the size of the finite element affects the calculation accuracy. There have been studied 11 computer models. The results obtained make it possible to establish the strengthening element optimal shape, size and thickness. The most optimal shape of the pad is a disc; this has a positive effect on reducing the level of mechanical stresses in the fracture zone of the beam. The strengthening element «disc pad» is used to combat fatigue failure of the brake beam structures of a mine hoisting machine. The article presents practical experience in the fight against fatigue failure of f mine hoisting machine steel structures
Use of computer simulation to establish parameters of steel structure strengthening elements
The article presents the results of computer simulation related to establishing the parameters of mine hoisting machine steel structure strengthening elements. The simulation was performed using the ANSYS computer program. The basis of this program is the finite element method therefore, selecting the type and the size of the finite element affects the calculation accuracy. There have been studied 11 computer models. The results obtained make it possible to establish the strengthening element optimal shape, size and thickness. The most optimal shape of the pad is a disc; this has a positive effect on reducing the level of mechanical stresses in the fracture zone of the beam. The strengthening element «disc pad» is used to combat fatigue failure of the brake beam structures of a mine hoisting machine. The article presents practical experience in the fight against fatigue failure of f mine hoisting machine steel structures
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