2,246 research outputs found
Invariant manifolds and the geometry of front propagation in fluid flows
Recent theoretical and experimental work has demonstrated the existence of
one-sided, invariant barriers to the propagation of reaction-diffusion fronts
in quasi-two-dimensional periodically-driven fluid flows. These barriers were
called burning invariant manifolds (BIMs). We provide a detailed theoretical
analysis of BIMs, providing criteria for their existence, a classification of
their stability, a formalization of their barrier property, and mechanisms by
which the barriers can be circumvented. This analysis assumes the sharp front
limit and negligible feedback of the front on the fluid velocity. A
low-dimensional dynamical systems analysis provides the core of our results.Comment: 14 pages, 11 figures. To appear in Chaos Focus Issue:
Chemo-Hydrodynamic Patterns and Instabilities (2012
A search for previously unrecognised metal-poor subdwarfs in the Hipparcos astrometric catalogue
We have identified 317 stars included in the Hipparcos astrometric catalogue
which have parallaxes measured to a precision of better than 15%, and whose
location in the (M_V, (B-V)_T) diagram implies a metallicity comparable to or
less than that of the intermediate-abundance globular cluster, M5. We have
undertaken an extensive literature search to locate Stromgren, Johnson/Cousins
and Walraven photometry for over 120 stars. In addition, we present new UBVRI
photometry of 201 of these candidate halo stars, together with similar data for
a further 14 known metal-poor subdwarfs. Those observations provide the first
extensive dataset of RI photometry of metal-poor, main-sequence stars with
well-determined trigonometric parallaxes. Finally, we have obtained
intermediate-resolution optical spectroscopy of 175 stars. We are able to
estimate abundances for 270 stars. The overwhelming majority have near-solar
abundance, with their inclusion in the present sample stemming from errors in
the colours listed in the Hipparcos catalogue. Only 44 stars show consistent
evidence of abundances below [Fe/H]= -1.0. Nine are additions to the small
sample of metal-poor subdwarfs with accurate photometry. We consider briefly
the implication of these results for cluster main-sequence fitting.Comment: to appear in Monthly Notices of the Royal Astronomical Society (some
tables appear out of order in the text
Associations of dry skin, skin care habits, wellâbeing, sleep quality and itch in nursing home residents : results of a multicentre, observational, crossâsectional study
Aim: Dry skin is one of the most frequent cutaneous problems in aged long-term care residents. Although it is clinically relevant, the impact on quality of life is unclear. The objective was to measure well-being, sleep quality and itch in nursing home residents being 65 years and older and to explore possible associations with demographics, dry skin and skincare habits.
Design: Multicentre, observational, cross-sectional.
Methods: Sleep quality was assessed with the Richards-Campbell Sleep Quality Questionnaire, well-being with the WHO-Five Well-being Index and itch with the 5-D Itch scale. Skin dryness was measured using the Overall Dry Skin score.
Results: A total of 51 residents were included. The item scores of the sleep quality and itch questionnaires were strongly associated with each other. Demographics, dry skin and skincare habits were not associated with the questionnaires. It is unclear whether basic skincare activities can improve the quality of life in this population
Interplay Between Time-Temperature-Transformation and the Liquid-Liquid Phase Transition in Water
We study the TIP5P water model proposed by Mahoney and Jorgensen, which is
closer to real water than previously-proposed classical pairwise additive
potentials. We simulate the model in a wide range of deeply supercooled states
and find (i) the existence of a non-monotonic ``nose-shaped'' temperature of
maximum density line and a non-reentrant spinodal, (ii) the presence of a low
temperature phase transition, (iii) the free evolution of bulk water to ice,
and (iv) the time-temperature-transformation curves at different densities.Comment: RevTeX4, 4 pages, 4 eps figure
Does preliminary optimisation of an anatomically correct skull-brain model using simple simulants produce clinically realistic ballistic injury fracture patterns?
Ballistic head injury remains a significant threat to military personnel. Studying such injuries requires a model that can be used with a military helmet. This paper describes further work on a skull-brain model using skulls made from three different polyurethane plastics and a series of skull âfillsâ to simulate brain (3, 5, 7 and 10% gelatine by mass and PermaGelâą). The models were subjected to ballistic impact from 7.62 Ă 39 mm mild steel core bullets. The first part of the work compares the different polyurethanes (mean bullet muzzle velocity of 708 m/s), and the second part compares the different fills (mean bullet muzzle velocity of 680 m/s). The impact events were filmed using high speed cameras. The resulting fracture patterns in the skulls were reviewed and scored by five clinicians experienced in assessing penetrating head injury. In over half of the models, one or more assessors felt aspects of the fracture pattern were close to real injury. Limitations of the model include the skull being manufactured in two parts and the lack of a realistic skin layer. Further work is ongoing to address these
A major star formation region in the receding tip of the stellar Galactic bar
We present an analysis of the optical spectroscopy of 58 stars in the
Galactic plane at \arcdeg, where a prominent excess in the flux
distribution and star counts have been observed in several spectral regions, in
particular in the Two Micron Galactic Survey (TMGS) catalog. The sources were
selected from the TMGS, to have a magnitude brighter than +5 mag and be
within 2 degrees of the Galactic plane. More than 60% of the spectra correspond
to stars of luminosity class I, and a significant proportion of the remainder
are very late giants which would also be fast evolving. This very high
concentration of young sources points to the existence of a major star
formation region in the Galactic plane, located just inside the assumed origin
of the Scutum spiral arm. Such regions can form due to the concentrations of
shocked gas where a galactic bar meets a spiral arm, as is observed at the ends
of the bars of face-on external galaxies. Thus, the presence of a massive star
formation region is very strong supporting evidence for the presence of a bar
in our Galaxy.Comment: 13 pages (latex) + 4 figures (eps), accepted in ApJ Let
A major star formation region in the receding tip of the stellar Galactic bar. II. Supplementary information and evidence that the bar is not the same structure as the triaxial bulge previouly reported
This paper is the second part of Garzon et al. (1997: ApJ 491, L31) in which
we presented an outline of the analysis of 60 spectra from a follow-up program
to the Two Micron Galactic Survey (TMGS) project in the l=27 deg., b=0 deg.
area. In this second part, we present a more detailed explanation of the
analysis as well a library of the spectra for more complete information for
each of the 60 stars, and further discussions on the implications for the
structure of the Galaxy.
This region contains a prominent excess in the flux distribution and star
counts previously observed in several spectral ranges, notably in the TMGS.
More than 50% of the spectra of the stars detected with m_K<5.0 mag, within a
very high confidence level, correspond to stars of luminosity class I, and a
significant proportion of the remainder are very late giants which must also be
rapidly evolving. We make the case, using all the available evidence, that we
are observing a region at the nearer end of the Galactic bar, where the Scutum
spiral arm breaks away, and that this is powerful evidence for the presence of
the bar. Alternative explanations do not give nearly such a satisfactory
account of the observations.
The space localization of one and, a fortiori, of both ends of the bar allows
us to infer a position angle for the bar of around 75 deg. with respect to the
Sun-Galactic centre line. The angle is different from that given by other
authors for the bar and this, we think, is because they refer to the triaxial
bulge and not to the bar as detected here.Comment: 21 pages, 1 table, 9 figures, accepted in A
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