Table of contents

The ground-state properties and low-lying excitations of a (quasi) one-dimensional system of longitudinally confined interacting bosons are studied. This is achieved by extending Haldane's harmonic-fluid description to open boundary conditions. The boson density, one-particle density matrix, and momentum distribution are obtained accounting for finite-size and boundary effects. Friedel oscillations are found in the density. Finite-size scaling of the momentum distribution at zero momentum is proposed as a method to obtain from the experiment the exponent that governs phase correlations. The strong correlations between bosons induced by reduced dimensionality and interactions are displayed by a Bijl-Jastrow wave function for the ground state, which is also derived.

The conventional assumption that the self-diffusion coefficient of a small tracer can be obtained by a local and instantaneous application of Einstein's relation in a temperature field with spatial and temporal heterogeneity is revisited. It is shown that hydrodynamic fluctuations contribute to the self-diffusion tensor in a universal way, i.e. independent of the size and shape of the tracer. The hydrodynamic contribution is anisotropic—it reflects knowledge of the global anisotropy in the temperature profile, leading to an anisotropic self-diffusion tensor for a spherical tracer. It is also retarded—it creates memory effects during the diffusion process due to hydrodynamic interactions.

Using a toy model, we examine the propagation of excitons in Cu₂O, which form localized pulses under certain experimental conditions. The formation of these waves is attributed to the effect of dispersion, non-linearity and the coupling of the excitons to phonons, which acts as a dissipative mechanism.

This letter proposes a novel image edge detection algorithm based on the difference of two synchronizing spatially extended nonlinear dynamical systems. The time evolution of each system is identified as a low-pass filtering process, whereas the difference of two synchronizing states is identified as the result of high-pass filtering. Two systems are weakly coupled and allowed to take a common image as their initial value, but have different time scales in their dynamical motions. Results are compared with those of standard image processing schemes. Some of the best image edges could be obtained by an appropriate balance between synchronization and desynchronization.

The mass and the decay width of a Higgs boson in the minimal standard model are evaluated by a variational method in the limit of strong self-coupling interaction. The non-perturbative technique provides an interpolation scheme between strong-coupling regime and weak-coupling limit where the standard perturbative results are recovered. In the strong-coupling limit the physical mass and the decay width of the Higgs boson are found to be very small as a consequence of mass renormalization. Thus it is argued that the eventual detection of a light Higgs boson would not rule out the existence of a strongly interacting Higgs sector.

Self-sustained oscillations in sinuous mode occur when a water jet impinges from below on a water/air free surface. Confined jet instability is experimentally investigated by image processing and velocity measurements. Despite small deformations of the surface, dynamic response of the jet provides unusual behaviour with comparable configurations (hole-tone, jet edge ...). The central feature is a bounded evolution of the oscillation frequency. Modal transitions are observed when physical parameters are varied. Each frequency jump is related to wavelength modification of the spatial pattern. Atypical evolution of the predominant length scale has to be connected to strong coupling with the weak deformations induced by the impinging jet on the free surface.

We study a one-dimensional discrete analog of the von Kármán flow, widely investigated in turbulence. A lattice of anharmonic oscillators is excited by both ends in order to create a large-scale structure in a highly nonlinear medium, in the presence of a dissipative term similar to the viscous term in a fluid. This system shows a striking similarity with a turbulent flow both at local and global scales. The properties of the nonlinear excitations of the lattice provide a partial understanding of this behavior.

We observed the presence of both a symmetric spectral broadening of the pump wave and a noise with frequencies close to the growth rate of a parametric instability in a magnetic mirror trapped plasma heated by microwaves. The microwave frequency agreed on certain surfaces in the trap with the local electron cyclotron resonance (ECR) frequency. Parametric instabilities introduce a system of interacting oscillators, namely plasma waves, providing a mechanism of phase randomization, different from the phase randomization due to single-particle motion considered so far for ECR heating in quasilinear theory. Including the effect of the observed potential noise we obtain a modified model for ECR heating exhibiting a shorter randomization time.

We report specific-heat measurements for a series of liquid crystals imbedded in a porous cylindrical geometry. Above the nematic-to-isotropic transition and dependent on nematic width (or chain length), the specific heat shows a small peak. In analogy to known ellipsometry results, the peak is believed to be the signature of a nematic prewetting transition.

In Co-Cu metastable alloys, suitable thermal treatments create Co nanoclusters that are responsible for the giant magnetoresistance phenomena. A detailed microscopic study by means of high-resolution X-ray diffraction and extended X-ray absorption spectroscopy has revealed an anomaly in the thermally induced segregation process, occurring at the same temperature regardless of the sample composition. This phenomenon roughens the nanocluster interface and degrades the sample magnetotransport properties.

We have studied the dynamics of a superfluid helium-4 meniscus on a solid substrate. In a pseudo–non-wetting situation, there is no hysteresis of the contact angle. We show that distortions of a liquid meniscus do propagate along the contact line. We have analyzed the propagation of pulses. We find a good agreement with theoretical predictions by Brochard for the dispersion relation of oscillation modes of the contact line.

We have performed a photoemission study of Ti₄O₇ around its two transition temperatures so as to cover the metallic, high-temperature insulating ("bipolaron-liquid") and low-temperature insulating (bipolaron-crystal) phases. While the spectra of the low-temperature insulating phase show a finite gap at the Fermi level, the spectra of the high-temperature insulating phase are gapless, which is interpreted as a soft Coulomb gap due to dynamical disorder. We suggest that the spectra of the high-temperature disordered phase of Fe₃O₄, which exhibits a charge order-disorder transition (Verwey transition), can be interpreted in terms of a Coulomb gap.

We analysed the electron-hole or, in other words, branch imbalance (BI) and the related electric potential V_imb which may arise in a mesoscopic superconductor/normal-metal (S/N) structure under non-equilibrium conditions in the presence of a supercurrent. Non-equilibrium conditions can be created in different ways: a) a quasiparticle current flowing between the N reservoirs; b) a temperature gradient between the N reservoirs and no quasiparticle current. It is shown that the voltage V_imb oscillates with the phase difference φ. In a cross-geometry structure the voltage V_imb arises in the vertical branch and affects the conditions for a transition to the π-state.

We use the exact determinantal representation derived by Kitanine, Maillet, and Terras for matrix elements of local spin operators between Bethe wave functions of the one-dimensional s = ½ Heisenberg model to calculate and numerically evaluate transition rates pertaining to dynamic spin structure factors. For real solutions z₁,..., z_r of the Bethe ansatz equations, the size of the determinants is of order r×r. We present applications to the zero-temperature spin fluctuations parallel and perpendicular to an external magnetic field.

We use the matrix product approach to construct all optimum ground states of general anisotropic spin-2 chains with nearest-neighbour interactions and common symmetries. These states are exact ground states of the model and their properties depend on up to three parameters. We find three different antiferromagnetic Haldane phases, one weak antiferromagnetic and one weak ferromagnetic phase. The antiferromagnetic phases can be described as spin liquids with exponentially decaying correlation functions. The variety of phases found with the matrix product ansatz also gives insight into the behaviour of spin chains with arbitrary higher spins.

A double-exchange model for degenerate e_g orbitals with intra- and inter-orbital interactions has been studied for the electron-doped manganites A_{1 − x}B_xMnO₃ (x > 0.5). We show that such a model reproduces the observed phase diagram and orbital ordering in the intermediate-bandwidth regime and the Jahn-Teller effect, considered to be crucial for the region x < 0.5, does not play a major role in this region. Brink and Khomskii have already pointed this out and stressed the relevance of the anistropic hopping across the degenerate e_g orbitals in the infinite Hund's coupling limit. From a more realistic calculation with finite Hund's coupling, we show that inclusion of interactions stabilizes the C-phase, the antiferromagnetic metallic A-phase moves closer to x = 0.5 while the ferromagnetic phase shrinks. This is in agreement with the recent observations of Kajimoto et al.and Akimoto et al.

Formation of RNA secondary structures is an example of the sequence-structure problem omnipresent in molecular biophysics. A basic theoretical issue concerns the phase behaviour of self-attracting random RNA sequences. By studying a simplified toy model of RNA folding, we show that there are two distinct possible phases for the random RNA below its melting transition—a molten phase in which an exponentially large number of allowed secondary structures have comparable free energies and coexist in thermal equilibrium, and a glass phase in which the equilibrium ensemble is dominated by one or a few structures with much lower free energies.

We describe the enforced unbinding of a bead from i) a supported membrane, and ii) a cell surface. The force necessary to unbind the bead is obtained and is shown to be within the range accessible in micromechanical experiments.

The adhesion dynamics of multicomponent membranes containing specific receptors (stickers) and repulsive macromolecules (repellers) is studied theoretically. We find different dynamic regimes with clearly distinct patterns of stickers and repellers at intermediate times. The pattern formation is shown to depend critically on the strength of the repeller barrier which opposes sticker binding. For strong barriers composed of long repellers, the nucleation time for sticker binding is large compared to typical diffusion times, and the stickers bind by condensation around a single nucleus. For weaker repeller barriers, many nuclei are formed initially. Due to the diffusion of stickers into the adhesion area, nuclei at the rim of this area subsequently grow faster, which results in circular sticker patterns. At sufficiently high sticker concentrations, the pattern evolution is similar to recent observations during T cell adhesion.

We present a unified model for the growth of a population of cells. We propose that sigmoidal growth in cellular systems is a self-organised process due to long-range interactions among the cells. The interaction is mediated through diffusive substances produced by them. The model considers a competition between cell drive to replicate and inhibitory interactions that are modeled by a power law of the distance between the cells. The different classes of solutions (Logistic, Richards-like, Gompertz, and Exponential) are determined by a relation between the interaction length and the fractal dimension of the cellular structure.