56,383 research outputs found
Radio-Optical Galaxy Shape Correlations in the COSMOS Field
We investigate the correlations in galaxy shapes between optical and radio
wavelengths using archival observations of the COSMOS field. Cross-correlation
studies between different wavebands will become increasingly important for
precision cosmology as future large surveys may be dominated by systematic
rather than statistical errors. In the case of weak lensing, galaxy shapes must
be measured to extraordinary accuracy (shear systematics of ) in
order to achieve good constraints on dark energy parameters. By using shape
information from overlapping surveys in optical and radio bands, robustness to
systematics may be significantly improved without loss of constraining power.
Here we use HST-ACS optical data, VLA radio data, and extensive simulations to
investigate both our ability to make precision measurements of source shapes
from realistic radio data, and to constrain the intrinsic astrophysical scatter
between the shapes of galaxies as measured in the optical and radio wavebands.
By producing a new image from the VLA-COSMOS L-band radio visibility data that
is well suited to galaxy shape measurements, we are able to extract precise
measurements of galaxy position angles. Comparing to corresponding measurements
from the HST optical image, we set a lower limit on the intrinsic astrophysical
scatter in position angles, between the optical and radio bands, of
radians (or ) at a confidence
level.Comment: 17 pages, 13 figure, 5 tables. Updated to match published version
with a number of typographical correction
Self-correction of 3D reconstruction from multi-view stereo images
We present a self-correction approach to improving the
3D reconstruction of a multi-view 3D photogrammetry system.
The self-correction approach has been able to repair
the reconstructed 3D surface damaged by depth discontinuities.
Due to self-occlusion, multi-view range images
have to be acquired and integrated into a watertight nonredundant
mesh model in order to cover the extended surface
of an imaged object. The integrated surface often suffers
from “dent” artifacts produced by depth discontinuities
in the multi-view range images. In this paper we propose
a novel approach to correcting the 3D integrated surface
such that the dent artifacts can be repaired automatically.
We show examples of 3D reconstruction to demonstrate the
improvement that can be achieved by the self-correction
approach. This self-correction approach can be extended
to integrate range images obtained from alternative range
capture devices
A Novel Framework for Highlight Reflectance Transformation Imaging
We propose a novel pipeline and related software tools for processing the multi-light image collections (MLICs) acquired in different application contexts to obtain shape and appearance information of captured surfaces, as well as to derive compact relightable representations of them. Our pipeline extends the popular Highlight Reflectance Transformation Imaging (H-RTI) framework, which is widely used in the Cultural Heritage domain. We support, in particular, perspective camera modeling, per-pixel interpolated light direction estimation, as well as light normalization correcting vignetting and uneven non-directional illumination. Furthermore, we propose two novel easy-to-use software tools to simplify all processing steps. The tools, in addition to support easy processing and encoding of pixel data, implement a variety of visualizations, as well as multiple reflectance-model-fitting options. Experimental tests on synthetic and real-world MLICs demonstrate the usefulness of the novel algorithmic framework and the potential benefits of the proposed tools for end-user applications.Terms: "European Union (EU)" & "Horizon 2020" / Action: H2020-EU.3.6.3. - Reflective societies - cultural heritage and European identity / Acronym: Scan4Reco / Grant number: 665091DSURF project (PRIN 2015) funded by the Italian Ministry of University and ResearchSardinian Regional Authorities under projects VIGEC and Vis&VideoLa
System calibration method for Fourier ptychographic microscopy
Fourier ptychographic microscopy (FPM) is a recently proposed quantitative
phase imaging technique with high resolution and wide field-of-view (FOV). In
current FPM imaging platforms, systematic error sources come from the
aberrations, LED intensity fluctuation, parameter imperfections and noise,
which will severely corrupt the reconstruction results with artifacts. Although
these problems have been researched and some special methods have been proposed
respectively, there is no method to solve all of them. However, the systematic
error is a mixture of various sources in the real situation. It is difficult to
distinguish a kind of error source from another due to the similar artifacts.
To this end, we report a system calibration procedure, termed SC-FPM, based on
the simulated annealing (SA) algorithm, LED intensity correction and adaptive
step-size strategy, which involves the evaluation of an error matric at each
iteration step, followed by the re-estimation of accurate parameters. The great
performance has been achieved both in simulation and experiments. The reported
system calibration scheme improves the robustness of FPM and relaxes the
experiment conditions, which makes the FPM more pragmatic.Comment: 18 pages, 9 figure
High-resolution 3D optical microscopy inside the beating zebrafish heart using prospective optical gating
3D fluorescence imaging is a fundamental tool in the study of functional and developmental biology, but effective imaging is particularly difficult in moving structures such as the beating heart. We have developed a non-invasive real-time optical gating system that is able to exploit the periodic nature of the motion to acquire high resolution 3D images of the normally-beating zebrafish heart without any unnecessary exposure of the sample to harmful excitation light. In order for the image stack to be artefact-free, it is essential to use a synchronization source that is invariant as the sample is scanned in 3D. We therefore describe a scheme whereby fluorescence image slices are scanned through the sample while a brightfield camera sharing the same objective lens is maintained at a fixed focus, with correction of sample drift also included. This enables us to maintain, throughout an extended 3D volume, the same standard of synchronization we have previously demonstrated in and near a single 2D plane. Thus we are able image the complete beating zebrafish heart exactly as if the heart had been artificially stopped, but sidestepping this undesirable interference with the heart and instead allowing the heart to beat as normal
Time Delay Estimation from Low Rate Samples: A Union of Subspaces Approach
Time delay estimation arises in many applications in which a multipath medium
has to be identified from pulses transmitted through the channel. Various
approaches have been proposed in the literature to identify time delays
introduced by multipath environments. However, these methods either operate on
the analog received signal, or require high sampling rates in order to achieve
reasonable time resolution. In this paper, our goal is to develop a unified
approach to time delay estimation from low rate samples of the output of a
multipath channel. Our methods result in perfect recovery of the multipath
delays from samples of the channel output at the lowest possible rate, even in
the presence of overlapping transmitted pulses. This rate depends only on the
number of multipath components and the transmission rate, but not on the
bandwidth of the probing signal. In addition, our development allows for a
variety of different sampling methods. By properly manipulating the low-rate
samples, we show that the time delays can be recovered using the well-known
ESPRIT algorithm. Combining results from sampling theory with those obtained in
the context of direction of arrival estimation methods, we develop necessary
and sufficient conditions on the transmitted pulse and the sampling functions
in order to ensure perfect recovery of the channel parameters at the minimal
possible rate. Our results can be viewed in a broader context, as a sampling
theorem for analog signals defined over an infinite union of subspaces
Evolution of online algorithms in ATLAS and CMS in Run 2
The Large Hadron Collider has entered a new era in Run 2, with centre-of-mass
energy of 13 TeV and instantaneous luminosity reaching
10 cm s for pp
collisions. In order to cope with those harsher conditions, the ATLAS and CMS
collaborations have improved their online selection infrastructure to keep a
high efficiency for important physics processes - like W, Z and Higgs bosons in
their leptonic and diphoton modes - whilst keeping the size of data stream
compatible with the bandwidth and disk resources available. In this note, we
describe some of the trigger improvements implemented for Run 2, including
algorithms for selection of electrons, photons, muons and hadronic final
states.Comment: 6 pages. Presented at The Fifth Annual Conference on Large Hadron
Collider Physics (LHCP 2017), Shanghai, China, May 15-20, 201
- …