6,349 research outputs found
Frequency offset tolerant synchronization signal design in NB-IoT
Timing detection is the first step and very important in wireless
communication systems. Timing detection performance is usually affected by the
frequency offset. Therefore, it is a challenge to design the synchronization
signal in massive narrowband Internet of Things (NB-IoT) scenarios where the
frequency offset is usually large due to the low cost requirement. In this
paper, we firstly proposed a new general synchronization signal structure with
a couple of sequences which are conjugated to remove the potential timing error
arose from large frequency offset. Then, we analyze the suitable sequence for
our proposed synchronization signal structure and discuss a special ZC sequence
as an example. Finally, the simulation results demonstrate our proposed
synchronization signal can work well when the frequency offset is large. It
means that our proposed synchronization signal design is very suitable for the
massive NB-IoT
Local Lipschitz Stability for Inverse Robin Problems in Some Elliptic and Parabolic Systems
In this work, we shall study the nonlinear inverse problems of recovering the
Robin coefficients in elliptic and parabolic systems of second order, and
establish their local Lipschitz stabilities. Some local Lipschitz stability was
derived for an elliptic inverse Robin problem. We shall first restructure the
arguments in \cite{chou04} for the local Lipschitz stability so that the
stability follows from three basic conditions for the elliptic inverse Robin
problem. The new arguments are then generalized to help establish a novel local
Lipschitz stability for parabolic inverse Robin problems
Convergence of an Adaptive Finite Element Method for Distributed Flux Reconstruction
We shall establish the convergence of an adaptive conforming finite element
method for the reconstruction of the distributed flux in a diffusion system.
The adaptive method is based on a posteriori error estimators for the
distributed flux, state and costate variables. The sequence of discrete
solutions produced by the adaptive algorithm is proved to converge to the true
triplet satisfying the optimality conditions in the energy norm and the
corresponding error estimator converges to zero asymptotically.Comment: 18 page
Randomized Algorithms for Large-scale Inverse Problems with General Regularizations
We shall investigate randomized algorithms for solving large-scale linear
inverse problems with general regularizations. We first present some techniques
to transform inverse problems of general form into the ones of standard form,
then apply randomized algorithms to reduce large-scale systems of standard form
to much smaller-scale systems and seek their regularized solutions in
combination with some popular choice rules for regularization parameters. Then
we will propose a second approach to solve large-scale ill-posed systems with
general regularizations. This involves a new randomized generalized SVD
algorithm that can essentially reduce the size of the original large-scale
ill-posed systems. The reduced systems can provide approximate regularized
solutions with about the same accuracy as the ones by the classical generalized
SVD, and more importantly, the new approach gains obvious robustness, stability
and computational time as it needs only to work on problems of much smaller
size. Numerical results are given to demonstrated the efficiency of the
algorithms
A Direct Sampling Method for Inverse Scattering Using Far-Field Data
This work is concerned with a direct sampling method (DSM) for inverse
acoustic scattering problems using far-field data. The method characterizes
some unknown obstacles, inhomogeneous media or cracks, directly through an
indicator function computed from the measured data. Using one or very few
incident waves, the DSM provides quite reasonable profiles of scatterers in
time-harmonic inverse acoustic scattering without a priori knowledge of either
the physical properties or the number of disconnected components of the
scatterer. We shall first derive the DSM using far-field data, then carry out a
systematic evaluation of the performances and distinctions of the DSM using
both near-field and far-field data. The numerical simulations are shown to
demonstrate interesting and promising potentials of the DSM: a) ability to
identify not only medium scatterers, but also obstacles, and even cracks, using
measurement data from one or few incident directions, b) robustness with
respect to large noise, and c) computational efficiency with only inner
products involved
A new representation of the light curve and its power density spectrum
We present a new representation of light curves, which is quite different
from the binning method. Instead of choosing uniform bins, the reciprocal of
interval between two successive photons is adopted to represent the counting
rate. A primary application of this light curve is to compute the power density
spectrum by means of Lomb Periodogram and to find possible periods. To verify
this new representation, we apply this method to artificial periodic data and
some known periodic celestial objects, and the periods are all correctly found.
Compared with the traditional fast Fourier transform method, our method does
not rely on the bin size and has a spontaneously high time resolution,
guaranteeing a wide frequency range in power density spectrum, and is
especially useful when the photons are rare for its little information losses.
Some other applications of the new light curve, like pulse identification,
variability and spectral time lag, are also discussed.Comment: 14 pages, 5 figures, submitted to MNRAS, comments are welcom
Role of the possible state in the reaction
The reaction near threshold is studied within
an effective Lagrangian method. The production process is described by
single-pion and single-kaon exchange. In addition to the role played by the
resonance of spin-parity , the effects of a newly
proposed () state with mass and width around MeV
and MeV are investigated. We show that our model leads to a good
description of the experimental data on the total cross section of the reaction by including the contributions from the
possible state. However, the theoretical calculations
by considering only the resonance fail to reproduce the
experimental data, especially for the enhancement close to the reaction
threshold. On the other hand, it is found that the single-pion exchange is
dominant. Furthermore, we also demonstrate that the angular distributions
provide direct information of this reaction, hence could be useful for the
investigation of the existence of the state and may
be tested by future experiments.Comment: 8 pages, 5 figure
Hyperon production from neutrino-nucleon reaction
The neutrino induced hyperon production processes may provide a unique clean place for studying
low energy interaction and hyperon resonances below
threshold. The production rates for some neutrino induced hyperon production
processes are estimated with theoretical models. Suggestions are made for the
study of hyperon production from neutrino-nucleon reaction at present and
future neutrino facilities.Comment: 19 pages, 10 figure
Unique determination of a penetrable scatterer of rectangular type for inverse Maxwell equations by a single incoming wave
This work is concerned with an inverse electromagnetic scattering problem in
two dimensions. We prove that in the TE polarization case, the knowledge of the
electric far-field pattern incited by a single incoming wave is sufficient to
uniquely determine the shape of a penetrable scatterer of rectangular type. As
a by-product, the uniqueness is also confirmed to inverse transmission problems
modelled by scalar Helmholtz equations with discontinuous normal derivatives at
the scattering interface.
Keywords: Uniqueness, inverse medium scattering, Maxwell equations, one
incoming wave, shape identification, right cornersComment: 2 figure
Overlapping Domain Decomposition Methods for Linear Inverse Problems
We shall derive and propose several efficient overlapping domain
decomposition methods for solving some typical linear inverse problems,
including the identiffication of the flux, the source strength and the initial
temperature in second order elliptic and parabolic systems. The methods are
iterative, and computationally very efficient: only local forward and adjoint
problems need to be solved in each subdomain, and the local minimizations have
explicit solutions. Numerical experiments are provided to demonstrate the
robustness and efficiency of the methods, in particular, the convergences seem
nearly optimal, i.e., they do not deteriorate or deteriorate only slightly when
the mesh size reduces.Comment: 25 pages, 8 figures, 8 Table
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