2,676 research outputs found
Dynamic Hyperspectral and Polarized Endoscopic Imaging
The health of rich, developed nations has seen drastic improvement
in the last two centuries. For it to continue improving at a similar
rate new or improved diagnostic and treatment technologies are required,
especially for those diseases such as cancer which are forecast
to constitute the majority of disease burden in the future. Optical
techniques such as microscopy have long played their part in the diagnostic
process. However there are several new biophotonic modalities
that aim to exploit various interactions between light and tissue to provide
enhanced diagnostic information. Many of these show promise in
a laboratory setting but few have progressed to a clinical setting. We
have designed and constructed a
flexible, multi-modal, multi-spectral
laparoscopic imaging system that could be used to demonstrate several
different techniques in a clinical setting.
The core of this system is a dynamic hyperspectral illumination system
based around a supercontinuum laser and Digital Micromirror
Device that can provide specified excitation light in the visible and
near infra-red ranges. This is a powerful tool for spectroscopic techniques
as it is not limited to interrogating a fixed range of wavelengths
and can switch between excitation bands instantaneously. The excitation
spectra can be customised to match particular
fluorophores or
absorption features, introducing new possibilities for spectral imaging.
A standard 10 mm diameter rigid endoscope was incorporated into
the system to reduce cost and demonstrate compatibility with existing
equipment. The polarization properties of two commercial endoscopes
were characterised and found to be unsuited to current polarization
imaging techniques as birefringent materials used in their construction introduce complex, spatially dependent transformations of the polarization
state. Preliminary exemplar data from phantoms and ex vivo
tissue was collected and the feasibility and accuracy of different analysis
techniques demonstrated including multiple class classification algorithms.
Finally, a novel visualisation method was implemented in
order to display the complex hyperspectral data sets in a meaningful
and intuitive way to the user
Algorithms for Least-Squares Noncartesian MR Image Reconstruction
Iterative least-squares MR reconstructions typically use the Conjugate
Gradient algorithm, despite known numerical issues. This paper demonstrates
that the more recent LSMR algorithm has favourable numerical properties, and is
to be preferred in situations where Toeplitz embedding cannot be used to
accelerate the Conjugate Gradient method.Comment: 11 pages, 5 figure
The Dynamical History of Chariklo and its Rings
Chariklo is the only small Solar system body confirmed to have rings. Given
the instability of its orbit, the presence of rings is surprising, and their
origin remains poorly understood. In this work, we study the dynamical history
of the Chariklo system by integrating almost 36,000 Chariklo clones backwards
in time for one Gyr under the influence of the Sun and the four giant planets.
By recording all close encounters between the clones and planets, we
investigate the likelihood that Chariklo's rings could have survived since its
capture to the Centaur population. Our results reveal that Chariklo's orbit
occupies a region of stable chaos, resulting in its orbit being marginally more
stable than those of the other Centaurs. Despite this, we find that it was most
likely captured to the Centaur population within the last 20 Myr, and that its
orbital evolution has been continually punctuated by regular close encounters
with the giant planets. The great majority (> 99%) of those encounters within
one Hill radius of the planet have only a small effect on the rings. We
conclude that close encounters with giant planets have not had a significant
effect on the ring structure. Encounters within the Roche limit of the giant
planets are rare, making ring creation through tidal disruption unlikely
LF-PPL: A Low-Level First Order Probabilistic Programming Language for Non-Differentiable Models
We develop a new Low-level, First-order Probabilistic Programming Language
(LF-PPL) suited for models containing a mix of continuous, discrete, and/or
piecewise-continuous variables. The key success of this language and its
compilation scheme is in its ability to automatically distinguish parameters
the density function is discontinuous with respect to, while further providing
runtime checks for boundary crossings. This enables the introduction of new
inference engines that are able to exploit gradient information, while
remaining efficient for models which are not everywhere differentiable. We
demonstrate this ability by incorporating a discontinuous Hamiltonian Monte
Carlo (DHMC) inference engine that is able to deliver automated and efficient
inference for non-differentiable models. Our system is backed up by a
mathematical formalism that ensures that any model expressed in this language
has a density with measure zero discontinuities to maintain the validity of the
inference engine.Comment: Published in the proceedings of the 22nd International Conference on
Artificial Intelligence and Statistics (AISTATS
Reading on the right when there’s nothing left? Probabilistic tractography reveals hemispheric asymmetry in pure alexia
We present a patient with reading inexpertise and right hemianopia following left posterior cerebral artery (PCA) stroke. We examine the extent of disruption to reading performance and the extent of white matter tract damage relative to a patient with more limited PCA infarction and isolated right hemianopia. We show white matter disconnection of the temporal occipital fusiform cortex in our pure alexia patient. Connectivity-based laterality indices revealed right hemisphere laterality in the alexia patient; this was not associated with improved reading function. We speculate that the degree of premorbid laterality may be a critical factor affecting the extent of reading dysfunction in alexia
A Single Lineage In Early Pleistocene Homo : Size Variation Continuity In Early Pleistocene Homo Crania From East Africa And Georgia
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97215/1/j.1558-5646.2012.01824.x.pd
Magnetic confinement of the solar tachocline: The oblique dipole
3D MHD global solar simulations coupling the turbulent convective zone and
the radiative zone have been carried out. Essential features of the Sun such as
differential rotation, meridional circulation and internal waves excitation are
recovered. These realistic models are used to test the possibility of having
the solar tachocline confined by a primordial inner magnetic field. We find
that the initially confined magnetic fields we consider open into the
convective envelope. Angular momentum is transported across the two zones by
magnetic torques and stresses, establishing the so-called Ferarro's law of
isorotation. In the parameter space studied, the confinement of the magnetic
field by meridional circulation penetration fails, also implying the failure of
the tachocline confinement by the magnetic field. Three-dimensional convective
motions are proven responsible for the lack of magnetic field confinement.
Those results are robust for the different magnetic field topologies
considered, i.e. aligned or oblique dipole.Comment: 4 pages, 5 figure
Accelerated Evolution of the ASPM Gene Controlling Brain Size Begins Prior to Human Brain Expansion
Primary microcephaly (MCPH) is a neurodevelopmental disorder characterized by global reduction in cerebral cortical volume. The microcephalic brain has a volume comparable to that of early hominids, raising the possibility that some MCPH genes may have been evolutionary targets in the expansion of the cerebral cortex in mammals and especially primates. Mutations in ASPM, which encodes the human homologue of a fly protein essential for spindle function, are the most common known cause of MCPH. Here we have isolated large genomic clones containing the complete ASPM gene, including promoter regions and introns, from chimpanzee, gorilla, orangutan, and rhesus macaque by transformation-associated recombination cloning in yeast. We have sequenced these clones and show that whereas much of the sequence of ASPM is substantially conserved among primates, specific segments are subject to high Ka/Ks ratios (nonsynonymous/synonymous DNA changes) consistent with strong positive selection for evolutionary change. The ASPM gene sequence shows accelerated evolution in the African hominoid clade, and this precedes hominid brain expansion by several million years. Gorilla and human lineages show particularly accelerated evolution in the IQ domain of ASPM. Moreover, ASPM regions under positive selection in primates are also the most highly diverged regions between primates and nonprimate mammals. We report the first direct application of TAR cloning technology to the study of human evolution. Our data suggest that evolutionary selection of specific segments of the ASPM sequence strongly relates to differences in cerebral cortical size
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