8 research outputs found
Rapid in situ imaging and whole genome sequencing of biofilm in neonatal feeding tubes: a clinical proof of concept
The bacterial flora of nasogastric feeding tubes and faecal samples were analysed for a low-birth weight (725g) neonate EGA 25 weeks in intensive care. Samples were collected at age 6 and 8 weeks of life. Optical coherence tomography (OCT) was used to visualise bacterial biofilms inside the nasogastric feeding tubes. The biofilm was heterogeneously distributed along the tube lumen wall, and had a depth of up to 500µm. The bacterial biofilm and faecal samples included Enterococcus faecalis and Enterobacter hormaechei. Representative strains, recovered from both feeding tubes and faecal samples, were whole genome sequenced using Illumina, Mi-Seq, which revealed indistinguishable strains, each with less than 28 SNP differences, of E. faecalis and E. hormaechei. The E. faecalis strains were from two sequence types (ST191 and ST211) and encoded for a number of traits related to biofilm formation (BopD), adherence (Epb pili), virulence (cps loci, gelatinase, SprE) and antibiotic resistances (IsaA, tetM). The E. hormaechei were all ST106, and encoded for blaACT-15 β–lactamase and fosfomycin resistance (fosA). This proof of concept study demonstrates that bacterial flora within the neonatal feeding tubes may influence the bacterial colonisation of the intestinal tract and can be visualised nondestructively using OCT
Do All Stars in the Solar Neighbourhood Form in Clusters?
We present a global study of low mass, young stellar object (YSO) surface
densities (Sigma) in nearby (< 500 pc) star forming regions based on a
comprehensive collection of Spitzer Space Telescope surveys. We show that the
distribution of YSO surface densities is a smooth distribution, being
adequately described by a lognormal function from a few to 10^3 YSOs per pc^2,
with a peak at ~22 stars pc^-2. The observed lognormal Sigma is consistent with
predictions of hierarchically structured star-formation at scales below 10 pc,
arising from the molecular cloud structures. We do not find evidence for
multiple discrete modes of star-formation (e.g. clustered and distributed).
Comparing the observed Sigma distribution to previous Sigma threshold
definitions of clusters show that they are arbitrary. We find that only a low
fraction (< 26$) of stars are formed in dense environments where their
formation/evolution (along with their circumstellar disks and/or planets) may
be affected by the close proximity of their low-mass neighbours.Comment: 7 Pages, 2 Figures, JENAM conference (Lisbon
Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
We present a review of the interplay between the evolution of circumstellar
disks and the formation of planets, both from the perspective of theoretical
models and dedicated observations. Based on this, we identify and discuss
fundamental questions concerning the formation and evolution of circumstellar
disks and planets which can be addressed in the near future with optical and
infrared long-baseline interferometers. Furthermore, the importance of
complementary observations with long-baseline (sub)millimeter interferometers
and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics
Review"; The final publication is available at http://www.springerlink.co
Connecting Planetary Composition with Formation
The rapid advances in observations of the different populations of
exoplanets, the characterization of their host stars and the links to the
properties of their planetary systems, the detailed studies of protoplanetary
disks, and the experimental study of the interiors and composition of the
massive planets in our solar system provide a firm basis for the next big
question in planet formation theory. How do the elemental and chemical
compositions of planets connect with their formation? The answer to this
requires that the various pieces of planet formation theory be linked together
in an end-to-end picture that is capable of addressing these large data sets.
In this review, we discuss the critical elements of such a picture and how they
affect the chemical and elemental make up of forming planets. Important issues
here include the initial state of forming and evolving disks, chemical and dust
processes within them, the migration of planets and the importance of planet
traps, the nature of angular momentum transport processes involving turbulence
and/or MHD disk winds, planet formation theory, and advanced treatments of disk
astrochemistry. All of these issues affect, and are affected by the chemistry
of disks which is driven by X-ray ionization of the host stars. We discuss how
these processes lead to a coherent end-to-end model and how this may address
the basic question.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018). 46 pages, 10
figure
Formation of Terrestrial Planets
The past decade has seen major progress in our understanding of terrestrial planet formation. Yet key questions remain. In this review we first address the growth of 100 km-scale planetesimals as a consequence of dust coagulation and concentration, with current models favoring the streaming instability. Planetesimals grow into Mars-sized (or larger) planetary embryos by a combination of pebble- and planetesimal accretion. Models for the final assembly of the inner Solar System must match constraints related to the terrestrial planets and asteroids including their orbital and compositional distributions and inferred growth timescales. Two current models -- the Grand-Tack and low-mass (or empty) primordial asteroid belt scenarios -- can each match the empirical constraints but both have key uncertainties that require further study. We present formation models for close-in super-Earths -- the closest current analogs to our own terrestrial planets despite their very different formation histories -- and for terrestrial exoplanets in gas giant systems. We explain why super-Earth systems cannot form in-situ but rather may be the result of inward gas-driven migration followed by the disruption of compact resonant chains. The Solar System is unlikely to have harbored an early system of super-Earths; rather, Jupiter's early formation may have blocked the ice giants' inward migration. Finally, we present a chain of events that may explain why our Solar System looks different than more than 99\% of exoplanet systems