1,622 research outputs found
Kernel-based high-dimensional histogram estimation for visual tracking
©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.Presented at the 15th IEEE International Conference on Image Processing, October 12–15, 2008, San Diego, California, U.S.A.DOI: 10.1109/ICIP.2008.4711862We propose an approach for non-rigid tracking that represents objects by their set of distribution parameters. Compared to joint histogram representations, a set of parameters such as mixed moments provides a significantly reduced size representation. The discriminating power is comparable to that of the corresponding full high dimensional histogram yet at far less spatial and computational complexity. The proposed method is robust in the presence of noise and illumination changes, and provides a natural extension to the use of mixture models. Experiments demonstrate that the proposed method outperforms both full color mean-shift and global covariance searches
Seroepidemiology of group A rotavirus in suburban São Paulo, Brazil
Age-specifc patterns of rotavirus infection were investigated using a randomly selected and
representative sample of sera from a suburban community of São Paulo, Brazil screened for
class-specifc antibodies to group A rotavirus. Age-serology of anti-rotavirus IgG showed
primary infection predominant in young infants with a median age of around 18 months
consistent with IgM serology suggesting highest rates of recent infection between ages 4 and 48
months. Anti-rotavirus serum IgA prevalence increased gradually with age. Paired samples
from infants, collected 1 month apart, indicated high exposure rates with seroconversion
occurring in several infants during the reported low transmission season. Between 5 and 10%
of adults had elevated IgM levels indicative of recent infection and, potentially, of an
important contribution adults may play to rotavirus transmission. Further understanding of the
dynamics of rotavirus transmission within populations, at group and serotype level, would
benefit the design and monitoring of future immunization programmes
Coherent electron transport by adiabatic passage in an imperfect donor chain
Coherent Tunneling Adiabatic Passage (CTAP) has been proposed as a long-range
physical qubit transport mechanism in solid-state quantum computing
architectures. Although the mechanism can be implemented in either a chain of
quantum dots or donors, a 1D chain of donors in Si is of particular interest
due to the natural confining potential of donors that can in principle help
reduce the gate densities in solid-state quantum computing architectures. Using
detailed atomistic modeling, we investigate CTAP in a more realistic triple
donor system in the presence of inevitable fabrication imperfections. In
particular, we investigate how an adiabatic pathway for CTAP is affected by
donor misplacements, and propose schemes to correct for such errors. We also
investigate the sensitivity of the adiabatic path to gate voltage fluctuations.
The tight-binding based atomistic treatment of straggle used here may benefit
understanding of other donor nanostructures, such as donor-based charge and
spin qubits. Finally, we derive an effective 3 \times 3 model of CTAP that
accurately resembles the voltage tuned lowest energy states of the
multi-million atom tight-binding simulations, and provides a translation
between intensive atomistic Hamiltonians and simplified effective Hamiltonians
while retaining the relevant atomic-scale information. This method can help
characterize multi-donor experimental structures quickly and accurately even in
the presence of imperfections, overcoming some of the numeric intractabilities
of finding optimal eigenstates for non-ideal donor placements.Comment: 9 pages, 8 figure
On the creation of thermal equations of state for use in Dioptas
Dioptas is a widely used software package for integrating and analysing 2-dimensional diffraction images. To help interpret the integrated diffraction profiles it produces, Dioptas users can input files that parameterise a material's thermal equation of state (EoS), enabling the positions of the Bragg peaks from that material to be calculated as a function of pressure and temperature. However, care is needed to ensure that these input files correctly describe the thermal EoS of interest. Here we describe the thermal EoS model used by Dioptas and show how existing thermal EoS should be reparameterised so as to be used correctly in Dioptas. Input EoS files suitable for use with Dioptas are provided for the following commonly-used pressure calibrants and pressure transmitting media: Al, Au, Cu, Mo, Nb, Pt, Ta, hcp-Fe, MgO, NaCl-B1, NaCl-B2, KCl-B2, and Ne.</p
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Neural Tractography Using an Unscented Kalman Filter
We describe a technique to simultaneously estimate a local neural fiber model and trace out its path. Existing techniques estimate the local fiber orientation at each voxel independently so there is no running knowledge of confidence in the estimated fiber model. We formulate fiber tracking as recursive estimation: at each step of tracing the fiber, the current estimate is guided by the previous. To do this we model the signal as a mixture of Gaussian tensors and perform tractography within a filter framework. Starting from a seed point, each fiber is traced to its termination using an unscented Kalman filter to simultaneously fit the local model and propagate in the most consistent direction. Despite the presence of noise and uncertainty, this provides a causal estimate of the local structure at each point along the fiber. Synthetic experiments demonstrate that this approach reduces signal reconstruction error and significantly improves the angular resolution at crossings and branchings. In vivo experiments confirm the ability to trace out fibers in areas known to contain such crossing and branching while providing inherent path regularization
Unveiling Dust-enshrouded Star Formation in the Early Universe: a Sub-mm Survey of the Hubble Deep Field
The advent of sensitive sub-mm array cameras now allows a proper census of
dust-enshrouded massive star-formation in very distant galaxies, previously
hidden activity to which even the faintest optical images are insensitive. We
present the deepest sub-mm survey of the sky to date, taken with the SCUBA
camera on the James Clerk Maxwell Telescope and centred on the Hubble Deep
Field. The high source density found in this image implies that the survey is
confusion-limited below a flux density of 2 mJy. However, within the central 80
arcsec radius independent analyses yield 5 reproducible sources with S(850um) >
2 mJy which simulations indicate can be ascribed to individual galaxies. We
give positions and flux densities for these, and furthermore show using
multi-frequency photometric data that the brightest sources in our map lie at
redshifts z~3. These results lead to integral source counts which are
completely inconsistent with a no-evolution model, and imply that massive
star-formation activity continues at redshifts > 2. The combined brightness of
the 5 most secure sources in our map is sufficient to account for 30 - 50% of
the previously unresolved sub-mm background, and we estimate statistically that
the entire background is resolved at about the 0.3 mJy level. Finally we
discuss possible optical identifications and redshift estimates for the
brightest sources. One source appears to be associated with an extreme
starburst galaxy at z~1, whilst the remaining four appear to lie in the
redshift range 2 < z < 4. This implies a star-formation density over this
redshift range that is at least five times higher than that inferred from the
ultraviolet output of HDF galaxies.Comment: 19 pages, 6 figures (to appear as a Nature Article
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Two-Tensor Tractography Using a Constrained Filter
We describe a technique to simultaneously estimate a weighted, positive-definite multi-tensor fiber model and perform tractography. Existing techniques estimate the local fiber orientation at each voxel independently so there is no running knowledge of confidence in the estimated fiber model. We formulate fiber tracking as recursive estimation: at each step of tracing the fiber, the current estimate is guided by the previous. To do this we model the signal as a weighted mixture of Gaussian tensors and perform tractography within a filter framework. Starting from a seed point, each fiber is traced to its termination using an unscented Kalman filter to simultaneously fit the local model and propagate in the most consistent direction. Further, we modify the Kalman filter to enforce model constraints, i.e. positive eigenvalues and convex weights. Despite the presence of noise and uncertainty, this provides a causal estimate of the local structure at each point along the fiber. Synthetic experiments demonstrate that this approach significantly improves the angular resolution at crossings and branchings while consistently estimating the mixture weights. In vivo experiments confirm the ability to trace out fibers in areas known to contain such crossing and branching while providing inherent path regularization
Brainstem Raphe Pallidus and the Adjacent Area Contain a Novel Action Site in the Melanocortin Circuitry Regulating Energy Balance
The central melanocortin system plays a critical role in the regulation of energy balance in rodents and humans. The melanocortin signals in both the hypothalamus and brainstem contribute to this regulation. However, how the melanocortin signals of the hypothalamus interact with those intrinsic to the brainstem in the regulation of energy balance is poorly understood. The brainstem raphe pallidus (RPa) and adjacent areas contain melanocortin 4 receptor (MC4-R)-bearing neurons and sympathetic premotor neurons regulating thermogenesis. Here we report that α-melanocyte-stimulating hormone (α-MSH)-immunoreactive (IR) fibers are in close apposition to MC4-R neurons in the RPa. Retrograde tracing studies revealed a unique direct projection from hypothalamic proopiomelanocortin (POMC) neurons to the RPa and adjacent areas of the brainstem in mice and rats. Furthermore, microinjection of the MC3/4-R agonist MTII into the RPa area dose-dependently stimulated oxygen consumption and inhibited feeding, whereas microinjection of the antagonist, SHU9119, enhanced feeding. These data suggest a novel pathway of hypothalamic POMC neuronal efferents to brainstem RPa area MC4-R neurons in the melanocortin circuitry that contribute to coordinate regulation of energy balance
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