246 research outputs found
Resonance Compression of Acoustic Beams in Crystals
The resonant excitation of an intense elastic wave through nonspecular reflection of a special pump wave in a crystal is described. Geometric criteria are found under which mode conversion, when the incident and reflected beams belong to different acoustic branches, coexists with total internal reflection of an acoustic beam. In this case, the entire energy of an incident pump wave is spent on the excitation of a narrow intense reflected beam close in structure to an eigenmode. A consistent choice of orientations of the sagittal plane and crystal surface that excludes the reflection of a parasitic wave of leakage is found. The resonance parameters have been found for a medium with an arbitrary anisotropy. General relations are concretized for monoclinic, orthorhombic, trigonal, tetragonal, cubic, and hexagonal systems. Estimates and illustrations are given for a series of such crystals. The intensity of the reflected beam increases with its narrowing, but its diffraction divergence also increases with this narrowing. Nevertheless, the intensity of the beam can be increased by a factor of 5–10 at sufficiently high frequencies while keeping its divergence at an acceptable level. Amplification by two orders of magnitude can be achieved by compressing the beam in two dimensions through its double reflection
Equation of motion for dislocations with inertial effects
An approximate equation of motion is proposed for screw and edge
dislocations, which accounts for retardation and for relativistic effects in
the subsonic range. Good quantitative agreement is found, in accelerated or in
decelerated regimes, with numerical results of a more fundamental nature.Comment: 6 pages, 4 figures, LaTe
Magnetostimulated Chandges of Microhardness in Potassium Acid Phthalate Crystals
A decrease in microhardness along the (010) cleavage in potassium acid
phthalate single crystals by 15--18% after the application of a permanent
magnetic field was revealed for the first time. It is shown that the effect
revealed is of the volume character. The role of interlayer water in the
processes stimulated by a magnetic field is studied., Interlayer water plays
does not cause the observed changes it only plays the part of an indicator of
these changes in potassium acid phthalate crystals in a magnetic field. It is
established that microhardness in the (100) plane of the crystal in an applied
a magnetic field first increases by 12--15% and then remains constant in time
within the accuracy of the experiment. The possibility of varying the crystal
structure of potassium acid phthalate crystals by applying magnetic fields
inducing rearrangement in the system of hydrogen bonds or in the defect
structure is discussed.Comment: 6 pages, 7 figure
Lattice Resistance to Dislocation Motion at the Nanoscale
In this letter we propose a model that demonstrates the effect of free
surface on the lattice resistance experienced by a moving dislocation in
nanodimensional systems. This effect manifests in an enhanced velocity of
dislocation due to the proximity of the dislocation line to the surface. To
verify this finding, molecular dynamics simulations for an edge dislocation in
bcc molybdenum are performed and the results are found to be in agreement with
the numerical implementations of this model. The reduction in this effect at
higher stresses and temperatures, as revealed by the simulations, confirms the
role of lattice resistance behind the observed change in the dislocation
velocity.Comment: 4 Figure
Magnetic structural effect in nonequilibrium defective solids
Scientific study of the effect of structural memory of nonequilibrium
defective solids about the processing in magnetic field (the magnetic
structural effect (MSE) was continued in this paper. The study was aimed to
reveal the universal nature of the MSE, which was investigated in several new
nonequilibrium defective solids. The results of investigation of the processing
in the vortical magnetic field (PVMF) and its effect on the structure of the
natural magnetite Fe3O4 and the SnO2 films were presented. The methods of
Mössbauer and X-ray spectroscopy were used. The PVMF reduction of a
defectiveness of Fe3O4 structure in the magnetite was detected. The MSE was
also observed in the Mössbauer spectra of diamagnetic tin oxide SnO2 films
after the PVMF. One of the possible explanations of the MSE was given in the
paper.Comment: 6 pages, 6 figures, 3 table
Dislocation dynamics: from microscopic models to macroscopic crystal plasticity
In this paper we study the connection between four models describing
dislocation dynamics: a generalized 2D Frenkel-Kontorova model at the atomic
level, the Peierls-Nabarro model, the discrete dislocation dynamics and a
macroscopic model with dislocation densities. We show how each model can be
deduced from the previous one at a smaller scale
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