Bubbles in liquids, soft and squeezy objects made of gas and vapour, yet so strong as to destroy any material and so mysterious as at times turning into tiny light bulbs, are the topic of the present report. Bubbles respond to pressure forces and reveal their full potential when periodically driven by sound waves. The basic equations for nonlinear bubble oscillation in sound fields are given, together with a survey of typical solutions. A bubble in a liquid can be considered as a representative example from nonlinear dynamical systems theory with its resonances, multiple attractors with their basins, bifurcations to chaos and not yet fully describable behaviour due to infinite complexity. Three stability conditions are treated for stable trapping of bubbles in standing sound fields: positional, spherical and diffusional stability. Chemical reactions may become important in that respect, when reacting gases fill the bubble, but the chemistry of bubbles is just touched upon and is beyond the scope of the present report. Bubble collapse, the runaway shrinking of a bubble, is presented in its current state of knowledge. Pressures and temperatures that are reached at this occasion are discussed, as well as the light emission in the form of short flashes. Aspherical bubble collapse, as for instance enforced by boundaries nearby, mitigates most of the phenomena encountered in spherical collapse, but introduces a new effect: jet formation, the self-piercing of a bubble with a high velocity liquid jet. Examples of this phenomenon are given from light induced bubbles. Two oscillating bubbles attract or repel each other, depending on their oscillations and their distance. Upon approaching, attraction may change to repulsion and vice versa. When being close, they also shoot self-piercing jets at each other. Systems of bubbles are treated as they appear after shock wave passage through a liquid and with their branched filaments that they attain in standing sound fields. The N -bubble problem is formulated in the spirit of the n-body problem of astrophysics, but with more complicated interaction forces. Simulations are compared with three-dimensional bubble dynamics obtained by stereoscopic high speed digital videography.

We report on structural, magnetic and electrical properties of Sr-doped LaMnO3 single crystals for doping levels 0.4 ≤ x ≤ 0.85. The complex structural and magnetic phase diagram can only be explained assuming significant contributions from the orbital degrees of freedom. Close to x = 0.6 a ferromagnetic metal is followed by an antiferromagnetic metallic phase below 200 K. This antiferromagnetic metallic phase exists in a monoclinic crystallographic structure. Following theoretical predictions this metallic antiferromagnet is expected to reveal an (x 2 -y 2 )-type orbital order. For higher Sr concentrations an antiferromagnetic insulator is established below room temperature.

Sound and light emission by bubbles is studied experimentally. Single bubbles kept in a bubble trap and single laser-generated bubbles are investigated using ultrafast and high-speed photography in combination with hydrophones. The optical observation at 20 million frames per second of the shock waves emitted has proven instrumental in revealing the dynamic process upon bubble collapse. When jet formation is initiated by a non-spherically symmetric environment, several distinct shock waves are emitted within a few hundred nanoseconds, originating from different sites of the bubble. The counterjet phenomenon is interpreted in this context as a secondary cavitation event. Furthermore, the light emission of laser-generated cavities-termed cavitation bubble luminescence-is studied with respect to the symmetry of collapse. The prospects of optical cavitation and multibubble trapping in the study of few-bubble systems and bubble interactions are briefly discussed. Finally, the behaviour of bubble clouds, their oscillations, acoustic noise and light emission are described. Depending on the strength of the driving sound field, period doubling and chaotic oscillations of the collective bubble dynamics are observed.

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Basic facts on the dynamics of bubbles in water are presented. Measurements on the free and forced radial oscillations of single spherical bubbles and their acoustic (shock waves) and optic (luminescence) emissions are given in photographic series and diagrams. Bubble cloud patterns and their dynamics and light emission in standing acoustic fields are discussed.