Scanning Electron Microscopy Observation of the Voltage Contrast Image of the Ferroelectric Domain Structure in the LiNbO3 Crystal

This paper reports a scanning electron microscopy study of the formation of the voltage contrast image of the ferroelectric domain structure in the LiNbO3 crystal. We investigated the formation of the pyroelectric voltage contrast image of the regular domain structure. For our experiment, we used ZY cut of a LiNbO3 crystal which had a regular domain structure with a domain width of -55 μm. The regular domain structure in the LiNbO3 crystal was formed by the method of thermo-electrical treatment after growth. The pyroelectric voltage contrast image of the regular domain structure in the scanning electron microscope was formed by applying the pyroelectric effect along polar axis Z. The difference in the voltage contrast in the neighboring domains connect with opposite directions of polar axis Z in the neighboring domains. It is shown that the voltage contrast of the ferroelectric domain structures is defined by the physical properties and orientation of the ferroelectric crystals

Correlated two-photon emission by transitions of Dirac-Volkov states in intense laser fields: QED predictions

In an intense laser field, an electron may decay by emitting a pair of photons. The two photons emitted during the process, which can be interpreted as a laser-dressed double Compton scattering, remain entangled in a quantifiable way: namely, the so-called concurrence of the photon polarizations gives a gauge-invariant measure of the correlation of the hard gamma rays. We calculate the differential rate and concurrence for a backscattering setup of the electron and photon beam, employing Volkov states and propagators for the electron lines, thus accounting nonperturbatively for the electron-laser interaction. The nonperturbative results are shown to differ significantly compared to those obtained from the usual double Compton scattering.Comment: 32 pages, 12 figure

Null Branes in Curved Backgrounds

We consider null bosonic p-branes in curved space-times. Some exact solutions of the classical equations of motion and of the constraints for the null membrane in general stationary, axially symmetrical, four dimensional, gravity background are found.Comment: 19 pages, LaTeX, no figures. Extended version. To appear in Phys. Rev.

Friedmann Universes and Exact Solutions in String Cosmology

We show that the classical null strings generate the Hilbert-Einstein gravity corresponding to D-dimensional Friedmann universes.Comment: 8 pages, LATE

Muon pair creation from positronium in a circularly polarized laser field

We study elementary particle reactions that result from the interaction of an atomic system with a very intense laser wave of circular polarization. As a specific example, we calculate the rate for the laser-driven reaction $e^+e^- \to \mu^+\mu^-$, where the electron and positron originate from a positronium atom or, alternatively, from a nonrelativistic $e^+e^-$ plasma. We distinguish accordingly between the coherent and incoherent channels of the process. Apart from numerical calculations, we derive by analytical means compact formulas for the corresponding reaction rates. The rate for the coherent channel in a laser field of circular polarization is shown to be damped because of the destructive interference of the partial waves that constitute the positronium ground-state wave packet. Conditions for the observation of the process via the dominant incoherent channel in a circularly polarized field are pointed out

Scanning Electron Microscopy Observation of the Interaction Between the Surface Acoustic Waves and Regular Domain Structures in the LiNbO3 Crystals

This paper reports a scanning electron microscope study of the interaction between the surface acoustic waves and regular domain structures in LiNbO3 crystals. The regular domain structures in LiNbO3 crystals were formed by the method of the thermo-electric treatment after growth. We investigated two modes of interaction: the surface-acoustic-waves propagate along and across the regular domain structures. It is shown that the regular domain structures in the first case can be used as an acoustical wave-guide, because the power-flow vector of the surface acoustic waves has the direction along the domain structure. Also we observed that the surface acoustic wave inverts the voltage contrast of the image in the scanning electron microscope by π during the process of the propagation across the domain walls

Three-dimensional quantification of soft tissue changes and its relationship to skeletal changes after Le Fort III, monobloc, and facial bipartition in syndromic craniosynostosis

To determine the effect of midface surgery on soft tissue changes and their relationship to hard tissue changes in patients with syndromic craniosynostosis. A retrospective analysis of patients who had undergone Le Fort III (LFIII), monobloc (MB), or facial bipartition (FB) was conducted. A 3D soft tissue mesh was generated from the preoperative scan and registered to the postoperative scan, after which the advancement was visualised. A total of 68 patients were included: 28 had undergone LFIII, 27 MB, and 13 FB. The included diagnoses were Apert (n = 23), Crouzon (n = 34), and craniofrontonasal syndrome (n = 11). After LFIII, most soft tissue advancement was seen around subnasale and pronasale (mean 15.1 ± 5.9 mm and 14.7 ± 5.7 mm, at age 7–12 years). After MB, a greater hard tissue than soft tissue advancement was seen for most landmarks, showing a high positive correlation. In patients undergoing FB without distraction (n = 10), mean preoperative inter-canthal distance was 48.9 mm, this reduced by 6.9 mm postoperatively. This study provides a comprehensive overview of the outcomes after midface surgery using 3D quantification for a better understanding of the soft tissue changes and their relationship to hard tissue changes.</p