In a thought-provoking paper, Couder and Fort [Phys. Rev. Lett. 97, 154101 (2006)] describe a version of the famous double-slit experiment performed with droplets bouncing on a vertically vibrated fluid surface. In the experiment, an interference pattern in the single-particle statistics is found even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes place between different classical paths with precise amplitude and phase relations. In the double-slit experiment with walking droplets, these relations are lost since one of the paths is singled out by the droplet. To support our conclusions, we have carried out our own double-slit experiment, and our results, in particular the long and variable slit passage times of the droplets, cast strong doubt on the feasibility of the interference claimed by Couder and Fort. To understand theoretically the limitations of wave-driven particle systems as analogs to quantum mechanics, we introduce a Schrödinger equation with a source term originating from a localized particle that generates a wave while being simultaneously guided by it. We show that the ensuing particle-wave dynamics can capture some characteristics of quantum mechanics such as orbital quantization. However, the particle-wave dynamics can not reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics.

High-energy gamma rays from the deexcitation of giant dipole resonance modes have been measured for the decay of 108 Sn* and 166 Er*. The structure of the observed resonances can be correlated with the shapes of these nuclei at high excitation energy (E* -60 MeV). For the deformed system 166 Er* a shape change with increasing temperature is suggested. PACS numbers: 21.10. Gv, 24.30.Cz, 25.70.Gh The shapes of nuclei arise from basic correlations in nuclear matter. It is important to study these correlations and find the limits where they break down. This is possible to do by subjecting the nucleus to extreme conditions, such as high rotation and internal exciation energy, and studying the shapes which then result. Much work has been done in recent years both theoretically and experimentally to understand the shapes of "cold" nuclei. This work expands these studies to the mostly unexplored region of high nuclear temperature.A recent development 1 in continuum spectroscopy has provided a new tool for studying high spin spin states in the unbound region where gamma-ray emission, although weak, can compete with particle evaporation. It relies on the observation of highenergy y rays (E y^\ 0 MeV) emitted predominantly in the first stages of the decay of compound nuclei formed in heavy-ion-induced fusion reactions. These gamma rays have been associated with the deexcitation of giant dipole isovector resonance (GDR) modes. This has been substantiated 1,2 by comparing the measured cross section for gamma decay to the predictions of the classical dipole sum rule. The dependence of the GDR strength on excitation energy E* has been studied, 3 and the GDR yield from the first step of the decay has been isolated. 4 The results are consistent with the statistical theory for nuclear decay and indicate that the observed GDR decay is from equilibrated systems.In the present work we use this tool to study the shapes of nuclei in regions of excitation energy not otherwise accessible. At low excitation energy, for resonances built on the ground state, it is well known that the shape of the GDR reflects the shape of the nucleus. 5 The average resonance energy is related to the nuclear symmetry energy and in deformed nuclei the resonance is split into components corresponding to vibrations along the three principal nuclear axes. In rotating nuclei, because of the Coriolis force, the resonance is further divided into a total of five components. However, because of the small Coriolis splitting and the finite widths of these components, only two major peaks can be expected to be identified experimentally for axially symmetric nuclei. For prolate nuclei approximately -y of the total GDR strength is expected to be found in the peak of highest energy, while the situation is reversed for oblate nuclei.This investigation focuses on the structure of the GDR up to excitation energies E* -60 MeV and angular momenta IH -AQH, and we find a significant difference in the shape and width of the GDR built on excited states between the (at T = 0 MeV)...

No abstract

Vortex ripples in sand are studied experimentally in a one-dimensional setup with periodic boundary conditions. The nonlinear evolution, far from the onset of instability, is analyzed in the framework of a simple model developed for homogeneous patterns. The interaction function describing the mass transport between neighboring ripples is extracted from experimental runs using a recently proposed method for data analysis, and the predictions of the model are compared to the experiment. An analytic explanation of the wavelength selection mechanism in the model is provided, and the width of the stable band of ripples is measured.

No abstract