The structures of the α‐alums RbCr(SO4)2·12H2O and CsCr(SeO4)2·12H2O at 293 and 12 K

The crystal structures of the α‐alums rubidium chromium bis(­sulfate) dodecahydrate, RbCr(SO₄)₂·12H₂O, and caesium chromium bis[tetraoxoselenate(VI)] dodecahydrate, CsCr(SeO₄)₂·12H₂O, have been determined by X‐ray diffraction at 293 and 12 K. The metal atoms lie on sites and the anions lie on threefold rotation axes. The accurate and extensive data sets lead to much more precise determinations than are available from earlier work, particularly at 12 K. The changes in the atomic displacement parameters between 293 and 12 K correspond to the respective predominances of intermolecular and intramolecular vibrational effects.     

A semiempirical theory of a one-layer cellular sound-absorbing lining with a perforated face panel

On the basis of the known approximate theories and the recent experimental data, a semiempirical theory of a resonance-type one-layer cellular sound-absorbing lining is developed. Approximate formulas are obtained for calculating the effective normal impedance with allowance for the geometric parameters of the sound-absorbing lining, the high sound-pressure levels, the presence of an entraining flow, and the nonlinear interaction of sound components of different frequencies within a given one-third-octave spectrum of noise. The results of numerical calculations by approximate formulas are compared with experiments and with the experimental and theoretical data reported by other authors. The proposed theory is found to agree well with experimental data.     

Properties of CdF2:Ga as a medium for real-time holography

The metastable nature of the excited state of bistable Ga centers in semiconducting CdF₂ crystals allows for the use of CdF₂:Ga and CdF₂:Ga,Y crystals as materials for real-time holography over a wide range of response times (1–1000 ms). The characteristics of these materials and optimal conditions for their use are discussed in the framework of a model that describes the decay of photo-induced gratings written in them. Received: 20 November 2000 / Published online: 20 April 2001     

Oscillator strengths and transition energies of diamond

The spectrum of the dielectric constant of three different samples of diamond in the 5–30-eV region is decomposed in thirteen elementary components. The main parameters of components are determined, and their nature is found on the basis of the band model.