A study of the ultrasonic treatment effect on microstructure and mechanical properties of commercial purity titanium

This work presents a study of the ultrasonic treatment effect on microstructure and mechanical properties of ac-received and recrystallized commercial purity titanium specimens by means XRD, EBSD and TEM. It was demonstrated that the dislocation density growth and the twins with special boundaries [sigma]7b and [sigma]11b increase within the surface grains during ultrasonic treatment depend on initial structural state of the titanium specimens. The relationship between the structural parametrs change and the surface layer microhardness value of the titanium specimens subjected to ultrasonic treatment was shown. It was found that differences in the hardened surface layer depth and the surface microhardness of ac-received and recrystallized titanium specimens result in the same yield and ultimate tensile strength increment during ultrasonic treatment

Detecting and characterizing ferroelectric domain boundaries using nonphase-matched second-harmonic generation

We demonstrate that tilted planar ferroelectric domain boundaries create tilted second harmonic beams in nonphase-matched second harmonic generation, and that the tilt of the boundary can be deduced from the harmonic direction

Quantum phase transition in the Frenkel-Kontorova chain: from pinned instanton glass to sliding phonon gas

We study analytically and numerically the one-dimensional quantum Frenkel-Kontorova chain in the regime when the classical model is located in the pinned phase characterized by the gaped phonon excitations and devil's staircase. By extensive quantum Monte Carlo simulations we show that for the effective Planck constant $\hbar$ smaller than the critical value $\hbar_c$ the quantum chain is in the pinned instanton glass phase. In this phase the elementary excitations have two branches: phonons, separated from zero energy by a finite gap, and instantons which have an exponentially small excitation energy. At $\hbar=\hbar_c$ the quantum phase transition takes place and for $\hbar>\hbar_c$ the pinned instanton glass is transformed into the sliding phonon gas with gapless phonon excitations. This transition is accompanied by the divergence of the spatial correlation length and appearence of sliding modes at $\hbar>\hbar_c$.Comment: revtex 16 pages, 18 figure

Chaotic Repellers in Antiferromagnetic Ising Model

For the first time we present the consideration of the antiferromagnetic Ising model in case of fully developed chaos and obtain the exact connection between this model and chaotic repellers. We describe the chaotic properties of this statistical mechanical system via the invariants characterizing a fractal set and show that in chaotic region it displays phase transition at {\it positive} "temperature" $\beta_c = 0.89$. We obtain the density of the invariant measure on the chaotic repeller.Comment: LaTeX file, 10 pages, 4 PS figurs upon reques

Dual-arm Z-scan Technique to Extract Dilute Solute Nonlinearities from Solution Measurements

We present a technique in which small solute nonlinearities may be extracted from large solvent signals by performing simultaneous Z-scans on two samples (solvent and solution). By using a dual-arm Z-scan apparatus with identical arms, fitting error in determining the solute nonlinearity is reduced because the irradiance fluctuations are correlated for both the solvent and solution measurements. To verify the sensitivity of this technique, the dispersion of nonlinear refraction of a squaraine molecule is measured. Utilizing this technique allows for the effects of the solvent n2 to be effectively eliminated, thus overcoming a longstanding problem in nonlinear optical characterization of organic dyes

Temporal, Spectral, and Polarization Dependence of the Nonlinear Optical Response of Carbon Disulfide

Carbon disulfide is the most popular material for applications of nonlinear optical (NLO) liquids, and is frequently used as a reference standard for NLO measurements. Although it has been the subject of many investigations, determination of the third-order optical nonlinearity of CS2 has been incomplete. This is in part because of several strong mechanisms for nonlinear refraction (NLR), leading to a complex pulse width dependence. We expand upon the recently developed beam deflection technique, which we apply, along with degenerate four-wave mixing and Z-scan, to quantitatively characterize (in detail) the NLO response of CS2, over a broad temporal range, spanning 6 orders of magnitude (∼32 fs to 17 ns). The third-order response function, consisting of both nearly instantaneous bound-electronic and noninstantaneous nuclear contributions, along with the polarization and wavelength dependence from 390 to 1550 nm, is extracted from these measurements. This paper provides a self-consistent, quantitative picture of the third-order NLO response of liquid CS2, establishing it as an accurate reference material over this broad temporal and spectral range. These results allow prediction of the outcome of any NLR experiment on CS2

Fractal Spin Glass Properties of Low Energy Configurations in the Frenkel-Kontorova chain

We study numerically and analytically the classical one-dimensional Frenkel-Kontorova chain in the regime of pinned phase characterized by phonon gap. Our results show the existence of exponentially many static equilibrium configurations which are exponentially close to the energy of the ground state. The energies of these configurations form a fractal quasi-degenerate band structure which is described on the basis of elementary excitations. Contrary to the ground state, the configurations inside these bands are disordered.Comment: revtex, 9 pages, 9 figure

Transient lysosomal activation is essential for p75 nerve growth factor receptor expression in myelinated Schwann cells during Wallerian degeneration

Myelinated Schwann cells in the peripheral nervous system express the p75 nerve growth factor receptor (p75NGFR) as a consequence of Schwann cell dedifferentiation during Wallerian degeneration. p75NGFR has been implicated in the remyelination of regenerating nerves. Although many studies have shown various mechanisms underlying Schwann cell dedifferentiation, the molecular mechanism contributing to the re-expression of p75NGFR in differentiated Schwann cells is largely unknown. In the present study, we found that lysosomes were transiently activated in Schwann cells after nerve injury and that the inhibition of lysosomal activation by chloroquine or lysosomal acidification inhibitors prevented p75NGFR expression at the mRNA transcriptional level in an ex vivo Wallerian degeneration model. Lysosomal acidification inhibitors suppressed demyelination, but not axonal degeneration, thereby suggesting that demyelination mediated by lysosomes may be an important signal for inducing p75NGFR expression. Tumor necrosis factor-α (TNF-α) has been suggested to be involved in regulating p75NGFR expression in Schwann cells. In this study, we found that removing TNF-α in vivo did not significantly suppress the induction of both lysosomes and p75NGFR. Thus, these findings suggest that lysosomal activation is tightly correlated with the induction of p75NGFR in demyelinating Schwann cells during Wallerian degeneration

Three-Photon Absorption Spectra and Bandgap Scaling In Direct-Gap Semiconductors

This paper presents three-photon absorption (3PA) measurement results for nine direct-gap semiconductors, including full 3PA spectra for ZnSe, ZnS, and GaAs. These results, along with our theory of 3PA using an eight-band Kane model (four bands with double spin degeneracy), help to explain the significant disagreements between experiments and theory in the literature to date. 3PA in the eight-band model exhibits quantum interference between the various possible pathways that is not observed in previous two-band theories. We present measurements of degenerate 3PA coefficients in InSb, GaAs, CdTe, CdSe, ZnTe, CdS, ZnSe, ZnO, and ZnS. We examine bandgap, Eg, scaling using -band tunneling and perturbation theories that show agreement with the predicted Eg−7 dependence; however, for those semiconductors for which we measured full 3PA spectra, we observe significant discrepancies with both two-band theories. On the other hand, our eight-band model shows excellent agreement with the spectral data. We then use our eight-band theory to predict the 3PA spectra for 15 different semiconductors in their zinc-blende form. These results allow prediction and interpretation of the 3PA coefficients for various narrow to wide bandgap semiconductors

Steering of a Bosonic Mode with a Double Quantum Dot

We investigate the transport and coherence properties of a double quantum dot coupled to a single damped boson mode. Our numerically results reveal how the properties of the boson distribution can be steered by altering parameters of the electronic system such as the energy difference between the dots. Quadrature amplitude variances and the Wigner function are employed to illustrate how the state of the boson mode can be controlled by a stationary electron current through the dots.Comment: 10 pages, 6 figures, to appear in Phys. Rev.