30 research outputs found
Effects of a nonlinear perturbation on dynamical tunneling in cold atoms
No full textWe perform a numerical analysis of the effects of a nonlinear perturbation on the quantum dynamics of two models describing noninteracting cold atoms in a standing wave of light with a periodical modulated amplitude A(t). One model is the driven pendulum, recently considered by D.A. Steck, W.H. Oskay, and M.G. Raizen [Science 293, 274 (2001)], and the other is a variant of the well-known kicked rotator model. In absence of the nonlinear perturbation, the system is invariant under some discrete symmetries and quantum dynamical tunneling between symmetric classical islands is found. The presence of nonlinearity destroys tunneling, breaking the symmetries of the system. Finally, further consequences of nonlinearity in the kicked rotator case are considered
Nonlinearity effects in the kicked oscillator
No full textThe quantum kicked oscillator is known to display a remarkable richness of dynamical behavior, from ballistic spreading to dynamical localization. Here we investigate the effects of a Gross-Pitaevskii nonlinearity on quantum motion, and provide evidence that the qualitative features depend strongly on the parameters of the system
Delocalized and resonant quantum transport in nonlinear generalizations of the kicked rotor model
No full textWe analyze the effects of a nonlinear cubic perturbation on the delta-kicked rotor. We consider two different models, in which the nonlinear term acts either in the position or in the momentum representation. We numerically investigate the modifications induced by the nonlinearity in the quantum transport in both localized and resonant regimes and a comparison between the results for the two models is presented. Analyzing the momentum distributions and the increase of the mean square momentum, we find that the quantum resonances asymptotically are very stable with respect to nonlinear perturbation of the rotor's phase evolution. For an intermittent time regime, the nonlinearity even enhances the resonant quantum transport, leading to superballistic motion
Functional and structural phenotyping of cardiomyocytes in the 3D organization of embryoid bodies exposed to arsenic trioxide
No full textChronic exposure to environmental pollutants threatens human health. Arsenic, a world-wide diffused toxicant, is associated to cardiac pathology in the adult and to congenital heart defects in the foetus. Poorly known are its effects on perinatal cardiomyocytes. Here, bioinformatic image-analysis tools were coupled with cellular and molecular analyses to obtain functional and structural quantitative metrics of the impairment induced by 0.1, 0.5 or 1.0 μM arsenic trioxide exposure on the perinatal-like cardiomyocyte component of mouse embryoid bodies, within their 3D complex cell organization. With this approach, we quantified alterations to the (a) beating activity; (b) sarcomere organization (texture, edge, repetitiveness, height and width of the Z bands); (c) cardiomyocyte size and shape; (d) volume occupied by cardiomyocytes within the EBs. Sarcomere organization and cell morphology impairment are paralleled by differential expression of sarcomeric α-actin and Tropomyosin proteins and of acta2, myh6 and myh7 genes. Also, significant increase of Cx40, Cx43 and Cx45 connexin genes and of Cx43 protein expression profiles is paralleled by large Cx43 immunofluorescence signals. These results provide new insights into the role of arsenic in impairing cytoskeletal components of perinatal-like cardiomyocytes which, in turn, affect cell size, shape and beating capacity
3D culture of ovarian follicles: a system towards their engineering?
No full textInfertility in women is a health priority. Designing a robust culture protocol capable of attaining complete follicle growth is an exciting challenge, for its potential clinical applications, but also as a model to observe and closely study the sequence of molecular events that lie behind the intricate relationship existing between the oocyte and surrounding follicle cells. Here, we describe the procedures used to maintain the ovarian follicle 3D architecture employing a variety of in vitro systems and several types of matrices. Collagen and alginate are the matrices that led to better results, including proof-of-concept of full-term development. Pioneer in its kind, these studies underlie the drawbacks encountered and the need for a culture system that allows more quantitative analyses and predictions, projecting the culture of the ovarian follicle into the realm of tissue engineering
