Binding between two-component bosons in one dimension

We investigate the ground state of one-dimensional few-atom Bose-Bose mixtures under harmonic confinement throughout the crossover from weak to strong inter-species attraction. The calculations are based on the numerically exact multi-configurational time-dependent Hartree method. For repulsive components we detail the condition for the formation of a molecular Tonks-Girardeau gas in the regime of intermediate inter-species interactions, and the formation of a molecular condensate for stronger coupling. Beyond a critical inter-species attraction, the system collapses to an overall bound state. Different pathways emerge for unequal particle numbers and intra-species interactions. In particular, for mixtures with one attractive component, this species can be viewed as an effective potential dimple in the trap center for the other, repulsive component.Comment: 10 pages, 10 figure

Excitations of attractive 1-D bosons: Binding vs. fermionization

The stationary states of few bosons in a one-dimensional harmonic trap are investigated throughout the crossover from weak to strongly attractive interactions. For sufficient attraction, three different classes of states emerge: (i) N-body bound states, (ii) bound states of smaller fragments, and (iii) gas-like states that fermionize, that is, map to ideal fermions in the limit of infinite attraction. The two-body correlations and momentum spectra characteristic of the three classes are discussed, and the results are illustrated using the soluble two-particle model.Comment: 7 pages, 5 figure

Gap solitons of a super-Tonks-Girardeau gas in a one-dimensional periodic potential

We study the stability of gap solitons of the super-Tonks-Girardeau bosonic gas in one-dimensional periodic potential. The linear stability analysis indicates that increasing the amplitude of periodic potential or decreasing the nonlinear interactions, the unstable gap solitons can become stable. In particular, the theoretical analysis and numerical calculations show that, comparing to the lower-family of gap solitons, the higher-family of gap solitons are easy to form near the bottoms of the linear Bloch band gaps. The numerical results also verify that the composition relations between various gap solitons and nonlinear Bloch waves are general and can exist in the super-Tonks-Girardeau phase.Comment: 7 pages,6 figure

Prediction of Aerodynamic Coefficients of Road Vehicles on Bridge Deck with and without Wind Protection by Means of CFD for Crosswind Stability Investigations

While planning a new bridge construction the risk of traffic accidents due to critical wind conditions should be carefully considered. The determination of aerodynamic forces and moments on vehicles is indispensable for stability investigations. However, the aerodynamic coefficients of vehicle-bridge systems depend on many factors which make it difficult to generalise the procedure. This paper is focusing on analysing a particular bridge geometry whereby aerodynamic coefficients were predicted by means of CFD. The accuracy of the numerical model was validated with the aid of experimental data from wind tunnel tests. Specifically, this work was conducted to investigate the effect of the wind barrier considering various wind flow angles and vehicle speeds. Mean forces and moments on the vehicle were analysed depending on both absolute and relative wind flows. The impact of performing relative motion between vehicle and bridge deck was investigated. Simulation results without wind barrier are qualitatively in good agreement with results found in literature. Nevertheless, the flow situation with wind barrier and relative motion is significantly more complex. Thus, CFD modelling has dominating advantages over wind tunnel tests in terms of both parameter variation and model accuracy. In this particular case CFD modelling is indeed essential in order to represent all possible wind flow angles and the relative motion between the vehicle and the bridge deck which remains difficult or rather hardly possible to perform in the wind tunnel

Fermi super-Tonks-Girardeau state for attractive Fermi gases in an optical lattice

We demonstrate that a kind of highly excited state of strongly attractive Hubbard model, named of Fermi super-Tonks-Girardeau state, can be realized in the spin-1/2 Fermi optical lattice system by a sudden switch of interaction from the strongly repulsive regime to the strongly attractive regime. In contrast to the ground state of the attractive Hubbard model, such a state is the lowest scattering state with no pairing between attractive fermions. With the aid of Bethe-ansatz method, we calculate energies of both the Fermi Tonks-Girardeau gas and the Fermi super-Tonks-Girardeau state of spin-1/2 ultracold fermions and show that both energies approach to the same limit as the strength of the interaction goes to infinity. By exactly solving the quench dynamics of the Hubbard model, we demonstrate that the Fermi super-Tonks-Girardeau state can be transferred from the initial repulsive ground state very efficiently. This allows the experimental study of properties of Fermi super-Tonks-Girardeau gas in optical lattices.Comment: 7 pages, 7 figure

The granularity of weakly occupied bosonic fields beyond the local density approximation

We examine ground state correlations for repulsive, quasi one-dimensional bosons in a harmonic trap. In particular, we focus on the few particle limit N=2,3,4,..., where exact numerical solutions of the many particle Schroedinger equation are available employing the Multi-Configuration Time-dependent Hartree method. Our numerical results for the inhomogeneous system are modeled with the analytical solution of the homogeneous problem using the Bethe ansatz and the local density approximation. Tuning the interaction strength from the weakly correlated Gross-Pitaevskii- to the strongly correlated Tonks-Girardeau regime reveals finite particle number effects in the second order correlation function beyond the local density approximation.Comment: 20 pages, 9 figures, submitted to NJ

A new approach to the spectral analysis of liquid membrane oscillators by Gabor transformation

Liquid membrane oscillators very frequently have an irregular oscillatory behavior. Fourier transformation cannot be used for these nonstationary oscillations to establish their power spectra. This important point seems to be overlooked in the field of chemical oscillators. A new approach is presented here based on Gabor transformation allowing one to obtain power spectra of any kind of oscillations that can be met experimentally. The proposed Gabor analysis is applied to a liquid membrane oscillator containing a cationic surfactant. It was found that the power spectra are strongly influenced by the presence of various added substances

On the possibility of molecular recognition of taste substances studied by Gabor analysis of oscillations

A liquid membrane oscillator containing nitromethane as membrane material has been investigated. The influence of substances responsible for taste belonging to four classes (sweetness, saltiness, sourness and bitterness) on oscillation patterns of liquid membrane oscillators with cationic surfactant benzyldimethyttetradecylammonium chloride (BDMTAC) was examined. A new approach based on Gabor transformation is proposed for obtaining the power spectra of the observed oscillating signals and for establishing "fingerprints" of the investigated substances. It was shown that two-dimensional form of these power spectra might be used efficiently for this purpose. (c) 2004 Elsevier B.V. All rights reserved