6,863 research outputs found
A new approach to nonlinear constrained Tikhonov regularization
We present a novel approach to nonlinear constrained Tikhonov regularization
from the viewpoint of optimization theory. A second-order sufficient optimality
condition is suggested as a nonlinearity condition to handle the nonlinearity
of the forward operator. The approach is exploited to derive convergence rates
results for a priori as well as a posteriori choice rules, e.g., discrepancy
principle and balancing principle, for selecting the regularization parameter.
The idea is further illustrated on a general class of parameter identification
problems, for which (new) source and nonlinearity conditions are derived and
the structural property of the nonlinearity term is revealed. A number of
examples including identifying distributed parameters in elliptic differential
equations are presented.Comment: 21 pages, to appear in Inverse Problem
A Two-stage Method for Inverse Medium Scattering
We present a novel numerical method to the time-harmonic inverse medium
scattering problem of recovering the refractive index from near-field scattered
data. The approach consists of two stages, one pruning step of detecting the
scatterer support, and one resolution enhancing step with mixed regularization.
The first step is strictly direct and of sampling type, and faithfully detects
the scatterer support. The second step is an innovative application of
nonsmooth mixed regularization, and it accurately resolves the scatterer sizes
as well as intensities. The model is efficiently solved by a semi-smooth
Newton-type method. Numerical results for two- and three-dimensional examples
indicate that the approach is accurate, computationally efficient, and robust
with respect to data noise.Comment: 18 pages, 5 figure
Spectral and Polarization Properties of Photospheric Emission From Stratified Jets
We explore the spectral and polarization properties of photospheric emissions
from stratified jets in which multiple components, separated by a sharp
velocity shear regions, are distributed in lateral direction. Propagation of
thermal photons injected at high optical depth region are calculated until they
escape from the photosphere. It is found that presence of the lateral structure
within the jet leads to non-thermal feature of the spectra and significant
polarization signal in the resulting emission. The deviation from thermal
spectra as well as the polarization degree tends to be enhanced as the velocity
gradient in the shear region increases. In particular, we show that emissions
from multi-component jet can reproduce the typical observed spectra of
gamma-ray bursts (GRBs) irrespective to the position of the observer when a
velocity shear region is closely spaced in various lateral ()
positions. The degree of polarization associated in the emission is significant
(> few%) at wide range of observer angles and can be higher than 30%.Comment: 21 pages, 12 figures, accepted for publication in Ap
Gradient-based estimation of Manning's friction coefficient from noisy data
We study the numerical recovery of Manning's roughness coefficient for the
diffusive wave approximation of the shallow water equation. We describe a
conjugate gradient method for the numerical inversion. Numerical results for
one-dimensional model are presented to illustrate the feasibility of the
approach. Also we provide a proof of the differentiability of the weak form
with respect to the coefficient as well as the continuity and boundedness of
the linearized operator under reasonable assumptions using the maximal
parabolic regularity theory.Comment: 19 pages, 3 figure
Massively parallel quantum computer simulator, eleven years later
A revised version of the massively parallel simulator of a universal quantum
computer, described in this journal eleven years ago, is used to benchmark
various gate-based quantum algorithms on some of the most powerful
supercomputers that exist today. Adaptive encoding of the wave function reduces
the memory requirement by a factor of eight, making it possible to simulate
universal quantum computers with up to 48 qubits on the Sunway TaihuLight and
on the K computer. The simulator exhibits close-to-ideal weak-scaling behavior
on the Sunway TaihuLight,on the K computer, on an IBM Blue Gene/Q, and on Intel
Xeon based clusters, implying that the combination of parallelization and
hardware can track the exponential scaling due to the increasing number of
qubits. Results of executing simple quantum circuits and Shor's factorization
algorithm on quantum computers containing up to 48 qubits are presented.Comment: Substantially rewritten + new data. Published in Computer Physics
Communicatio
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