355 research outputs found
Topo-Geometric Filtration Scheme for Geometric Active Contours and Level Sets: Application to Cerebrovascular Segmentation
One of the main problems of the existing methods for the
segmentation of cerebral vasculature is the appearance in the segmentation
result of wrong topological artefacts such as the kissing vessels.
In this paper, a new approach for the detection and correction of such
errors is presented. The proposed technique combines robust topological
information given by Persistent Homology with complementary geometrical
information of the vascular tree. The method was evaluated on 20
images depicting cerebral arteries. Detection and correction success rates
were 81.80% and 68.77%, respectively
Mapping the phase diagram of strongly interacting matter
We employ a conformal mapping to explore the thermodynamics of strongly
interacting matter at finite values of the baryon chemical potential .
This method allows us to identify the singularity corresponding to the critical
point of a second-order phase transition at finite , given information
only at . The scheme is potentially useful for computing thermodynamic
properties of strongly interacting hot and dense matter in lattice gauge
theory. The technique is illustrated by an application to a chiral effective
model.Comment: 5 pages, 3 figures; published versio
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
Chiral phase transition in the presence of spinodal decomposition
The thermodynamics of a first order chiral phase transition is considered in
the presence of spinodal phase separation within the Nambu-Jona-Lasinio (NJL)
model. The properties of the basic thermodynamic observables in the coexistence
phase are discussed for zero and non-zero quark masses. We focus on observables
that probe the chiral phase transition. In particular, the behavior of the
specific heat and entropy as well as charge fluctuations are calculated and
analyzed. We show that the specific heat and charge susceptibilities diverge at
the isothermal spinodal lines. We determine the scaling behavior and compute
the critical exponent of the net quark number susceptibility at the
isothermal spinodal lines within the NJL model and the Ginsburg-Landau theory.
We show that in the chiral limit the critical exponent at the
tricritical point as well as along the isothermal spinodal lines. On the other
hand, for finite quark masses the critical exponent at the spinodal lines,
, differs from that at the critical end point, ,
indicating a change in the universality class. These results are independent of
the particular choice of the chiral Lagrangian and should be common for all
mean field approaches.Comment: 12 pages, 11 figure
"Free" Constituent Quarks and Dilepton Production in Heavy Ion Collisions
An approach is suggested, invoking vitally the notion of constituent massive
quarks (valons) which can survive and propagate rather than hadrons (except of
pions) within the hot and dense matter formed below the chiral transition
temperature in course of the heavy ion collisions at high energies. This
approach is shown to be quite good for description of the experimentally
observed excess in dilepton yield at masses 250 MeV < M < 700 MeV over the
prompt resonance decay mechanism (CERES cocktail) predictions. In certain
aspects, it looks to be even more successful, than the conventional approaches:
it seems to match the data somewhat better at dilepton masses before the
two-pion threshold and before the rho-meson peak as well as at higher dilepton
masses (beyond the phi-meson one). The approach implies no specific assumptions
on the equation of state (EOS) or peculiarities of phase transitions in the
expanding nuclear matter.Comment: 13 pages, 3 PNG figures. submitted to Sov. Nucl. Phy
Thermal states of coldest and hottest neutron stars in soft X-ray transients
We calculate the thermal structure and quiescent thermal luminosity of
accreting neutron stars (warmed by deep crustal heating in accreted matter) in
soft X-ray transients (SXTs). We consider neutron stars with nucleon and
hyperon cores and with accreted envelopes. It is assumed that an envelope has
an outer helium layer (of variable depth) and deeper layers of heavier
elements, either with iron or with much heavier nuclei (of atomic weight A >
100) on the top (Haensel & Zdunik 1990, 2003, astro-ph/0305220). The relation
between the internal and surface stellar temperatures is obtained and fitted.
The quiescent luminosity of the hottest (low-mass) and coldest (high-mass)
neutron stars is calculated, together with the ranges of its possible
variations due to variable thickness of the helium layer. The results are
compared with observations of SXTs, particularly, containing the coldest (SAX
J1808.4-3658) and the hottest (Aql X-1) neutron stars. The observations of SAX
J1808.4-3658 in a quiescent state on March 24, 2001 (Campana et al. 2002,
astro-ph/0206376) can be explained only if this SXT contains a massive neutron
star with a nucleon/hyperon core; a hyperon core with a not too low fraction of
electrons is preferable. Future observations may discriminate between the
various models of hyperon/nucleon dense matter. The thermal emission of SAX
J1808.4-3658 is also sensitive to the models of plasma ionization in the
outermost surface layers and can serve for testing such models.Comment: 12 pages, 5 figures, 4 tables, LaTeX2e with aa.cls v.5.3 (included).
Accepted by A&
Spin susceptibility of neutron matter at zero temperature
The Auxiliary Field Diffusion Monte Carlo method is applied to compute the
spin susceptibility and the compressibility of neutron matter at zero
temperature. Results are given for realistic interactions which include both a
two-body potential of the Argonne type and the Urbana IX three-body potential.
Simulations have been carried out for about 60 neutrons. We find an overall
reduction of the spin susceptibilty by about a factor 3 with respect to the
Pauli susceptibility for a wide range of densities. Results for the
compressibility of neutron matter are also presented and compared with other
available estimates obtained for semirealistic nucleon-nucleon interactions by
using other techniques
Pionic contribution to relativistic Fermi Liquid parameters
We calculate pionic contribution to the relativistic Fermi Liquid parameters
(RFLPs) using Chiral Effective Lagrangian. The RFLPs so determined are then
used to calculate chemical potential, exchange and nuclear symmetry energies
due to interaction. We also evaluate two loop ring diagrams involving
, and meson exchanges and compare results with what one
obtains from the relativistic Fermi Liquid theory (RFLT).Comment: 6 pages, 2 figures, Published in Canadian Journal of Physics, vol.
88, issue 8, pp. 585-59
Long-term, Prolonged-release Tacrolimus-based Immunosuppression in De Novo Liver Transplant Recipients : 5-year Prospective Follow-up of Patients in the DIAMOND Study
Background. Immunosuppression with calcineurin inhibitors (CNIs) is reportedly associated with risk of renal impairment in liver transplant recipients. It is believed that this can be mitigated by decreasing initial exposure to CNIs or delaying CNI introduction until 3-4 d posttransplantation. The ADVAGRAF studied in combination with mycophenolate mofetil and basili ximab in liver transplantation (DIAMOND) trial evaluated different administration strategies for prolonged-release tacrolimus (PR-T). Methods. DIAMOND was a 24-wk, open-label, phase 3b trial in de novo liver transplant recipients randomized to: PR-T 0.2 mg/kg/d (Arm 1); PR-T 0.15-0.175 mg/kg/d plus basiliximab (Arm 2); or PR-T 0.2 mg/kg/d delayed until day 5 posttransplant plus basiliximab (Arm 3). In a 5-y follow-up, patients were maintained on an immunosuppressive regimen according to standard clinical practice (NCT02057484). Primary endpoint: graft survival (Kaplan-Meier analysis). Results. Follow-up study included 856 patients. Overall graft survival was 84.6% and 73.5% at 1 and 5 y post transplant, respectively. Five-year rates for Arms 1, 2, and 3 were 74.7%, 71.5%, and 74.5%, respectively. At 5 y, death-censored graft survival in the entire cohort was 74,7%. Overall graft survival in patients remaining on PR-T for z30 d was 79.1%. Graft survival in patients who remained on PR-T at 5 y was 87.3%. Patient survival was 86.6% at 1 y and 76.3% at 5 y, with survival rates similar in the 3 treatment arms at 5 y. Estimated glomerular filtration rate at the end of the 24-wk initial study and 5 y posttransplant was 62.1 and 61.5 mi./min/1.73 m(2), respectively, and was similar between the 3 treatment arms at 5 y. Overall, 18 (2.9%) patients had z1 adverse drug reaction, considered possibly related to PR-T in 6 patients. Conclusions. In the DIAMOND study patient cohort, renal function, graft survival, and patient survival were similar between treatment arms at 5 y posttransplant.Peer reviewe
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