Tracking quasiclassical chaos in ultracold boson gases

We study the dynamics of an ultracold boson gas in a lattice submitted to a constant force. We track the route of the system towards chaos created by the many-body-induced nonlinearity and show that relevant information can be extracted from an experimentally accessible quantity, the gas mean position. The threshold nonlinearity for the appearance of chaotic behavior is deduced from Kolmogorov-Arnold-Moser arguments and agrees with the value obtained by calculating the associated Lyapunov exponent.     

Preparation, characterization, and heck reaction of siloxane films derived from carbosilane dendrons with a bromophenyl group at the focal point and up to 27 SiCl3 groups at the periphery

Multidentate organosiloxane thin films were prepared on SiO2/Si surfaces by solution phase deposition of carbosilane dendrons containing a bromophenyl group at the focal point and 3 (Br-G0), 9 (Br-G1), and 27 (Br-G2) SiCl3 groups at the periphery. The films were characterized by contact angle goniometry, ellipsometry, and X-ray photoelectron spectroscopy (XPS). The results indicated that about six Br-G0 molecules covered the same surface area as three Br-G1 molecules and one Br-G2 molecule. Hence, the density of the bromophenyl groups in the films could be defined by the size (generation) of the dendron adsorbates. We also demonstrated that the bromophenyl groups on the film surfaces could serve as a handle for attaching conjugated molecules via formation of C-C bonds. Thus, upon treatment of the films with 4-fluorostyrene under Heck reaction conditions, XPS analysis showed that about 90, 66, and 51% of the bromine atoms in the films prepared from Br-G0, Br-G1, and Br-G2 were consumed, and 94, 82, and 58% of the consumed bromine atoms were replaced by fluorostyryl groups. The remaining bromophenyl groups were probably not accessible to the reactants because of their unfavorable orientation. The overall yields for the surface Heck reaction were estimated to be 84, 54, and 30% for the films prepared from Br-G0, Br-G1, and Br-G2, respectively.     

Modifications of in vitro skin penetration under solar irradiation: evaluation on flow-through diffusion cells

The effect of solar irradiation on ex vivo dermatomed hairless rat skin samples maintained in culture on flow-through diffusion cells for at least 24 h was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and by histological observations. Transepidermal water loss (TEWL) measurements and kinetic analysis of the permeation of both tritiated water and 14C caffeine through the skin were performed after full-spectrum solar exposure involving the use of a xenon arc solar simulator. After a UV exposure of less than 420 mJ/cm2, skin integrity and permeation of both water and caffeine did not change significantly. In contrast, after a 420 mJ/cm2 UV exposure, the epidermis appeared more contracted, associated with an increase of 55% of TEWL and 220% of the skin permeation of tritiated water after 6 h. The data suggested a dramatic alteration of the skin barrier integrity. Moreover, the flux of 14C caffeine increased rapidly by 338% of the absorption of water 12 h after irradiation. These results reveal the presence of a threshold UV exposure that would not modify skin penetration.