26,892 research outputs found
Picosecond Laser Ablation of Polyhydroxyalkanoates (PHAs): Comparative Study of Neat and Blended Material Response
Polyhydroxyalkanoates (PHAs) have emerged as a promising biodegradable and biocompatible material for scaffold manufacturing in the tissue engineering field and food packaging. Surface modification is usually required to improve cell biocompatibility and/or reduce bacteria proliferation. Picosecond laser ablation was applied for surface micro structuring of short- and medium-chain length-PHAs and its blend. The response of each material as a function of laser energy and wavelength was analyzed. Picosecond pulsed laser modified the surface topography without affecting the material properties. UV wavelength irradiation showed halved ablation thresholds compared to visible (VIS) wavelength, revealing a greater photochemical nature of the ablation process at ultraviolet (UV) wavelength. Nevertheless, the ablation rate and, therefore, ablation efficiency did not show a clear dependence on beam wavelength. The different mechanical behavior of the considered PHAs did not lead to different ablation thresholds on each polymer at a constant wavelength, suggesting the interplay of the material mechanical parameters to equalize ablation thresholds. Blended-PHA showed a significant reduction in the ablation threshold under VIS irradiation respect to the neat PHAs. Picosecond ablation was proved to be a convenient technique for micro structuring of PHAs to generate surface microfeatures appropriate to influence cell behavior and improve the biocompatibility of scaffolds in tissue engineerin
Regularly Varying Measures on Metric Spaces: Hidden Regular Variation and Hidden Jumps
We develop a framework for regularly varying measures on complete separable
metric spaces with a closed cone removed, extending
material in Hult & Lindskog (2006), Das, Mitra & Resnick (2013). Our framework
provides a flexible way to consider hidden regular variation and allows
simultaneous regular variation properties to exist at different scales and
provides potential for more accurate estimation of probabilities of risk
regions. We apply our framework to iid random variables in
with marginal distributions having regularly varying
tails and to c\`adl\`ag L\'evy processes whose L\'evy measures have regularly
varying tails. In both cases, an infinite number of regular variation
properties coexist distinguished by different scaling functions and state
spaces.Comment: 40 page
Theory of integer quantum Hall effect in insulating bilayer graphene
A variational ground state for insulating bilayer graphene (BLG), subject to
quantizing magnetic fields, is proposed. Due to the Zeeman coupling, the layer
anti-ferromagnet (LAF) order parameter in fully gapped BLG gets projected onto
the spin easy plane, and simultaneously a ferromagnet order, which can further
be enhanced by exchange interaction, develops in the direction of the magnetic
field. The activation gap for the Hall state then displays a crossover
from quadratic to linear scaling with the magnetic field, as it gets stronger,
and I obtain excellent agreement with a number of recent experiments with
realistic strengths for the ferromagnetic interaction. A component of the LAF
order, parallel to the external magnetic field, gives birth to additional
incompressible Hall states at filling , whereas the remote hopping
in BLG yields Hall states. Evolution of the LAF order in tilted
magnetic fields, scaling of the gap at , the effect of external electric
fields on various Hall plateaus, and different possible hierarchies of
fractional quantum Hall states are highlighted.Comment: Published version: 5 pages, 2 figures (Supplementary: 6 pages, 2
figures); New references, typos correcte
Sub-wavelength focusing meta-lens
We show that planar a plasmonic metamaterial with spatially variable
meta-atom parameters can focus transmitted light into sub-wavelength hot-spots
located beyond the near-field of the metamaterial. By nano-structuring a gold
film we created an array of meta-lenses generating foci of 160 nm
(0.2{\lambda}) in diameter when illuminated by a wavelength of 800 nm. We
attribute the occurrence of sub-wavelength hotspots beyond the near field to
the phenomenon of superoscillation
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