13,119 research outputs found
Optimal and fast rotational alignment of volumes with missing data in Fourier space
AbstractElectron tomography of intact cells has the potential to reveal the entire cellular content at a resolution corresponding to individual macromolecular complexes. Characterization of macromolecular complexes in tomograms is nevertheless an extremely challenging task due to the high level of noise, and due to the limited tilt angle that results in missing data in Fourier space. By identifying particles of the same type and averaging their 3D volumes, it is possible to obtain a structure at a more useful resolution for biological interpretation. Currently, classification and averaging of sub-tomograms is limited by the speed of computational methods that optimize alignment between two sub-tomographic volumes. The alignment optimization is hampered by the fact that the missing data in Fourier space has to be taken into account during the rotational search. A similar problem appears in single particle electron microscopy where the random conical tilt procedure may require averaging of volumes with a missing cone in Fourier space. We present a fast implementation of a method guaranteed to find an optimal rotational alignment that maximizes the constrained cross-correlation function (cCCF) computed over the actual overlap of data in Fourier space
Nanometer-scale Tomographic Reconstruction of 3D Electrostatic Potentials in GaAs/AlGaAs Core-Shell Nanowires
We report on the development of Electron Holographic Tomography towards a
versatile potential measurement technique, overcoming several limitations, such
as a limited tilt range, previously hampering a reproducible and accurate
electrostatic potential reconstruction in three dimensions. Most notably,
tomographic reconstruction is performed on optimally sampled polar grids taking
into account symmetry and other spatial constraints of the nanostructure.
Furthermore, holographic tilt series acquisition and alignment have been
automated and adapted to three dimensions. We demonstrate 6 nm spatial and 0.2
V signal resolution by reconstructing various, previously hidden, potential
details of a GaAs/AlGaAs core-shell nanowire. The improved tomographic
reconstruction opens pathways towards the detection of minute potentials in
nanostructures and an increase in speed and accuracy in related techniques such
as X-ray tomography
Electron tomography at 2.4 {\AA} resolution
Transmission electron microscopy (TEM) is a powerful imaging tool that has
found broad application in materials science, nanoscience and biology(1-3).
With the introduction of aberration-corrected electron lenses, both the spatial
resolution and image quality in TEM have been significantly improved(4,5) and
resolution below 0.5 {\AA} has been demonstrated(6). To reveal the 3D structure
of thin samples, electron tomography is the method of choice(7-11), with
resolutions of ~1 nm^3 currently achievable(10,11). Recently, discrete
tomography has been used to generate a 3D atomic reconstruction of a silver
nanoparticle 2-3 nm in diameter(12), but this statistical method assumes prior
knowledge of the particle's lattice structure and requires that the atoms fit
rigidly on that lattice. Here we report the experimental demonstration of a
general electron tomography method that achieves atomic scale resolution
without initial assumptions about the sample structure. By combining a novel
projection alignment and tomographic reconstruction method with scanning
transmission electron microscopy, we have determined the 3D structure of a ~10
nm gold nanoparticle at 2.4 {\AA} resolution. While we cannot definitively
locate all of the atoms inside the nanoparticle, individual atoms are observed
in some regions of the particle and several grains are identified at three
dimensions. The 3D surface morphology and internal lattice structure revealed
are consistent with a distorted icosahedral multiply-twinned particle. We
anticipate that this general method can be applied not only to determine the 3D
structure of nanomaterials at atomic scale resolution(13-15), but also to
improve the spatial resolution and image quality in other tomography
fields(7,9,16-20).Comment: 27 pages, 17 figure
SOPHIE velocimetry of Kepler transit candidates XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator
We present the detection and characterization of the transiting warm Jupiter
KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We
combine the analysis of Kepler photometry with Doppler spectroscopy and
line-profile tomography of time-series spectra obtained with the SOPHIE
spectrograph to establish its planetary nature and derive its properties. To
derive reliable estimates for the uncertainties on the tomographic model
parameters, we devised an empirical method to calculate statistically
independent error bars on the time-series spectra. KOI-12b has a radius of
1.430.13 and a 3 upper mass limit of
10. It orbits a fast-rotating star (sin =
60.00.9 km s) with mass and radius of 1.450.09
and 1.630.15 , located at 42640 pc
from the Earth. Doppler tomography allowed a higher precision on the obliquity
to be reached by comparison with the analysis of the Rossiter-McLaughlin radial
velocity anomaly, and we found that KOI-12b lies on a prograde, slightly
misaligned orbit with a low sky-projected obliquity =
12.6. The properties of this planetary system,
with a 11.4 magnitude host-star, make of KOI-12b a precious target for future
atmospheric characterization.Comment: 19 pages, 10 figure
Inherited crustal deformation along the East Gondwana margin revealed by seismic anisotropy tomography
Acknowledgments We thank Mallory Young for providing phase velocity measurements in mainland Australia and Tasmania. Robert Musgrave is thanked for making available his tilt-filtered magnetic intensity map. In the short term, data may be made available by contacting the authors (S.P. or N.R.). A new database of passive seismic data recorded in Australia is planned as part of a national geophysics data facility for easy access download. Details on the status of this database may be obtained from the authors (S.P., N.R., or A.M.R.). There are no restrictions on access for noncommercial use. Commercial users should seek written permission from the authors (S.P. or N.R.). Ross Cayley publishes with the permission of the Director of the Geological Survey of Victoria.Peer reviewedPublisher PD
High-speed in vitro intensity diffraction tomography
We demonstrate a label-free, scan-free intensity diffraction tomography technique utilizing annular illumination (aIDT) to rapidly characterize large-volume three-dimensional (3-D) refractive index distributions in vitro. By optimally matching the illumination geometry to the microscope pupil, our technique reduces the data requirement by 60 times to achieve high-speed 10-Hz volume rates. Using eight intensity images, we recover volumes of ∼350 μm  ×  100 μm  ×  20  μm, with near diffraction-limited lateral resolution of   ∼  487  nm and axial resolution of   ∼  3.4  μm. The attained large volume rate and high-resolution enable 3-D quantitative phase imaging of complex living biological samples across multiple length scales. We demonstrate aIDT’s capabilities on unicellular diatom microalgae, epithelial buccal cell clusters with native bacteria, and live Caenorhabditis elegans specimens. Within these samples, we recover macroscale cellular structures, subcellular organelles, and dynamic micro-organism tissues with minimal motion artifacts. Quantifying such features has significant utility in oncology, immunology, and cellular pathophysiology, where these morphological features are evaluated for changes in the presence of disease, parasites, and new drug treatments. Finally, we simulate the aIDT system to highlight the accuracy and sensitivity of the proposed technique. aIDT shows promise as a powerful high-speed, label-free computational microscopy approach for applications where natural imaging is required to evaluate environmental effects on a sample in real time.https://arxiv.org/abs/1904.06004Accepted manuscrip
Synergy between the Large Synoptic Survey Telescope and the Square Kilometre Array
We provide an overview of the science benefits of combining information from
the Square Kilometre Array (SKA) and the Large Synoptic Survey Telescope
(LSST). We first summarise the capabilities and timeline of the LSST and
overview its science goals. We then discuss the science questions in common
between the two projects, and how they can be best addressed by combining the
data from both telescopes. We describe how weak gravitational lensing and
galaxy clustering studies with LSST and SKA can provide improved constraints on
the causes of the cosmological acceleration. We summarise the benefits to
galaxy evolution studies of combining deep optical multi-band imaging with
radio observations. Finally, we discuss the excellent match between one of the
most unique features of the LSST, its temporal cadence in the optical waveband,
and the time resolution of the SKA.Comment: SKA Synergies Chapter, Advancing Astrophysics with the SKA (AASKA14)
Conference, Giardini Naxos (Italy), June 9th-13th 201
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