IR laser and heat-induced changes in annulus fibrosus collagen structure

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.     

Influence of the relative magnitude of the Jahn-Teller effect and level splitting in a cubic crystal field on the properties of the ground state of vacancy defects in semiconductors

The spatial structure of a vacancy and the properties of its electronic energy levels in a semiconductor with a lattice possessing point symmetry T _d are considered for an arbitrary relationship between the Jahn-Teller stabilization energy (associated with the F ₂ vibrational mode) and the t ₂-a ₁ splitting (Δ) caused by the cubic crystal field. The position of the minimum of the adiabatic potential and the distortion of the electronic density are calculated for the vacancy ground state for different relative values of Δ and coupling constants of the vacancy to the F ₂ vibrational mode. It is shown that, if the ground state of a carrier bound to a vacancy is a t ₂ state, the trigonal symmetry of the environment of the vacancy persists for any values of Δ, but the amount of displacements of atoms near the vacancy and the localization of the wave function of the bound carrier on the broken bond earmarked by the Jahn-Teller effect can depend heavily on Δ and are maximal at Δ → 0. This is also the case when the ground state of the vacancy is the a ₁ state, but the magnitude of Δ does not exceed a certain value, which is determined by the coupling constants and the elastic constant. The relation between Δ and the coupling constants is also shown to affect the properties of trigonal vacancy-shallow-donor complexes. For these complexes, calculations are performed of the dependence of the dipole direction determining the optical properties of the vacancy defect on the distortion of vacancy orbitals caused by the donor entering into the complex.     

Fermi-edge polaritons in Bragg multiple-quantum-well structures

The polariton propagation in one-dimensional photonic crystals and quasicrystals based on highly doped quantum-well structures has been theoretically studied. The superradiant and photonic crystal regimes have been considered and expressions for band gap edges for light waves in the Bragg structures have been obtained. The reflection and absorption spectra of such systems have been calculated and the so-called two-wave approximation to their study has been applied. The optical properties of the doped multiple-quantum-well structures are compared with those of undoped ones.     

Photonic-crystal waveguide for the second-harmonic generation

The possibility of efficient second-harmonic generation in the optical range in a planar dielectric waveguide with the active region in the form of a one-dimensional photonic crystal has been theoretically shown. The true phase matching can be achieved by controlling wave dispersion in the photonic crystal. The dispersion equations for the photonic crystal and three-layer waveguide have been self-consistently solved. It is shown that the coherence length may exceed 10 mm.     

Thermal stability of collagen in intervertebral disc tissues

The thermal stability of collagen in intervertebral disc tissues was studied using differential scanning calorimetry. It was found that the melting of collagen in a native tissue was complete at 62–75°C (ΔH = 62.4 J/g) under heating excised annulus fibrosus and nucleus pulposus samples. On heating an intact structure up to 80°C, the denaturation of collagen did not occur. It was shown that the degradation of a proteoglycan component in the test tissues had no effect on the thermal stability of collagen.     

Injection of holes into organic molecular solids

A model is proposed for injection of carriers (holes) from a metal into organic molecular solids. It is shown that the total injection current is restricted by the process of tunneling between the levels of a molecule and states in the metal. The role played by phonons in the tunneling transition is studied in detail, and the contribution from these transitions to the total injection current is estimated over a wide temperature range.     

Furoxano[3,4‐b]pyrazines: The first synthesis and x‐ray structure

Novel furoxanopyrazines have been synthesized via reaction of 2‐alkoxy‐3,5‐dinitro‐6‐chloropyrazines with sodium azide.