6,191 research outputs found
How robust is the evidence of an emerging or increasing female excess in physical morbidity between childhood and adolescence? Results of a systematic literature review and meta-analyses
For asthma and psychological morbidity, it is well established that higher prevalence among males in childhood is replaced by higher prevalence among females by adolescence. This review investigates whether there is evidence for a similar emerging female ‘excess’ in relation to a broad range of physical morbidity measures. Establishing whether this pattern is generalised or health outcome-specific will further understandings of the aetiology of gender differences in health. Databases (Medline; Embase; CINAHL; PsycINFO; ERIC) were searched for English language studies (published 1992–2010) presenting physical morbidity prevalence data for males and females, for at least two age-bands within the age-range 4–17 years. A three-stage screening process (initial sifting; detailed inspection; extraction of full papers), was followed by study quality appraisals. Of 11 245 identified studies, 41 met the inclusion criteria. Most (n = 31) presented self-report survey data (five longitudinal, 26 cross-sectional); 10 presented routinely collected data (GP/hospital statistics). Extracted data, supplemented by additional data obtained from authors of the included studies, were used to calculate odds ratios of a female excess, or female:male incident rate ratios as appropriate. To test whether these changed with age, the values were logged and regressed on age in random effects meta-regressions. These showed strongest evidence of an emerging/increasing female excess for self-reported measures of headache, abdominal pain, tiredness, migraine and self-assessed health. Type 1 diabetes and epilepsy, based on routinely collected data, did not show a significant emerging/increasing female excess. For most physical morbidity measures reviewed, the evidence broadly points towards an emerging/increasing female excess during the transition to adolescence, although results varied by morbidity measure and study design, and suggest that this may occur at a younger age than previously thought
Analysis of milling of dry compacted ribbons by distinct element method
Fine cohesive powders are often dry granulated to improve their flowability. Roller compaction is commonly used to produce dense ribbons which are then milled. The material properties of the powder and the conditions in the roller compactor affect the strength of the ribbons, however there is no method in the literature to predict the size distribution of the product of ribbon milling. Here we introduce a method, by using the Distinct Element Method (DEM) to determine the prevailing impact velocities and stresses in the mill, with bonded spheres representing the ribbons. The bond strength is calibrated by matching experimental results of three point bend measurements and predictions from numerical simulations. The ribbons are then exposed to the dynamic conditions predicted by the DEM, by dropping them from a controlled height to cause fragmentation, and subsequently stressing them in a shear cell under the conditions again predicted by the DEM. The fragments are sheared under these conditions to represent repeated passage of bars over the fragments at the mill base. Sieve analysis is used here to determine the particle size distribution under given mill conditions. The predicted size distribution of the mill product compares well with the plant data. It is found that the mill speed and length of ribbons fed to the mill have no significant influence on the product size distribution for the range tested
Late-Type Red Supergiants: Too Cool for the Magellanic Clouds?
We have identified seven red supergiants (RSGs) in the Large Magellanic Cloud
(LMC) and four RSGs in the Small Magellanic Cloud (SMC), all of which have
spectral types that are considerably later than the average type observed in
their parent galaxy. Using moderate-resolution optical spectrophotometry and
the MARCS stellar atmosphere models, we determine their physical properties and
place them on the H-R diagram for comparison with the predictions of current
stellar evolutionary tracks. The radial velocities of these stars suggest that
they are likely all members of the Clouds rather than foreground dwarfs or halo
giants. Their locations in the H-R diagram also show us that those stars are
cooler than the current evolutionary tracks allow, appearing to the right of
the Hayashi limit, a region in which stars are no longer in hydrodynamic
equilibrium. These stars exhibit considerable variability in their V
magnitudes, and three of these stars also show changes in their effective
temperatures (and spectral types) on the time-scales of months. One of these
stars, [M2002] SMC 055188, was caught in an M4.5 I state, as late as that seen
in HV 11423 at its recent extreme: considerable later, and cooler, than any
other supergiant in the SMC. In addition, we find evidence of variable
extinction due to circumstellar dust and changes in the stars' luminosities,
also consistent with our recent findings for HV 11423 - when these stars are
hotter they are also dustier and more luminous. We suggest that these stars
have unusual properties because they are in an unstable (and short-lived)
evolutionary phase.Comment: 26 pages, 6 figures; submitted to the Astrophysical Journa
Low-Frequency Radio Transients in the Galactic Center
We report the detection of a new radio transient source, GCRT J1746-2757,
located only 1.1 degrees north of the Galactic center. Consistent with other
radio transients toward the Galactic center, this source brightened and faded
on a time scale of a few months. No X-ray counterpart was detected. We also
report new 0.33 GHz measurements of the radio counterpart to the X-ray
transient source, XTE J1748-288, previously detected and monitored at higher
radio frequencies. We show that the spectrum of XTE J1748-288 steepened
considerably during a period of a few months after its peak. We also discuss
the need for a more efficient means of finding additional radio transients
Dark-Energy Dynamics Required to Solve the Cosmic Coincidence
Dynamic dark energy (DDE) models are often designed to solve the cosmic
coincidence (why, just now, is the dark energy density , the same
order of magnitude as the matter density ?) by guaranteeing for significant fractions of the age of the universe. This
typically entails ad-hoc tracking or oscillatory behaviour in the model.
However, such behaviour is neither sufficient nor necessary to solve the
coincidence problem. What must be shown is that a significant fraction of
observers see . Precisely when, and for how long, must a
DDE model have in order to solve the coincidence? We
explore the coincidence problem in dynamic dark energy models using the
temporal distribution of terrestrial-planet-bound observers. We find that any
dark energy model fitting current observational constraints on and
the equation of state parameters and , does have for a large fraction of observers in the universe. This demotivates DDE
models specifically designed to solve the coincidence using long or repeated
periods of .Comment: 16 pages, 8 figures, Submitted to Phys. Rev.
On the nature of the hard X-ray source IGR J2018+4043
We found a very likely counterpart to the recently discovered hard X-ray
source IGR J2018+4043 in the multi-wavelength observations of the source field.
The source, originally discovered in the 20-40 keV band, is now confidently
detected also in the 40-80 keV band, with a flux of (1.4 +/- 0.4) x 10(-11) erg
cm(-2) s(-1). A 5 ks Swift observation of the IGR J2018+4043 field revealed a
hard point-like source with the observed 0.5-10 keV flux of 3.4(+0.7)(-0.8) x
10(-12) erg cm(-2) s(-1) (90% confidence level) at alpha = 20h18m38.55s, delta
= +40d41m00.4s (with a 4.2" uncertainty). The combined Swift-INTEGRAL spectrum
can be described by an absorbed power-law model with photon index gamma = 1.3
+/- 0.2 and N_H = 6.1(+3.2)(-2.2) x 10(22) cm(-2). In archival optical and
infrared data we found a slightly extended and highly absorbed object at the
Swift source position. There is also an extended VLA 1.4 GHz source peaked at a
beam-width distance from the optical and X-ray positions. The observed
morphology and multiwavelength spectra of IGR J2018+4043 are consistent with
those expected for an obscured accreting object, i.e. an AGN or a Galactic
X-ray binary. The identification suggests possible connection of IGR J2018+4043
to the bright gamma-ray source GEV J2020+4023 (3EG J2020+4017) detected by COS
B and CGRO EGRET in the gamma-Cygni SNR field.Comment: 5 pages, 3 figures, uses emulateapj styl
Stochastic series expansion method for quantum Ising models with arbitrary interactions
A quantum Monte Carlo algorithm for the transverse Ising model with arbitrary
short- or long-range interactions is presented. The algorithm is based on
sampling the diagonal matrix elements of the power series expansion of the
density matrix (stochastic series expansion), and avoids the interaction
summations necessary in conventional methods. In the case of long-range
interactions, the scaling of the computation time with the system size N is
therefore reduced from N^2 to Nln(N). The method is tested on a one-dimensional
ferromagnet in a transverse field, with interactions decaying as 1/r^2.Comment: 9 pages, 5 figure
Cognitive Computation sans Representation
The Computational Theory of Mind (CTM) holds that cognitive processes are essentially computational, and hence computation provides the scientific key to explaining mentality. The Representational Theory of Mind (RTM) holds that representational content is the key feature in distinguishing mental from non-mental systems. I argue that there is a deep incompatibility between these two theoretical frameworks, and that the acceptance of CTM provides strong grounds for rejecting RTM. The focal point of the incompatibility is the fact that representational content is extrinsic to formal procedures as such, and the intended interpretation of syntax makes no difference to the execution of an algorithm. So the unique 'content' postulated by RTM is superfluous to the formal procedures of CTM. And once these procedures are implemented in a physical mechanism, it is exclusively the causal properties of the physical mechanism that are responsible for all aspects of the system's behaviour. So once again, postulated content is rendered superfluous. To the extent that semantic content may appear to play a role in behaviour, it must be syntactically encoded within the system, and just as in a standard computational artefact, so too with the human mind/brain - it's pure syntax all the way down to the level of physical implementation. Hence 'content' is at most a convenient meta-level gloss, projected from the outside by human theorists, which itself can play no role in cognitive processing
Thinking strategically about assessment
Drawing upon the literature on strategy formulation in organisations, this paper argues for a focus on strategy as process. It relates this to the need to think strategically about assessment, a need engendered by resource pressures, developments in learning and the demands of external stakeholders. It is argued that in practice assessment strategies are often formed at the level of practice, but that this produces contradiction and confusion at higher levels. Such tensions cannot be managed away, but they can be reflected on and mitigated. The paper suggests a framework for the construction of assessment strategies at different levels of an institution. However, the main conclusion is that the process of constructing such strategies should be an opportunity for learning and reflection, rather than one of compliance
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