Metastable state

New developments in thin-film magnetism are reviewed with an emphasis on the ultrathin regime. The scope includes relatively simple metallic systems in overlayer, sandwich, and superlattice configurations. Sample fabrication, characterization, and magnetic measurement techniques are outlined by highlighting some of the more modern experimental innovations. Current issues and advances that demonstrate the symbiotic relationship between experiment and theory are then examined, including the surface magnetic anisotropy, the two-dimensional critical behavior, the creation of metastable phases via epitaxy, and phenomena associated with coupled magnetic layers. The review ends with a brief account of the impact of the various contemporary developments on the applications area.

The frequency response of pinned vortex lattice in type-II superconductors is investigated. If frequency is not too low than the AC-absorption is caused by oscillations of the vortex lattice near equilibrium state (Campbell regime). We calculate the field and temperature dependencies ofboth Campbell penetration depth and surface resistance, taking into account the effect of the thermal depinning. In the region of low frequencies jumps of lattice regions between different metastable states (two-level systems) come into play and give main contribution to the AC-response. The field and temperature dependencies of the penetration depth and surface resistance in the last region are also found.

Paraglacial geomorphology is the study of earth-surface processes, sediments, landforms, landsystems and landscapes that are directly conditioned by former glaciation and deglaciation. The withdrawal of glacier ice exposes landscapes that are in an unstable or metastable state, and consequently liable to modification, erosion and sediment release at rates greatly exceeding background denudation rates. This paper (1) reviews research on paraglacial processes, landforms and landscape change in a range of geomorphological settings; (2) explores the importance of paraglacial landscape modification and sediment recycling as a component of alternating glacial/nonglacial landscape evolution; (3) assesses the nature and significance of paraglacial facies in Quaternary stratigraphic sequences; and (4) develops a general model of the sequence of paraglacial landscape modification and the changing nature of paraglacial landsystems. Six paraglacial landsystems are identified: rock slopes, drift-mantled slopes, glacier forelands, and alluvial, lacustrine and coastal systems. Each contains a wide range of paraglacial landforms and sediment facies. Collectively these landforms and sediments (e.g. talus accumulations, debris cones, alluvial fans, valley fills, deltas and coastal barrier structures) can be conceptualised as storage components of an interrupted sediment cascade with four primary sources (rockwalls, drift-mantled slopes, valley-floor glacigenic deposits and coastal glacigenic deposits) and four terminal sediment sinks (alluvial valley-fill deposits, lacustrine deposits, coastal/ nearshore deposits and shelf/offshore deposits). Paraglacial sediment stores and sinks may form major sources of readily erodible sediment during the early stages of glacial cycles, leading to high rates of sediment transport during periods of glacier or ice-sheet expansion. Probably because of the limited preservation potential of paraglacial sediments that were subsequently overrun by glacier ice, identification of paraglacial facies in both terrestrial and marine settings has been almost exclusively limited to sequences that postdate the Last Glacial Maximum. The unifying concept of paraglacial geomorphology is that of glacially conditioned sediment availability. Relaxation of landscape elements to nonglacial conditions operates over timescales of 10 1->10 4 years, and is conditioned by both process and spatial scale. Rate of sediment reworking can be described by an exhaustion model. In the case of primary reworking of glacigenic sediment, the rate of reworking declines approximately exponentially through time, though extrinsic perturbation may rejuvenate paraglacial sediment flux long after termination of the initial period of paraglacial adjustment. Landscape-scale (particularly alluvial and coastal) systems may exhibit intrinsically complex responses due to reworking of secondary paraglacial sediment stores. The long relaxation time of such systems implies that many areas deglaciated in the Late Pleistocene or Early Holocene have still not fully adjusted (in terms of sediment supply) to nonglacial conditions.

Approximately 250 papers were presented. This meeting addressed the fundamental science of imperfection in semiconductor materials. A wide range of defects of both fundamental and technological interest that include native defects, impurities, dislocations, and defects at surfaces and interfaces in a variety of semiconductor mate-'\ rials (Si, Ge, diamond, III-V and II-VI compounds, and related alloys) were discussed. Properties of interest included defect structures (atomic and electronic), defect-3-ICDS-16 COMMITTEES

Systems Biology (system-level understanding in biological science), from the physical-chemical point of view, is involved with irreversible thermodynamics and nonlinear kinetic theory of open systems which are founded on nonequilibrium statistical mechanics. We describe a modern thermo-statistical approach for dealing with complex systems, in particular biological systems. We consider the case of a very peculiar complex behavior in open boson systems sufficiently away, from equilibrium, which appear to have large relevance in the functioning of biological systems. This is, on the one hand, the so-called Fröhlich-Bose-Einstein-like condensation leading in steady-state conditions to the emergence of a particular case of quantum-large-scale coherent ordering, of the type of a selforganizing-synergetic dissipative structure. Moreover, additional complexity emerges in the form of propagation, in this condensate, of signals (information) consisting of nearly undamped and undistorted, long-distance propagating, solitary waves (the pseudoparticle soliton). It can be accompanied by a so-called Fröhlich-Cherenkov cone of emission of polar vibrations, and it is also possible the formation of metastable states of the form of the so-called bioelectrets. These are phenomena apparently working in biological processes, which are presently gaining relevant status on the basis of eventually providing a large-scale quantum-coherent behavior in cytoskeletons of neurons and the conscious (non-computational) activity in the brain. Emphasis is centered on the quantum-mechanical-statistical irreversible thermodynamics of these open systems, and the informational characteristics of the phenomena. Ways for their experimental evidencing are pointed out and discussed.

The Principle of the Glitch states that for any device which makes a discrete decision based upon a continuous range of possible inputs, there are inputs for which it will take arbitrarily long to reach a decision. The appropriate mathematical setting for studying this principle is described. This involves defining the concept of continuity for mappings on sets of functions. It can then be shown that the glitch principle follows from the continuous behavior of the device.

Using the smali-polaron theory of diffusion we obtain a very good fit of the experimental data on hydrogen diffusion in tantalum between 15 and 500 K. It is shown that the phenomenon has three regimes: (a) At T>250 K the transport occurs mainly b~ hydrogen tunneling between tetrahedral sites. (b) At 200 K > T> 15 K metastable states having octahedral symmetry play the main role. (c) The dominance of tetrahedral diffusion restarts at T< 10 K.

Course 7 COMPUTING THE NUMBER OF METASTABLE STATES IN INFINITE-RANGE MODELS Giorgio Parisi Dipartimento di Fisica, INFM, SMC and INFN, Universitdi Roma La Sapienza, PA Moro 2, 00185 Rome, Italy A. Bovier, F. Dunlop, F. den Hollander, A. van Enter and J. Dalibard, eds. Les Houches, Session LXXXIII, 2005 Mathematical Statistical Physics 006 Elsevier BV All rights reserved 295 Content 1. Introduction 299 2. The TAP equations 303 3. A simple analysis of the solutions of the Bethe equations 307 4. The direct ...

We propose a model for the passage between metastable states of mind dynamics. As changing points we use the rapid transition processes simultaneously detectable in EEG signals related to different cortical areas. Our model consists of a non-Poissonian intermittent process, which signals that the brain is in a condition of complexity, upon which a Poisson process is superimposed. We provide an analytical solution for the waitingtime distribution for the model, which is well obeyed by physiological data. Although the role of the Poisson process remains unexplained, the model is able to reproduce many behaviors reported in literature, although they seem contradictory.

The dynamics of a soft-spin version of the van Hemmen spin-glass model is considered in the thermodynamic limit. Phase and bifurcation diagrams for quenched distributions are given. Phase coexistence, metastability, and hysteretic phenomena are found.

The sequence distribution and crystalline structure of a series of poly(ethylene-co-vinyl acetate) (EVA) copolymers with different VA contents were investigated with high-resolution nuclear magnetic resonance spectroscopy (NMR). It was found that most of the VA segments are isolated in the main chain, though three kinds of sequence distributions (VA -VA head to tail, VA -E -VA head to tail, and VA -E -E -VA head to tail) exist in the EVA copolymers with higher VA content. Furthermore, two kinds of alkyl-branching signals were detected in the high temperature 13 C NMR spectra of EVA copolymers. Solid-state 13 C NMR spectroscopic investigation indicated that only orthorhombic phase exists in the crystalline region of the EVA copolymers with lower VA content. For the EVA copolymers with higher VA content, however, besides the occurrence of orthorhombic crystalline phase, monoclinic phase was also detected. As a metastable state, monoclinic phase is mainly affected by VA content as well as the thermal treating history. q

In these notes I will review the results that have been obtained in these last years on the computation of the number of metastable states in infinite-range models of disordered systems. This is a particular case of the problem of computing the exponentially large number of stationary points of a random function. Quite surprisingly supersymmetry plays a crucial role in this problem. A careful analysis of the physical implication of supersymmetry and of supersymmetry breaking will be presented: the most spectacular one is that in the Sherrington-Kirkpatrick model for spin glasses most of the stationary points are saddles, as predicted long time ago.

The frozen phase of mean field spin glass models displays, in the thermodynamic limit, a very high number of stable and metastable states. Such a feature is the consequence of the disorder and the frustration characterizing spin glasses and causing the onset of many different configurations of spins minimizing the thermodynamic potential, organized in the phase space in a rather complicated way. In order to comprehend the structure of the landscape of the thermodynamic potential below a given critical temperature a very ...

The purpose of this Letters section is to provide rapid dissemination of important new results in the fields regularly covered by Physics of Fluids. Results of extended research should not be presented as a series of letters in place of comprehensive articles. Letters cannot exceed three printed pages in length, including space allowed for title, $gures, tables, references and an abstract limited to about IO0 words. There is a three-month time limit, from date of receipt to acceptance, for processing Letter manuscripts. Authors must also submit a brief statement justifying rapid publication in the Letters section.

Quantum communication places stringent requirements on single-photon sources. Here we report a theoretical study of the cavity Purcell enhancement of two diamond point defects, the nickel-nitrogen (NE8) and silicon-vacancy (SiV) centers, for high-performance, near on-demand single-photon generation. By coupling the centers strongly to high-finesse optical photonic-bandgap cavities with modest quality factor Q = O(10 4 ) and small mode volume V = O(λ 3 ), these system can deliver picosecond single-photon pulses at their zero-phonon lines with probabilities of 0.954 (NE8) and 0.812 (SiV) under a realistic optical excitation scheme. The undesirable blinking effect due to transitions via metastable states can also be suppressed with O(10 −4 ) blinking probability. We analyze the application of these enhanced centers, including the previously-studied cavity-enhanced nitrogenvacancy (NV) center, to long-distance BB84 quantum key distribution (QKD) in fiber-based, openair terrestrial and satellite-ground setups. In this comparative study, we show that they can deliver performance comparable with decoy state implementation with weak coherent sources, and are most suitable for open-air communication.

The existence of singly, doubly, and triply charged diatomic molecular ions was observed by using an Accelerator Mass Spectrometry (AMS) technique. The mean lifetimes of 3 MeV boron diatomic molecular ions were measured. No isotopic effects on the mean lifetimes of boron diatomic molecules were observed for charge state 3+. Also, the mean lifetime of SiF^3+ was measured.

A new seawater standard has been developed for oceanographic and engineering applications that consists of three independent thermodynamic potential functions, derived from extended distinct sets of very accurate experimental data. The results have been formulated as Releases of the International Association for the Properties of Water and Steam, IAPWS (1996, 2006, 2008) and are to be adopted internationally by other organizations in subsequent years. In order to successfully perform computations such as phase equilibria from combinations of these potential functions, mutual compatibility and consistency of these independent mathematical functions must be ensured. In this article, a brief review of their separate development and ranges of validity is given. We analyse background details on the conditions specified at their reference states, the triple point and the standard ocean state, to ensure the mutual consistency of the different formulations, and we consider the necessity and possibility of numerically evaluating metastable states of liquid water. Computed from this formulation in quadruple precision (128 bit floating point numbers), tables of numerical reference values are provided as anchor points for the consistent incorporation of additional potential functions in the future, and as unambiguous benchmarks to be used in the determination of numerical uncertainty estimates of double-precision implementations on different platforms that may be customized for special purposes.

Consider Glauber dynamics for the Ising model on the hypercubic lattice with a positive magnetic field. Starting from the minus configuration, the system initially settles into a metastable state with negative magnetization. Slowly the system relaxes to a stable state with positive magnetization. Schonmann and Shlosman showed that in the two dimensional case the relaxation time is a simple function of the energy required to create a critical Wulff droplet. The dilute Ising model is obtained from the regular Ising model by deleting a fraction of the edges of the underlying graph. In this paper we show that even an arbitrarily small dilution can dramatically reduce the relaxation time. This is because of a catalyst effect-rare regions of high dilution speed up the transition from minus phase to plus phase.

The structure and the orientation of thermotropic hexagonal columnar liquid crystals are studied by grazing incidence X-ray diffraction (GIXD) for different discotic compounds in the geometry of open supported thin films. Whatever the film deposition mode (either spin-coating or vacuum evaporation) and the film thickness, a degenerate planar alignment with the liquid crystalline columns parallel to the substrate is found. However, if a specific thermal process is applied to the liquid crystal film, homeotropic anchoring (columns normal to the interface) can be stabilized in a metastable state.

The main objective of this and its accompanying articles is to derive a mathematical theory associated with the thermohaline circulations (THC). This article provides a general transition and stability theory for the Boussinesq system, governing the motion and states of the large-scale ocean circulation. First, it is shown that the first transition is either to multiple steady states or to oscillations (periodic solutions), determined by the sign of a nondimensional parameter K, depending on the geometry of the physical domain and the thermal and saline Rayleigh numbers. Second, for both the multiple equilibria and periodic solutions transitions, both Type-I (continuous) and Type-II (jump) transitions can occur, and precise criteria are derived in terms of two computable nondimensional parameters b 1 and b 2. Associated with Type-II transitions are the hysteresis phenomena, and the physical reality is represented by either metastable states or by a local attractor away from the basic solution, showing more complex dynamical behavior. Third, a convection scale law is introduced, leading to an introduction of proper friction terms in the model in order to derive the correct circulation length scale. In particular, the dynamic transitions of the model with the derived friction terms suggest that the THC favors the continuous transitions to stable multiple equilibria. Applications of the theoretical analysis and results to different flow regimes will be explored in the accompanying articles.

Phase diagram of microcanonical ensembles of self-attracting particles is studied for two types of short-range potential regularizations: self-gravitating fermions and classical particles interacting via attractive soft −(r 2 + r 2 0) −1/2 Coulomb potential. When the range of regularization is sufficiently short, the self-attracting systems exhibit gravitational or collapse-like transition. As the fermionic degeneracy or the softness radius increases, the gravitational phase transition crosses over to a normal first-order phase transition, becomes second-order at a critical point, and finally disappears. Applicability of a commonly used saddle-point or mean-field approximation and importance of metastable states is discussed.

A brief overview is given of developments in thermal analysis and calorimetry (TA&C) in the last few decades. The overview is followed by a discussion of the trends anticipated, the (un)desirability of these trends and the actions that need to be taken. Over the last few decades, the popularity of TA&C has increased at an impressive rate. However, educational institutes are paying less and less attention to analytical expertise, including TA&C. This means the number of practitioners is steadily decreasing and TA&C is increasingly becoming a`purely analytical tool' for users. Moreover, TA&C is seen as a simple and cheap method which has reached the limits of its potential. It seems that the success of TA&C is having a paralyzing effect, causing developments to stagnate. Due to the lack of practitioners, there is not enough technology push to drive new developments that are of a scienti®c rather than commercial interest, and there threatens to be a lack of contact between the TA&C community and the scienti®c community. As a result, the competence level of TA&C users threatens to decrease, simply because there are fewer examples of`state of the art' TA&C work in the form of studies and publications, and because the number of training facilities is decreasing. This is an alarming trend. Suggestions are offered for reversing this trend and a proposal is made for a concrete approach to ensure that the necessary actions with regard to TA&C will be implemented via National Societies for Information, Communication and Education and National Expertise Centers for Development. The quantitative capabilities of TA&C and past and future developments are illustrated with reference to polymers on the basis of examples of quantitative DSC, high-rate calorimetry, high-pressure DSC, real-time X-ray and SALLS and temperature-modulated reaction calorimetry. The combining of TA&C and scanning probe microscopy (SPM), with the aim of providing time-and position-resolved analyses of materials, is discussed as an example of a promising development.

We present a comparative study of several dynamical systems of increasing complexity, namely, the logistic map with additive noise, one, two and many globally-coupled standard maps, and the Hamiltonian Mean Field model (i.e., the classical inertial infinitely-ranged ferromagnetically coupled XY spin model). We emphasize the appearance, in all of these systems, of metastable states and their ultimate crossover to the equilibrium state. We comment on the underlying mechanisms responsible for these phenomena (weak chaos) and compare common characteristics. We point out that this ubiquitous behavior appears to be associated to the features of the nonextensive generalization of the Boltzmann-Gibbs statistical mechanics.

A quantum field theoretical model for the dynamics of the disoriented chiral condensate is presented. A unified approach to relate the quantum field theory directly to the formation, decay and signals of the DCC and its evolution is taken. We use a background field analysis of the O(4) sigma model keeping one-loop quantum corrections (quadratic order in the fluctuations). An evolution of the quantum fluctuations in an external, expanding metric which simulates the expansion of the plasma, is carried out. We examine, in detail, the amplification of the low momentum pion modes with two competing effects, the expansion rate of the plasma and the transition rate of the vacuum configuration from a metastable state into a stable state.We show the effect of DCC formation on the multiplicity distributions and the Bose-Einstein correlations.

A correlated quantum many-body method is applied to describe resonance states of atomic Bose-Einstein condensates (BEC) in a realistic shallow trap (as opposed to infinite traps commonly used). The realistic van der Waals interaction is adopted as the interatomic interaction. We calculate experimentally measurable decay rates of the lowest quasi-bound state in the shallow trap. The most striking result is the observation of a new metastable branch besides the usual one for attractive BEC in a pure harmonic trap. As the particle number increases the new metastable branch appears, then gradually disappears and finally usual metastable branch (associated with the attractive BEC in a harmonic trap) appears, eventually leading to the collapse of the condensate.

%e present a study of charge-density-wave metastable states below 4.2 K in thermally quenched NbSe3. These states and their ensuing relaxation are manifest most strongly in the Shubnikov-de Haas (SdH) oscillations. The quenched metastable state remains without any change for time scales ranging from several minutes to several hours before a sharp relaxation is observed. Sharp jumps in the magnetoresistance and the amplitudes of the SdH oscillations are observed when the metastable states relax spontaneously. %'e present evidence that these relaxations are not driven by the magnetic field, H, the current, or a combination of the two. The SdH oscillation frequencies with H parallel to c indicate a 12% decrease in the extremal area of the conduction-electron Fermi surface after relaxation to the equilibrium state. However, the determination of the Hall coefhcient suggests that this change is not simply related to a change in the carrier concentration.

Oxygen diffuses in silicon with an activation energy of 2.53-2.56 eV. In hydrogenated samples, this activation energy is found to decrease to 1.6-2.0 eV. In this paper, a microscopic mechanism for hydrogenenhanced oxygen diffusion in p-doped silicon is proposed. A path for joint diffusion of O and H is obtained from an ab initio molecular-dynamics simulation in which the O atom is ''kicked'' away from its equilibrium position with a given initial kinetic energy. After reaching a maximum potential energy of 1.46 eV above the ground state, the system relaxes to a metastable state on which a Si-Si bond is broken and the H atom saturates one of the dangling bonds. With an extra 0.16 eV, the Si-H bond is broken and the system relaxes to an equivalent ground-state configuration. Therefore, the migration pathway is an intriguing two-step mechanism. This path represents a 0.54-eV reduction in the static barrier when compared with the diffusion of isolated O in Si, in excellent agreement with experiments. This mechanism elucidates the role played by the H atom in the process: it not only serves to ''open up'' a Si-Si bond to be attacked by the oxygen, but it also helps in reducing the energy of an important intermediate state in the diffusion pathway. ͓S0163-1829͑99͒03607-3͔ PHYSICAL REVIEW B

We study a generalization of the Heston model, which consists of two coupled stochastic differential equations, one for the stock price and the other one for the volatility. We consider a cubic nonlinearity in the first equation and a correlation between the two Wiener processes, which model the two white noise sources. This model can be useful to describe the market dynamics characterized by different regimes corresponding to normal and extreme days. We analyze the effect of the noise on the statistical properties of the escape time with reference to the noise enhanced stability (NES) phenomenon, that is the noise induced enhancement of the lifetime of a metastable state. We observe NES effect in our model with stochastic volatility. We investigate the role of the correlation between the two noise sources on the NES effect.

An overview is given of the current spectroscopic effort on the Livermore electron beam ion trap facilities. The effort focuses on four aspects: spectral line position, line intensity, temporal evolution, and line shape. Examples of line position measurements include studies of the K-shell transitions in heliumlike Kr 34+ and the 2s-2p intrashell transitions in lithiumlike Th 87+ and U 89+, which provide benchmark values for testing the theory of relativistic and quantuna electrodynamical contributions in high-Z ions. Examples of line intensity measurements are provided by measurements of the electron-impact excitation and dielectronic recombination cross sections of the heliumlike transition-metal ions Ti 2~ through Co 25+. A discussion of radiative lifetime measurements of metastable levels in heliumlike ions is given to illustrate our time-resolved spectroscopy techniques in the microsecond range. We also present a measurement of the spectral lineshape that illustrates the very low ion temperatures that can be achieved in an EBIT.

Energetic pulsed atomic oxygen beams were generated by laser-driven evaporation of cryogenically frozen ozone/oxygen films and thin films of indium-tin oxide (ITO). Mass and energy characterization of beams from the ozone/oxygen films were carried out by mass spectrometry. The peak flux, found to occur at 10 eV, is estimated from this data to be 3 x 10(20) m(-2) s(-1). Analysis

We have investigated the influence of a driving force on the elastic coupling (Labusch parameter) of the field-cooled state of the flux line lattice (FLL) in 400 nm thick YBa2Cu3O7 superconducting films. We found that the FLL of a field-cooled state without driving forces is not in an equilibrium state. Results obtained for magnetic fields applied at 0 • and 30 • relative to CuO2 planes, show an enhancement of the elastic coupling of the films at driving current densities several orders of magnitude smaller than the critical one. Our results indicate that the FLL appears to be in a relatively ordered, metastable state after field cooling without driving forces.

It has recently been proposed that all deep earthquakes (> 400 km depth) are caused by a shear instability associated with the transformation of roetastable olivine to its high-pressure polymorphs within the cold core of subducting slabs (Green and Burnley, 1989; Kirby et al., 1991). If so, then the seismogenic zone would narrow with depth below 400 km following slab isotherms. Because the ratio of fault slip to length does not increase markedly with depth, and stress orientations indicate that deep fault planes are not parallel to the subducting slab, a fault plane large enough to generate a very large, deep earthquake would not fit within a narrow seismogenic zone and multiple fault planes would be needed. If the fault planes are not parallel due to spatial variations in stress, a deviatoric non-double-couple component

Spherical dust clusters composed of several concentric shells are experimentally investigated with particular interest on transitions between different configurations and transitions of particles between different shells. Transitions between different ground and metastable configurations are frequently observed. The experimental analysis allows us to derive the energy differences of different configurations from particles traveling between shells. The observed transitions and transition probabilities are compared to molecular dynamics simulations.

We address the problem of how to incorporate quantum effects into the calculation of finite-temperature decay rates for a metastable state of a quantum field theory. To do this, we consider the Gross-Neveu model with an explicit chiral symmetry breaking term, which allows for a metastable state. This theory can be shown to have a "critical bubble" which is a solution to the exact equations of motions (i.e. to all orders in perturbation theory, including all higher derivative, quantum and thermal corrections). This configuration mediates the thermal activation of the metastable vacuum to the true ground state, with a decay rate Γ ∝ exp(−F c /T ), where F c is the free energy of the critical bubble. We then compare this exact calculation to various approximations that have been used in previous work. We find that these approximations all overestimate the activation rate. Furthermore, we study the effect of finite baryon number upon the bubble profile and the activation barriers. We find that beyond a critical baryon number the activation barriers disappear altogether. 1

showed the existence of a metastable state of the nitrogen molecule with a 3 + coefficient for diffusion through ground-state nitrogen of about one quarter of that of the well-known A ~, state. Both states were populated by pre-breakdown discharges through pure nitrogen. This paper presents further results on the diffusion of metastable excited molecules through nitrogen. The effects of varying background gas number density N and the reduced electric field E/N were explored, and data were taken in two ionization chambers with two different cathode materials. Consistent results are obtained with the different chambers and cathodes. The characteristic times for the decay of metastable population density are independent of E/N but scale with I/N, consistent with the existence of two slowly diffusing metastable states of nitrogen. The values at 295 _+ 4 K of the product D m N, where D m is the metastable diffusion coefficient, are 551 + 25 am-~ s-t ((5.51 + 0.25) × 1016 cm-I s-l) for the first slowly diffusing state and 158 + 17 am-! s-t for the second. Both states show very small quenching in collisions with ground-state nitrogen molecules. The first state 3 +

We introduce, and numerically study, a system of N symplectically and globally coupled standard maps localized in a d = 1 lattice array. The global coupling is modulated through a factor r −α , being r the distance between maps. Thus, interactions are long-range (nonintegrable) when 0 ≤ α ≤ 1, and short-range (integrable) when α > 1. We verify that the largest Lyapunov exponent λM scales as λM ∝ N −κ(α) , where κ(α) is positive when interactions are long-range, yielding weak chaos in the thermodynamic limit N → ∞ (hence λM → 0). In the short-range case, κ(α) appears to vanish, and the behaviour corresponds to strong chaos. We show that, for certain values of the control parameters of the system, long-lasting metastable states can be present. Their duration tc scales as tc ∝ N β(α) , where β(α) appears to be numerically consistent with the following behavior: β > 0 for 0 ≤ α < 1, and zero for α ≥ 1. All these results exhibit major conjectures formulated within nonextensive statistical mechanics (NSM). Moreover, they exhibit strong similarity between the present discrete-time system, and the α-XY Hamiltonian ferromagnetic model, also studied in the frame of NSM.

A Bose-Einstein condensate in an external potential consisting of a superposition of a harmonic and a random potential is considered theoretically. From a semi-quantitative analysis we find the size, shape and excitation energy as a function of the disorder strength. For positive scattering length and sufficiently strong disorder the condensate decays into fragments each of the size of the Larkin length L. This state is stable over a large range of particle numbers. The frequency of the breathing mode scales as 1/L 2 . For negative scattering length a condensate of size L may exist as a metastable state. These findings are generalized to anisotropic traps.

A correlation between two noise processes driving the thermally activated particles in a symmetric triple well potential, may cause a symmetry breaking and a difference in relative stability of the two side wells with respect to the middle one. This leads to an asymmetric localization of population and splitting of Kramers' rate of escape from the middle well, ensuring a preferential distribution of the products in the course of a parallel reaction.