Modern Physics Letters B

The dependence of spontaneous emission on atomic motion for an atom undergoing two-photon transition and moving along the axis of a Fabry-Perot cavity is analyzed here. For this purpose we consider the strong coupling limit of atom and cavity field mode and demonstrate the effects of atomic velocity and spatial mode structure of cavity mode on the excitation probability of atom.

The rapid increase of the Josephson free energy as the temperature of a tunneling junction drops below the superconducting transition temperature T_c is shown to make this transition of first order in a system in which the phase difference ϕ across the junction is constrained to have a nonzero value. Taking this effect into account, we introduce an availability potential governing the nonisothermal dynamics of the junction which, in contrast with previous results, has no artifacts like latent heat being released upon entering the — high temperature — normal state or a value in this state which depends on the — superconducting — phase difference. The thermodynamic analysis is preceded by a detailed calculation of the Josephson coupling in a model of two ideal BCS superconductors coupled by a tunneling Hamiltonian.

Anomalous state of ice, which is a novel stable structures made from water molecules, can be induced to form under the action of ions in very dilute solutions, perhaps from a similar physical mechanism that forms ice VI. These stable structures change the UV transmission characteristic of water. Different structures formed from different ions are shown to have similar UV transmission characteristics. These structures can be filtered, concentrated and photographed using a transmission electron-microscope. A dipole-dipole interaction model is constructed to suggest an explanation of the elongated shape of these structures.

Various physical properties of water with I_E structures are measured. Compared with oridinary water, there is an approximate 20% decrease in dielectric constant for I_E water at MHz as an increase of emf generated by I_E water between two identical stainless steel electrodes, and an increase in resistivity to AC current. Fluorescence at 298 nm peak is seen in I_E water but not in ordinary water. From the thermal variation of UV absorption spectrum, one can estimate the amount of I_E structure to be up to 3%. The elevation of boiling point due to I_E structure can then be used to calculate the molecular weight of I_E structure to be the same as water molecule.

Starting from the extensional model Hückel Hamiltonian containing the next-neighbor hopping interactions, the energy band structure and their variation have been studied for polydiacetylenes (PDA’s). With the increase of the next-neighbor hopping interaction parameter ρ the results show that: (1) the electronic state symmetry is broken, (2) the locations and the widths of energy bands have been changed, and (3) the energy gap becomes narrower and the total bandwidth broader. Finally, the effect of the nextneighbor hopping interactions on the band-structure is discussed.

Anisotropies in the Compton profile of microclusters of sodium as a function of the cluster size as well as the direction of the scattering vector is presented. The anisotropy is the result of the shape deformations of the cluster which can be described in terms of a modified harmonic oscillator potential as suggested by Clemenger.¹