1,525 research outputs found
Multi-wavelength Radio Continuum Emission Studies of Dust-free Red Giants
Multi-wavelength centimeter continuum observations of non-dusty,
non-pulsating K spectral-type red giants directly sample their chromospheres
and wind acceleration zones. Such stars are feeble emitters at these
wavelengths however, and previous observations have provided only a small
number of modest S/N measurements slowly accumulated over three decades. We
present multi-wavelength Karl G. Jansky Very Large Array thermal continuum
observations of the wind acceleration zones of two dust-free red giants,
Arcturus (Alpha Boo: K2 III) and Aldebaran (Alpha Tau: K5 III). Importantly,
most of our observations of each star were carried out over just a few days, so
that we obtained a snapshot of the different stellar atmospheric layers sampled
at different wavelengths, independent of any long-term variability. We report
the first detections at several wavelengths for each star including a detection
at 10 cm (3.0 GHz: S band) for both stars and a 20 cm (1.5 GHz: L band)
detection for Alpha Boo. This is the first time single luminosity class III red
giants have been detected at these continuum wavelengths. Our long-wavelength
data sample the outer layers of Alpha Boo's atmosphere where its wind velocity
is approaching its terminal value and the ionization balance is becoming
frozen-in. For Alpha Tau, however, our long-wavelength data are still sampling
its inner atmosphere, where the wind is still accelerating probably due to its
lower mass-loss rate. We compare our data with published semi-empirical models
based on ultraviolet data, and the marked deviations highlight the need for new
atmospheric models to be developed. Spectral indices are used to discuss the
possible properties of the stellar atmospheres, and we find evidence for a
rapidly cooling wind in the case of Alpha Boo. Finally, we develop a simple
analytical wind model for Alpha Boo based on our new long-wavelength flux
measurements
Temporal Evolution of the Size and Temperature of Betelgeuse's Extended Atmosphere
We use the Very Large Array (VLA) in the A configuration with the Pie Town
(PT) Very Long Baseline Array (VLBA) antenna to spatially resolve the extended
atmosphere of Betelgeuse over multiple epochs at 0.7, 1.3, 2.0, 3.5, and 6.1
cm. The extended atmosphere deviates from circular symmetry at all wavelengths
while at some epochs we find possible evidence for small pockets of gas
significantly cooler than the mean global temperature. We find no evidence for
the recently reported e-MERLIN radio hotspots in any of our multi-epoch VLA/PT
data, despite having sufficient spatial resolution and sensitivity at short
wavelengths, and conclude that these radio hotspots are most likely
interferometric artefacts. The mean gas temperature of the extended atmosphere
has a typical value of 3000 K at 2 and decreases to 1800 K at 6
, in broad agreement with the findings of the single epoch study
from Lim et al. (1998). The overall temperature profile of the extended
atmosphere between can be
described by a power law of the form ,
with temporal variability of a few 100 K evident at some epochs. Finally, we
present over 12 years of V band photometry, part of which overlaps our
multi-epoch radio data. We find a correlation between the fractional flux
density variability at V band with most radio wavelengths. This correlation is
likely due to shock waves induced by stellar pulsations, which heat the inner
atmosphere and ionize the more extended atmosphere through radiative means.
Stellar pulsations may play an important role in exciting Betelgeuse's extended
atmosphere
Dynamics at the angle of repose: jamming, bistability, and collapse
When a sandpile relaxes under vibration, it is known that its measured angle
of repose is bistable in a range of values bounded by a material-dependent
maximal angle of stability; thus, at the same angle of repose, a sandpile can
be stationary or avalanching, depending on its history. In the nearly jammed
slow dynamical regime, sandpile collapse to a zero angle of repose can also
occur, as a rare event. We claim here that fluctuations of {\it dilatancy} (or
local density) are the key ingredient that can explain such varied phenomena.
In this work, we model the dynamics of the angle of repose and of the density
fluctuations, in the presence of external noise, by means of coupled stochastic
equations. Among other things, we are able to describe sandpile collapse in
terms of an activated process, where an effective temperature (related to the
density as well as to the external vibration intensity) competes against the
configurational barriers created by the density fluctuations.Comment: 15 pages, 1 figure. Minor changes and update
Cooperativity in sandpiles: statistics of bridge geometries
Bridges form dynamically in granular media as a result of spatiotemporal
inhomogeneities. We classify bridges as linear and complex, and analyse their
geometrical characteristics. In particular, we find that the length
distribution of linear bridges is exponential. We then turn to the analysis of
the orientational distribution of linear bridges and find that, in three
dimensions, they are {\it vertically diffusive but horizontally
superdiffusive}; thus, when they exist, long linear bridges form `domes'. Our
results are in good accord with Monte Carlo simulations of bridge structure; we
make predictions for quantities that are experimentally accessible, and suggest
that bridges are very closely related to force chains.Comment: 15 pages, 10 figures. Minor changes and update
Clinical signs predictive of severe illness in young Pakistani infants
Objective: Early detection of specific signs and symptoms to predict severe illness is essential to prevent infant mortality. As a continuation of the results from the multicenter Young Infants Clinical Signs and Symptoms (YICSS) study, we present here the performance of the seven-sign algorithm in 3 age categories (0-6 days, 7-27 days and 28-59 days) in Pakistani infants aged 0-59 days.Results: From September 2003 to November 2004, 2950 infants were enrolled (age group 0-6 days = 1633, 7-27 days = 817, 28-59 days = 500). The common reason for seeking care was umbilical redness or discharge (29.2%) in the 0-6 days group. Older age groups presented with cough (16.9%) in the 7-27 age group and (26.9%) infants in the 28-59 days group. Severe infection/sepsis was the most common primary diagnoses in infants requiring hospitalization across all age groups. The algorithm performed well in every age group, with a sensitivity of 85.9% and specificity of 71.6% in the 0-6 days age group and a sensitivity of 80.5% and specificity of 80.2% in the 28-59 days group; the sensitivity was slightly lower in the 7-27 age group (72.4%) but the specificity remained high (83.1%)
A double blind community-based randomized trial of Amoxicillin Versus Placebo for fast breathing Pneumonia in children aged 2-59 months in Karachi, Pakistan (RETAPP)
Background: Fast breathing pneumonia is characterized by tachypnoea in the absence of danger signs and is mostly viral in etiology. Current guidelines recommend antibiotic therapy for all children with fast breathing pneumonia in resource limited settings, presuming that most pneumonia is bacterial. High quality clinical trial evidence to challenge or support the continued use of antibiotics, as recommended by the World Health Organization is lacking.
Methods/Design: This is a randomized double blinded placebo-controlled non-inferiority trial using parallel assignment with 1:1 allocation ratio, to be conducted in low income squatter settlements of urban Karachi, Pakistan. Children 2-59 months old with fast breathing, without any WHO-defined danger signs and seeking care at the primary health care center are randomized to receive either three days of placebo or amoxicillin. From prior studies, a sample size of 2430 children is required over a period of 28 months. Primary outcome is the difference in cumulative treatment failure between the two groups, defined as a new clinical sign based on preset definitions indicating illness progression or mortality and confirmed by two independent primary health care physicians on day 0, 1, 2 or 3 of therapy. Secondary outcomes include relapse measured between days 5-14. Modified per protocol analysis comparing hazards of treatment failure with 95 % confidence intervals in the placebo arm with hazards in the amoxicillin arm will be done.
Discussion:This study will provide evidence to support or refute the use of antibiotics for fast breathing pneumonia paving a way for guideline change
Competition and cooperation:aspects of dynamics in sandpiles
In this article, we review some of our approaches to granular dynamics, now
well known to consist of both fast and slow relaxational processes. In the
first case, grains typically compete with each other, while in the second, they
cooperate. A typical result of {\it cooperation} is the formation of stable
bridges, signatures of spatiotemporal inhomogeneities; we review their
geometrical characteristics and compare theoretical results with those of
independent simulations. {\it Cooperative} excitations due to local density
fluctuations are also responsible for relaxation at the angle of repose; the
{\it competition} between these fluctuations and external driving forces, can,
on the other hand, result in a (rare) collapse of the sandpile to the
horizontal. Both these features are present in a theory reviewed here. An arena
where the effects of cooperation versus competition are felt most keenly is
granular compaction; we review here a random graph model, where three-spin
interactions are used to model compaction under tapping. The compaction curve
shows distinct regions where 'fast' and 'slow' dynamics apply, separated by
what we have called the {\it single-particle relaxation threshold}. In the
final section of this paper, we explore the effect of shape -- jagged vs.
regular -- on the compaction of packings near their jamming limit. One of our
major results is an entropic landscape that, while microscopically rough,
manifests {\it Edwards' flatness} at a macroscopic level. Another major result
is that of surface intermittency under low-intensity shaking.Comment: 36 pages, 23 figures, minor correction
Recognition and blocking of innate immunity cells by Candida albicans chitin
Peer reviewedPublisher PD
The miR-17-5p microRNA is a key regulator of the G1/S phase cell cycle transition
Novel targets of the oncogenic miR-17-92 cluster have been identified and the mechanism of regulation of proliferation at the G1/S phase cell cycle transition via the miR-17-5p microRNA has been elucidated
Advanced EFL learners' beliefs about language learning and teaching: a comparison between grammar, pronunciation, and vocabulary
This paper reports on the results of a study exploring learners’ beliefs on the learning and teaching of English grammar, pronunciation and vocabulary at tertiary level. While the importance of learners’ beliefs on the acquisition process is generally recognized, few studies have focussed on and compared learners’ views on different components of the language system. A questionnaire containing semantic scale and Likert scale items probing learners’ views on grammar, pronunciation and vocabulary was designed and completed by 117 native speakers of Dutch in Flanders, who were studying English at university. The analysis of the responses revealed that (i) vocabulary was considered to be different from grammar and pronunciation, both in the extent to which an incorrect use could lead to communication breakdown and with respect to the learners’ language learning strategies, (ii) learners believed in the feasibility of achieving a native-like proficiency in all three components, and (iii) in-class grammar, pronunciation and vocabulary exercises were considered to be useful, even at tertiary level. The results are discussed in light of pedagogical approaches to language teaching
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