Showing papers in "Reports on Progress in Physics in 2002"

Electrostatic correlations: from plasma to biology

Abstract: Electrostatic correlations play an important role in physics, chemistry and biology. In plasmas they result in thermodynamic instability similar to the liquid–gas phase transition of simple molecular fluids. For charged colloidal suspensions the electrostatic correlations are responsible for screening and colloidal charge renormalization. In aqueous solutions containing multivalent counterions they can lead to charge inversion and flocculation. In biological systems the correlations account for the organization of cytoskeleton and the compaction of genetic material. In spite of their ubiquity, the true importance of electrostatic correlations has come to be fully appreciated only quite recently. In this paper, we will review the thermodynamic consequences of electrostatic correlations in a variety of systems ranging from classical plasmas to molecular biology.

The physics of traffic jams

Abstract: Traffic flow is a kind of many-body system of strongly interacting vehicles. Traffic jams are a typical signature of the complex behaviour of vehicular traffic. Various models are presented to understand the rich variety of physical phenomena exhibited by traffic. Analytical and numerical techniques are applied to study these models. Particularly, we present detailed results obtained mainly from the microscopic car-following models. A typical phenomenon is the dynamical jamming transition from the free traffic (FT) at low density to the congested traffic at high density. The jamming transition exhibits the phase diagram similar to a conventional gas-liquid phase transition: the FT and congested traffic correspond to the gas and liquid phases, respectively. The dynamical transition is described by the time-dependent Ginzburg-Landau equation for the phase transition. The jamming transition curve is given by the spinodal line. The metastability exists in the region between the spinodal and phase separation lines. The jams in the congested traffic reveal various density waves. Some of these density waves show typical nonlinear waves such as soliton, triangular shock and kink. The density waves are described by the nonlinear wave equations: the Korteweg-de-Vries (KdV) equation, the Burgers equation and the Modified KdV equation. Subjects like the traffic flow such as bus-route system and pedestrian flow are touched as well. The bus-route system with many buses exhibits the bunching transition where buses bunch together with proceeding ahead. Such dynamic models as the car-following model are proposed to investigate the bunching transition and bus delay. A recurrent bus exhibits the dynamical transition between the delay and schedule-time phases. The delay transition is described in terms of the nonlinear map. The pedestrian flow also reveals the jamming transition from the free flow at low density to the clogging at high density. Some models are presented to study the pedestrian flow. When the clogging occurs, the pedestrian flow shows the scaling behaviour.

Fluorescence correlation spectroscopy: the technique and its applications

Abstract: Fluorescence correlation spectroscopy (FCS) is an experimental technique using statistical analysis of the fluctuations of fluorescence in a system in order to decipher dynamic molecular events, such as diffusion or conformational fluctuations of biomolecules. First introduced by Magde et al to measure the diffusion and binding of ethidium bromide onto double-stranded DNA, the technique has been undergoing a renaissance since 1993 with the implementation of confocal microscopy FCS. Since then, a flurry of experiments has implemented FCS to characterize the photochemistry of dyes, the translational and rotational mobilities of fluorescent molecules, as well as to monitor conformational fluctuations of green fluorescent proteins and DNA molecules. In this review, we present the analytical formalism of an FCS measurement, as well as practical considerations for the design of an FCS setup and experiment. We then review the recent applications of FCS in analytical chemistry, biophysics and cell biology, specifically emphasizing the advantages and pitfalls of the technique compared to alternative spectroscopic tools. We also discuss recent extensions of FCS in single-molecule spectroscopy, offering alternative data processing of fluorescence signals to glean more information on the kinetic processes.

Extrinsic magnetotransport phenomena in ferromagnetic oxides

Abstract: Magnetic oxides show a variety of extrinsic magnetotransport phenomena: grain-boundary, tunnelling and domain-wall magnetoresistance. In view of these phenomena the role of some magnetic oxides is outstanding: these are believed to be half-metallic having only one spin-subband at the Fermi level. These fully spin-polarized oxides have great potential for applications in spin-electronic devices and have, accordingly, attracted intense research activity in recent years. This review is focused on extrinsic magnetotransport effects in ferromagnetic oxides. It consists of two parts; the second part is devoted to an overview of experimental data and theoretical models for extrinsic magnetotransport phenomena. Here a critical discussion of domain-wall scattering is given. Results on surface and interfacial magnetism in oxides are presented. Spin-polarized tunnelling in ferromagnetic junctions is reviewed and grain-boundary magnetoresistance is interpreted within a model of spin-polarized tunnelling through natural oxide barriers. The situation in ferromagnetic oxides is compared with data and models for conventional ferromagnets. The first part of the review summarizes basic material properties, especially data on the spin polarization and evidence for half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed. An outlook on the further development of oxide spin-electronics concludes this review.

Magneto-optical studies of current distributions in high-Tc superconductors

Abstract: In the past few years magneto-optical flux imaging (MOI) has come to take an increasing role in the investigation and understanding of critical current densities in high-Tc superconductors (HTS). This has been related to the significant progress in quantitative high-resolution magneto-optical imaging of flux distributions together with the model-independent determination of the corresponding current distributions. We review in this article the magneto-optical imaging technique and experiments on thin films, single crystals, polycrystalline bulk ceramics, tapes and melt-textured HTS materials and analyse systematically the properties determining the spatial distribution and the magnitude of the supercurrents. First of all, the current distribution is determined by the sample geometry. Due to the boundary conditions at the sample borders, the current distribution in samples of arbitrary shape splits up into domains of nearly uniform parallel current flow which are separated by current domain boundaries, where the current streamlines are sharply bent. Qualitatively, the current pattern is described by the Bean model; however, changes due to a spatially dependent electric field distribution which is induced by flux creep or flux flow have to be taken into account. For small magnetic fields, the Meissner phase coexists with pinned vortex phases and the geometry-dependent Meissner screening currents contribute to the observed current patterns. The influence of additional factors on the current domain patterns are systematically analysed: local magnetic field dependence of jc(B), current anisotropy, inhomogeneities and local transport properties of grain boundaries. We then continue to an overview of the current distribution and current-limiting factors of materials, relevant to technical applications like melt-textured samples, coated conductors and tapes. Finally, a selection of magneto-optical experiments which give direct insight into vortex pinning and depinning mechanisms are reviewed.

Si/Ge nanostructures

Abstract: A review is given on the formation mechanisms and the properties of Si/Ge nanostructures that have been synthesized by self-assembling and self-ordering during heteroepitaxy of \mbox{silicon-germanium} alloys on single-crystal silicon substrates. The properties of electronic subbands in smooth strained Si/SiGe quantum well structures are presented as a basis for characterizing coherent Si/Ge nanostructures with free motion of carriers in a reduced number of dimensions. The low-dimensional band structure of valence band states confined in strained Si/Ge and Si/SiGe nanostructures is analysed by optical and electrical spectroscopy. The nanostructures presented were fabricated by self-assembly induced by elastic strain relaxation without applying any patterning technique. Misfit lattice strain of SiGe material deposited on Si substrates can relax by bunching of atomic surface steps with SiGe agglomeration at the step edges or by nucleation of Ge-rich islands in the Stranski-Krastanow growth mode. The size, density and composition of such Si/Ge nanostructures representing quantum wires and dots, respectively, can be tuned in a wide range by the growth parameters. Local strain fields extending into the Si host influence the nucleation and the lateral arrangement of nanostructures in subsequent layers and can be applied for self-ordering of nanostructures in the vertical as well as the lateral direction. Interband and intra-valence-band photocurrent, absorption and photoluminescence spectroscopy as well as C-V and admittance measurements reveal a consistent view of the band structure in Si/Ge quantum dot structures. This is in good agreement with model calculations based on band offsets, deformation potentials and effective electron masses known from earlier studies of Si/SiGe quantum well structures. The effective valence band offsets of hole states within Si/Ge nanostructures reach about 400?meV. Typical quantization energies of about 40?meV due to lateral confinement and Coulomb charging energies up to about 15?meV were observed for holes confined in 20?nm sized Si/Ge dots. Future applications of Si/Ge nanostructures such as photodetectors with improved performance or novel functionality are discussed.

Astrophysical and astrochemical insights into the origin of life

Abstract: Stellar nucleosynthesis of heavy elements such as carbon allowed the formation of organic molecules in space, which appear to be widespread in our Galaxy. The physical and chemical conditions—including density, temperature, ultraviolet (UV) radiation and energetic particles—determine reaction pathways and the complexity of organic molecules in different space environments. Dense interstellar clouds are the birth sites of stars of all masses and their planetary systems. During the protostellar collapse, interstellar organic molecules in gaseous and solid phases are integrated into protostellar disks from which planets and smaller solar

Two-dimensional turbulence: a review of some recent experiments

Abstract: A review of recent experiments in two-dimensional turbulence is presented. Work on flowing soap films and on thin layers of fluid driven electromagnetically is covered. Theoretical notions of turbulence in two and three dimensions are introduced.

Review of soft x-ray laser researches and developments

Abstract: In this paper, the author reviews the plasma-based x-ray lasers which we have already demonstrated saturated amplification whose wavelengths are between 50 and 6?nm. Section?1 describes the motivation of this review paper which includes basic ideas, developments and their applications of x-ray lasers. In section?2, the author describes the early x-ray laser researches on the recombination and the electron collisional excitation schemes including the hydrogen-like and lithium-like ion recombination schemes and the electron collisional excitation scheme. Section?3 describes the first demonstration of significant lasing at Livermore for the electron collisional excitation scheme of neon-like selenium ions at a wavelength of 20.6 and 20.9?nm and Princeton for the recombination scheme of hydrogen-like carbon ions at a wavelength of 18.2?nm. In section?4, the author describes the electron collisional excitation type soft x-ray lasers which are at present the most successful x-ray lasers. The subjects with which the author deals are saturated amplification neon-like soft x-ray lasers, improvement of neon-like soft x-ray laser performance using multi-layer mirrors, atomic physics issues of the neon-like soft x-ray lasers, gain guiding of the x-ray laser beam propagation, discharge-pumped compact repetitive neon-like ion soft x-ray lasers, the collisional excitation nickel-like ion soft x-ray lasers, high gain and saturated amplification nickel-like soft x-ray lasers at wavelengths as short as 7?nm, the short wavelength nickel-like x-ray lasers whose wavelengths are close to the longest wavelength edge the water window of 4.4?nm, transient collisional excitation scheme which is currently the most popular soft x-ray lasers pumped by short-pulse compact lasers with a laser energy of a few J to a few tens of?J. In section?5, the author describes various plasma-based x-ray laser schemes other than the recombination and the collisional schemes, such as the optical field ionization schemes and inner-shell ionization schemes. Section?6 includes soft x-ray laser applications such as soft x-ray holography, soft x-ray interferometers, soft x-ray microscopy and other applications. In section?7, the author summarizes this review paper and he proposes a future direction for x-ray laser researches.

Limits to magnetic resonance microscopy

Abstract: The last quarter of the twentieth century saw the development of magnetic resonance imaging (MRI) grow from a laboratory demonstration to a multi-billion dollar worldwide industry. There is a clinical body scanner in almost every hospital of the developed nations. The field of magnetic resonance microscopy (MRM), after mostly being abandoned by researchers in the first decade of MRI, has become an established branch of the science. This paper reviews the development of MRM over the last decade with an emphasis on the current state of the art. The fundamental principles of imaging and signal detection are examined to determine the physical principles which limit the available resolution. The limits are discussed with reference to liquid, solid and gas phase microscopy. In each area, the novel approaches employed by researchers to push back the limits of resolution are discussed. Although the limits to resolution are well known, the developments and applications of MRM have not reached their limit.

Quantum well structures in thin metal films: simple model physics in reality?

Abstract: The quantum wells formed by ultra-thin metallic films on appropriate metallic substrates provide a real example of the simple undergraduate physics problem in quantum mechanics of the `particle in a box'. Photoemission provides a direct probe of the energy of the resulting quantized bound states. In this review the relationship of this simple model system to the real metallic quantum well (QW) is explored, including the way that the exact nature of the boundaries can be taken into account in a relative simple way through the `phase accumulation model'. More detailed aspects of the photoemission probe of QW states are also discussed, notably of the physical processes governing the photon energy dependence of the cross sections, of the influence of temperature, and the processes governing the observed peak widths. These aspects are illustrated with the results of experiments and theoretical studies, especially for the model systems Ag on Fe(100), Ag on V(100) and Cu on fcc Co(100).

Investigating surface magnetism by means of photoexcitation electron emission microscopy

Abstract: The imaging of surfaces by means of photoexcitation electron emission microscopy (PEEM) has recently received considerable interest. This is mainly due to the extended use and availability of brilliant synchrotron radiation in the soft x-ray regime which generally facilitates studies with surface specificity and chemical selectivity. The most popular application of the x-ray PEEM (XPEEM) technique concerns studies of magnetic systems and phenomena. By exploiting the high degree of circular or linear polarization of the synchrotron light, the magnetic microstructure in both ferromagnets and antiferromagnets can be visualized. In this contribution we demonstrate the unique potential and the versatility of the PEEM approach, and review the current status with a certain emphasis on experiments with soft x-ray excitation. In some cases, the high-energy excitation studies can be complemented by laboratory experiments employing threshold photoemission with ultraviolet light (UV-PEEM). Current limitations and future developments and perspectives of the PEEM technique applied to magnetic systems are discussed.

Boson peak and terahertz frequency dynamics of vitreous silica

Abstract: This paper describes the progress that has been made in the past decade in the investigation of the peculiar dynamic properties of vitreous silica (v-SiO2) and related glasses in the terahertz (THz) frequency range. The reason why we focus our attention on v-SiO2 is that it is one of the principal network glasses and exhibits all features typical of glasses. These are the increased inelastic scattering of light and neutrons at THz frequencies, the so-called Boson or Bose peak, as well as unusual thermal properties such as specific heats and thermal conductivities at low temperatures. During the last decade, experimental techniques such as the inelastic scattering of light, neutrons and x-rays have been greatly improved, and these have provided considerable experimental information about the atomic vibrations in v-SiO2 and related glasses in the THz frequency region. In addition, molecular dynamics simulations have proved successful for these complex systems. They form the basis for this perspective on the major advances in this decade from a new and tutorial point of view.

Wavefronts in time-delayed reaction-diffusion systems. Theory and comparison to experiment

Abstract: We review the recent theoretical progress in the formulation and solution of the front speed problem for time-delayed reaction-diffusion systems. Most of the review is focused on hyperbolic equations. They have been widely used in recent years, because they allow for analytical solutions and yield a realistic description of some relevant phenomena. The theoretical methods are applied to a range of applications, including population dynamics, forest fire models, bistable systems and combustion wavefronts. We also present a detailed account of successful predictions of the models, as assessed by comparison to experimental data for some biophysical systems, without making use of any free parameters. Areas where the work reviewed may contribute to future progress are discussed.

Vortex dynamics and mutual friction in superconductors and Fermi superfluids

Abstract: Excitations in vortex cores in superconductors and other Fermi superfluids are single-particle excitations with a peculiar energy spectrum. These excitations are responsible for many important thermodynamic properties such as specific heat, London penetration length, etc. They also determine the dynamic characteristics of superconductors and superfluids through their interaction with vortices. Flux flow resistance, the Hall effect in type?II superconductors and the mutual friction in superfluids are the most important phenomena which strongly depend on vortex core excitations. These phenomena determine the electromagnetic responses of type?II superconductors and the hydrodynamic behaviour of superfluids and are of great significance for practical applications of superconducting devices and for understanding the most fundamental properties of correlated electrons and other Fermi particles. In this review we consider the dynamic properties of superconductors and superfluids and outline the basic ideas and results on the vortex dynamics in clean superfluid Fermi systems. The forces acting on moving vortices are discussed including the problem of the transverse force which was a matter of confusion for quite some time. We formulate the equations of the vortex dynamics, which include all the forces and the inertial term associated with excitations bound to the moving vortex.

Gas surface interactions studied with state-prepared molecules

Abstract: The interaction of gas-phase molecules with solid surfaces is complicated by the many molecular and surface degrees-of-freedom (DOFs) which may affect the scattering process. This review covers experimental work in which the quantum state populations of molecules incident on a surface are prepared or selected in some manner, and the scattering of these prepared molecules is followed. Experiments are discussed in which essentially all (electronic, vibrational, rotational, and translational) molecular DOFs are controlled. Two main techniques to produce a flux of state-prepared molecules for surface studies have been developed; both are natural extensions of existing gas-phase scattering work. The first employs direct optical excitation and relies on the associated selection rules to generate population in a desired state. The second uses inhomogeneous electric or magnetic fields as a filter to transmit a particular state and reject others. Specific applications of each of these techniques are reviewed with emphasis placed on the insight gained from the quantum state specific nature of the incident molecules.

Progress in planetary lightning

Abstract: We review the progress in the last decade in the field of planetary lightning. We provide background covering terrestrial lightning and newly discovered associated phenomena such as sprites. We concentrate on the theory and observations regarding lightning at Jupiter, especially the discoveries made by the Galileo orbiter and entry probe. Recent observations of Titan's atmosphere and a theory of possible lightning at Titan are reviewed. We discuss the potential for lightning detection by the Huygens probe that will enter Titan's atmosphere in 2005. Directions for future progress in planetary lightning are outlined.

High-frequency applications of high-temperature superconductor thin films

Abstract: High-temperature superconducting thin films offer unique properties which can be utilized for a variety of high-frequency device applications in many areas related to the strongly progressing market of information technology. One important property is an exceptionally low level of microwave absorption at temperatures attainable with low power cryocoolers. This unique property has initiated the development of various novel type of microwave devices and commercialized subsystems with special emphasis on application in advanced microwave communication systems. The second important achievement related to efforts in oxide thin and multilayer technology was the reproducible fabrication of low-noise Josephson junctions in high-temperature superconducting thin films. As a consequence of this achievement, several novel nonlinear high-frequency devices, most of them exploiting the unique features of the ac Josephson effect, have been developed and found to exhibit challenging properties to be utilized in basic metrology and Terahertz technology. On the longer timescale, the achievements in integrated high-temperature superconductor circuit technology may offer a strong potential for the development of digital devices with possible clock frequencies in the range of 100 GHz.

Electronic, magnetic and spectroscopic properties of manganese nanostructures

Abstract: This paper presents a review of the electronic, magnetic and spectroscopic properties of manganese (Mn)-based nanostructures. In the last few years a variety of techniques have been used to prepare mesoscopic transition-metal islands and novel effects associated with the electronic structure in nanoscale systems have been reported. Mn in the atomic configuration possesses a moment as high as 5μB so it should be very interesting to dope semiconductors with Mn for spin injection or to use Mn itself for permanent magnets. In this paper the introduction (section 1) focuses mainly on metallic Mn nanostructures which are the core of this review. Nevertheless we try to present a general overview of various kinds of Mn structures as well as several theoretical methods with their own limitations to handle the corresponding problems. More precisely, section 2 outlines a variety of bulk, surface, interface and cluster structures with their resulting magnetism as far as Mn is concerned. Actually, in these past two decades, considerable interest has been devoted to Mn nanostructures deposited on various metallic substrates (section 3). Because of its exotic structural and magnetic properties, Mn is indeed an interesting candidate for ultra-thin film growth as it is expected to accept different local configurations. Experimentally, one may attempt to stabilize normally high-temperature phases of Mn by epitaxial growth on a suitable substrate. Specifically, we shall point out the frequently occurring, important situation of magnetically stabilized surface alloys. Next (section 4) we first focus on spectroscopic properties of Mn compounds as well as Mn adsorbates upon graphite and other substrates both experimentally and theoretically. Moreover, we recall a few remarks about Mn impurities with respect to the Kondo problem and also with respect to semiconductors and spintronics. In the latter field, practical applications actually require room-temperature Mn ferromagnetism which is not that easy to obtain. Finally, in section 5, we point out that a given Mn nanostructure generally exhibits a non-collinear (NCL) structure which is often the most stable one among all the collinear and NCL ones. This fact explains why constrained collinear calculations have often disagreed with the corresponding experimental data. Section 6 is devoted to a short discussion where we recall a few important points that have been developed in this paper.

Resonant x-ray scattering in manganites: study of the orbital degree of freedom

Abstract: The orbital degree of freedom of electrons and its interplay with spin, charge and lattice degrees of freedom are some of the central issues in colossal magnetoresistive manganites. The orbital degree of freedom has until recently remained hidden, since it does not couple directly to most experimental probes. Development of synchrotron light sources has changed the situation; by the resonant x-ray scattering (RXS) technique the orbital ordering has successfully been observed. In this article, we review progress in the recent studies of RXS in manganites. We start with a detailed review of the RXS experiments applied to the orbital-ordered manganites and other correlated electron systems. We derive the scattering cross section of RXS, where the tensor character of the atomic scattering factor (ASF) with respect to the x-ray polarization is stressed. Microscopic mechanisms of the anisotropic tensor character of the ASF are introduced and numerical results of the ASF and the scattering intensity are presented. The azimuthal angle scan is a unique experimental method to identify RXS from the orbital degree of freedom. A theory of the azimuthal angle and polarization dependence of the RXS intensity is presented. The theoretical results show good agreement with the experiments in manganites. Apart from the microscopic description of the ASF, a theoretical framework of RXS to relate directly to the 3d orbital is presented. The scattering cross section is represented by the correlation function of the pseudo-spin operator for the orbital degree of freedom. A theory is extended to the resonant inelastic x-ray scattering and methods to observe excitations of the orbital degree of freedom are proposed.

Frequency standards and frequency measurement

Abstract: Recent years have brought major breakthroughs in the development, operation and mutual comparison of frequency standards in the microwave as well as in the optical frequency domain. Several cold-atom fountains have been developed, using caesium as well as rubidium atoms. Some of them have been compared among each other. Mutual agreement of the order of one part in 1015 was demonstrated for two caesium fountains operated side by side but also for two operated simultaneously in the US and Germany. Ultra-narrow resonances of optical transition lines were observed using single trapped ions, and a maximum line quality factor in excess of 1014 was reported. Measurements of frequencies in the optical range of atomic transitions in neutral hydrogen and calcium, as well as in ions of indium, mercury, strontium and ytterbium, were performed. The last-named achievements were to a large extent enabled by the use of Kerr-effect mode-locked Ti:sapphire femtosecond lasers and techniques of broadening the output spectrum of these lasers to an octave-wide comb. This paper reviews the current status in these fields, with similar emphasis on the standards and on the feasibility to transfer the properties of the standards from a local laboratory to a broader community.

The greenhouse effect and climate change revisited

Abstract: On any planet with an atmosphere, the surface is warmed not only by the Sun directly but also by downward-propagating infrared radiation emitted by the atmosphere. On the Earth, this phenomenon, known as the greenhouse effect, keeps the mean surface temperature some 33 K warmer than it would otherwise be and is therefore essential to life. The radiative processes which are responsible for the greenhouse effect involve mainly minor atmospheric constituents, the amounts of which can change either naturally or as a by-product of human activities. The growth due to the latter is definitely tending to force a general global surface warming, although because of problems in modelling complicated feedback processes, for example those involving water vapour, ozone, clouds and the oceans, the precise rates of change and the local patterns which should be expected are not simple to predict. This article updates an earlier review which discussed the physical processes involved in the greenhouse effect and theoretical and experimental work directed towards an understanding of the effect on the climate of recent and expected changes in atmospheric composition. In the last ten years, progress in data acquisition and analysis, and in numerical climate modelling, has tended to confirm earlier predictions of the likelihood of significant rises in the mean surface temperature of the planet in the next 50-100 years, although this remains controversial.

Mercury: the planet and its orbit

Abstract: The planet closest to the Sun, Mercury, is the subject of renewed attention among planetary scientists, as two major space missions will visit it within the next decade. These will be the first to return to Mercury, after the flybys by NASA's Mariner 10 spacecraft in 1974-5. The difficulties of observing this planet from the Earth make such missions necessary for further progress in understanding its origin, evolution and present state. This review provides an overview of what is known about Mercury and what are the major outstanding issues. Mercury's orbital and rotation periods are in a unique 2:3 resonance; an analysis of the orbital dynamics of Mercury is presented here, as well as Mercury's special role in testing theories of gravitation. These derivations provide a good insight into the complexities of planetary motion in general, and how, in the case of Mercury, its proximity to the Sun can be described and exploited in terms of general relativity. Mercury's surface, superficially similar to that of the Moon, presents intriguing differences, representing a different, and more complex history in which the role of early volcanism remains to be clarified and understood. Mercury's interior presents the most important puzzles: it has the highest uncompressed density among the terrestrial planets, implying a very large, mostly iron core. This does not appear to be the completely solidified yet, as Mariner 10 found a planetary magnetic field that is probably generated by an internal dynamo, in a liquid outer layer of the large iron core. The current state of the core, once established, will provide a constraint for its evolution from the time of the planet's formation. Mercury's environment is highly variable. There is only a tenuous exosphere around Mercury; its source is not well understood, although there are competing models for its formation and dynamics. The planetary magnetic field appears to be strong enough to form a magnetosphere around the planet, through its interaction with the solar wind. This magnetosphere may have similarities with that of the Earth, but is more likely to be dominated by global dynamics that could make it collapse at least at the time of large solar outbursts. The future understanding of the planet will now await the arrival of the new space missions. The review concludes with a brief description of these missions.

Time and frequency distribution using satellites

Abstract: I will discuss how time and frequency information can be distributed using satellites. I will focus on using the signals transmitted by the US global positioning system satellites, but I will also discuss other satellite-based systems such as the Russian GLONASS system, the proposed European Galileo System and two-way satellite time transfer, which uses active ground stations that communicate with each other through an active satellite.

Quantum causality, stochastics, trajectories and information

Abstract: A history of the discovery of `new' quantum mechanics and the paradoxes of its probabilistic interpretation are briefly reviewed from the modern point of view of quantum probability and information. Modern quantum theory, which has been developed during the last 20 years for the treatment of quantum open systems including quantum noise, decoherence, quantum diffusions and spontaneous jumps occurring under continuous in time observation, is not yet a part of the standard curriculum of quantum physics. It is argued that the conventional formalism of quantum mechanics is insufficient for the description of quantum events, such as spontaneous decays say, and the new experimental phenomena related to individual quantum measurements, but they have all received an adequate mathematical treatment in quantum stochastics of open systems. Moreover, the only reasonable probabilistic interpretation of quantum mechanics put forward by Max Born was, in fact, in irreconcilable contradiction with traditional mechanical reality and causality. This led to numerous quantum paradoxes, some of them due to the great inventors of quantum theory such as Einstein and Schrodinger. They are reconsidered in this paper from the modern point of view of quantum stochastics and information. The development of quantum measurement theory, initiated by von Neumann, indicated a possibility for resolution of this interpretational crisis by divorcing the algebra of the dynamical generators and the algebra of the actual observables, or Bell's beables. It is shown that within this approach quantum causality can be rehabilitated in the form of a superselection rule for compatibility of the actual histories with the potential future. This rule, together with the self-compatibility of the measurements ensuring the consistency of the histories, is called the nondemolition, or causality principle in modern quantum theory. The application of this rule in the form of dynamical commutation relations leads to the derivation of the von Neumann projection postulate, and also to the more general reductions, instantaneous, spontaneous, and even continuous in time. This gives a dynamical solution, in the form of the quantum stochastic filtering equations, of the notorious measurement problem which was tackled unsuccessfully by many famous physicists starting with Schrodinger and Bohr. It has been recently proved that the quantum stochastic model for the continuous in time measurements is equivalent to a Dirac type boundary-value problem for the secondary quantized input `offer waves from future' in one extra dimension, and to a reduction of the algebra of the consistent histories of past events to an Abelian subalgebra for the `trajectories of the output particles'. This supports the corpuscular-wave duality in the form of the thesis that everything in the future are quantized waves, while everything in the past are trajectories of the recorded particles.

High-lying collective rotational states in nuclei

Abstract: A review of the latest works concerning the ? decay of high-lying collective rotational states is given. The study of warm rotating nuclei is based on several experiments made with large ?-spectroscopy arrays, including EUROBALL. The analysis techniques, mainly based on the fluctuations of counts of ?-coincidence spectra, are briefly described, while the obtained results are discussed in detail. The work presented here focuses on several properties of nuclei in the order to chaos transition region, such as (i)?the importance of the two-body residual interaction in the description of the warm rotation; (ii)?the collectivity of the excited rotational states; (iii)?the conservation of quantum number with thermal energy; (iv)?the dependence of the band mixing process on mass and deformation. Altogether, the results discussed in this review show a consistent picture of the problem of excited rotation in the regime of strongly interacting bands. The present limits and perspectives are also briefly given.

Precision electroweak tests of the Standard Model

Abstract: The present status of precision electroweak data is reviewed. These data include measurements of e+e-→f\barf, taken at the Z resonance at LEP, which are used to determine the mass and width of the Z-boson. In addition, measurements have also been made of the forward-backward asymmetries for leptons and heavy-quarks, and also the final state polarization of the τ-lepton. At SLAC, where the electron beam was polarized, measurements were made of the left-right polarized asymmetry, ALR, and the left-right forward-backward asymmetries for b- and c-quarks. The mass, mW, and width, ΓW, of the W-boson have been measured at the Tevatron and at LEP, and the mass of the top-quark, mt, has been measured at the Tevatron. These data, plus other electroweak data, are used in global electroweak fits in which various Standard Model (SM) parameters are determined. A comparison is made between the results of the direct measurements of mW and mt with the indirect results coming from electroweak radiative corrections. Using all precision electroweak data, fits are also made to determine limits on the mass of the Higgs boson, mH. The influence on these limits of specific measurements, particularly those which are somewhat inconsistent with the SM, is explored. The data are also analysed in terms of the quasi-model-independent variables. Finally, the impact on the electroweak fits of the improvements in the determination of the W-boson and top-quark masses, expected from the Tevatron Run 2, is examined.

The Higgs particle in the standard model: experimental results from LEP

Abstract: At present, all the data obtained from the many experiments in particle physics are in agreement with the standard model. In the standard model there is one particle, the Higgs particle, that is responsible for giving masses to all particles with mass. In this sense, the Higgs particle occupies a unique position. Before the latter part of the year 2000, however, the Higgs particle was not observed experimentally. It is the purpose of this report to describe the first possible evidence for this particle, obtained by the four collaborations using the Large Electron-Positron colliding accelerator (LEP) at CERN, Geneva, Switzerland. The data were taken with the LEP centre-of-mass energy between 200 and 209 GeV. The result is dominated by the observation of an excess of four-jet events by ALEPH, one of the four experiments at LEP. Its mass, which is a free parameter in the standard model, is about 115 GeV/c2.

The influence of microscopic structures on rotational motion in nuclei

Abstract: This paper will concentrate on a study of the role and influence of microscopic structures on the properties of rotational bands in nuclei. Collective rotational features are well known in nuclei. Much of the review will discuss examples taken from experimental investigations of highly/superdeformed structures and their theoretical interpretation, which provide some of best and clearest rotational phenomena observed in nuclei. These structures have well-defined rotational properties that can be described by a collective model. The link between the deformation of these structures and the valence particle configuration has been established in many nuclei and recent experimental data are presented. Detailed investigations with new, very sensitive, instrumentation have revealed some extremely interesting and unexpected phenomena, such as the observation of identical rotational bands in neighbouring nuclei and energy staggering between adjacent states within a single band. The experimental and theoretical aspects of these new features will be discussed. The spectroscopy of highly/superdeformed structures has been studied extensively and many bands observed in a given nucleus which arise from particle-hole excitations. Measurements are now available, through the strength of magnetic dipole transitions, of the properties of specific single-particle orbitals. In the medium mass (A~60) region highly deformed states have been observed to decay by both proton and alpha emission in addition to the normal γ-decay mode. The decay widths, which are retarded for these channels, are related to the microscopic structures of the states involved. Investigations of rotational motion in exotic triaxial and hyperdeformed nuclear shapes are also reviewed. Recent work on `smooth band termination', in medium to medium-heavy nuclei, which results when a deformed collectively rotating nucleus gradually changes from a near-prolate to a non-collective oblate shape, has revealed detailed information on the configurations responsible and the effects on the bands as the spin contribution is exhausted. The concept of `magnetic rotation', which gives rise to regular `rotational-like' sequences of states in nuclei that are almost spherical, is discussed. This phenomenon is also found to primarily result from microscopic effects within the nucleus. A discussion of these two latter phenomena has been included in this paper, since they provide an important contribution to the topic under review.

Antimatter in cosmic rays

Abstract: The current status of the antimatter problem is reviewed starting with theoretical developments over the last decades and then emphasizing the observational part. So far no antimatter was observed in agreement with numerous baryogenesis theories which expect no antimatter in our universe, although some primordial antimatter, theoretically, is not excluded and even predicted in a number of models. We analyse what we can learn from observations: what are the manifestations of antimatter, what are the difficulties in detecting it and what is the current experimental situation and perspective in the observation of antimatter.