3,487 research outputs found
Spiral arm crossings inferred from ridges in Gaia stellar velocity distributions
The solar neighborhood contains disc stars that have recently crossed spiral
arms in the Galaxy. We propose that boundaries in local velocity distributions
separate stars that have recently crossed or been perturbed by a particular arm
from those that haven't. Ridges in the stellar velocity distributions
constructed from the second Gaia data release trace orbits that could have
touched nearby spiral arms at apocentre or pericentre. The multiple ridges and
arcs seen in local velocity distributions are consistent with the presence of
multiple spiral features and different pattern speeds and imply that the outer
Galaxy is flocculent rather than grand design.Comment: For a movie https://youtu.be/5nbtNYDobc
Scaling properties of growing noninfinitesimal perturbations in space-time chaos
We study the spatiotemporal dynamics of random spatially distributed
noninfinitesimal perturbations in one-dimensional chaotic extended systems. We
find that an initial perturbation of finite size grows in time
obeying the tangent space dynamic equations (Lyapunov vectors) up to a
characteristic time , where is the largest Lyapunov exponent and
is a constant. For times perturbations exhibit spatial
correlations up to a typical distance . For times larger than
finite perturbations are no longer described by tangent space
equations, memory of spatial correlations is progressively destroyed and
perturbations become spatiotemporal white noise. We are able to explain these
results by mapping the problem to the Kardar-Parisi-Zhang universality class of
surface growth.Comment: 4.5 pages LaTeX (RevTeX4) format, 3 eps figs included. Submitted to
Phys Rev
Galaxy and mass assembly (GAMA) : The wavelength-dependent sizes and profiles of galaxies revealed by MegaMorph
We investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical-near-infrared imaging from the Galaxy AndMass Assembly survey.We fit single-component,wavelength-dependent, elliptical Sérsic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by n and colour, the recovered wavelength variations in effective radius (Re) and Sérsic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (nr 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger Re must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.Peer reviewe
Zein-based nanospheres and nanocapsules for the encapsulation and oral delivery of quercetin
In this study, the ability of zein nanospheres (NS) and zein nanocapsules containing wheat germ oil (NC) to
enhance the bioavailability and efficacy of quercetin was evaluated. Both types of nanocarriers had similar
physico-chemical properties, including size (between 230 and 250 nm), spherical shape, negative zeta potential,
and surface hydrophobicity. However, NS displayed a higher ability than NC to interact with the intestinal
epithelium, as evidenced by an oral biodistribution study in rats. Moreover, both types of nanocarriers offered
similar loading efficiencies and release profiles in simulated fluids. In C. elegans, the encapsulation of quercetin in
nanospheres (Q-NS) was found to be two twice more effective than the free form of quercetin in reducing lipid
accumulation. For nanocapsules, the presence of wheat germ oil significantly increased the storage of lipids in
C. elegans; although the incorporation of quercetin (Q-NC) significantly counteracted the presence of the oil.
Finally, nanoparticles improved the oral absorption of quercetin in Wistar rats, offering a relative oral
bioavailability of 26% and 57% for Q-NS and Q-NC, respectively, compared to a 5% for the control formulation.
Overall, the study suggests that zein nanocarriers, particularly nanospheres, could be useful in improving the
bioavailability and efficacy of quercetin
- …