206 research outputs found
Extraction of Airways with Probabilistic State-space Models and Bayesian Smoothing
Segmenting tree structures is common in several image processing
applications. In medical image analysis, reliable segmentations of airways,
vessels, neurons and other tree structures can enable important clinical
applications. We present a framework for tracking tree structures comprising of
elongated branches using probabilistic state-space models and Bayesian
smoothing. Unlike most existing methods that proceed with sequential tracking
of branches, we present an exploratory method, that is less sensitive to local
anomalies in the data due to acquisition noise and/or interfering structures.
The evolution of individual branches is modelled using a process model and the
observed data is incorporated into the update step of the Bayesian smoother
using a measurement model that is based on a multi-scale blob detector.
Bayesian smoothing is performed using the RTS (Rauch-Tung-Striebel) smoother,
which provides Gaussian density estimates of branch states at each tracking
step. We select likely branch seed points automatically based on the response
of the blob detection and track from all such seed points using the RTS
smoother. We use covariance of the marginal posterior density estimated for
each branch to discriminate false positive and true positive branches. The
method is evaluated on 3D chest CT scans to track airways. We show that the
presented method results in additional branches compared to a baseline method
based on region growing on probability images.Comment: 10 pages. Pre-print of the paper accepted at Workshop on Graphs in
Biomedical Image Analysis. MICCAI 2017. Quebec Cit
Tracking Target Signal Strengths on a Grid using Sparsity
Multi-target tracking is mainly challenged by the nonlinearity present in the
measurement equation, and the difficulty in fast and accurate data association.
To overcome these challenges, the present paper introduces a grid-based model
in which the state captures target signal strengths on a known spatial grid
(TSSG). This model leads to \emph{linear} state and measurement equations,
which bypass data association and can afford state estimation via
sparsity-aware Kalman filtering (KF). Leveraging the grid-induced sparsity of
the novel model, two types of sparsity-cognizant TSSG-KF trackers are
developed: one effects sparsity through -norm regularization, and the
other invokes sparsity as an extra measurement. Iterative extended KF and
Gauss-Newton algorithms are developed for reduced-complexity tracking, along
with accurate error covariance updates for assessing performance of the
resultant sparsity-aware state estimators. Based on TSSG state estimates, more
informative target position and track estimates can be obtained in a follow-up
step, ensuring that track association and position estimation errors do not
propagate back into TSSG state estimates. The novel TSSG trackers do not
require knowing the number of targets or their signal strengths, and exhibit
considerably lower complexity than the benchmark hidden Markov model filter,
especially for a large number of targets. Numerical simulations demonstrate
that sparsity-cognizant trackers enjoy improved root mean-square error
performance at reduced complexity when compared to their sparsity-agnostic
counterparts.Comment: Submitted to IEEE Trans. on Signal Processin
Chiral-invariant CP-violating Effective Interactions in Z Decays to three Jets
Tests of CP violation by appropriate momentum correlations in jets
and in particular in probe CP-violating effective couplings --
that manifest themselves as form factors -- which conserve the quark chirality
and quark flavour. By giving two examples we show that such couplings can be
induced at one-loop order in extensions of the Standard Model with CP violation
beyond the Kobayashi-Maskawa phase. In one of the models we compute the
chirality-conserving part of the CP-violating -gluon amplitude for
massless quarks, determine the resulting effective dimension
couplings in the local limit, and discuss the possible size of the effects.
Finally we show that in models with excited quarks the chiral-invariant
CP-violating effective interactions could be quite large if appropriate
couplings are of a size characteristic of a strong interactionComment: 14 pages, LaTeX with 4 postscript figures, epsf macro include
Implications of a W^+W^- (ZZ) - Higgs - t c-bar$ Interaction for e^+e^- -> t c-bar \nu_e \nu_e-bar, t c-bar e^+ e^-, t c-bar Z and for t -> cW^+W^-, cZZ in a Two Higgs Doublet Model
The Standard Model with one extra Higgs doublet may give rise to enhanced
TREE-LEVEL flavor-changing-scalar coupling of a neutral Higgs to a pair of
top-charm quarks. This coupling may drive a large TREE-LEVEL effective
W^+W^-(ZZ) - Higgs - t c-bar interaction. As a result we find that the
reactions e^+e^- -> t c-bar \nu_e \nu_e-bar, t c-bar e^+ e^-, t c-bar Z and the
two rare top decays t -> cW^+W^-, t -> cZZ become very sensitive probes of such
an effective interaction. The most promising ones, e^+e^- -> t c-bar \nu_e
\nu_e-bar, t c-bar e^+ e^-, may yield several hundreds and up to thousands of
such events at the Next Linear Collider with a center of mass energy of
\sqrt{s}=0.5 - 2 TeV if the mass of the lightest neutral Higgs is a few hundred
GeV. The rare decays t -> cW^+W^- and t -> cZZ may be accessible at the LHC if
the mass of the lightest neutral Higgs lies in the narrow window 150 GeV < m_h
< 200 GeV.Comment: 18 pages, plain latex, 12 figures embadded in the text using epsfi
Frequency Tracking and Parameter Estimation for Robust Quantum State-Estimation
In this paper we consider the problem of tracking the state of a quantum
system via a continuous measurement. If the system Hamiltonian is known
precisely, this merely requires integrating the appropriate stochastic master
equation. However, even a small error in the assumed Hamiltonian can render
this approach useless. The natural answer to this problem is to include the
parameters of the Hamiltonian as part of the estimation problem, and the full
Bayesian solution to this task provides a state-estimate that is robust against
uncertainties. However, this approach requires considerable computational
overhead. Here we consider a single qubit in which the Hamiltonian contains a
single unknown parameter. We show that classical frequency estimation
techniques greatly reduce the computational overhead associated with Bayesian
estimation and provide accurate estimates for the qubit frequencyComment: 6 figures, 13 page
Flavor changing Z-decays from scalar interactions at a Giga-Z Linear Collider
The flavor changing decay Z -> d_I \bar{d}_J is investigated with special
emphasis on the b \bar{s} final state. Various models for flavor violation are
considered: two Higgs doublet models (2HDM's), supersymmetry (SUSY) with flavor
violation in the up and down-type squark mass matrices and SUSY with flavor
violation mediated by R-parity-violating interaction. We find that, within the
SUSY scenarios for flavor violation, the branching ratio for the decay Z -> b
\bar{s} can reach 10^{-6} for large \tan\beta values, while the typical size
for this branching ratio in the 2HDM's considered is about two orders of
magnitudes smaller at best. Thus, flavor changing SUSY signatures in radiative
Z decays such as Z -> b \bar{s} may be accessible to future ``Z factories''
such as a Giga-Z version of the TESLA design.Comment: 27 pages, 15 figures, REVTeX4. A new section added and a few minor
corrections were made in the tex
Flavourful Production at Hadron Colliders
We ask what new states may lie at or below the TeV scale, with sizable
flavour-dependent couplings to light quarks, putting them within reach of
hadron colliders via resonant production, or in association with Standard Model
states. In particular, we focus on the compatibility of such states with
stringent flavour-changing neutral current and electric-dipole moment
constraints. We argue that the broadest and most theoretically plausible
flavour structure of the new couplings is that they are hierarchical, as are
Standard Model Yukawa couplings, although the hierarchical pattern may well be
different. We point out that, without the need for any more elaborate or
restrictive structure, new scalars with "diquark" couplings to standard quarks
are particularly immune to existing constraints, and that such scalars may
arise within a variety of theoretical paradigms. In particular, there can be
substantial couplings to a pair of light quarks or to one light and one heavy
quark. For example, the latter possibility may provide a flavour-safe
interpretation of the asymmetry in top quark production observed at the
Tevatron. We thereby motivate searches for diquark scalars at the Tevatron and
LHC, and argue that their discovery represents one of our best chances for new
insight into the Flavour Puzzle of the Standard Model.Comment: 18 pp., 8 figures, references adde
Flavor changing scalar couplings and production at hadron colliders
We calculate the contributions of the flavor changing scalar ()
couplings arised from topcolor-assisted technicolor () models at
tree-level to the and production at the Tevatron and
experiments. We find that the production cross sections are very small at the
Tevatron with , which is smaller than 5 fb in most of the
parameter space of models. However, the virtual effects of the
couplings on the production can be easily detected at the
with via the final state
().Comment: 10 pages,5 figure
Top-Charm Associated Production in High Energy Collisions
The possibility of exploring the flavor changing neutral current
couplings in the production vertex for the reaction \epem\to
t\bar c + \bar tc is examined. Using a model independent parameterization for
the effective Lagrangian to describe the most general three-point interactions,
production cross sections are found to be relatively small at LEP II, but
potentially sizeable at higher energy \epem colliders. The kinematic
characteristics of the signal are studied and a set of cuts are devised for
clean separation of the signal from background. The resulting sensitivity to
anomalous flavor changing couplings at LEP II with an integrated luminosity of
pb is found to be comparable to their present indirect
constraints from loop processes, while at higher energy colliders with
TeV center-of-mass energy and 50-200 fb luminosity, one expects to reach
a sensitivity at or below the percentage level.Comment: Latex, 22 page
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