654 research outputs found
Pseudofinite structures and simplicity
We explore a notion of pseudofinite dimension, introduced by Hrushovski and
Wagner, on an infinite ultraproduct of finite structures. Certain conditions on
pseudofinite dimension are identified that guarantee simplicity or
supersimplicity of the underlying theory, and that a drop in pseudofinite
dimension is equivalent to forking. Under a suitable assumption, a
measure-theoretic condition is shown to be equivalent to local stability. Many
examples are explored, including vector spaces over finite fields viewed as
2-sorted finite structures, and homocyclic groups. Connections are made to
products of sets in finite groups, in particular to word maps, and a
generalization of Tao's algebraic regularity lemma is noted
Invariant measures concentrated on countable structures
Let L be a countable language. We say that a countable infinite L-structure M
admits an invariant measure when there is a probability measure on the space of
L-structures with the same underlying set as M that is invariant under
permutations of that set, and that assigns measure one to the isomorphism class
of M. We show that M admits an invariant measure if and only if it has trivial
definable closure, i.e., the pointwise stabilizer in Aut(M) of an arbitrary
finite tuple of M fixes no additional points. When M is a Fraisse limit in a
relational language, this amounts to requiring that the age of M have strong
amalgamation. Our results give rise to new instances of structures that admit
invariant measures and structures that do not.Comment: 46 pages, 2 figures. Small changes following referee suggestion
Commentary on Gibson et al. (2017): Gestational age and the severity of neonatal abstinence syndrome
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Intestinal Dysbiosis and the Developing Lung: The Role of Toll-Like Receptor 4 in the Gut-Lung Axis.
BackgroundIn extremely premature infants, postnatal growth restriction (PNGR) is common and increases the risk of developing bronchopulmonary dysplasia (BPD) and pulmonary hypertension (PH). Mechanisms by which poor nutrition impacts lung development are unknown, but alterations in the gut microbiota appear to play a role. In a rodent model, PNGR plus hyperoxia causes BPD and PH and increases intestinal Enterobacteriaceae, Gram-negative organisms that stimulate Toll-like receptor 4 (TLR4). We hypothesized that intestinal dysbiosis activates intestinal TLR4 triggering systemic inflammation which impacts lung development.MethodsRat pups were assigned to litters of 17 (PNGR) or 10 (normal growth) at birth and exposed to room air or 75% oxygen for 14 days. Half of the pups were treated with the TLR4 inhibitor TAK-242 from birth or beginning at day 3. After 14 days, pulmonary arterial pressure was evaluated by echocardiography and hearts were examined for right ventricular hypertrophy (RVH). Lungs and serum samples were analyzed by western blotting and immunohistochemistry.ResultsPostnatal growth restriction + hyperoxia increased pulmonary arterial pressure and RVH with trends toward increased plasma IL1β and decreased IκBα, the inhibitor of NFκB, in lung tissue. Treatment with the TLR4 inhibitor attenuated PH and inflammation.ConclusionPostnatal growth restriction induces an increase in intestinal Enterobacteriaceae leading to PH. Activation of the TLR4 pathway is a promising mechanism by which intestinal dysbiosis impacts the developing lung
A comprehensive X-ray and multiwavelength study of the Colliding Galaxy Pair NGC2207/IC2163
We present a comprehensive study of the total X-ray emission from the
colliding galaxy pair NGC2207/IC2163, based on Chandra, Spitzer, and GALEX
data. We detect 28 ultra-luminous X-ray sources (ULXs), 7 of which were not
detected previously due to X-ray variability. Twelve sources show significant
long-term variability, with no correlated spectral changes. Seven sources are
transient candidates. One ULX coincides with an extremely blue star cluster
(B-V = -0.7). We confirm that the global relation between the number and
luminosity of ULXs and the integrated star formation rate (SFR) of the host
galaxy also holds on local scales. We investigate the effects of dust
extinction and/or age on the X-ray binary (XRB) population on sub-galactic
scales. The distributions of Nx and Lx are peaked at L(IR)/L(NUV)~1, which may
be associated with an age of ~10 Myr for the underlying stellar population. We
find that ~1/3 of the XRBs are located in close proximity to young star
complexes. The luminosity function of the X-ray binaries is consistent with
that typical for high-mass X-ray binaries, and appears unaffected by
variability. We disentangle and compare the X-ray diffuse spectrum with that of
the bright XRBs. The hot interstellar medium dominates the diffuse X-ray
emission at E<1 keV, has a temperature kT=0.28 (+0.05/-0.04) keV and intrinsic
0.5-2 keV luminosity of 7.9e+40 erg/s, a factor of ~2.3 higher than the average
thermal luminosity produced per unit SFR in local star-forming galaxies. The
total X-ray output of NGC2207/IC2163 is 1.5e+41 erg/s, and the corresponding
total integrated SFR is 23.7 Msol/yr.Comment: 24 pages, 11 figures, 11 tables. Accepted for publication in The
Astrophysical Journa
Luminous X-Ray Sources in Arp 147
The Chandra X-Ray Observatory was used to image the collisional ring galaxy
Arp 147 for 42 ks. We detect 9 X-ray sources with luminosities in the range of
1.4 - 7 x 10^{39} ergs/sec in or near the blue knots of star formation
associated with the ring. A source with an isotropic X-ray luminosity of 1.4 x
10^{40} ergs/sec is detected in the nuclear region of the intruder galaxy.
X-ray sources associated with a foreground star and a background quasar are
used to improve the registration of the X-ray image with respect to HST high
resolution optical images. The intruder galaxy, which apparently contained
little gas before the collision, shows no X-ray sources other than the one in
the nuclear bulge which may be a poorly fed supermassive black hole. These
observations confirm the conventional wisdom that collisions of gas rich
galaxies trigger large rates of star formation which, in turn, generate
substantial numbers of X-ray sources, some of which have luminosities above the
Eddington limit for accreting stellar-massComment: 9 pages, 5 figure
The Effect of New Zealand Kanuka, Manuka and Clover Honeys on Bacterial Growth Dynamics and Cellular Morphology Varies According to the Species
Treatment of chronic wounds is becoming increasingly difficult due to antibiotic resistance. Complex natural products with antimicrobial activity, such as honey, are now under the spotlight as alternative treatments to antibiotics. Several studies have shown honey to have broad-spectrum antibacterial activity at concentrations present in honey dressings, and resistance to honey has not been attainable in the laboratory. However not all honeys are the same and few studies have used honey that is well defined both in geographic and chemical terms. Here we have used a range of concentrations of clover honey and a suite of manuka and kanuka honeys from known geographical locations, and for which the floral source and concentration of methylglyoxal and hydrogen peroxide potential were defined, to determine their effect on growth and cellular morphology of four bacteria: Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. While the general trend in effectiveness of growth inhibition was manuka>manuka-kanuka blend>kanuka>clover, the honeys had varying and diverse effects on the growth and cellular morphology of each bacterium, and each organism had a unique response profile to these honeys. P. aeruginosa showed a markedly different pattern of growth inhibition to the other three organisms when treated with sub-inhibitory concentrations of honey, being equally sensitive to all honeys, including clover, and the least sensitive to honey overall. While hydrogen peroxide potential contributed to the antibacterial activity of the manuka and kanuka honeys, it was never essential for complete growth inhibition. Cell morphology analysis also showed a varied and diverse set of responses to the honeys that included cell length changes, cell lysis, and alterations to DNA appearance. These changes are likely to reflect the different regulatory circuits of the organisms that are activated by the stress of honey treatment. © 2013 Lu et al
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