International Journal of Modern Physics B

Gas bubbles are the most potent naturally-occurring entities that influence the acoustic environment in liquids. Upon entrainment under breaking waves, waterfalls, or rainfall over water, each bubble undergoes small amplitude decaying pulsations with a natural frequency that varies approximately inversely with the bubble radius, giving rise to the "plink" of a dripping tap or the roar of a cataract. When they occur in their millions per cubic metre in the top few metres of the ocean, bubbles can dominate the underwater sound field. Similarly, when driven by an incident sound field, bubbles exhibit a strong pulsation resonance. Acoustic scatter by bubbles can confound sonar in the shallow waters which typify many modern maritime military operations. If they are driven by sound fields of sufficient amplitude, the bubble pulsations can become highly nonlinear. These nonlinearities might be exploited to enhance sonar, or to monitor the bubble population. Such oceanic monitoring is important, for example, because of the significant contribution made by bubbles to the greenhouse gas budget. In industry, bubble monitoring is required for sparging, electrochemical processes, the production of paints, pharamaceuticals and foodstuffs. At yet higher amplitudes of pulsation, gas compression within the collapsing bubble can generate temperatures of several thousand Kelvin whilst, in the liquid, shock waves and shear can produce erosion and bioeffects. Not only can these effects be exploited in industrial cleaning and manufacturing, and research into novel chemical processes, but we need to understand (and if possible control) their occurrence when biomedical ultrasound is passed through the body. This is because the potential of such bubble-related physical and chemical processes to damage tissue will be desireable in some circumstances (e.g. ultrasonic kidney stone therapy), and undesireable in others (e.g. foetal scanning). This paper describes this range of behaviour. Further information on these topics, including sound and video files, can be found at .

We consider the large Nernst signal discovered by Ong and collaborators in hole-doped cuprates, in particular in the pseudogap regime. Based on our previous quantitative calculations together with Huse [Phys. Rev. Lett.89, 287001 (2002)], we discuss the interpretation of the experimental observations as arising from superconducting fluctuations and its relation to the vortex scenario proposed by Ong. We also comment on the implications of the Nernst analysis for understanding the full range of pseudogap phenomena.

Temperature-dependence of the thermoelectric power of the semi-conducting CuO, ZnO and TiO₂ substituted for PbO in eutectic lead vanadate glasses was presented in a range of compositions. The high-temperature thermoelectric power was satisfactorily explained by Heikes' relation and the data also showed evidence of small polaron formation in thesae glasses. Thermo EMF measurements indicate that all the glass samples including unsubstituted lead metavanadate are n-type at room temperature. As temperature is increased ZnO and TiO₂ substituted samples change from n-type to p-type. The CuO substituted system remains n-type like the unsubstituted system even at high temperatures. When Heike's formula is applied to all the systems at room temperature, the amount of disorder was found to be the same in all the systems. When Emin's formula is used for the estimation of W_D, the activation energy due to disorder, in ZnO and TiO₂ substituted samples, unusually large values of W_D (~ 0.6 eV) are obtained. The present results indicate that the Emin's formula cannot be directly used to estimate the disorder energy in ZnO and TiO₂ sustituted lead vanadates. The temperature dependent change of sign of the thermoelectric power S, in these systems may arise due to change in V⁴⁺/V⁵⁺ ratio with the change of temperature or due to the onset of band type of conduction as in MnO or other extrinsic compensated semi-conductors.

Amperes law states that the magnetic moment of a ring is given by current times the area enclosed. Also from equilibrium statistical mechanics, it is known that magnetic moment is the derivative of free energy with respect to magnetic field. In this work, we analyze a quantum double ring system interacting with a reservoir. A simple S-Matrix model is used for system-reservoir coupling. We see complete agreement between the aforesaid two definitions when coupling between system and reservoir is weak, increasing the strength of coupling parameter, however, leads to disagreement between the two, thereby signifying the important role played by the coupling parameter in mesoscopic systems.

Transport properties of a one-dimensional (1D) chain with randomly attached dimer impurities are investigated. Using the transfer-matrix technique, we present numerical results of the transmission coefficient as a function of the electron energy. It is found that an extended state exists in such a random 1D system and many resonant energies appear in periodic conditions. We present an analytic expression for the energy of the extended state which is determined by the potential of dimer-impurity and the hopping between the dots of the dimer.

By use of the double-time Green's function method in the cubic-lattice S=1/2 anisotropic antiferromagnetic two-sublattice Heisenberg model, in the Tyablikov approximation, the staggered magnetization m, the correlation function and the static susceptibility are investigated. And the effects of spatial anisotropy are explored. The magnetic properties of this model are found to be dependent of anisotropy.