1,474 research outputs found
1-D Cluster Array at the Three Phase Contact Line in Diluted Colloids Subjected to A.C. Electric Fields
Colloidal particles provide an efficient mean of building multiple scale
structured materials from colloidal dispersions. In this Brief Report, we
account for experimental evidence on the formation of a colloidal cluster array
at a three-phase contact line. We study the influence of low frequency external
alternating electric fields on a diluted colloidal dispersion opened to the
air. We focus on the cluster formation and their evolution in the meniscus by
measuring characteristic times and lengths. We observe that the clusters are
separated by a well-defined length and that, in our experimental conditions,
they survive between five a fifteen minutes. These new results could be of
technological relevance in building tailored colloidal structures in
non-patterned substrates.Comment: There is supplementary information (see refs. 24, 27), which is
available upon request ([email protected]
Mechanics reveals the biological trigger in wrinkly fingers
The final publication is available at Springer via http://dx.doi.org/10.1007/s10439-016-1764-6Fingertips wrinkle due to long exposure to water. The biological reason for this morphological change is unclear and still not fully understood. There are two main hypotheses for the underlying mechanism of fingertip wrinkling: the ‘shrink’ model (in which the wrinkling is driven by the contraction of the lower layers of skin, associated with the shrinking of the underlying vasculature), and the ‘swell’ model (in which the wrinkling is driven by the swelling of the upper layers of the skin, associated with osmosis). In reality, contraction of the lower layers of the skin and swelling of the upper layers will happen simultaneously. However, the relative importance of these two mechanisms to drive fingertip wrinkling also remains unclear. Simulating the swelling in the upper layers of skin alone, which is associated with neurological disorders, we found that wrinkles appeared above an increase of volume of ˜10%.˜10%. Therefore, the upper layers can not exceed this swelling level in order to not contradict in vivo observations in patients with such neurological disorders. Simulating the contraction of the lower layers of the skin alone, we found that the volume have to decrease a ˜20%˜20% to observe wrinkles. Furthermore, we found that the combined effect of both mechanisms leads to pronounced wrinkles even at low levels of swelling and contraction when individually they do not. This latter results indicates that the collaborative effect of both hypothesis are needed to induce wrinkles in the fingertips. Our results demonstrate how models from continuum mechanics can be successfully applied to testing hypotheses for the mechanisms that underly fingertip wrinkling, and how these effects can be quantified.Peer ReviewedPostprint (published version
A theoretical model of the endothelial cell morphology due to different waveforms
Endothelial cells are key units in the regulatory biological process of blood vessels. They represent an interface to transmit variations on the fluid dynamic changes. They are able to adapt its cytoskeleton, by means of microtubules reorientation and F-actin reorganization, due to new mechanical environments. Moreover, they are responsible for initiating a huge cascade of biological processes, such as the release of endothelins (ET-1), in charge of the constriction of the vessel and growth factors such as TGF-ß and PDGF. Although a huge efforts have been made in the experimental characterization and description of these two issues the computational modeling has not gained such an attention. In this work we study the 3D remodeling of endothelial cells based on the main features of blood flow. In particular we study how different oscillatory shear index and the time average wall shear stresses modify the endothelial cell shape. We found our model fitted the experimental works presented before in in vitro studies. We also include our model within a computational fluid dynamics simulation of a carotid artery to evaluate endothelial cell shape index which is a key predictor of atheroma plaque formation. Moreover, our approach can be coupled with models of collagen and smooth muscle cell growth, where remodeling and the associated release of chemical substance are involved.Peer ReviewedPostprint (author's final draft
Density dependence of the symmetry energy from neutron skin thickness in finite nuclei
The density dependence of the symmetry energy around saturation density,
characterized by the slope parameter L, is studied using information provided
by the neutron skin thickness in finite nuclei. An estimate for L is obtained
from experimental data on neutron skins extracted from antiprotonic atoms. We
also discuss the ability of parity-violating elastic electron scattering to
obtain information on the neutron skin thickness in 208Pb and to constrain the
density dependence of the nuclear symmetry energy. The size and shape of the
neutron density distribution of 208Pb predicted by mean-field models is briefly
addressed. We conclude with a comparative overview of the L values predicted by
several existing determinations.Comment: 17 pages, 10 figures, submitted to EPJA special volume on Nuclear
Symmetry Energ
Octupole deformation properties of the Barcelona-Catania-Paris energy density functionals
We discuss the octupole deformation properties of the recently proposed
Barcelona-Catania-Paris (BCP) energy density functionals for two sets of
isotopes, those of radium and barium, where it is believed that octupole
deformation plays a role in the description of the ground state. The analysis
is carried out in the mean field framework (Hartree- Fock- Bogoliubov
approximation) by using the axially symmetric octupole moment as a constraint.
The main ingredients entering the octupole collective Hamiltonian are evaluated
and the lowest lying octupole eigenstates are obtained. In this way we restore,
in an approximate way, the parity symmetry spontaneously broken by the mean
field and also incorporate octupole fluctuations around the ground state
solution. For each isotope the energy of the lowest lying state and the
and transition probabilities have been computed and compared to
both the experimental data and the results obtained in the same framework with
the Gogny D1S interaction, which are used here as a well established benchmark.
Finally, the octupolarity of the configurations involved in the way down to
fission of Pu, which is strongly connected to the asymmetric fragment
mass distribution, is studied. We confirm with this thorough study the
suitability of the BCP functionals to describe octupole related phenomena.Comment: 13 pages, 13 figure
Nuclear symmetry energy and neutron skin thickness
The relation between the slope of the nuclear symmetry energy at saturation
density and the neutron skin thickness is investigated. Constraints on the
slope of the symmetry energy are deduced from the neutron skin data obtained in
experiments with antiprotonic atoms. Two types of neutron skin are
distinguished: the "surface" and the "bulk". A combination of both types forms
neutron skin in most of nuclei. A prescription to calculate neutron skin
thickness and the slope of symmetry energy parameter from the parity
violating asymmetry measured in the PREX experiment is proposed.Comment: 12 pages, 5 figures, Presented at XXXII Mazurian Lakes Conference on
Physics, Piaski, Poland, September 11-18, 201
Bi-Directional Energy Cascades and the Origin of Kinetic Alfv\'enic and Whistler Turbulence in the Solar Wind
The observed sub-proton scale turbulence spectrum in the solar wind raises
the question of how that turbulence originates. Observations of keV energetic
electrons during solar quite-time suggest them as possible source of free
energy to drive the turbulence. Using particle-in-cell simulations, we explore
how free energy in energetic electrons, released by an electron two-stream
instability drives Weibel-like electromagnetic waves that excite wave-wave
interactions. Consequently, both kinetic Alfv\'enic and whistler waves are
excited that evolve through inverse and forward magnetic energy cascades.Comment: 12 pages, 5 figures, Submitted to Physical Review Letter
Accurate nuclear masses from a three parameter Kohn-Sham DFT approach (BCPM)
Given the promising features of the recently proposed Barcelona-Catania-Paris
(BCP) functional \cite{Baldo.08}, it is the purpose of this paper to still
improve on it. It is, for instance, shown that the number of open parameters
can be reduced from 4-5 to 2-3, i.e. by practically a factor of two. One
parameter is tightly fixed by a fine-tuning of the bulk, a second by the
surface energy. The third is the strength of the spin-orbit potential on which
the final result does not depend within the scatter of the values used in
Skyrme and Gogny like functionals. An energy rms value of 1.58 MeV is obtained
from a fit of these three parameters to the 579 measured masses reported in the
Audi and Waspra 2003 compilation. This rms value compares favorably with the
one obtained using other successful mean field theories. Charge radii are also
well reproduced when compared with experiment. The energies of some excited
states, mostly the isoscalar giant monopole resonances, are studied within this
model as well.Comment: 23 pages, 12 figure
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