40,485 research outputs found
Numerical correction of anti-symmetric aberrations in single HRTEM images of weakly scattering 2D-objects
Here, we present a numerical post-processing method for removing the effect
of anti-symmetric residual aberrations in high-resolution transmission electron
microscopy (HRTEM) images of weakly scattering 2D-objects. The method is based
on applying the same aberrations with the opposite phase to the Fourier
transform of the recorded image intensity and subsequently inverting the
Fourier transform. We present the theoretical justification of the method and
its verification based on simulated images in the case of low-order
anti-symmetric aberrations. Ultimately the method is applied to experimental
hardware aberration-corrected HRTEM images of single-layer graphene and MoSe2
resulting in images with strongly reduced residual low-order aberrations, and
consequently improved interpretability. Alternatively, this method can be used
to estimate by trial and error the residual anti-symmetric aberrations in HRTEM
images of weakly scattering objects
Identification of Parametric Underspread Linear Systems and Super-Resolution Radar
Identification of time-varying linear systems, which introduce both
time-shifts (delays) and frequency-shifts (Doppler-shifts), is a central task
in many engineering applications. This paper studies the problem of
identification of underspread linear systems (ULSs), whose responses lie within
a unit-area region in the delay Doppler space, by probing them with a known
input signal. It is shown that sufficiently-underspread parametric linear
systems, described by a finite set of delays and Doppler-shifts, are
identifiable from a single observation as long as the time bandwidth product of
the input signal is proportional to the square of the total number of delay
Doppler pairs in the system. In addition, an algorithm is developed that
enables identification of parametric ULSs from an input train of pulses in
polynomial time by exploiting recent results on sub-Nyquist sampling for time
delay estimation and classical results on recovery of frequencies from a sum of
complex exponentials. Finally, application of these results to super-resolution
target detection using radar is discussed. Specifically, it is shown that the
proposed procedure allows to distinguish between multiple targets with very
close proximity in the delay Doppler space, resulting in a resolution that
substantially exceeds that of standard matched-filtering based techniques
without introducing leakage effects inherent in recently proposed compressed
sensing-based radar methods.Comment: Revised version of a journal paper submitted to IEEE Trans. Signal
Processing: 30 pages, 17 figure
FRESH â FRI-based single-image super-resolution algorithm
In this paper, we consider the problem of single image super-resolution and propose a novel algorithm that outperforms state-of-the-art methods without the need of learning patches pairs from external data sets. We achieve this by modeling images and, more precisely, lines of images as piecewise smooth functions and propose a resolution enhancement method for this type of functions. The method makes use of the theory of sampling signals with finite rate of innovation (FRI) and combines it with traditional linear reconstruction methods. We combine the two reconstructions by leveraging from the multi-resolution analysis in wavelet theory and show how an FRI reconstruction and a linear reconstruction can be fused using filter banks. We then apply this method along vertical, horizontal, and diagonal directions in an image to obtain a single-image super-resolution algorithm. We also propose a further improvement of the method based on learning from the errors of our super-resolution result at lower resolution levels. Simulation results show that our method outperforms state-of-the-art algorithms under different blurring kernels
Ground-based NIR emission spectroscopy of HD189733b
We investigate the K and L band dayside emission of the hot-Jupiter HD
189733b with three nights of secondary eclipse data obtained with the SpeX
instrument on the NASA IRTF. The observations for each of these three nights
use equivalent instrument settings and the data from one of the nights has
previously reported by Swain et al (2010). We describe an improved data
analysis method that, in conjunction with the multi-night data set, allows
increased spectral resolution (R~175) leading to high-confidence identification
of spectral features. We confirm the previously reported strong emission at
~3.3 microns and, by assuming a 5% vibrational temperature excess for methane,
we show that non-LTE emission from the methane nu3 branch is a physically
plausible source of this emission. We consider two possible energy sources that
could power non-LTE emission and additional modelling is needed to obtain a
detailed understanding of the physics of the emission mechanism. The validity
of the data analysis method and the presence of strong 3.3 microns emission is
independently confirmed by simultaneous, long-slit, L band spectroscopy of HD
189733b and a comparison star.Comment: ApJ accepte
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