116 research outputs found
Topology optimization of freeform large-area metasurfaces
We demonstrate optimization of optical metasurfaces over --
degrees of freedom in two and three dimensions, 100--1000+ wavelengths
() in diameter, with 100+ parameters per . In particular,
we show how topology optimization, with one degree of freedom per
high-resolution "pixel," can be extended to large areas with the help of a
locally periodic approximation that was previously only used for a few
parameters per . In this way, we can computationally discover
completely unexpected metasurface designs for challenging multi-frequency,
multi-angle problems, including designs for fully coupled multi-layer
structures with arbitrary per-layer patterns. Unlike typical metasurface
designs based on subwavelength unit cells, our approach can discover both sub-
and supra-wavelength patterns and can obtain both the near and far fields
Sideways adiabaticity: Beyond ray optics for slowly varying metasurfaces
Optical metasurfaces (subwavelength-patterned surfaces typically described by
variable effective surface impedances) are typically modeled by an
approximation akin to ray optics: the reflection or transmission of an incident
wave at each point of the surface is computed as if the surface were "locally
uniform", and then the total field is obtained by summing all of these local
scattered fields via a Huygens principle. (Similar approximations are found in
scalar diffraction theory and in ray optics for curved surfaces.) In this
paper, we develop a precise theory of such approximations for
variable-impedance surfaces. Not only do we obtain a type of adiabatic theorem
showing that the "zeroth-order" locally uniform approximation converges in the
limit as the surface varies more and more slowly, including a way to quantify
the rate of convergence, but we also obtain an infinite series of higher-order
corrections. These corrections, which can be computed to any desired order by
performing integral operations on the surface fields, allow rapidly varying
surfaces to be modeled with arbitrary accuracy, and also allow one to validate
designs based on the zeroth-order approximation (which is often surprisingly
accurate) without resorting to expensive brute-force Maxwell solvers. We show
that our formulation works arbitrarily close to the surface, and can even
compute coupling to guided modes, whereas in the far-field limit our
zeroth-order result simplifies to an expression similar to what has been used
by other authors
Efficient inverse design of large-area metasurfaces for incoherent light
Incoherent light is ubiquitous, yet designing optical devices that can handle
its random nature is very challenging, since directly averaging over many
incoherent incident beams can require a huge number of scattering calculations.
We show how to instead solve this problem with a reciprocity technique which
leads to three orders of magnitude speedup: one Maxwell solve (using any
numerical technique) instead of thousands. This improvement enables us to
perform efficient inverse design, large scale optimization of the metasurface
for applications such as light collimators and concentrators. We show the
impact of the angular distribution of incident light on the resulting
performance, and show especially promising designs for the case of "annular"
beams distributed only over nonzero angles
Physics-enhanced deep surrogates for PDEs
We present a ''physics-enhanced deep-surrogate'' (''PEDS'') approach towards
developing fast surrogate models for complex physical systems, which is
described by partial differential equations (PDEs) and similar models.
Specifically, a unique combination of a low-fidelity, explainable physics
simulator and a neural network generator is proposed, which is trained
end-to-end to globally match the output of an expensive high-fidelity numerical
solver. We consider low-fidelity models derived from coarser discretizations
and/or by simplifying the physical equations, which are several orders of
magnitude faster than a high-fidelity ''brute-force'' PDE solver. The neural
network generates an approximate input, which is adaptively mixed with a
downsampled guess and fed into the low-fidelity simulator. In this way, by
incorporating the limited physical knowledge from the differentiable
low-fidelity model ''layer'', we ensure that the conservation laws and
symmetries governing the system are respected by the design of our hybrid
system. Experiments on three test problems -- diffusion, reaction-diffusion,
and electromagnetic scattering models -- show that a PEDS surrogate can be up
to 3 more accurate than a ''black-box'' neural network with limited
data ( training points), and reduces the data needed by at least
a factor of 100 for a target error of , comparable to fabrication
uncertainty. PEDS even appears to learn with a steeper asymptotic power law
than black-box surrogates. In summary, PEDS provides a general, data-driven
strategy to bridge the gap between a vast array of simplified physical models
with corresponding brute-force numerical solvers, offering accuracy, speed,
data efficiency, as well as physical insights into the process
Physics-informed neural networks with hard constraints for inverse design
Inverse design arises in a variety of areas in engineering such as acoustic,
mechanics, thermal/electronic transport, electromagnetism, and optics. Topology
optimization is a major form of inverse design, where we optimize a designed
geometry to achieve targeted properties and the geometry is parameterized by a
density function. This optimization is challenging, because it has a very high
dimensionality and is usually constrained by partial differential equations
(PDEs) and additional inequalities. Here, we propose a new deep learning method
-- physics-informed neural networks with hard constraints (hPINNs) -- for
solving topology optimization. hPINN leverages the recent development of PINNs
for solving PDEs, and thus does not rely on any numerical PDE solver. However,
all the constraints in PINNs are soft constraints, and hence we impose hard
constraints by using the penalty method and the augmented Lagrangian method. We
demonstrate the effectiveness of hPINN for a holography problem in optics and a
fluid problem of Stokes flow. We achieve the same objective as conventional
PDE-constrained optimization methods based on adjoint methods and numerical PDE
solvers, but find that the design obtained from hPINN is often simpler and
smoother for problems whose solution is not unique. Moreover, the
implementation of inverse design with hPINN can be easier than that of
conventional methods
Seismicity induced during the development of the Rittershoffen geothermal field, France
The development of the Rittershoffen deep geothermal field (Alsace, Upper Rhine Graben) between 2012 and 2014 induced unfelt seismicity with a local magnitude of less than 1.6. This seismicity occurred during two types of operations: (1) mud losses in the Muschelkalk formation during the drilling of both wells of the doublet and (2) thermal and hydraulic stimulations of the GRT-1 well. Seismicity was also observed 4 days after the main hydraulic stimulation, although no specific operation was performed. During chemical stimulation, however, no induced seismicity was detected. In the context of all field development operations and their injection parameters (flow rates, overpressures, volumes), we detail the occurrence or lack of seismicity, its magnitude distribution and its spatial distribution. The observations suggest the presence of the rock stress memory effect (Kaiser effect) of the geothermal reservoir as well as uncritically stressed zones connected to the GRT-1 well and/or rock cohesion. A reduction of the seismic rate concurrent with an increase of injectivity was noticed as well as the reactivation of a couple of faults, including the Rittershoffen fault, which was targeted by the wells. These results are derived from the homogeneous and consistent catalogue of more than 1300 local earthquakes that is provided. This reference catalogue is based on a standard detection method, whose output was manually verified and improved. The given absolute locations have been computed in a calibrated, geologically realistic 3D velocity model. Our work builds on previous analyses addressing the seismicity induced by the GRT-1 hydraulic stimulation and places the results into a historical context, thus considering the full dynamics of the observed phenomena. This paper also complements existing descriptions of the hydrothermal characteristics of the deep reservoir by providing insights separate from the wells
Inverse design of large-area metasurfaces
We present a computational framework for efficient optimization-based
"inverse design" of large-area "metasurfaces" (subwavelength-patterned
surfaces) for applications such as multi-wavelength and multi-angle
optimizations, and demultiplexers. To optimize surfaces that can be thousands
of wavelengths in diameter, with thousands (or millions) of parameters, the key
is a fast approximate solver for the scattered field. We employ a "locally
periodic" approximation in which the scattering problem is approximated by a
composition of periodic scattering problems from each unit cell of the surface,
and validate it against brute-force Maxwell solutions. This is an extension of
ideas in previous metasurface designs, but with greatly increased flexibility,
e.g. to automatically balance tradeoffs between multiple frequencies, or to
optimize a photonic device given only partial information about the desired
field. Our approach even extends beyond the metasurface regime to
non-subwavelength structures where additional diffracted orders must be
included (but the period is not large enough to apply scalar diffraction
theory).Comment: 18 pages, 8 figure
Neutralizing Aptamers from Whole-Cell SELEX Inhibit the RET Receptor Tyrosine Kinase
Targeting large transmembrane molecules, including receptor tyrosine kinases, is a major pharmacological challenge. Specific oligonucleotide ligands (aptamers) can be generated for a variety of targets through the iterative evolution of a random pool of sequences (SELEX). Nuclease-resistant aptamers that recognize the human receptor tyrosine kinase RET were obtained using RET-expressing cells as targets in a modified SELEX procedure. Remarkably, one of these aptamers blocked RET-dependent intracellular signaling pathways by interfering with receptor dimerization when the latter was induced by the physiological ligand or by an activating mutation. This strategy is generally applicable to transmembrane receptors and opens the way to targeting other members of this class of proteins that are of major biomedical importance
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