1,773 research outputs found
Enhanced X-ray variability from V1647 Ori, the young star in outburst illuminating McNeil's Nebula
We report a ~38 ks X-ray observation of McNeil's Nebula obtained with XMM on
2004 April 4. V1647 Ori, the young star in outburst illuminating McNeil's
Nebula, is detected with XMM and appears variable in X-rays. We investigate the
hardness ratio variability and time variations of the event energy distribution
with quantile analysis, and show that the large increase of the count rate from
V1647 Ori observed during the second half of the observation is not associated
with any large plasma temperature variations as for typical X-ray flares from
young low-mass stars. X-ray spectral fitting shows that the bulk (~75%) of the
intrinsic X-ray emission in the 0.5-8 keV energy band comes from a soft plasma
component (0.9 keV) reminiscent of the X-ray spectrum of the classical T Tauri
star TW Hya, for which X-ray emission is believed to be generated by an
accretion shock onto the photosphere of a low-mass star. The hard plasma
component (4.2 keV) contributes ~25% of the total X-ray emission, and can be
understood only in the framework of plasma heating sustained by magnetic
reconnection events. We find a hydrogen column density of NH=4.1E22 cm-2, which
points out a significant excess of hydrogen column density compared to the
value derived from optical/IR observations, consistent with the picture of the
rise of a wind/jet unveiled from ground optical spectroscopy. The X-ray flux
observed with XMM ranges from roughly the flux observed by Chandra on 2004
March 22 (~10 times greater than the pre-outburst X-ray flux) to a value two
times greater than that caught by Chandra on 2004 March 7 (~200 times greater
than the pre-outburst X-ray flux). We have investigated the possibility that
V1647 Ori displays a periodic variation in X-ray brightness as suggested by the
combined Chandra+XMM data set (abridged).Comment: 11 pages and 8 Figures. Accepted for publication by Astronomy &
Astrophysic
Furthering alternative cultures of valuation in higher education research
The value of higher education is often implicit or assumed in educational research. The underlying and antecedent premises that shape and influence debates about value remain unchallenged which perpetuates the dominant, but limiting, terms of the debate and fosters reductionism. I proceed on the premise that analyses of value are not self–supporting or self-referential but are embedded within prevailing cultures of valuation. I contend that challenging, and providing alternatives to, dominant narratives of higher education requires an appreciation of those cultures. I therefore highlight some of the existing cultures of valuation and their influence. I then propose Sayer’s concept of lay normativity as a culture of valuation and discuss how it translates into the practices of research into higher education, specifically the practice of analysis. I animate the discussion by detecting the presence of lay normativity in the evaluative space of the capability approach
Non-steroidal anti-inflammatory drug use does not appear to be associated with increased cardiovascular mortality in patients with inflammatory polyarthritis: results from a primary care based inception cohort of patients
Secondary literacy across the curriculum: Challenges and possibilities
This paper discusses the challenges and possibilities attendant upon successfully implementing literacy across the curriculum initiatives – or ‘school language policies’ as they have come to be known - particularly at the secondary or high school level. It provides a theoretical background to these issues, exploring previous academic discussions of school language policies, and highlights key areas of concern as well as opportunity with respect to school implementation of such policies. As such, it provides a necessary conceptual background to the subsequent papers in this special issue, which focus upon the Secondary Schools’ Literacy Initiative (SSLI) – a New Zealand funded programme that aims to establish cross-curricular language and literacy policies in secondary schools
Folk Classification and Factor Rotations:Whales, Sharks, and the Problems With the Hierarchical Taxonomy of Psychopathology (HiTOP)
The Hierarchical Taxonomy of Psychopathology (HiTOP) uses factor analysis to group self-reported symptoms of mental illness (i.e., like goes with like). It is hailed as a significant improvement over other diagnostic taxonomies. However, the purported advantages and fundamental assumptions of HiTOP have received little, if any, scientific scrutiny. We critically evaluated five fundamental claims about HiTOP. We conclude that HiTOP does not demonstrate a high degree of verisimilitude and has the potential to hinder progress on understanding the etiology of psychopathology. It does not lend itself to theory building or taxonomic evolution, and it cannot account for multifinality, equifinality, or developmental and etiological processes. In its current form, HiTOP is not ready to use in clinical settings and may result in algorithmic bias against underrepresented groups. We recommend a bifurcation strategy moving forward in which the Diagnostic and Statistical Manual of Mental Disorders is used in clinical settings while researchers focus on developing a falsifiable theory-based classification system
The Hierarchical Taxonomy of Psychopathology (HiTOP) Is Not an Improvement Over the DSM
DeYoung and colleagues did not sufficiently address three fundamental flaws with HiTOP. First, HiTOP was created using a simple structure factor analytic approach, which does not adequately represent the dimensional space of the symptoms of psychopathology. Consequently, HiTOP is not the empirical structure of psychopathology. Second, factor analysis and dimensional ratings do not fix the problems inherent to descriptive (folk) classification; self-reported symptoms are still the basis upon which clinical judgments about people are made. Finally, HiTOP is not ready to use in real-world clinical settings. There is currently no empirical evidence demonstrating that clinicians who use HiTOP have better clinical outcomes than those who use the DSM. In sum, HiTOP is a factor analytic variation of the DSM that does not get us closer to a more valid and useful taxonomy
Analysis of a microscopic stochastic model of microtubule dynamic instability
A novel theoretical model of dynamic instability of a system of linear (1D)
microtubules (MTs) in a bounded domain is introduced for studying the role of a
cell edge in vivo and analyzing the effect of competition for a limited amount
of tubulin. The model differs from earlier models in that the evolution of MTs
is based on the rates of single unit (e.g., a heterodimer per protofilament)
transformations, in contrast to postulating effective rates/frequencies of
larger-scale changes, extracted, e.g., from the length history plots of MTs.
Spontaneous GTP hydrolysis with finite rate after polymerization is assumed,
and theoretical estimates of an effective catastrophe frequency as well as
other parameters characterizing MT length distributions and cap size are
derived. We implement a simple cap model which does not include vectorial
hydrolysis. We demonstrate that our theoretical predictions, such as steady
state concentration of free tubulin, and parameters of MT length distributions,
are in agreement with the numerical simulations. The present model establishes
a quantitative link between microscopic parameters governing the dynamics of
MTs and macroscopic characteristics of MTs in a closed system. Lastly, we use a
computational Monte Carlo model to provide an explanation for non-exponential
MT length distributions observed in experiments. In particular, we show that
appearance of such non-exponential distributions in the experiments can occur
because the true steady state has not been reached, and/or due to the presence
of a cell edge.Comment: 14 pages, 7 figure
Turbulent protostellar discs
Aspects of turbulence in protostellar accretion discs are being reviewed. The
emergence of dead zones due to poor ionization and alternatives to the
magneto-rotational instability are discussed. The coupling between dust and gas
in protostellar accretion discs is explained and turbulent drag is compared
with laminar drag in the Stokes and Epstein regimes. Finally, the significance
of magnetic field generation in turbulent discs is emphasized in connection
with driving outflows and with star-disc coupling.Comment: 16 pages, 7 figures, proceedings of Nobel Symposium 135: Physics of
Planetary System
Ultrasound detection by clupeiform fishes
It has previously been shown that at least one species of fish ~the American shad! in the order clupeiforms ~herrings, shads, and relatives! is able to detect sounds up to 180 kHz. However, it has not been clear whether other members of this order are also able to detect ultrasound. It is now demonstrated, using auditory brainstem response ~ABR!, that at least one additional species, the gulf menhaden ~Brevoortia patronus!, is able to detect ultrasound, while several other species including the bay anchovy ~Anchoa mitchilli!, scaled sardine ~Harengula jaguana!, and Spanish sardine ~Sardinella aurita! only detect sounds to about 4 kHz. ABR is used to confirm ultrasonic hearing in the American shad. The results suggest that ultrasound detection may be limited to one subfamily of clupeiforms, the Alosinae. It is suggested that ultrasound detection involves the utricle of the inner ear and speculate as to why, despite having similar ear structures, only one group may detect ultrasound
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