4,902 research outputs found
Kinetics of the evaporative cooling of an atomic beam
We compare two distincts models of evaporative cooling of a magnetically
guided atomic beam: a continuous one, consisting in approximating the atomic
distribution function by a truncated equilibrium distribution, and a
discrete-step one, in which the evaporation process is described in terms of
successive steps consisting in a truncation of the distribution followed by
rethermalization. Calculations are performed for the semi-linear potential
relevant for experiments. We show that it is possible to map one model onto the
other, allowing us to infer, for the discrete-step model, the rethermalization
kinetics, which turns out to be strongly dependent upon the shape of the
confining potential.Comment: Submitted to Phys. Rev.
The water clock of Proteus mirabilis paces colony periodic and synchronous swarming
For decades, the origin of the concentric ring pattern of bacterial swarming colonies has puzzled microbiologists. Thanks to _in situ_ and real time infrared microspectroscopy and the brilliance of the infrared beam at SOLEIL synchrotron, we demonstrate here that _Proteus mirabilis_ swarming is paced by a periodic variation of the water activity at colony's edge. This periodic variation originates a phase transition within the extracellular matrix water H bond network which switches on and off the exopolysaccharides viscoelasticity and, consequently, the ability of bacterial cells to swarm. A dynamic behaviour emerges from the global properties of the multicellular entity which here relies on the ability of the bacterial cells to tune exoproducts synthesis in order to undergo sharp transitions above/below a given water activity threshold
Mesoscopic ensembles of polar bosons in triple-well potentials
Mesoscopic dipolar Bose gases in triple-well potentials offer a minimal
system for the analysis of the long-range character of the dipole-dipole
interactions. We show that this long-range character may be clearly revealed by
a variety of possible ground-state phases. In addition, an appropriate control
of short-range and dipolar interactions may lead to novel scenarios for the
dynamics of atoms and polar molecules in lattices, including the dynamical
creation of mesoscopic Schr\"odinger cats, which may be employed as a source of
highly-nonclassical states for Heisenberg-limited interferometry.Comment: 4 pages, 3 figures. Identical to the published version, including
supplemental material (4 pages, 6 figures)
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