Far infrared and millimetre dielectric response of incommensurate and ferroelectric K2SeO4

Dielectric response of K₂SeO₄ in the spectral region 5–460cm^–1 was determined using transmissivity and reflectivity measurements as a function of temperature between 80 and 300K. The spectral features above 20cm^–1 are interpreted using results of lattice vibrational analysis in three known commensurate phases. The low-frequency dielectric anomaly in the incommensurate phase can be roughly described by critical slowing-down of a Debye relaxation given rise to by the overdamped infrared active phason mode which softens at the incommensurate-commensurate transition.     

Composite-meson model with vector dominance based onU(2) invariant four-quark interactions

An effective Lagrangian for composite σ, π, ω and ρ mesons is derived from a four-quark theory of the Nambu-Jona-Lasinio type. We study the various mutual relations between the renormalized parameters of this model. If electro-weak interactions are added, the model provides a dynamical foundation of vector-meson dominance.     

On some regularities in multinucleon transfer reactions with heavy ions

Multinucleon transfer reactions have been investigated by bombarding ²³²Th and ¹⁹⁷Au targets with 137 MeV ¹⁶O ions. An exponential yield dependence on the Q-values was observed for nucleon exchange reactions.     

Polar phonons and specific features of the ferroelectric states in cadmium titanate

Polarized spectra of reflectance R(ν) and transmittance Tr(ν) of single-crystal CdTiO₃ samples have been obtained in the frequency range 7 < ν < 1000 cm^?1 and for temperatures from 5 to 300 K using IR Fourier spectroscopy and submillimeter-range techniques. Dispersion analysis was carried out in terms of the additive-oscillator model, and dielectric responses ε(ν) and ε″(ν) were calculated. The polar modes were assigned to particular symmetry types, and their oscillator parameters (dielectric contributions, normal frequencies, damping constants) were determined. The numerical values of the components of the static permittivity tensor, ε₁₁ and ε₃₃, are shown to be almost fully determined by the total dielectric contributions due to the B_3u and B_1u phonons, respectively. In the low-frequency domain, lines showing anomalous behavior of the oscillator parameters, which is characteristic of soft ferroelectric modes, were observed. It is shown that, in CdTiO₃ at cryogenic temperatures, there exist several different polar states with switching in the direction of the spontaneous polarization vector.     

Adaptive correction of human-eye aberrations in a subjective feedback loop

An adaptive optical system with a subjective feedback loop is used to improve the visual acuity and to determine the aberrations of the human eye. Corrections of as many as 12 low-order aberration modes were made, based on the perceived sharpness of the test object observed through the adaptive optical system. The acuity of vision was improved by adjustment of the weights of the orthogonal modes produced by a deformable mirror. Objective measurements of the correcting aspherical figures, obtained in independent subjective correction cycles for one person, demonstrated good repeatability. Participants in the study with strong ocular aberrations reported moderate to significant improvement of their visual acuity, estimated with the U.S. Air Force 1951 acuity chart.