289 research outputs found
High-quality Image Restoration from Partial Mixed Adaptive-Random Measurements
A novel framework to construct an efficient sensing (measurement) matrix,
called mixed adaptive-random (MAR) matrix, is introduced for directly acquiring
a compressed image representation. The mixed sampling (sensing) procedure
hybridizes adaptive edge measurements extracted from a low-resolution image
with uniform random measurements predefined for the high-resolution image to be
recovered. The mixed sensing matrix seamlessly captures important information
of an image, and meanwhile approximately satisfies the restricted isometry
property. To recover the high-resolution image from MAR measurements, the total
variation algorithm based on the compressive sensing theory is employed for
solving the Lagrangian regularization problem. Both peak signal-to-noise ratio
and structural similarity results demonstrate the MAR sensing framework shows
much better recovery performance than the completely random sensing one. The
work is particularly helpful for high-performance and lost-cost data
acquisition.Comment: 16 pages, 8 figure
Maxwell-Hydrodynamic Model for Simulating Nonlinear Terahertz Generation from Plasmonic Metasurfaces
The interaction between the electromagnetic field and plasmonic
nanostructures leads to both the strong linear response and inherent nonlinear
behavior. In this paper, a time-domain hydrodynamic model for describing the
motion of electrons in plasmonic nanostructures is presented, in which both
surface and bulk contributions of nonlinearity are considered. A coupled
Maxwell-hydrodynamic system capturing full-wave physics and free electron
dynamics is numerically solved with the parallel finite-difference time-domain
(FDTD) method. The validation of the proposed method is presented to simulate
linear and nonlinear responses from a plasmonic metasurface. The linear
response is compared with the Drude dispersion model and the nonlinear
terahertz emission from a difference-frequency generation process is validated
with theoretical analyses. The proposed scheme is fundamentally important to
design nonlinear plasmonic nanodevices, especially for efficient and broadband
THz emitters.Comment: 8 pages, 7 figures, IEEE Journal on Multiscale and Multiphysics
Computational Techniques, 201
Casimir Force for Arbitrary Objects Using the Argument Principle and Boundary Element Methods
Recent progress in the simulation of Casimir forces between various objects
has allowed traditional computational electromagnetic solvers to be used to
find Casimir forces in arbitrary three-dimensional objects. The underlying
theory to these approaches requires knowledge and manipulation of quantum field
theory and statistical physics. We present a calculation of the Casimir force
using the method of moments via the argument principle. This simplified
derivation allows greater freedom in the moment matrix where the argument
principle can be used to calculate Casimir forces for arbitrary geometries and
materials with the use of various computational electromagnetic techniques.Comment: 6 pages, 2 figure
Exploring the Way to Approach the Efficiency Limit of Perovskite Solar Cells by Drift-Diffusion Model
Drift-diffusion model is an indispensable modeling tool to understand the
carrier dynamics (transport, recombination, and collection) and simulate
practical-efficiency of solar cells (SCs) through taking into account various
carrier recombination losses existing in multilayered device structures.
Exploring the way to predict and approach the SC efficiency limit by using the
drift-diffusion model will enable us to gain more physical insights and design
guidelines for emerging photovoltaics, particularly perovskite solar cells. Our
work finds out that two procedures are the prerequisites for predicting and
approaching the SC efficiency limit. Firstly, the intrinsic radiative
recombination needs to be corrected after adopting optical designs which will
significantly affect the open-circuit voltage at its Shockley-Queisser limit.
Through considering a detailed balance between emission and absorption of
semiconductor materials at the thermal equilibrium, and the Boltzmann
statistics at the non-equilibrium, we offer a different approach to derive the
accurate expression of intrinsic radiative recombination with the optical
corrections for semiconductor materials. The new expression captures light
trapping of the absorbed photons and angular restriction of the emitted photons
simultaneously, which are ignored in the traditional Roosbroeck-Shockley
expression. Secondly, the contact characteristics of the electrodes need to be
carefully engineered to eliminate the charge accumulation and surface
recombination at the electrodes. The selective contact or blocking layer
incorporated nonselective contact that inhibits the surface recombination at
the electrode is another important prerequisite. With the two procedures, the
accurate prediction of efficiency limit and precise evaluation of efficiency
degradation for perovskite solar cells are attainable by the drift-diffusion
model.Comment: 32 pages, 11 figure
Efficient Volumetric Method of Moments for Modeling Plasmonic Thin-Film Solar Cells with Periodic Structures
Metallic nanoparticles (NPs) support localized surface plasmon resonances
(LSPRs), which enable to concentrate sunlight at the active layer of solar
cells. However, full-wave modeling of the plasmonic solar cells faces great
challenges in terms of huge computational workload and bad matrix condition. It
is tremendously difficult to accurately and efficiently simulate near-field
multiple scattering effects from plasmonic NPs embedded into solar cells. In
this work, a preconditioned volume integral equation (VIE) is proposed to model
plasmonic organic solar cells (OSCs). The diagonal block preconditioner is
applied to different material domains of the device structure. As a result,
better convergence and higher computing efficiency are achieved. Moreover, the
calculation is further accelerated by two-dimensional periodic Green's
functions. Using the proposed method, the dependences of optical absorption on
the wavelengths and incident angles are investigated. Angular responses of the
plasmonic OSCs show the super-Lambertian absorption on the plasmon resonance
but near-Lambertian absorption off the plasmon resonance. The volumetric method
of moments and explored physical understanding are of great help to investigate
the optical responses of OSCs.Comment: 11 pages, 6 figure
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