79 research outputs found
Reionisation scenarios and the temperature of the IGM
We examine the temperature structure of the IGM due to the passage of
individual ionisation fronts using a radiative transfer (RT) code coupled to a
particle-mesh (PM) N-body code. Multiple simulations were performed with
different spectra of ionising radiation: a power law (goes as nu^{-0.5}),
miniquasar, starburst, and a time-varying spectrum that evolves from a
starburst spectrum to a power law. The RT is sufficiently resolved in time and
space to correctly model both the ionisation state and the temperature across
the ionisation front. We find the post-ionisation temperature of the reionised
intergalactic medium (IGM) is sensitive to the spectrum of the source of
ionising radiation, which may be used to place strong constraints on the nature
of the sources of reionisation. Radiative transfer effects also produce large
fluctuations in the HeII to HI number density ratio eta. The spread in values
is smaller than measured, except for the time-varying spectrum. For this case,
the spread evolves as the spectral nature of the ionising background changes.
Large values for eta are found in partially ionised HeII as the power-law
spectrum begins to dominate the starburst, suggesting that the large eta values
measured may be indicating the onset of the HeII reionisation epoch.Comment: Accepted to MNRAS. Version with high resolution colour figures
available at http://www.roe.ac.uk/~ert/Publications/Tittley_Meiksin_07.pd
Surficial geologic materials of the Central City Quadrangle
https://ir.uiowa.edu/igs_ofm/1006/thumbnail.jp
A Lyman-alpha-only AGN from the Sloan Digital Sky Survey
The Sloan Digital Sky Survey has discovered a z=2.4917 radio-loud active
galactic nucleus (AGN) with a luminous, variable, low-polarization UV
continuum, H I two-photon emission, and a moderately broad Lyman-alpha line
(FWHM = 1430 km/s) but without obvious metal-line emission. SDSS
J113658.36+024220.1 does have associated metal-line absorption in three
distinct, narrow systems spanning a velocity range of 2710 km/s. Despite
certain spectral similarities, SDSS J1136+0242 is not a Lyman-break galaxy.
Instead, the Ly-alpha and two-photon emission can be attributed to an extended,
low-metallicity narrow-line region. The unpolarized continuum argues that we
see SDSS J1136+0242 very close to the axis of any ionization cone present. We
can conceive of two plausible explanations for why we see a strong UV continuum
but no broad-line emission in this `face-on radio galaxy' model for SDSS
J1136+0242: the continuum could be relativistically beamed synchrotron emission
which swamps the broad-line emission; or, more likely, SDSS J1136+0242 could be
similar to PG 1407+265, a quasar in which for some unknown reason the
high-ionization emission lines are very broad, very weak, and highly
blueshifted.Comment: AJ, in press, 10 pages emulateapj forma
The Physical Nature of Lyman Alpha Emitting Galaxies at z=3.1
We selected 40 candidate Lyman Alpha Emitting galaxies (LAEs) at z ~=3.1 with
observed frame equivalent widths >150A and inferred emission line fluxes
>2.5x10^-17 ergs/cm^2/s from deep narrow-band and broad-band MUSYC images of
the Extended Chandra Deep Field South. Covering 992 sq. arcmin, this is the
largest ``blank field'' surveyed for LAEs at z ~3, allowing an improved
estimate of the space density of this population of 3+-1x10^-4 h_70^3/Mpc^3.
Spectroscopic follow-up of 23 candidates yielded 18 redshifts, all at z ~=3.1.
Over 80% of the LAEs are dimmer in continuum magnitude than the typical Lyman
break galaxy spectroscopic limit of R= 25.5 (AB), with a median continuum
magnitude R ~=27 and very blue continuum colors, (V-z) ~=0. Over 80% of the
LAEs have the right UVR colors to be selected as Lyman break galaxies, but only
10% also have R<=25.5. Stacking the UBVRIzJK fluxes reveals that LAEs have
stellar masses ~=5x10^8 h_70^-2 M_sun and minimal dust extinction, A_V < ~ 0.1.
Inferred star formation rates are ~=6 h_70^-2 M_sun/yr, yielding a cosmic star
formation rate density of 2x10^-3 h_70 M_sun/yr/Mpc^3. None of our LAE
candidates show evidence for rest-frame emission line equivalent widths
EW_rest>240A which might imply a non-standard IMF. One candidate is detected by
Chandra, implying an AGN fraction of 2+-2% for LAE candidate samples. In
summary, LAEs at z ~ 3 have rapid star formation, low stellar mass, little dust
obscuration and no evidence for a substantial AGN component.Comment: ApJ Letters, in press, very minor revisions to match accepted
version, 4 pages with 2 color figure
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
Recommended from our members
Genome-wide dose-dependent inhibition of histone deacetylases studies reveal their roles in enhancer remodeling and suppression of oncogenic super-enhancers.
Histone deacetylase inhibitors (HDACIs) are known to alter gene expression by both up- and down-regulation of protein-coding genes in normal and cancer cells. However, the exact regulatory mechanisms of action remain uncharacterized. Here we investigated genome wide dose-dependent epigenetic and transcriptome changes in response to HDACI largazole in a transformed and a non-transformed cell line. Exposure to low nanomolar largazole concentrations
Risk factors for intensive care admission in children with severe acute asthma in the Netherlands:a prospective multicentre study
Rationale: Severe acute asthma (SAA) can be fatal, but is often preventable. We previously observed in a retrospective cohort study, a three-fold increase in SAA paediatric intensive care (PICU) admissions between 2003 and 2013 in the Netherlands, with a significant increase during those years of numbers of children without treatment of inhaled corticosteroids (ICS). Objectives: To determine whether steroid-naïve children are at higher risk of PICU admission among those hospitalised for SAA. Furthermore, we included the secondary risk factors tobacco smoke exposure, allergic sensitisation, previous admissions and viral infections. Methods: A prospective, nationwide multicentre study of children with SAA (2-18 years) admitted to all Dutch PICUs and four general wards between 2016 and 2018. Potential risk factors for PICU admission were assessed using logistic regression analyses. Measurements and main results: 110 PICU and 111 general ward patients were included. The proportion of steroid-naïve children did not differ significantly between PICU and ward patients. PICU children were significantly older and more exposed to tobacco smoke, with symptoms >1 week prior to admission. Viral susceptibility was not a significant risk factor for PICU admission. Conclusions: Children with SAA admitted to a PICU were comparable to those admitted to a general ward with respect to ICS treatment prior to admission. Preventable risk factors for PICU admission were >7 days of symptoms without adjustment of therapy and exposure to tobacco smoke. Physicians who treat children with asthma must be aware of these risk factors
Overcoming acculturation: physical education recruits' experiences of an alternative pedagogical approach to games teaching
© 2015 Association for Physical Education Background: Physical education teacher education (PETE) programmes have been identified as a critical platform to encourage the exploration of alternative teaching approaches by pre-service teachers. However, the socio-cultural constraint of acculturation or past physical education and sporting experiences results in the maintenance of the status quo of a teacher-driven, reproductive paradigm. Previous studies have reported successfully overcoming the powerful influence of acculturation, resulting in a change in PETE students' custodial teaching beliefs and receptiveness to alternative teaching approaches. However, to date, limited information has been reported about how PETE students' acculturation shaped their receptiveness to an alternative teaching approach. This is particularly the case for PETE recruits identified in the literature as most resistant to change. Purpose: To explore the features and experiences of an alternative games teaching approach that appealed to PETE recruits identified as most resistant to change, requiring a specific sample of PETE recruits with strong, custodial, traditional physical education teaching beliefs, and whom are high-achieving sporting products of this traditional culture. The alternative teaching approach explored in this study is the constraints-led approach (CLA), which is similar operationally to Teaching Games for Understanding, but distinguished by a neurobiological theoretical framework (nonlinear pedagogy) that informs learning design. Participants and setting: A purposive sample of 10 Australian PETE students was recruited for the study. All participants initially had strong, custodial, traditional physical education teaching beliefs, and were successful sporting products of this teaching approach. After experiencing the CLA as learners during a games unit, participants demonstrated receptiveness to the alternative pedagogy. Data collection and analysis: Semi-structured interviews and written reflections were sources of data collection. Each participant was interviewed separately, once prior to participation in the games unit to explore their positive physical education experiences, and then again after participation to explore the specific games unit learning experiences that influenced their receptiveness to the alternative pedagogy. Participants completed written reflections about their personal experiences after selected practical sessions. Data were qualitatively analysed using grounded theory. Findings: Thorough examination of the data resulted in establishment of two prominent themes related to the appeal of the CLA for the participants: (i) psychomotor (effective in developing skill) and (ii) inclusivity (included students of varying skill level). The efficacy of the CLA in skill development was clearly an important mediator of receptiveness for highly successful products of a traditional culture. This significant finding could be explained by three key factors: the acculturation of the participants, the motor learning theory underpinning the alternative pedagogy and the unit learning design and delivery. The inclusive nature of the CLA provided a solution to the problem of exclusion, which also made the approach attractive to participants. Conclusions: PETE educators could consider these findings when introducing an alternative pedagogy aimed at challenging PETE recruits' custodial, traditional teaching beliefs. To mediate receptiveness, it is important that the learning theory underpinning the alternative approach is operationalised in a research-informed pedagogical learning design that facilitates students' perceptions of the effectiveness of the approach through experiencing and or observing it working
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