566 research outputs found
The Independence Axiom and Asset Returns
This paper integrates models of atemporal risk preference that relax the independence axiom into a recursive intertemporal asset-pricing framework. The resulting models are amenable to empirical analysis using market data and standard Euler equation methods. We are thereby able to provide the first non-laboratory-based evidence regarding the usefulness of several new theories of risk preference for addressing standard problems in dynamic economics. Using both stock and bond returns data, we find that a model incorporating risk preferences that exhibit firstorder risk aversion accounts for significantly more of the mean and autocorrelation properties of the data than models that exhibit only second-order risk aversion. Unlike the latter class of models which require parameter estimates that are outside of the admissible parameter space, e.g., negative rates of time preference, the model with first-order risk aversion generates point estimates that are economically meaningful. We also examine the relationship between first-order risk aversion and models that employ exogenous stochastic switching processes for consumption growth.
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
The relation between solar cell flight performance data and materials and manufacturing data Final report
Flight performance data for solar cell power systems in satellites and correlation with manufacturing methods and material
High-efficiency degenerate four wave-mixing in triply resonant nanobeam cavities
We demonstrate high-efficiency, degenerate four-wave mixing in triply
resonant Kerr photonic crystal (PhC) nanobeam cavities. Using a
combination of temporal coupled mode theory and nonlinear finite-difference
time-domain (FDTD) simulations, we study the nonlinear dynamics of resonant
four-wave mixing processes and demonstrate the possibility of observing
high-efficiency limit cycles and steady-state conversion corresponding to
% depletion of the pump light at low powers, even including
effects due to losses, self- and cross-phase modulation, and imperfect
frequency matching. Assuming operation in the telecom range, we predict close
to perfect quantum efficiencies at reasonably low 50 mW input powers in
silicon micrometer-scale cavities
Overlapping domains for topology optimization of large-area metasurfaces
We introduce an overlapping-domain approach to large-area metasurface design,
in which each simulated domain consists of a unit cell and overlapping regions
from the neighboring cells plus PML absorbers. We show that our approach
generates greatly improved metalens quality compared to designs produced using
a locally periodic approximation, thanks to better accuracy
with similar computational cost. We use the new approach with topology
optimization to design large-area () high-NA (0.71) multichrome and
broadband achromatic lenses with high focusing efficiency (),
greatly improving upon previously reported works
Optimal economie dispatch for the nigerian grid system considering voltage and line flow constraints
The electric power industries worldwide have undergone considerable changes especially from vertical structure to full deregulated entities. These changes are now introducing new problems in terms of operations, controls and planning of the entire grid systems. This calls for a more reliable analytical tool ever than before. One feasible solution is to perform the Optimal Economic Dispatch (OED) paradigm on this restructured power system so as to provide fairness to all operators. In this paper, the economic dispatch problem with voltage and line flow constraints has been formulated for the hydro-thermal generating units feeding the Nigerian power system. In order to solve the arising power flow problem a MATLAB based simulation package, MATPOWER version 3.0 has been suitably modified to obtain feasible solutions for different loading system scenarios. The results obtained showed that the OED offered a better optimal power schedules, power loss minimization and reduced total fuel cost than earlier work based on Micro-Genetic Algorithm, (MGA) and Conventional Genetic Algorithm (CGA)
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
End-to-End Optimization of Metasurfaces for Imaging with Compressed Sensing
We present a framework for the end-to-end optimization of metasurface imaging
systems that reconstruct targets using compressed sensing, a technique for
solving underdetermined imaging problems when the target object exhibits
sparsity (i.e. the object can be described by a small number of non-zero
values, but the positions of these values are unknown). We nest an iterative,
unapproximated compressed sensing reconstruction algorithm into our end-to-end
optimization pipeline, resulting in an interpretable, data-efficient method for
maximally leveraging metaoptics to exploit object sparsity. We apply our
framework to super-resolution imaging and high-resolution depth imaging with a
phase-change material: in both situations, our end-to-end framework
computationally discovers optimal metasurface structures for compressed sensing
recovery, automatically balancing a number of complicated design
considerations. The optimized metasurface imaging systems are robust to noise,
significantly improving over random scattering surfaces and approaching the
ideal compressed sensing performance of a Gaussian matrix, showing how a
physical metasurface system can demonstrably approach the mathematical limits
of compressed sensing
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