6,116 research outputs found
A Darboux theorem for generalized contact manifolds
We consider a manifold M equipped with 1-forms which satisfy certain contact like properties. We prove a generalization of the classical Darboux theorem for such manifolds
Chelating silica nanoparticles for efficient antibiotic delivery and particle imaging in Gram-negative bacteria
Candida albicans enhances meropenem tolerance of Pseudomonas aeruginosa in a dual-species biofilm
Background: Pseudomonas aeruginosa is an opportunistic bacterium that infects the airways of cystic fibrosis patients, surfaces of surgical and burn wounds, and indwelling medical devices. Patients are prone to secondary fungal infections, with Candida albicans being commonly co-isolated with P. aeruginosa. Both P. aeruginosa and C. albicans are able to form extensive biofilms on the surfaces ofmucosa and medical devices. Objectives: To determine whether the presence of C. albicans enhances antibiotic tolerance of P. aeruginosa in a dual-species biofilm.
Methods: Single- and dual-species biofilms were established in microtitre plates and the survival of each species was measured following treatment with clinically relevant antibiotics. Scanning electron microscopy and confocal microscopy were used to visualize biofilm structure.
Results: C. albicans enhances P. aeruginosa biofilm tolerance to meropenem at the clinically relevant concentration of 5 mg/L. This effect is specific to biofilm cultures and is dependent upon C. albicans extracellular matrix polysaccharides, mannan and glucan, with C. albicans cells deficient in glycosylation structures not enhancing P. aeruginosa tolerance tomeropenem.
Conclusions: We propose that fungal mannan and glucan secreted into the extracellular matrix of P. aeruginosa/C. albicans dual-species biofilms play a central role in enhancing P. aeruginosa tolerance to meropenem, which has direct implications for the treatment of coinfected patients
A multi-wavelength study of Supernova Remnants in six nearby galaxies. I: Detection of new X-ray selected Supernova Remnants with Chandra
We present results from a study of the Supernova Remnant (SNR) population in
a sample of six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4449, NGC
4395 and NGC 5204) based on Chandra archival data. We have detected 244
discrete X-ray sources down to a limiting flux of 10^{-15} erg/s. We identify
37 X-ray selected thermal SNRs based on their X-ray colors or spectra, 30 of
which are new discoveries. In many cases the X-ray classification is confirmed
based on counterparts with SNRs identified in other wavelengths. Three of the
galaxies in our sample (NGC 4214, NGC 4395 and NGC 5204) are studied for the
first time, resulting in the discovery of 13 thermal SNRs. We discuss the
properties (luminosity, temperature, density) of the X-ray detected SNRs in the
galaxies of our sample in order to address their dependence on their
environment. We find that X-ray selected SNRs in irregular galaxies appear to
be more luminous than those in spirals. We attribute this to the lower
metalicities and therefore more massive progenitor stars of irregular galaxies
or the higher local densities of the ISM. We also discuss the X-ray selected
SNR populations in the context of the Star Formation Rate of their host
galaxies. A comparison of the numbers of observed luminous X-ray selected SNRs
with those expected based on the luminosity functions of X-ray SNRs in the MCs
and M33 suggest different luminosity distributions between the SNRs in spiral
and irregular galaxies with the latter tending to have flatter distributions.Comment: 56 pages, 14 figures, 26 tables. Accepted for publication in Ap
Stress transmission in granular matter
The transmission of forces through a disordered granular system is studied by
means of a geometrical-topological approach that reduces the granular packing
into a set of layers. This layered structure constitutes the skeleton through
which the force chains set up. Given the granular packing, and the region where
the force is applied, such a skeleton is uniquely defined. Within this
framework, we write an equation for the transmission of the vertical forces
that can be solved recursively layer by layer. We find that a special class of
analytical solutions for this equation are L\'evi-stable distributions. We
discuss the link between criticality and fragility and we show how the
disordered packing naturally induces the formation of force-chains and arches.
We point out that critical regimes, with power law distributions, are
associated with the roughness of the topological layers. Whereas, fragility is
associated with local changes in the force network induced by local granular
rearrangements or by changes in the applied force. The results are compared
with recent experimental observations in particulate matter and with computer
simulations.Comment: 14 pages, Latex, 5 EPS figure
Orchestrator conversation : distributed management of cloud applications
Managing cloud applications is complex, and the current state of the art is not addressing this issue. The ever-growing software ecosystem continues to increase the knowledge required to manage cloud applications at a time when there is already an IT skills shortage. Solving this issue requires capturing IT operation knowledge in software so that this knowledge can be reused by system administrators who do not have it. The presented research tackles this issue by introducing a new and fundamentally different way to approach cloud application management: a hierarchical collection of independent software agents, collectively managing the cloud application. Each agent encapsulates knowledge of how to manage specific parts of the cloud application, is driven by sending and receiving cloud models, and collaborates with other agents by communicating using conversations. The entirety of communication and collaboration in this collection is called the orchestrator conversation. A thorough evaluation shows the orchestrator conversation makes it possible to encapsulate IT operations knowledge that current solutions cannot, reduces the complexity of managing a cloud application, and happens inherently concurrent. The evaluation also shows that the conversation figures out how to deploy a single big data cluster in less than 100 milliseconds, which scales linearly to less than 10 seconds for 100 clusters, resulting in a minimal overhead compared with the deployment time of at least 20 minutes with the state of the art
Vacuum fluctuation force on a rigid Casimir cavity in a gravitational field
We discuss the possibility of verifying the equivalence principle for the
zero-point energy of quantum electrodynamics, by evaluating the force, produced
by vacuum fluctuations, acting on a rigid Casimir cavity in a weak
gravitational field. The resulting force has opposite direction with respect to
the gravitational acceleration; the order of magnitude for a multi-layer cavity
configuration is derived and experimental feasibility is discussed, taking into
account current technological resources.Comment: 13 pages, Latex. In the revised version, the presentation has been
improve
Models of everywhere revisited: a technological perspective
The concept âmodels of everywhereâ was first introduced in the mid 2000s as a means of reasoning about the
environmental science of a place, changing the nature of the underlying modelling process, from one in which
general model structures are used to one in which modelling becomes a learning process about specific places, in
particular capturing the idiosyncrasies of that place. At one level, this is a straightforward concept, but at another
it is a rich multi-dimensional conceptual framework involving the following key dimensions: models of everywhere,
models of everything and models at all times, being constantly re-evaluated against the most current
evidence. This is a compelling approach with the potential to deal with epistemic uncertainties and nonlinearities.
However, the approach has, as yet, not been fully utilised or explored. This paper examines the
concept of models of everywhere in the light of recent advances in technology. The paper argues that, when first
proposed, technology was a limiting factor but now, with advances in areas such as Internet of Things, cloud
computing and data analytics, many of the barriers have been alleviated. Consequently, it is timely to look again
at the concept of models of everywhere in practical conditions as part of a trans-disciplinary effort to tackle the
remaining research questions. The paper concludes by identifying the key elements of a research agenda that
should underpin such experimentation and deployment
X-ray Bright Optically Inactive Galaxies (XBONG) in XMM-Newton/SDSS fields: more diluted than absorbed?
We explore the properties of X-ray Bright Optically Inactive Galaxies (XBONG)
detected in the 0.5-8 keV spectral band in 20 public XMM fields overlapping
with the SDSS. We constrain our sample to optically extended systems with log
(f_X/f_o > -2) that have spectroscopic identifications available from the SDSS
(r<19.2 mag). The resulting sample contains 12 objects with L_X (0.5-8keV)= 5 x
10^41 - 2x10^44 erg s-1 in the redshift range 0.06 < z < 0.45. The X-ray
emission in four cases is extended suggesting the presence of hot gas
associated with a cluster or group of galaxies. The X-ray spectral fits show
that two additional sources are best fit with a thermal component emission (kT
\~ 1 keV). Three sources aremost likely associated with AGN: their X-ray
spectrum is described by a steep photon index ~ 1.9 typical of unobscured AGN
while, they are very luminous in X-rays (L_X (0.5-8 keV) ~ 10^43 - 10^44 erg
s-1.) Finally, three more sources could be associated with either normal
galaxies or unobscured Low Luminosity AGN (L_X < 10^42 erg s-1). We find no
evidence for significant X-ray absorbing columns in any of our XBONGs. The
above suggest that XBONGs, selected in the total 0.5-8 keV band, comprise a
mixed bag of objects primarily including normal elliptical galaxies and type-1
AGN whose optical nuclear spectrum is probably diluted by the strong stellar
continuum. Nevertheless, as our sample is not statistically complete we cannot
exclude the possibility that a fraction of optically fainter XBONG may be
associated with heavily obscured AGN.Comment: 8 pages to appear in MNRA
A Darboux theorem for generalized contact manifolds
We consider a manifold M equipped with 1-forms which satisfy certain contact like properties. We prove a generalization of the classical Darboux theorem for such manifolds
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