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The creation of atoms of antihydrogen under controlled conditions has opened up a new era in physics with antimatter. We describe the experimental realisation of low energy antihydrogen, via the mixing of carefully prepared clouds of positrons and antiprotons, and some of the progress that has been made in the last few years in characterising properties of the nascent anti-atoms. Ongoing efforts aimed at trapping the anti-atoms in magnetic field minima are discussed. Some of the motivations for undertaking experiments with antihydrogen are presented. Keywords: antihydrogen; CPT; positrons; antiprotons; Penning traps

When the probability of measuring a particular value of some quantity varies inversely as a power of that value, the quantity is said to follow a power law, also known variously as Zipf's law or the Pareto distribution. Power laws appear widely in physics, biology, earth and planetary sciences, economics and finance, computer science, demography and the social sciences. For instance, the distributions of the sizes of cities, earthquakes, forest fires, solar flares, moon craters and people's personal fortunes all appear to follow power laws. The origin of power-law behaviour has been a topic of debate in the scientific community for more than a century. Here we review some of the empirical evidence for the existence of power-law forms and the theories proposed to explain them.

The organization of structures at the mesoscale is assumed to be the most important mechanism for the majority of friction types. Evidence is provided for the hypothesis that defect organization is fundamental to both tribological and internal friction.

An outline of recent work on complex networks is given from the point of view of a physical. Motivation, achievements and goals are discussed with some of the typical applications from a wide range of academic fields. An introduction to the relevant literature and useful resources is also given.

Our main objective in this review is that of analysing the cooperative interaction between randomness, nonlinearities and spatial coupling in extended systems. We shall report experimental, analytical and numerical evidences that an unexpected ordering influence appears when the intensity of a forcing external noise is increased. Different generic pattern-forming theoretical models will be considered, together with specific realistic scenarios ranging from electronic circuits to chemical reactions.

This contribution summarizes and explains various principles from physics which are used for the simulation of traffic flows in large street networks, the modelling of destination, transport mode, and route choice, or the simulation of urban growth and regional development. The methods stem from many-particle physics, from kinetic gas theory, or fluid dynamics. They involve energy and entropy considerations, transfer the law of gravity, apply cellular automata and require methods from evolutionary game theory. In this way, one can determine interaction forces among driver--vehicle units, reproduce breakdowns of traffic including features of synchronized congested flow, or understand changing usage patterns of alternative roads. One can also describe daily activity patterns based on decision models, simulate migration streams and model urban growth as a particular kind of aggregation process.

We review novel methods for the investigation, control and manipulation of neutral atoms in optical lattices. These setups allow unprecedented quantum control over large numbers of atoms and thus are very promising for applications in quantum information processing. After introducing optical lattices we discuss the superfluid (SF) and Mott insulating (MI) states of neutral atoms trapped in such lattices and investigate the SF-MI transition as observed experimentally recently. In the second part of the paper we give an overview of proposals for quantum information processing and show different ways to entangle the trapped atoms, in particular the usage of cold collisions and Rydberg atoms. Finally, we discuss briefly the implementation of quantum simulators, entanglement enhanced atom interferometers, and ideas for robust quantum memory in optical lattices.

In 2002 physicists around the world celebrated the centenary of the birth of Paul Dirac, OM, FRS, Nobel Laureate, who was one of the greatest physicists of the 20th century. He made towering contributions to the formulation of quantum mechanics and he was one of the principal creators of quantum field theory. In 1928 he combined relativity and quantum mechanics in the Dirac equation, which provides a natural description for the spin of the electron and which led to the prediction, by Dirac himself, of the existence of anti-matter. In this article I try to explain, in the simplest terms, these major contributions to physics and to give some flavour of the man himself.

Collapsible tubes, which occur all over the body, have unique properties from the point of view of both physics and physiology. A brief review is attempted of first the basic observable properties, followed by simple theory to explain the steady-flow aspects and an overview of the somewhat more complex theories for unsteady flow, in particular the flow-induced oscillations. The experimental evidence from laboratory studies is reviewed with particular emphasis on the dynamical system aspects. A final section looks at the current position and prospects.

The most accurate experiments currently are those based on frequency measurement. These experiments include the determination of fundamental constants, which can be used to link frequency to the other base units of the SI system. This article discusses the development of atomic frequency standards and their application in metrology, in particular the determination of fundamental constants. Further advancements in frequency standards and metrology are considered, as well as the implications for fundamental physics.

We explore in the framework of quantum computation the notion of computability, which holds a central position in mathematics and theoretical computer science. A quantum algorithm that exploits the quantum adiabatic processes is considered for Hilbert's tenth problem, which is equivalent to the Turing halting problem and known to be mathematically non-computable. Generalized quantum algorithms are also considered for some other mathematical non-computables in the same and in different non-computability classes. The key element of all these algorithms is the measurability of both the values of physical observables and the quantum-mechanical probability distributions for these values. It is argued that computability, and thus the limits of mathematics, ought to be determined not solely by mathematics itself butt also by physical principles.

Optical microcavities allow control over the interaction between light and matter, thus making them an important testing ground for basic optical physics. This review focuses on two of these interactions, spontaneous emission and energy transfer. Emphasis is placed on the underlying concepts, which are presented in the context of recent developments. Practical application of the microcavity concept to devices is now well underway and a discussion of these aspects forms an integral part of the review. This field is far from mature and though much has been accomplished, many questions in this area remain, some of which are identified and discussed.

Miniaturized magnetic devices are ubiquitous in the hard disks of computers and in tape storage systems. Giant magnetoresistance was discovered as recently as 1988 but already sensors using the effect are being incorporated into read heads for the highest density hard disk systems. As a result of intensive research and development, storage density on hard disks has increased dramatically at a rate greater than 60% per year. At sub-micron and nano-scale dimensions the properties of magnetic devices are strongly affected by their size and shape in a complex way resulting from the interplay between different types of magnetic energy. In some cases this causes a deterioration in the performance of existing devices, however it has also enabled entirely new devices to be proposed. Arrays of nanomagnets could be used for ultra-high density storage on hard disks or for fast and dense, non-volatile, solid state memory. Storage applications are possible because hysteresis in the nanomagnets creates two oppositely magnetized states which are stable in zero applied field and can store binary data. Magnetic sensors based on giant magnetoresistance in layered magnetic structures are among the most sensitive available for operation at room temperature and above. This paper describes the physical properties of nanomagnets and their role in present and future applications.

Metastable phases may be stabilized at interfaces due to lower surface or interface energies in comparison with the equilibrium phase. An example for this kind of stabilization effect is the phenomenon of surface melting, where a liquid-like film forms at the surface below the actual melting point. The excess energy necessary for the formation of the metastable, undercooled liquid phase is overcompensated by the gain in surface energy. Similar effects have been found in interface controlled materials such as thin films or nanocrystalline materials. In thin films, incoherent interfaces between the film and the underlying substrate contribute significantly to the total energy. The lower interface energy of a metastable film can stabilize the non-equilibrium phase as in the case of surface melting. A study is reviewed of thin Fe(Zr) alloy films which serves as a model system for the investigation of the interface effects. If deposited on suitable substrates, these films grow in the amorphous phase whereas in bulk materials the crystalline solid solution is more stable. Crystallization of the initially amorphous films sets in at a critical thickness where the driving force for crystallization can overcome the stabilizing effect of the interface. Under the experimental conditions, diffusional transport is negligible so that no phase separation can occur. Upon increasing the solute concentration, a polymorphic crystal-to-glass transformation (CGT) is encountered in the volume at a critical solute concentration. At concentrations close to the CGT, the relative stabilities of the competing phases, i.e. the crystalline solid solution and the amorphous alloy, approach each other. Therefore, the chemical composition of the films plays a role equivalent to the temperature in the case of surface melting. In the vicinity of the CGT, the interface energy contributions may dominate phase formation. As a result, a dramatic increase of the critical thickness for crystallization is observed with increasing solute concentration. A thermodynamic model based on the competing energetic contributions can explain the results. A generalized phase diagram is used for the description of interface effects in glass forming systems. Precursor effects like wetting at interfaces close to the conditions for phase transitions in bulk materials are also expected to be significant in systems with a high density of incoherent interfaces. The interfaces may serve as nucleation centres which play an important role for phase transformations in these materials.

The ferroelastic hysteresis is correlated with the propagation of twin walls under external stress. The wall thickness at T < < T(sub c) varies between 1 nm and 7 nm for different materials. Individual twin walls can act as fast diffusion paths for dopants and lattice imperfections. Several twin walls can combine to form hierarchical structures on a mesoscopic length scale (between, say 10 nm and 100 nm). Their features (needle domains, comb patterns, tweed and tartan patterns) are mainly determined by strain interactions with long correlation lengths. The formation of needle domains often leads to coarsening of the microstructure; their geometrical features are described in some detail.

Liquid crystals are interesting both for fundamental reasons and because of their application in display device technology. I give an overview of the liquid crystal phases. I then describe in more detail some of the basic physics of nematic liquid crystals, concentrating on those pieces of physics which underly display device technology. Finally I give a brief description of some of the most important liquid crystal applications.

We review dynamic processes in supercooled liquids and glasses as studied by dielectric spectroscopy. It is the only experimental technique which allows one to follow the tremendous slow-down of diffusive motion of particles in disordered condensed matter over more than 18 decades in frequency or time. The dielectric techniques used are treated in detail. As an introduction for non-specialists, the time and temperature evolution of the basic spectral features associated with various dynamic relaxation processes are discussed in detail. Among them are the structural relaxation, the occurrence of fast processes and the boson peak. The relevance of these features for glass formation is discussed. The present article may also serve as a review for recent experimental and theoretical studies on glass-forming liquids.

The reason why atomic physicists are interested in celestial mechanics is simple: the gravitational and Coulombic potentials are mathematically identical and a one-electron atom is, therefore, governed by the same Hamiltonian as is the Kepler problem. However, once one goes beyond the two-body Kepler problem the connections between atomic physics and celestial mechanics become less direct. For example, the three-body problem, arguably the raison d'etre of celestial mechanics for several centuries, has received relatively little attention from atomic physicists because it does not have a direct quantum counterpart: three quantum particles cannot mutually attract one another and at the same time interact through a purely Coulombic force law. Nevertheless, in the last five years several research groups have discovered that quantum analogues of a particular limit of the three-body problem, the restricted three-body problem, not only exist but contain dramatically new physics. This article will describe this work and in particular will demonstrate the possibility of producing localized electronic states in atoms that are direct analogs of the coherent states of the harmonic oscillator. These coherent wavepackets behave in a similar way to the coherent states of the harmonic oscillator and the resulting atom mimics a 'classical' or Bohr atom although external fields must be used to maintain their integrity. Such wavepacket states are of as much fundamental interest in laser chemistry as they are in atomic, molecular, optical, and solid state physics. The potential applications of time-evolving quantum wavepackets seem limitless; some examples of their uses include: the exploration of the boundary between classical and quantum mechanics, the investigation of the interpretation of quantum mechanics by creating experimental realizations of such classic experiments as Schrodinger's Cat, the control of chemical reaction dynamics to achieve laser isotope separation, the storage of coherence for quantum computational or communications purposes, and the construction of optical switches and modulators.

The enormous contribution of Richard Feynman to modern physics is well known, both to teaching through his famous Feynman Lectures on Physics, and to research with his Feynman diagram approach to quantum field theory and his path integral formulation of quantum mechanics. Less well known perhaps is his long-standing interest in the physics of computation and this is the subject of this paper. Feynman lectured on computation at Caltech for most of the last decade of his life, first with John Hopfield and Carver Mead, and then with Gerry Sussman. The story of how these lectures came to be written up as the Feynman Lectures on Computation is briefly recounted. Feynman also discussed the fundamentals of computation with other legendary figures of the computer science and physics community such as Ed Fredkin, Rolf Landauer, Carver Mead, Marvin Minsky and John Wheeler. He was also instrumental in stimulating developments in both nanotechnology and quantum computing. During the 1980s Feynman re-visited long-standing interests both in parallel computing with Geoffrey Fox and Danny Hillis, and in reversible computation and quantum computing with Charles Bennett, Norman Margolus, Torn Toffbli and Wojciech Zurek. This paper records Feynman's links with the computational community and includes some reminiscences about his involvement with the fundamentals of computing.

We describe some aspects of complex behaviour that can be present in biopolymers. The study is based on a nonlinear thermodynamics of non-equilibrium, dissipative systems. Such complexity consists of a Frohlich - Bose - Einstein-like condensation and propagation of Schrodinger - Davydov soliton-wave-like excitations, which are of relevance in Bioenergetics. The question of the soliton lifetime under physiological conditions is discussed, and comparison made with experiments performed in the case of an organic molecular polymer. Further complex behaviour apparently present in ultrasonic medical imaging, dubbed the Frohlich - Cherenkov effect, is briefly discussed.

After a brief introduction to discotic liquid crystals, we describe recent progress in elucidating the properties of the columnar phases as one-dimensional electrical conductors (or molecular wires), fast photoconductors, light emitting diodes and ferroelectrics, all of which have potentially important practical applications.

The subject of anholonomy in physics has recently been emphasized via discussions of the Berry phase. A particular example of this phenomenon, which does not require the adiabatic condition is the familiar Aharonov - Bohm (AB) effect. We herein review the AB effect and show that two additional phenomena, namely the Aharonov - Casher effect and rotating superconducting quantum interference device systems, can be analysed using identical mathematical frameworks.

The historical development that led to the modern concept of amplification and lasing without inversion is reviewed. The two basic mechanisms for amplification without inversion and their theoretical formulation are discussed. Finally, the three experiments that confirm the occurrence of these effects are described.

This article discusses the concept of information and its intimate relationship with physics. After an introduction of all the necessary quantum mechanical and information theoretical concepts we analyse Landauer's principle which states that the erasure of information is inevitably accompanied by the generation of heat. We employ this principle to rederive a number of results in classical and quantum information theory whose rigorous mathematical derivations are difficult. This demonstrates the usefulness of Landauer's principle and provides an introduction to the physical theory of information.