675 research outputs found
Protist predation can favour cooperation within bacterial species
Here, we studied how protist predation affects cooperation in the opportunistic pathogen bacterium Pseudomonas aeruginosa, which uses quorum sensing (QS) cell-to-cell signalling to regulate the production of public goods. By competing wild-type bacteria with QS mutants (cheats), we show that a functioning QS system confers an elevated resistance to predation. Surprisingly, cheats were unable to exploit this resistance in the presence of cooperators, which suggests that resistance does not appear to result from activation of QS-regulated public goods. Instead, elevated resistance of wild-type bacteria was related to the ability to form more predation-resistant biofilms. This could be explained by the expression of QS-regulated resistance traits in densely populated biofilms and floating cell aggregations, or alternatively, by a pleiotropic cost of cheating where less resistant cheats are selectively removed from biofilms. These results show that trophic interactions among species can maintain cooperation within species, and have further implications for P. aeruginosa virulence in environmental reservoirs by potentially enriching the cooperative and highly infective strains with functional QS system
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
Relativistic hydrodynamics for heavy-ion collisions
Relativistic hydrodynamics is essential to our current understanding of
nucleus-nucleus collisions at ultrarelativistic energies (current experiments
at the Relativistic Heavy Ion Collider, forthcoming experiments at the CERN
Large Hadron Collider). This is an introduction to relativistic hydrodynamics
for graduate students. It includes a detailed derivation of the equations, and
a description of the hydrodynamical evolution of a heavy-ion collisions. Some
knowledge of thermodynamics and special relativity is assumed.Comment: Lectures given at the Advanced School on Quark-Gluon Plasma, Indian
Institute of Technology, Bombay, 3-13 July, 200
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
Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter
The bulk viscosity of the neutron star matter due to the direct Urca
processes involving nucleons, electrons and muons is studied taking into
account possible superfluidity of nucleons in the neutron star cores. The cases
of singlet-state pairing or triplet-state pairing (without and with nodes of
the superfluid gap at the Fermi surface) of nucleons are considered. It is
shown that the superfluidity may strongly reduce the bulk viscosity. The
practical expressions for the superfluid reduction factors are obtained. For
illustration, the bulk viscosity is calculated for two models of dense matter
composed of neutrons, protons,electrons and muons. The presence of muons
affects the bulk viscosity due to the direct Urca reactions involving electrons
and produces additional comparable contribution due to the direct Urca
reactions involving muons. The results can be useful for studying damping of
vibrations of neutron stars with superfluid cores.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy
and Astrophysic
The effects of antibiotic combination treatments on Pseudomonas aeruginosa tolerance evolution and coexistence with Stenotrophomonas maltophilia
Pseudomonas aeruginosa bacterium is a common pathogen of Cystic Fibrosis (CF) patients due to its ability to evolve resistance to antibiotics during treatments. While P. aeruginosa resistance evolution is well characterised in monocultures, it is less well understood in polymicrobial CF infections. Here, we investigated how exposure to ciprofloxacin, colistin, or tobramycin antibiotics, administered at sub-MIC doses alone and in combination, shaped the tolerance evolution of P. aeruginosa (PAO1 lab and clinical CF LESB58 strains) in the absence and presence of a commonly co-occurring species, Stenotrophomonas maltophilia. Increases in antibiotic tolerances were primarily driven by the presence of that antibiotic in the treatment. We observed a reciprocal cross-tolerance between ciprofloxacin and tobramycin, and when combined these antibiotics selected increased MICs for all antibiotics. Though the presence of S. maltophilia did not affect the tolerance or the MIC evolution, it drove P. aeruginosa into extinction more frequently in the presence of tobramycin due to its relatively greater innate tobramycin tolerance. In contrast, P. aeruginosa dominated and drove S. maltophilia extinct in most other treatments. Together, our findings suggest that besides driving high-level antibiotic tolerance evolution, sub-MIC antibiotic exposure can alter competitive bacterial interactions, leading to target pathogen extinctions in multi-species communities.Funding provided by: University of YorkCrossref Funder Registry ID: http://dx.doi.org/10.13039/100009001Award Number:See Methods in paper for collection. MIC values (MIC data.csv) derived from visual inspection of antibiotic growth measurements plotted as a growth curve.
Optical density data has been blank-corrected, and in the case of the antibiotic growth measurements (Antibiotic growth data.csv) averaged over ≤3 technical replicates
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
Non-equilibrium beta processes in superfluid neutron star cores
The influence of nucleons superfluidity on the beta relaxation time of
degenerate neutron star cores, composed of neutrons, protons and electrons, is
investigated. We numerically calculate the implied reduction factors for both
direct and modified Urca reactions, with isotropic pairing of protons or
anisotropic pairing of neutrons. We find that due to the non-zero value of the
temperature and/or to the vanishing of anisotropic gaps in some directions of
the phase-space, superfluidity does not always completely inhibit beta
relaxation, allowing for some reactions if the superfluid gap amplitude is not
too large in respect to both the typical thermal energy and the chemical
potential mismatch. We even observe that if the ratio between the critical
temperature and the actual temperature is very small, a suprathermal regime is
reached for which superfluidity is almost irrelevant. On the contrary, if the
gap is large enough, the composition of the nuclear matter can stay frozen for
very long durations, unless the departure from beta equilibrium is at least as
important as the gap amplitude. These results are crucial for precise
estimation of the superfluidity effect on the cooling/slowing-down of pulsars
and we provide online subroutines to be implemented in codes for simulating
such evolutions.Comment: 11 pages, 6 Figs., published, minor changes, subroutines can be found
on line at http://luth2.obspm.fr/~etu/villain/Micro/Resolution.htm
Net-proton probability distribution in heavy ion collisions
We compute net-proton probability distributions in heavy ion collisions
within the hadron resonance gas model. The model results are compared with data
taken by the STAR Collaboration in Au-Au collisions at sqrt(s_{NN})= 200 GeV
for different centralities. We show that in peripheral Au-Au collisions the
measured distributions, and the resulting first four moments of net-proton
fluctuations, are consistent with results obtained from the hadron resonance
gas model. However, data taken in central Au-Au collisions differ from the
predictions of the model. The observed deviations can not be attributed to
uncertainties in model parameters. We discuss possible interpretations of the
observed deviations.Comment: 4 pages, 2 figure
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