thanks to a fellowship from the French Ministry of Education. From 1995 on he was a staff member at the Physics Department of the University of Genova, first as Researcher and then as Associate Professor in Physics of Matter. He has been a Visiting Professor at Los Alamos National Laboratory (USA) and the Blaise Pascal University (Clemont-Ferrand, France). His research interests lie in theoretical and computational condensed matter physics and chemistry ranging from the theory of stochastic processes (escape rate theories) to surface diffusion of atoms and aggregates and crystal growth. More recently he has focused his interest in the computational modeling of nanoparticles, with special attention to their structural properties and growth dynamics. He is the author of about 120 papers in peer-reviewed journals.Julius Jellinek was born in the republic of Ukraine of the former Soviet Union. He graduated with distinction in theoretical high-energy physics from the

A review is presented of the design and application of genetic algorithms for the geometry optimisation of clusters and nanoparticles, where the interactions between atoms, ions or molecules are described by a variety of potential energy functions. A general introduction to genetic algorithms is followed by a detailed description of the genetic algorithm program that we have developed to identify the lowest energy isomers for a variety of atomic and molecular clusters. Examples are presented of its application to model Morse clusters, ionic MgO clusters and bimetallic "nanoalloy" clusters. Finally, a number of recent innovations and possible future developments are discussed.

A detailed review of the literature on ultrasonic propagation properties of mammalian tissues and organs has revealed 144 papers containing compilable data. Over 1300 lines of parametric data are listed, including the tissue, species, age, specimen preparation, anatomical structure, pathology, temperature, measurement method, frequency, velocity, attenuation, acoustic impedance, and density.

An unambiguous determination of the three-dimensional structure of nanoparticles is challenging. Electron tomography requires a series of images taken for many different specimen orientations. This approach is ideal for stable and stationary structures. But ultrasmall nanoparticles are intrinsically structurally unstable and may interact with the incident electron beam, constraining the electron beam density that can be used and the duration of the observation. Here we use aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 3096 atoms can be identified with either Ino-decahedral, cuboctahedral or icosahedral geometries. Comparison with theoretical modelling of the system suggests that the structures are consistent with energetic considerations. The discovery that nanoscale gold particles function as active and selective catalysts for a variety of important chemical reactions has provoked much research interest in recent years. We believe that the detailed structure information we provide will help to unravel the role of these nanoclusters in size- and structure-specific catalytic reactions. We note that the technique will be of use in investigations of other supported ultrasmall metal cluster systems.