7,792 research outputs found
Noise Robustness of a Combined Phase Retrieval and Reconstruction Method for Phase-Contrast Tomography
Classical reconstruction methods for phase-contrast tomography consist of two
stages: phase retrieval and tomographic reconstruction. A novel algebraic
method combining the two was suggested by Kostenko et al. (Opt. Express, 21,
12185, 2013) and preliminary results demonstrating improved reconstruction
compared to a two-stage method given. Using simulated free-space propagation
experiments with a single sample-detector distance, we thoroughly compare the
novel method with the two-stage method to address limitations of the
preliminary results. We demonstrate that the novel method is substantially more
robust towards noise; our simulations point to a possible reduction in counting
times by an order of magnitude
Discrete tomography: Magic numbers for -fold symmetry
We consider the problem of distinguishing convex subsets of -cyclotomic
model sets by (discrete parallel) X-rays in prescribed
-directions. In this context, a `magic number' has
the property that any two convex subsets of can be distinguished
by their X-rays in any set of prescribed
-directions. Recent calculations suggest that (with one exception
in the case ) the least possible magic number for -cyclotomic model
sets might just be , where .Comment: 5 pages, 2 figures; new computer calculations based on the results of
arXiv:1101.4149 and arXiv:1211.6318; presented at ICQ 12 (Cracow, Poland
Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes
We introduce the concept of computerized tomographic microscopy in magnetic
resonance imaging using the magnetic fields and field gradients from a
ferromagnetic probe. We investigate a configuration where a two-dimensional
sample is under the influence of a large static polarizing field, a small
perpendicular radio-frequency field, and a magnetic field from a ferromagnetic
sphere. We demonstrate that, despite the non-uniform and non-linear nature of
the fields from a microscopic magnetic sphere, the concepts of computerized
tomography can be applied to obtain proper image reconstruction from the
original spectral data by sequentially varying the relative sample-sphere
angular orientation. The analysis shows that the recent proposal for atomic
resolution magnetic resonance imaging of discrete periodic crystal lattice
planes using ferromagnetic probes can also be extended to two-dimensional
imaging of non-crystalline samples with resolution ranging from micrometer to
Angstrom scales.Comment: 9 pages, 11 figure
Entangled resource for interfacing single- and dual-rail optical qubits
Today's most widely used method of encoding quantum information in optical
qubits is the dual-rail basis, often carried out through the polarisation of a
single photon. On the other hand, many stationary carriers of quantum
information - such as atoms - couple to light via the single-rail encoding in
which the qubit is encoded in the number of photons. As such, interconversion
between the two encodings is paramount in order to achieve cohesive quantum
networks. In this paper, we demonstrate this by generating an entangled
resource between the two encodings and using it to teleport a dual-rail qubit
onto its single-rail counterpart. This work completes the set of tools
necessary for the interconversion between the three primary encodings of the
qubit in the optical field: single-rail, dual-rail and continuous-variable.Comment: Published in Quantu
Magic numbers in the discrete tomography of cyclotomic model sets
We report recent progress in the problem of distinguishing convex subsets of
cyclotomic model sets by (discrete parallel) X-rays in prescribed
-directions. It turns out that for any of these model sets
there exists a `magic number' such that any two
convex subsets of can be distinguished by their X-rays in any set
of prescribed -directions. In particular, for
pentagonal, octagonal, decagonal and dodecagonal model sets, the least possible
numbers are in that very order 11, 9, 11 and 13.Comment: 6 pages, 1 figure; based on the results of arXiv:1101.4149 [math.MG];
presented at Aperiodic 2012 (Cairns, Australia
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
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