apoma Laboratory - Previous Work

	apoma Laboratory Previous Work
Studies on high-temperature superconductivity have further on been pursued. It has been shown, for instance, that a definite relationship exists between the mechanism of superconductivity and the dynamics of the lattice, which involves displacements of ions, structural transitions and a peculiar dynamics of localized vibration modes of the oxygen ions surrounding the copper centres active in superconductivity. A definite answer to the problem is still missing (L. Vasiliu-Doloc). Structural studies of X-ray scattering have been conducted, especially for phase defects in modulated structures and superlattices. A new theory of sound attenuation has been put forward for quasi-one-dimensional solids undertaking a charge-density-wave transition, near the critical point; the theory emphasizes the role played by the dynamics of the phase of the order parameter, and it has been applied to the compound (TaSe₄)I₂. The Hubbard model in one dimension has been approached by the classical standard theory of perturbations in the dilute limit of fermions; some Bethe-ansatz results have been reproduced thereby (F. D. Buzatu). Other one-dimensional models of fermions have been treated in the same way, with application to measurable quantities of their critical behaviour (V. Barsan). A new model of electrons - the electron crystal - in anisotropic materials has also been suggested, and solved for its basic properties; the model exhibits a variety of Wigner crystallization. The behaviour of the structure factor of a many-particle system has been made more specific in the long-wavelength limit. A new feature of the diffusion mechanisms has been identified in the presence of the off-centre atomic positions of substitutional impurities in alkali halides; a geometric factor affects the diffusion rate in all cases, irrespective of the diffusion mechanism (F. Despa). Transport phenomena in condensed matter have been treated in a new way, reproducing the old results and obtaining new ones, regarding thermoconductivity, thermopower and electrical conductivity. One of the new results is that of getting finite, boundary scattering contribution at all temperatures for the phonon transport. The dynamics of the electrons in certain highly anisotropic latticial structures has been investigated in the presence of the magnetic field, predicting correctly the field-induced spin density waves. The existence of the off-centre sites has been proven for the alkali cations in certain alkali-doped fullerides. In other compounds of this class micro-clusters of alkali cations have been identified, squeezed in the octahedral sites; with a variable range of ionicity, size and geometrical shapes, the latter of high symmetry. The effect of the alkali vacancies on the NMR-spectrum of the ternary alkali-doped fullerides has also been elucidated. The dynamics of the vibrations and rotations of the spherical molecule of fullerene has been investigated, concluding that the two types of modes are decoupled to a definite approximation, beyond which both the deformation and anharmonical effects do occur. The stability of the metallic and molecular clusters has been investigated, spin corelations in magneto-resistive materials have been pursued further on; Ising-like models of molecular lattices, mathematical methods of phase transitions, superfluidity and anharmonic crystals (N. Angelescu, M. Bundaru), relationship between Bose and Fermi statistics in two dimensions have been investigated. Correlations in interacting many-fermion systems have been investigated, with regard to the dimensionality effects. Electronic multi-media have been developed, including electronic nethworking, authoring, editing and publishing (C. Schiaua). The wavefunction method for waves propagation in waveguides has been developed, by exploiting the quantum-mechanical analogies (N. Marinescu); and glasses have been doped with optically active metals. The theory of the binding of the atomic clusters has been given (L. C. Cune).

apoma Laboratory

Previous Work

Studies on high-temperature superconductivity have further on been pursued. It has been shown, for instance, that a definite relationship exists between the mechanism of superconductivity and the dynamics of the lattice, which involves displacements of ions, structural transitions and a peculiar dynamics of localized vibration modes of the oxygen ions surrounding the copper centres active in superconductivity. A definite answer to the problem is still missing (L. Vasiliu-Doloc).

Structural studies of X-ray scattering have been conducted, especially for phase defects in modulated structures and superlattices.

A new theory of sound attenuation has been put forward for quasi-one-dimensional solids undertaking a charge-density-wave transition, near the critical point; the theory emphasizes the role played by the dynamics of the phase of the order parameter, and it has been applied to the compound (TaSe₄)I₂.

The Hubbard model in one dimension has been approached by the classical standard theory of perturbations in the dilute limit of fermions; some Bethe-ansatz results have been reproduced thereby (F. D. Buzatu). Other one-dimensional models of fermions have been treated in the same way, with application to measurable quantities of their critical behaviour (V. Barsan). A new model of electrons - the electron crystal - in anisotropic materials has also been suggested, and solved for its basic properties; the model exhibits a variety of Wigner crystallization. The behaviour of the structure factor of a many-particle system has been made more specific in the long-wavelength limit.

A new feature of the diffusion mechanisms has been identified in the presence of the off-centre atomic positions of substitutional impurities in alkali halides; a geometric factor affects the diffusion rate in all cases, irrespective of the diffusion mechanism (F. Despa).

Transport phenomena in condensed matter have been treated in a new way, reproducing the old results and obtaining new ones, regarding thermoconductivity, thermopower and electrical conductivity. One of the new results is that of getting finite, boundary scattering contribution at all temperatures for the phonon transport.

The dynamics of the electrons in certain highly anisotropic latticial structures has been investigated in the presence of the magnetic field, predicting correctly the field-induced spin density waves.

The existence of the off-centre sites has been proven for the alkali cations in certain alkali-doped fullerides. In other compounds of this class micro-clusters of alkali cations have been identified, squeezed in the octahedral sites; with a variable range of ionicity, size and geometrical shapes, the latter of high symmetry.

The effect of the alkali vacancies on the NMR-spectrum of the ternary alkali-doped fullerides has also been elucidated.

The dynamics of the vibrations and rotations of the spherical molecule of fullerene has been investigated, concluding that the two types of modes are decoupled to a definite approximation, beyond which both the deformation and anharmonical effects do occur.

The stability of the metallic and molecular clusters has been investigated, spin corelations in magneto-resistive materials have been pursued further on; Ising-like models of molecular lattices, mathematical methods of phase transitions, superfluidity and anharmonic crystals (N. Angelescu, M. Bundaru), relationship between Bose and Fermi statistics in two dimensions have been investigated.

Correlations in interacting many-fermion systems have been investigated, with regard to the dimensionality effects.

Electronic multi-media have been developed, including electronic nethworking, authoring, editing and publishing (C. Schiaua).

The wavefunction method for waves propagation in waveguides has been developed, by exploiting the quantum-mechanical analogies (N. Marinescu); and glasses have been doped with optically active metals.

The theory of the binding of the atomic clusters has been given (L. C. Cune).