Structure and properties of confined sodium nitrite

The temperature evolution of the structure of NaNO(2) nanocomposite ferroelectric material in a porous glass with 7 nm pores was studied by neutron diffraction in temperature region from room temperature up to the melting, i.e. in the ferro- and paraelectric phases. It is demonstrated that in the ferroelectric phase the structure is consistent with the structure of the bulk, but above the ferroelectric phase transition (and up to approximately 513 K) a volume premelted state is formed, manifesting itself in a growth of amplitudes of ion thermal vibrations, a steep increase of elementary cell volume and "softening" of lattice. For the first time the temperature dependence of order parameter eta for confined sodium nitrite is determined. eta (T) follows a power law with T(C)=425.6+/- 2.1 K and beta= 0.31+/- 0.04, which is essentially different from that for bulk NaNO(2). Our obtained data are in a good agreement with the results of earlier dielectric and neutron diffraction measurements.     

First measurement of a phonon dispersion curve by inelastic X-ray scattering

Inelastic scattering of 13.8 keV X-rays with very high energy resolution of E=55 meV was used to measure the phonon dispersion curves for theLA andLO modes in the [00] direction in Be. The results agree with inelastic neutron scattering data known from the literature. The X-ray scattering intensities of the phonon excitations for different momentum transfers are in very good agreement with the prediction from the scattering law.     

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

Vacuum-field level shifts in a single trapped ion mediated by a single distant mirror

A distant mirror leads to a vacuum-induced level shift in a laser-excited atom. This effect has been measured with a single mirror 25 cm away from a single, trapped barium ion. This dispersive action is the counterpart to the mirror's dissipative effect, which has been shown earlier to effect a change in the ion's spontaneous decay [Nature (London) 413, 495 (2001)]]. The experimental data are well described by eight-level optical Bloch equations which are amended to take into account the presence of the mirror according to the model in Phys. Rev. A 66, 023816 (2002)]. Observed deviations from simple dispersive behavior are attributed to multilevel effects.     

Investigations of residual stresses in carbon fibre/aluminium-composites using X-ray diffraction

Investigations of residual stresses have been carried out on unidirectionally carbon fibre reinforced aluminium using X-ray diffraction. It was found that the carbon exists in compression parallel to the fibre axis and in tension perpendicular to the fibre axis after the fabrication of the MMCs by a liquid infiltration process. Furthermore, it was observed that the intermetallic phase Al₃Ni was in tension (+ 100 MPa) parallel to the fibre axis and in considerable residual compression (– 400 MPa) perpendicular to the fibre axis.