177 research outputs found
Hydrogen-enhanced local plasticity in aluminum: an ab initio study
Dislocation core properties of Al with and without H impurities are studied
using the Peierls-Nabarro model with parameters determined by ab initio
calculations. We find that H not only facilitates dislocation emission from the
crack tip but also enhances dislocation mobility dramatically, leading to
macroscopically softening and thinning of the material ahead of the crack tip.
We observe strong binding between H and dislocation cores, with the binding
energy depending on dislocation character. This dependence can directly affect
the mechanical properties of Al by inhibiting dislocation cross-slip and
developing slip planarity.Comment: 4 pages, 3 figure
Screw dislocation in zirconium: An ab initio study
Plasticity in zirconium is controlled by 1/3 screw dislocations
gliding in the prism planes of the hexagonal close-packed structure. This
prismatic and not basal glide is observed for a given set of transition metals
like zirconium and is known to be related to the number of valence electrons in
the d band. We use ab initio calculations based on the density functional
theory to study the core structure of screw dislocations in zirconium.
Dislocations are found to dissociate in the prism plane in two partial
dislocations, each with a pure screw character. Ab initio calculations also
show that the dissociation in the basal plane is unstable. We calculate then
the Peierls barrier for a screw dislocation gliding in the prism plane and
obtain a small barrier. The Peierls stress deduced from this barrier is lower
than 21 MPa, which is in agreement with experimental data. The ability of an
empirical potential relying on the embedded atom method (EAM) to model
dislocations in zirconium is also tested against these ab initio calculations
Mesoscopic Analysis of Structure and Strength of Dislocation Junctions in FCC Metals
We develop a finite element based dislocation dynamics model to simulate the
structure and strength of dislocation junctions in FCC crystals. The model is
based on anisotropic elasticity theory supplemented by the explicit inclusion
of the separation of perfect dislocations into partial dislocations bounding a
stacking fault. We demonstrate that the model reproduces in precise detail the
structure of the Lomer-Cottrell lock already obtained from atomistic
simulations. In light of this success, we also examine the strength of
junctions culminating in a stress-strength diagram which is the locus of points
in stress space corresponding to dissolution of the junction.Comment: 9 Pages + 4 Figure
Fingering Instability of Dislocations and Related Defects
We identify a fundamental morphological instability of mobile dislocations in
crystals and related line defects. A positive gradient in the local driving
force along the direction of defect motion destabilizes long-wavelength
vibrational modes, producing a ``fingering'' pattern. The minimum unstable
wavelength scales as the inverse square root of the force gradient. We
demonstrate the instability's onset in simulations of a screw dislocation in Al
(via molecular dynamics) and of a vortex in a 3-d XY ``rotator'' model.Comment: 4 pages, 3 figure
Plastic Flow in Two-Dimensional Solids
A time-dependent Ginzburg-Landau model of plastic deformation in
two-dimensional solids is presented. The fundamental dynamic variables are the
displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t.
Damping is assumed to arise from the shear viscosity in the momentum equation.
The elastic energy density is a periodic function of the shear and tetragonal
strains, which enables formation of slips at large strains. In this work we
neglect defects such as vacancies, interstitials, or grain boundaries. The
simplest slip consists of two edge dislocations with opposite Burgers vectors.
The formation energy of a slip is minimized if its orientation is parallel or
perpendicular to the flow in simple shear deformation and if it makes angles of
with respect to the stretched direction in uniaxial stretching.
High-density dislocations produced in plastic flow do not disappear even if
the flow is stopped. Thus large applied strains give rise to metastable,
structurally disordered states. We divide the elastic energy into an elastic
part due to affine deformation and a defect part. The latter represents degree
of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at
http://stat.scphys.kyoto-u.ac.jp/index-e.htm
Temperature effects on dislocation core energies in silicon and germanium
Temperature effects on the energetics of the 90-degree partial dislocation in
silicon and germanium are investigated, using non-equilibrium methods to
estimate free energies, coupled with Monte Carlo simulations. Atomic
interactions are described by Tersoff and EDIP interatomic potentials. Our
results indicate that the vibrational entropy has the effect of increasing the
difference in free energy between the two possible reconstructions of the
90-degree partial, namely, the single-period and the double-period geometries.
This effect further increases the energetic stability of the double-period
reconstruction at high temperatures. The results also indicate that anharmonic
effects may play an important role in determining the structural properties of
these defects in the high-temperature regime.Comment: 8 pages in two-column physical-review format with six figure
Implications of SU(2) symmetry on the dynamics of population difference in the two-component atomic vapor
We present an exact many body solution for the dynamics of the population
difference induced by an rf-field in the two-component atomic cloud
characterized by equal scattering lengths. This situation is very close to the
actual JILA experiments with the two-component Rb vapor. We show that no
intrinsic decoherence exists for , provided the exact SU(2) symmetry
holds. This contrasts with finite dissipation of the normal modes even in the
presence of the SU(2) symmetry. The intrinsic decoherence for \ may
occur as long as deviations from the exact SU(2) symmetry are taken into
account. Such decoherence, however, should be characterized by very long times
governed by the smallness of the deviations from the symmetry. We suggest
testing the evolution of by conducting echo-type experiments.Comment: 5 RevTex pages, no figures, typos correcte
ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΈΡ ΡΠ²Π»Π΅Π½ΠΈΠΉ Π² Π±Π°ΡΠ±ΠΎΡΠ°ΠΆΠ½ΠΎΠΉ Π·ΠΎΠ½Π΅ ΠΏΠ»Π°Π²ΠΈΠ»ΡΠ½ΠΎΠ³ΠΎ Π°Π³ΡΠ΅Π³Π°ΡΠ° Β«ΠΠΎΠ±Π΅Π΄Π°Β» ΠΌΠ΅ΡΠΎΠ΄ΠΎΠΌ Ρ ΠΎΠ»ΠΎΠ΄Π½ΠΎΠ³ΠΎ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π‘ΠΎΠΎΠ±ΡΠ΅Π½ΠΈΠ΅ 3. ΠΠΈΠ΄ΡΠΎΠ³Π°Π·ΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΠΊΠ° ΠΊΠΎΠΌΠ±ΠΈΠ½ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠΈ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ Π³Π°Π·ΠΎΠΌ Ρ ΠΏΠΎΠΌΠΎΡΡΡ Π΄ΠΎΠ½Π½ΠΎΠΉ ΠΈ Π±ΠΎΠΊΠΎΠ²ΠΎΠΉ ΡΡΡΠΌ
Hydro-gas regularities of liquid combined blowing by gas were studied using cold modeling method at Archimedes criterion for lateral Arl = 12Γ·120 and bottom blowing Arb = 5Γ·60 simulating Pobeda bubbling unit. The blowing was performed simultaneously by bottom lance vertically fixed in centre of reactor and by the lateral lance which was attached at an angle 5Β° to the horizontal axis. The quantitative estimation of instantaneous and average circulation velocities (Vav) of liquid flow elements in different bath areas, depending on the location of blowing zone and Archimedes criterion, was performed. The liquid motion trajectory was determined. A vortex zone was revealed near the liquid surface and the reactor shell, where instantaneous velocity of the liquid flow elements changes from 69.9 to 181.1 mm/s and Vav = 123.8 mm/s. The circulation flows fade in the bulk of liquid and Vav decreases from 123.8 to 47.0 and 54.1 mm/s. It was shown that, in general, circulation velocity depends on the blowing intensity and appears to be higher for the zone of overlapping of lateral and bottom streams. The dynamic blowing conditions, which ensure the direct contact of lateral and bottom jets leading to their interflow and increased spatter formation, were identified. The characteristics of 3 types of surface oscillations for interface phases βpure liquid- gas-liquid layerβ, as well as the estimation of the lateral and bottom blowing impact on the type of oscillation were provided. It has been noted that the introduction of the bottom blowing (Arb = 5) causes the wave-like motion of liquid (the 2nd type) along with the transverse oscillations of the 1st type, and at higher values of Arb = 25 the angular oscillations of the 3rd type develop. It has been shown that the presence of a lateral jet at the combined blowing decreases angles of bath swinging to 8β12Β° to horizontal axis. For the estimation of oscillation intensity, Ξhl = (hl )max β (hl )min value, which means the difference between maximum (hl )max and minimum (hl )min height of liquid for the full-wave oscillations (Ο), was introduced. The height of liquid (hl ) was plotted as a function of Ο, Arl , Arb, Ξhl was determined on the basis of obtained graph values, which varied upon modeling over the range of 7.7β69.5 mm. The relation between the liquid circulation velocity and the oscillation value (Ξhl ) was established for different bath zones and dynamic conditions of the blowing. The impact of all oscillations types on potential erosive lining wear of Pobeda bubbling unit and the completeness of adoption of charging material nearby the bath surface was investigated.ΠΠ΅ΡΠΎΠ΄ΠΎΠΌ Ρ
ΠΎΠ»ΠΎΠ΄Π½ΠΎΠ³ΠΎ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π² ΠΈΠ½ΡΠ΅ΡΠ²Π°Π»Π°Ρ
Π²Π΅Π»ΠΈΡΠΈΠ½ ΠΊΡΠΈΡΠ΅ΡΠΈΡ ΠΡΡ
ΠΈΠΌΠ΅Π΄Π° Π΄Π»Ρ Π±ΠΎΠΊΠΎΠ²ΠΎΠ³ΠΎ (ArΠ± = 12Γ·120) ΠΈ Π΄ΠΎΠ½Π½ΠΎΠ³ΠΎ (ArΠ΄ = 5Γ·60) Π΄ΡΡΡΡ ΠΏΡΠΈΠΌΠ΅Π½ΠΈΡΠ΅Π»ΡΠ½ΠΎ ΠΊ ΡΡΠ»ΠΎΠ²ΠΈΡΠΌ ΡΠ°Π±ΠΎΡΡ Π±Π°ΡΠ±ΠΎΡΠ°ΠΆΠ½ΠΎΠ³ΠΎ ΠΏΠ»Π°Π²ΠΈΠ»ΡΠ½ΠΎΠ³ΠΎ Π°Π³ΡΠ΅Π³Π°ΡΠ° Β«ΠΠΎΠ±Π΅Π΄Π°Β» (ΠΠΠ) ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Ρ Π³ΠΈΠ΄ΡΠΎΠ³Π°Π·ΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠ΅ Π·Π°ΠΊΠΎΠ½ΠΎΠΌΠ΅ΡΠ½ΠΎΡΡΠΈ ΠΊΠΎΠΌΠ±ΠΈΠ½ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠΈ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ Π³Π°Π·ΠΎΠΌ. ΠΡΠΎΠ΄ΡΠ²ΠΊΡ ΠΎΡΡΡΠ΅ΡΡΠ²Π»ΡΠ»ΠΈ ΠΎΠ΄Π½ΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎ Π΄ΠΎΠ½Π½ΠΎΠΉ ΡΡΡΠΌΠΎΠΉ, ΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½Π½ΠΎΠΉ Π²Π΅ΡΡΠΈΠΊΠ°Π»ΡΠ½ΠΎ ΠΏΠΎ ΡΠ΅Π½ΡΡΡ ΡΠ΅Π°ΠΊΡΠΎΡΠ°, ΠΈ Π±ΠΎΠΊΠΎΠ²ΠΎΠΉ, ΡΠ°ΡΠΏΠΎΠ»ΠΎΠΆΠ΅Π½Π½ΠΎΠΉ ΠΏΠΎΠ΄ ΡΠ³Π»ΠΎΠΌ 5Β° ΠΊ Π³ΠΎΡΠΈΠ·ΠΎΠ½ΡΠ°Π»ΡΠ½ΠΎΠΉ ΠΎΡΠΈ. ΠΡΠΎΠ²Π΅Π΄Π΅Π½Π° ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²Π΅Π½Π½Π°Ρ ΠΎΡΠ΅Π½ΠΊΠ° ΠΌΠ³Π½ΠΎΠ²Π΅Π½Π½ΠΎΠΉ ΠΈ ΡΡΠ΅Π΄Π½Π΅ΠΉ (VΡΡ) ΡΠΊΠΎΡΠΎΡΡΠ΅ΠΉ ΡΠΈΡΠΊΡΠ»ΡΡΠΈΠΈ ΡΠ»Π΅ΠΌΠ΅Π½ΡΠΎΠ² ΠΏΠΎΡΠΎΠΊΠ° ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ Π½Π° ΡΠ°Π·Π½ΡΡ
ΡΡΠ°ΡΡΠΊΠ°Ρ
Π²Π°Π½Π½Ρ Π² Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΎΡ ΠΌΠ΅ΡΡΠΎΠ½Π°Ρ
ΠΎΠΆΠ΄Π΅Π½ΠΈΡ Π·ΠΎΠ½Ρ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠΈ ΠΈ ΠΊΡΠΈΡΠ΅ΡΠΈΠ΅Π² ΠΡΡ
ΠΈΠΌΠ΅Π΄Π°. ΠΠΏΡΠ΅Π΄Π΅Π»Π΅Π½Π° ΡΡΠ°Π΅ΠΊΡΠΎΡΠΈΡ Π΄Π²ΠΈΠΆΠ΅Π½ΠΈΡ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ. ΠΠ±Π»ΠΈΠ·ΠΈ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ ΠΈ ΠΊΠΎΡΠΏΡΡΠ° ΡΠ΅Π°ΠΊΡΠΎΡΠ° ΠΎΠ±Π½Π°ΡΡΠΆΠ΅Π½Π° Π²ΠΈΡ
ΡΠ΅Π²Π°Ρ Π·ΠΎΠ½Π°, Π³Π΄Π΅ ΠΌΠ³Π½ΠΎΠ²Π΅Π½Π½Π°Ρ ΡΠΊΠΎΡΠΎΡΡΡ Π΄Π²ΠΈΠΆΠ΅Π½ΠΈΡ ΡΠ»Π΅ΠΌΠ΅Π½ΡΠ° ΠΏΠΎΡΠΎΠΊΠ° ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ ΠΈΠ·ΠΌΠ΅Π½ΡΠ΅ΡΡΡ ΠΎΡ 69,9 Π΄ΠΎ 183,1 ΠΌΠΌ/Ρ ΠΈ VΡΡ = 123,8 ΠΌΠΌ/Ρ. Π ΠΎΠ±ΡΠ΅ΠΌΠ΅ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ ΡΠΈΡΠΊΡΠ»ΡΡΠΈΠΎΠ½Π½ΡΠ΅ ΠΏΠΎΡΠΎΠΊΠΈ Π·Π°ΡΡΡ
Π°ΡΡ, ΠΈ VΡΡ ΡΠΌΠ΅Π½ΡΡΠ°Π΅ΡΡΡ ΠΎΡ 123,8 Π΄ΠΎ 47,0 ΠΈ 54,1 ΠΌΠΌ/Ρ. ΠΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ Π² ΠΎΠ±ΡΠ΅ΠΌ ΡΠ»ΡΡΠ°Π΅ ΡΠΊΠΎΡΠΎΡΡΡ ΡΠΈΡΠΊΡΠ»ΡΡΠΈΠΈ Π·Π°Π²ΠΈΡΠΈΡ ΠΎΡ ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠΈ Π½Π° ΡΡΡΠΌΠ°Ρ
ΠΈ ΡΡΠ°Π½ΠΎΠ²ΠΈΡΡΡ Π²ΡΡΠ΅ Π΄Π»Ρ ΠΎΠ±Π»Π°ΡΡΠΈ Π½Π°Π»ΠΎΠΆΠ΅Π½ΠΈΡ Π±ΠΎΠΊΠΎΠ²ΠΎΠΉ ΠΈ Π΄ΠΎΠ½Π½ΠΎΠΉ ΡΡΡΡΠΉ. ΠΠΏΡΠ΅Π΄Π΅Π»Π΅Π½Ρ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΡΡΠ»ΠΎΠ²ΠΈΡ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠΈ, ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°ΡΡΠΈΠ΅ Π½Π΅ΠΏΠΎΡΡΠ΅Π΄ΡΡΠ²Π΅Π½Π½ΡΠΉ ΠΊΠΎΠ½ΡΠ°ΠΊΡ Π±ΠΎΠΊΠΎΠ²ΠΎΠ³ΠΎ ΠΈ Π΄ΠΎΠ½Π½ΠΎΠ³ΠΎ ΡΠ°ΠΊΠ΅Π»ΠΎΠ², ΠΏΡΠΈΠ²ΠΎΠ΄ΡΡΠΈΠΉ ΠΊ ΡΠ»ΠΈΡΠ½ΠΈΡ ΠΏΠΎΡΠΎΠΊΠΎΠ² ΠΈ ΠΏΠΎΠ²ΡΡΠ΅Π½Π½ΠΎΠΌΡ Π±ΡΡΠ·Π³ΠΎΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ. ΠΡΠΈΠ²Π΅Π΄Π΅Π½Π° Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊΠ° 3 Π²ΠΈΠ΄ΠΎΠ² ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΠΉ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ ΡΠ°Π·Π΄Π΅Π»Π° ΡΠ°Π· Β«ΡΠΈΡΡΠ°Ρ ΠΆΠΈΠ΄ΠΊΠΎΡΡΡ β Π³Π°Π·ΠΎΠΆΠΈΠ΄ΠΊΠΎΡΡΠ½ΡΠΉ ΡΠ»ΠΎΠΉΒ» ΠΈ Π΄Π°Π½Π° ΠΎΡΠ΅Π½ΠΊΠ° Π²Π»ΠΈΡΠ½ΠΈΡ Π±ΠΎΠΊΠΎΠ²ΠΎΠ³ΠΎ ΠΈ Π΄ΠΎΠ½Π½ΠΎΠ³ΠΎ Π΄ΡΡΡΡ Π½Π° ΡΠ°Π·Π½ΠΎΠ²ΠΈΠ΄Π½ΠΎΡΡΡ Π²ΠΎΠ·Π½ΠΈΠΊΠ°ΡΡΠΈΡ
ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΠΉ. ΠΡΠΌΠ΅ΡΠ΅Π½ΠΎ, ΡΡΠΎ Π²Π²ΠΎΠ΄ Π΄ΠΎΠ½Π½ΠΎΠ³ΠΎ Π΄ΡΡΡΡ (ArΠ΄ = 5) ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡ, Π½Π°ΡΡΠ΄Ρ Ρ ΠΏΠΎΠΏΠ΅ΡΠ΅ΡΠ½ΡΠΌΠΈ ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΡΠΌΠΈ 1-Π³ΠΎ ΡΠΈΠΏΠ°, ΠΊ ΠΏΠΎΡΠ²Π»Π΅Π½ΠΈΡ Π²ΠΎΠ»Π½ΠΎΠΎΠ±ΡΠ°Π·Π½ΠΎΠ³ΠΎ Π΄Π²ΠΈΠΆΠ΅Π½ΠΈΡ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ (2-ΠΉ ΡΠΈΠΏ), Π° ΠΏΡΠΈ Π±ΠΎΠ»Π΅Π΅ Π²ΡΡΠΎΠΊΠΈΡ
Π·Π½Π°ΡΠ΅Π½ΠΈΡΡ
ArΠ΄ = 25 β ΠΊ ΡΠ³Π»ΠΎΠ²ΡΠΌ ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΡΠΌ (3-ΠΉ ΡΠΈΠΏ). ΠΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ ΠΏΡΠΈ ΠΊΠΎΠΌΠ±ΠΈΠ½ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠ΅ Π½Π°Π»ΠΈΡΠΈΠ΅ Π±ΠΎΠΊΠΎΠ²ΠΎΠ³ΠΎ ΡΠ°ΠΊΠ΅Π»Π° ΡΠΌΠ΅Π½ΡΡΠ°Π΅Ρ ΡΠ³Π»Ρ ΡΠ°ΡΠΊΠ°ΡΠΈΠ²Π°Π½ΠΈΡ Π²Π°Π½Π½Ρ ΠΊ Π³ΠΎΡΠΈΠ·ΠΎΠ½ΡΡ Π΄ΠΎ 8β12Β°. ΠΠ»Ρ ΠΎΡΠ΅Π½ΠΊΠΈ ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΠΉ Π²Π²Π΅Π΄Π΅Π½Π° Π²Π΅Π»ΠΈΡΠΈΠ½Π° ΞhΠΆ = (hΠΆ)max β (hΠΆ)min, Ρ.Π΅. ΡΠ°Π·Π½ΠΎΡΡΡ ΠΌΠ΅ΠΆΠ΄Ρ ΠΌΠ°ΠΊΡΠΈΠΌΠ°Π»ΡΠ½ΠΎΠΉ (hΠΆ)max ΠΈ ΠΌΠΈΠ½ΠΈΠΌΠ°Π»ΡΠ½ΠΎΠΉ (hΠΆ)min Π²ΡΡΠΎΡΠΎΠΉ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ Π·Π° ΠΏΠΎΠ»Π½ΡΠΉ ΡΠΈΠΊΠ» ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΠΉ (Ο). ΠΠΎΡΡΡΠΎΠ΅Π½Ρ Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ Π²ΡΡΠΎΡΡ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ (hΠΆ) ΠΎΡ Ο, ArΠ± ΠΈ ArΠ΄, Π½Π° ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΈΠΈ ΠΊΠΎΡΠΎΡΡΡ
ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½Ρ Π²Π΅Π»ΠΈΡΠΈΠ½Ρ ΞhΠΆ, Π²Π°ΡΡΠΈΡΡΠ΅ΠΌΡΠ΅ ΠΏΡΠΈ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ Π² ΠΈΠ½ΡΠ΅ΡΠ²Π°Π»Π΅ 7,7β69,5 ΠΌΠΌ. ΠΠ»Ρ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΠΎΠ±Π»Π°ΡΡΠ΅ΠΉ Π²Π°Π½Π½Ρ ΠΈ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΠ»ΠΎΠ²ΠΈΠΉ ΠΏΡΠΎΠ΄ΡΠ²ΠΊΠΈ ΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½Π° Π²Π·Π°ΠΈΠΌΠΎΡΠ²ΡΠ·Ρ ΠΌΠ΅ΠΆΠ΄Ρ ΡΠΊΠΎΡΠΎΡΡΡΡ ΡΠΈΡΠΊΡΠ»ΡΡΠΈΠΈ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠΈ ΠΈ Π²Π΅Π»ΠΈΡΠΈΠ½ΠΎΠΉ ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΠΉ (ΞhΠΆ). Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½ΠΎ Π²Π»ΠΈΡΠ½ΠΈΠ΅ Π²ΡΠ΅Ρ
Π²ΠΈΠ΄ΠΎΠ² ΠΊΠΎΠ»Π΅Π±Π°Π½ΠΈΠΉ Π½Π° Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΡΠΉ ΡΡΠΎΠ·ΠΈΠ²Π½ΡΠΉ ΠΈΠ·Π½ΠΎΡ ΡΡΡΠ΅ΡΠΎΠ²ΠΊΠΈ ΠΠΠ ΠΈ ΠΏΠΎΠ»Π½ΠΎΡΡ ΡΡΠ²ΠΎΠ΅Π½ΠΈΡ ΡΠΈΡ
ΡΠΎΠ²ΡΡ
ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ² Π²Π±Π»ΠΈΠ·ΠΈ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ Π²Π°Π½Π½Ρ
Atomic structure of dislocation kinks in silicon
We investigate the physics of the core reconstruction and associated
structural excitations (reconstruction defects and kinks) of dislocations in
silicon, using a linear-scaling density-matrix technique. The two predominant
dislocations (the 90-degree and 30-degree partials) are examined, focusing for
the 90-degree case on the single-period core reconstruction. In both cases, we
observe strongly reconstructed bonds at the dislocation cores, as suggested in
previous studies. As a consequence, relatively low formation energies and high
migration barriers are generally associated with reconstructed
(dangling-bond-free) kinks. Complexes formed of a kink plus a reconstruction
defect are found to be strongly bound in the 30-degree partial, while the
opposite is true in the case of 90-degree partial, where such complexes are
found to be only marginally stable at zero temperature with very low
dissociation barriers. For the 30-degree partial, our calculated formation
energies and migration barriers of kinks are seen to compare favorably with
experiment. Our results for the kink energies on the 90-degree partial are
consistent with a recently proposed alternative double-period structure for the
core of this dislocation.Comment: 12 pages, two-column style with 8 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#rn_di
Feedback-control of quantum systems using continuous state-estimation
We present a formulation of feedback in quantum systems in which the best
estimates of the dynamical variables are obtained continuously from the
measurement record, and fed back to control the system. We apply this method to
the problem of cooling and confining a single quantum degree of freedom, and
compare it to current schemes in which the measurement signal is fed back
directly in the manner usually considered in existing treatments of quantum
feedback. Direct feedback may be combined with feedback by estimation, and the
resulting combination, performed on a linear system, is closely analogous to
classical LQG control theory with residual feedback.Comment: 12 pages, multicol revtex, revised and extende
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