311 research outputs found
Thermodynamic behaviour of two-dimensional vesicles revisited
We study pressurised self-avoiding ring polymers in two dimensions using
Monte Carlo simulations, scaling arguments and Flory-type theories, through
models which generalise the model of Leibler, Singh and Fisher [Phys. Rev.
Lett. Vol. 59, 1989 (1987)]. We demonstrate the existence of a thermodynamic
phase transition at a non-zero scaled pressure , where , with the number of monomers and the pressure
, keeping constant, in a class of such models.
This transition is driven by bond energetics and can be either continuous or
discontinuous. It can be interpreted as a shape transition in which the ring
polymer takes the shape, above the critical pressure, of a regular N-gon whose
sides scale smoothly with pressure, while staying unfaceted below this critical
pressure. In the general case, we argue that the transition is replaced by a
sharp crossover. The area, however, scales with for all positive in
all such models, consistent with earlier scaling theories.Comment: 6 pages, 4 figures, EPL forma
Computational multi-spectral video imaging
Multi-spectral imagers reveal information unperceivable to humans and
conventional cameras. Here, we demonstrate a compact single-shot multi-spectral
video-imaging camera by placing a micro-structured diffractive filter in close
proximity to the image sensor. The diffractive filter converts spectral
information to a spatial code on the sensor pixels. Following a calibration
step, this code can be inverted via regularization-based linear algebra, to
compute the multi-spectral image. We experimentally demonstrated spectral
resolution of 9.6nm within the visible band (430nm to 718nm). We further show
that the spatial resolution is enhanced by over 30% compared to the case
without the diffractive filter. We also demonstrate Vis-IR imaging with the
same sensor. Furthermore, our camera is able to computationally trade-off
spectral resolution against the field of view in software without any change in
hardware as long as sufficient sensor pixels are utilized for information
encoding. Since no absorptive color filters are utilized, sensitivity is
preserved as well. Finally, the diffractive filters can be easily manufactured
using optical lithography and replication techniques
Learning Wavefront Coding for Extended Depth of Field Imaging
Depth of field is an important factor of imaging systems that highly affects
the quality of the acquired spatial information. Extended depth of field (EDoF)
imaging is a challenging ill-posed problem and has been extensively addressed
in the literature. We propose a computational imaging approach for EDoF, where
we employ wavefront coding via a diffractive optical element (DOE) and we
achieve deblurring through a convolutional neural network. Thanks to the
end-to-end differentiable modeling of optical image formation and computational
post-processing, we jointly optimize the optical design, i.e., DOE, and the
deblurring through standard gradient descent methods. Based on the properties
of the underlying refractive lens and the desired EDoF range, we provide an
analytical expression for the search space of the DOE, which is instrumental in
the convergence of the end-to-end network. We achieve superior EDoF imaging
performance compared to the state of the art, where we demonstrate results with
minimal artifacts in various scenarios, including deep 3D scenes and broadband
imaging
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