1,101 research outputs found
The development of the professional values and practice standard in the secondary graduate initial teacher training route in England
The paper reports on a pilot research project to investigate how trainee teachers develop an understanding of the competences that must be reached in the area of professional practice and values , which is one of the standards that needs to be met before the award of Qualified Teacher Status in England. Data were collected from secondary trainee teachers, their placement mentors in schools and university tutors. Data have been interpreted in the context of potential threats to the professionalism of teachers, through the introduction of managerialist influences in public funded education. The main findings are: that trainees think that the most dominant influence on developing understanding of professional values are their school placements ; there were little differences in the responses from four subject areas studied ; mentors and other lead teachers play an important role in the development of understanding of professional values; the grades awarded by mentors when assessing professional practice and values varies between the four subjects studied. The explanation for these findings is complex and is related to the understanding and interpretation of the standard by both mentors and trainee teachers. The findings highlight some of the difficulties in attempting to assess competency standards in an area that is underpinned by values and suggest that initial teacher training can best assist the development of the standard when it is approached in a critical way by all parties.</p
A fitting formula for the merger timescale of galaxies in hierarchical clustering
We study galaxy mergers using a high-resolution cosmological hydro/N-body
simulation with star formation, and compare the measured merger timescales with
theoretical predictions based on the Chandrasekhar formula. In contrast to
Navarro et al., our numerical results indicate, that the commonly used equation
for the merger timescale given by Lacey and Cole, systematically underestimates
the merger timescales for minor mergers and overestimates those for major
mergers. This behavior is partly explained by the poor performance of their
expression for the Coulomb logarithm, \ln (m_pri/m_sat). The two alternative
forms \ln (1+m_pri/m_sat) and 1/2\ln [1+(m_pri/m_sat)^2] for the Coulomb
logarithm can account for the mass dependence of merger timescale successfully,
but both of them underestimate the merger time scale by a factor 2. Since \ln
(1+m_pri/m_sat) represents the mass dependence slightly better we adopt this
expression for the Coulomb logarithm. Furthermore, we find that the dependence
of the merger timescale on the circularity parameter \epsilon is much weaker
than the widely adopted power-law \epsilon^{0.78}, whereas
0.94*{\epsilon}^{0.60}+0.60 provides a good match to the data. Based on these
findings, we present an accurate and convenient fitting formula for the merger
timescale of galaxies in cold dark matter models.Comment: 16 pages, 14 figures, accepted for publication in ApJ, minor changes
in the last few sentences of the discussio
A standardised assessment scheme for conventional EEG in preterm infants
Objective: To develop a standardised scheme for assessing normal and abnormal electroencephalography (EEG) features of preterm infants. To assess the interobserver agreement of this assessment scheme. Methods: We created a standardised EEG assessment scheme for 6 different post-menstrual age (PMA) groups using 4 EEG categories. Two experts, not involved in the development of the scheme, evaluated this on 24 infants <32 weeks gestational age (GA) using random 2 hour EEG epochs. Where disagreements were found, the features were checked and modified. Finally, the two experts independently evaluated 2 hour EEG epochs from an additional 12 infants <37 weeks GA. The percentage of agreement was calculated as the ratio of agreements to the sum of agreements plus disagreements. Results: Good agreement in all patients and EEG feature category was obtained, with a median agreement between 80% and 100% over the 4 EEG assessment categories. No difference was found in agreement rates between the normal and abnormal features (p = 0.959). Conclusions: We developed a standard EEG assessment scheme for preterm infants that shows good interobserver agreement. Significance: This will provide information to Neonatal Intensive Care Unit (NICU) staff about brain activity and maturation. We hope this will prove useful for many centres seeking to use neuromonitoring during critical care for preterm infants
Gravitational detection of a low-mass dark satellite at cosmological distance
The mass-function of dwarf satellite galaxies that are observed around Local
Group galaxies substantially differs from simulations based on cold dark
matter: the simulations predict many more dwarf galaxies than are seen. The
Local Group, however, may be anomalous in this regard. A massive dark satellite
in an early-type lens galaxy at z = 0.222 was recently found using a new method
based on gravitational lensing, suggesting that the mass fraction contained in
substructure could be higher than is predicted from simulations. The lack of
very low mass detections, however, prohibited any constraint on their mass
function. Here we report the presence of a 1.9 +/- 0.1 x 10^8 M_sun dark
satellite in the Einstein-ring system JVAS B1938+666 at z = 0.881, where M_sun
denotes solar mass. This satellite galaxy has a mass similar to the Sagittarius
galaxy, which is a satellite of the Milky Way. We determine the logarithmic
slope of the mass function for substructure beyond the local Universe to be
alpha = 1.1^+0.6_-0.4, with an average mass-fraction of f = 3.3^+3.6_-1.8 %, by
combining data on both of these recently discovered galaxies. Our results are
consistent with the predictions from cold dark matter simulations at the 95 per
cent confidence level, and therefore agree with the view that galaxies formed
hierarchically in a Universe composed of cold dark matter.Comment: 25 pages, 7 figures, accepted for publication in Nature (19 January
2012
Mergers and Mass Accretion Rates in Galaxy Assembly: The Millennium Simulation Compared to Observations of z~2 Galaxies
Recent observations of UV-/optically selected, massive star forming galaxies
at z~2 indicate that the baryonic mass assembly and star formation history is
dominated by continuous rapid accretion of gas and internal secular evolution,
rather than by major mergers. We use the Millennium Simulation to build new
halo merger trees, and extract halo merger fractions and mass accretion rates.
We find that even for halos not undergoing major mergers the mass accretion
rates are plausibly sufficient to account for the high star formation rates
observed in z~2 disks. On the other hand, the fraction of major mergers in the
Millennium Simulation is sufficient to account for the number counts of
submillimeter galaxies (SMGs), in support of observational evidence that these
are major mergers. When following the fate of these two populations in the
Millennium Simulation to z=0, we find that subsequent mergers are not frequent
enough to convert all z~2 turbulent disks into elliptical galaxies at z=0.
Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at
z~2 into observed massive cluster ellipticals at z=0. We argue therefore, that
secular and internal evolution must play an important role in the evolution of
a significant fraction of z~2 UV-/optically and submillimeter selected galaxy
populations.Comment: 5 pages, 4 figures, Accepted for publication in Ap
Red Galaxy Growth and the Halo Occupation Distribution
We have traced the past 7 Gyr of red galaxy stellar mass growth within dark
matter halos. We have determined the halo occupation distribution, which
describes how galaxies reside within dark matter halos, using the observed
luminosity function and clustering of 40,696 0.2<z<1.0 red galaxies in Bootes.
Half of 10^{11.9} Msun/h halos host a red central galaxy, and this fraction
increases with increasing halo mass. We do not observe any evolution of the
relationship between red galaxy stellar mass and host halo mass, although we
expect both galaxy stellar masses and halo masses to evolve over cosmic time.
We find that the stellar mass contained within the red population has doubled
since z=1, with the stellar mass within red satellite galaxies tripling over
this redshift range. In cluster mass halos most of the stellar mass resides
within satellite galaxies and the intra-cluster light, with a minority of the
stellar mass residing within central galaxies. The stellar masses of the most
luminous red central galaxies are proportional to halo mass to the power of a
third. We thus conclude that halo mergers do not always lead to rapid growth of
central galaxies. While very massive halos often double in mass over the past 7
Gyr, the stellar masses of their central galaxies typically grow by only 30%.Comment: Accepted for publication in the ApJ. 34 pages, 22 Figures, 5 Table
Cultural relativism and the discourse of intercultural communication: aporias of praxis in the intercultural public sphere
The premise of much intercultural communication pedagogy and research is to educate people from different cultures towards open and transformative positions of mutual understanding and respect. This discourse in the instance of its articulation realises and sustains Intercultural Communication epistemologically – as an academic field of social enquiry, and judgementally – as one which locates itself on a moral terrain. By adopting an ethical stance towards difference, the discourse of intercultural communication finds itself caught in a series of aporias, or performative contradictions, where interculturalists are projected simultaneously into positions of cultural relativism on the one hand and ideological totalism on the other. Such aporias arise because the theoretical premises upon which the discourse relies are problematic. We trace these thematics to a politics of presence operating within the discourse of intercultural communication and links this to questions of judgement and truth in the intercultural public sphere. We propose that the politics of presence be set aside in favour of an intercultural praxis which is oriented to responsibility rather than to truth
A 700 year-old Pulsar in the Supernova Remnant Kes 75
Since their discovery 30 years ago, pulsars have been understood to be
neutron stars (NSs) born rotating rapidly (~ 10-100 ms). These neutron stars
are thought to be created in supernova explosions involving massive stars,
which give rise to expanding supernova remnants (SNRs). With over 220 Galactic
SNRs known (Green 1998) and over 1200 radio pulsars detected (Camilo et al.
2000), it is quite surprising that few associations between the two populations
have been identified with any certainty. Here we report the discovery of a
remarkable 0.3 sec X-ray pulsar, PSR J1846-0258, associated with the supernova
remnant Kes 75. With a characteristic age of only 723 yr, consistent with the
age of Kes 75, PSR J1846-0258 is the youngest pulsar yet discovered and is
being rapidly spun down by torques from a large magnetic dipole of strength ~
5E13 G, just above the so-called quantum critical field. PSR J1846-0258 resides
in this transitional regime where the magnetic field is hypothesized to
separate the regular pulsars from the so-called magnetars. PSR J1846-0258 is
evidently a Crab-like pulsar, however, its period, spin-down rate, spin-down
conversion efficiency, are each an order-of-magnitude greater, likely the
result of its extreme magnetic field.Comment: 4 pages, 3 figures, LaTex, emulateapj.sty. Submitted to The
Astrophysical Journa
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