875 research outputs found
Charged Particle Radiation Damage in Semiconductors, I- Experimental Proton Irradiation of Solar Cells
Proton irradiation of solar cell
Cross-comparison of MRCGP & MRCP(UK) in a database linkage study of 2,284 candidates taking both examinations: assessment of validity and differential performance by ethnicity.
MRCGP and MRCP(UK) are the main entry qualifications for UK doctors entering general [family] practice or hospital [internal] medicine. The performance of MRCP(UK) candidates who subsequently take MRCGP allows validation of each assessment. In the UK, underperformance of ethnic minority doctors taking MRCGP has had a high political profile, with a Judicial Review in the High Court in April 2014 for alleged racial discrimination. Although the legal challenge was dismissed, substantial performance differences between white and BME (Black and Minority Ethnic) doctors undoubtedly exist. Understanding ethnic differences can be helped by comparing the performance of doctors who take both MRCGP and MRCP(UK)
The Importance of Broad Emission-Line Widths in Single Epoch Black Hole Mass Estimates
Estimates of the mass of super-massive black holes (BHs) in distant active
galactic nuclei (AGNs) can be obtained efficiently only through single-epoch
spectra, using a combination of their broad emission-line widths and continuum
luminosities. Yet the reliability and accuracy of the method, and the resulting
mass estimates, M_BH, remain uncertain. A recent study by Croom using a sample
of SDSS, 2QZ and 2SLAQ quasars suggests that line widths contribute little
information about the BH mass in these single-epoch estimates and can be
replaced by a constant value without significant loss of accuracy. In this
Letter, we use a sample of nearby reverberation-mapped AGNs to show that this
conclusion is not universally applicable. We use the bulge luminosity (L_Bulge)
of these local objects to test how well the known M_BH - L_Bulge correlation is
recovered when using randomly assigned line widths instead of the measured ones
to estimate M_BH. We find that line widths provide significant information
about M_BH, and that for this sample, the line width information is just as
significant as that provided by the continuum luminosities. We discuss the
effects of observational biases upon the analysis of Croom and suggest that the
results can probably be explained as a bias of flux-limited, shallow quasar
samples.Comment: 10 text pages + 4 Figures + 1 Table. Accepted for publication in ApJ
Letter
Dilemmas and solutions- experiences of a national Family Medicine applied knowledge licensing test during a pandemic
ABSTRACT: Background: The unprecedented COVID-19 pandemic brought significant challenges to all of medicine, including primary care training and examinations. The MRCGP AKT is high-stakes licensing 200-item MCQ for UK trainee family physicians and is part of an assessment tripos that, up to the onset of the pandemic, included a Clinical Skills Assessment using Simulated Patients and workplace based assessment. The AKT is blueprinted onto a curriculum content specification and computer delivered three times a year at test centres across the UK. It tests the knowledge base underpinning independent general practice within the context of the UK National Health Service. We report on the challenges and dilemmas faced during the pandemic, decisions taken, and lessons learned. Rapid exam changes needed to be made, and communicated effectively to candidates, whilst maintaining standards and fairness to candidates.
Summary of Work: Challenges included lockdown travel restrictions, reduced capacity, social distancing and shielding candidates being unable to leave home. The April 2020 AKT was cancelled and prioritisation measures implemented to ensure candidates at the end of their training could enter the (stressed) workforce. We engaged with a wide range of stakeholders, carefully looked at remote testing, made contingency plans prioritised for those unable to sit exams and changed exam regulations to ensure fairness to candidates. In this emergency, we delivered a previously published exam which some candidates were unaware they had sat previously, and assessed how these candidates performed. We compared cohort performance before and during the pandemic.
Summary of Results: We summarise why we did not remote test, how we obtained key worker status, and adapted contingency plans. Analysis of candidates who had previously sat the same exam showed they performed less well. Despite wide-ranging changes in training and workplace experience, there was no significant difference in cohort performance overall pre-and peri-pandemic.
Discussion and Conclusions: COVID-19 constraints changed trainees clinical exposure, restricted training and supervisor support. However, exam preparedness did not appear adversely affected when measured by overall pass rates. Unexpectedly, candidates who sat an identical exam did not benefit from previous exposure. Take-home Messages: Involving stakeholders in key decisions and regular communications are essential. Test security and standards were not compromised
Reverberation Mapping Results from MDM Observatory
We present results from a multi-month reverberation mapping campaign
undertaken primarily at MDM Observatory with supporting observations from
around the world. We measure broad line region (BLR) radii and black hole
masses for six objects. A velocity-resolved analysis of the H_beta response
shows the presence of diverse kinematic signatures in the BLR.Comment: To appear in the Proceedings of the IAU Symposium No. 267:
Co-Evolution of Central Black Holes and Galaxies, Rio de Janeiro, 200
Photometric AGN reverberation mapping - an efficient tool for BLR sizes, black hole masses and host-subtracted AGN luminosities
Photometric reverberation mapping employs a wide bandpass to measure the AGN
continuum variations and a suitable band, usually a narrow band (NB), to trace
the echo of an emission line in the broad line region (BLR). The narrow band
catches both the emission line and the underlying continuum, and one needs to
extract the pure emission line light curve. We performed a test on two local
AGNs, PG0003+199 (=Mrk335) and Ark120, observing well-sampled broad- (B, V) and
narrow-band light curves with the robotic 15cm telescope VYSOS-6 on Cerro
Armazones, Chile. In PG0003+199, H_alpha dominates the flux in the NB by 85%,
allowing us to measure the time lag of H_alpha against B without the need to
correct for the continuum contribution. In Ark120, H_beta contributes only 50%
to the flux in the NB. The cross correlation of the B and NB light curves shows
two distinct peaks of similar strength, one at lag zero from the autocorrelated
continuum and one from the emission line at tau_cent = 47.5 +/- 3.4 days. We
constructed a synthetic H_beta light curve, by subtracting a scaled V light
curve, which traces the continuum, from the NB light curve. The cross
correlation of this synthetic H_beta light curve with the B light curve shows
only one major peak at tau_cent = 48.0 +/- 3.3 days, while the peak from the
autocorrelated continuum at lag zero is absent. We conclude that, as long as
the emission line contributes at least 50% to the bandpass, the pure emission
line light curve can be reconstructed from photometric monitoring data so that
the time lag can be measured. For both objects the lags we find are consistent
with spectroscopic reverberation results. While the dense sampling (median 2
days) enables us to determine tau_cent with small (10%) formal errors, we
caution that gaps in the light curves may lead to much larger systematic
uncertainties. (Abstract shortened, see the manuscript.)Comment: 12 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
The Size of the Narrow-Line Emitting Region in the Seyfert 1 Galaxy NGC 5548 from Emission-Line Variability
The narrow [O III] 4959, 5007 emission-line fluxes in the spectrum of the
well-studied Seyfert 1 galaxy NGC 5548 are shown to vary with time. From this
we show that the narrow line-emitting region has a radius of only 1-3 pc and is
denser (n ~ 10^5 cm^{-3}) than previously supposed. The [O III] line width is
consistent with virial motions at this radius given previous determinations of
the black hole mass.Since the [O III] emission-line flux is usually assumed to
be constant and is therefore used to calibrate spectroscopic monitoring data,
the variability has ramifications for the long-term secular variations of
continuum and emission-line fluxes, though it has no effect on shorter-term
reverberation studies. We present corrected optical continuum and broad Hbeta
emission-line light curves for the period 1988 to 2008.Comment: 11 pages, 5 figures, 6 tables. Accepted for publication in Ap
Chemical abundances of damped Lyman alpha systems in the XQ-100 survey
The XQ-100 survey has provided high signal-noise spectra of 100 redshift
3-4.5 quasars with the X-Shooter spectrograph. The metal abundances for 13
elements in the 41 damped Lyman alpha systems (DLAs) identified in the XQ-100
sample are presented, and an investigation into abundances of a variety of DLA
classes is conducted. The XQ-100 DLA sample contains five DLAs within 5000 km/s
of their host quasar (proximate DLAs; PDLAs) as well as three sightlines which
contain two DLAs within 10,000 km/s of each other along the same line-of-sight
(multiple DLAs; MDLAs). Combined with previous observations in the literature,
we demonstrate that PDLAs with logN(HI)<21.0 show lower [S/H] and [Fe/H]
(relative to intervening systems with similar redshift and N(HI)), whilst
higher [S/H] and [Si/H] are seen in PDLAs with logN(HI)>21.0. These abundance
discrepancies are independent of their line-of-sight velocity separation from
the host quasar, and the velocity width of the metal lines (v90). Contrary to
previous studies, MDLAs show no difference in [alpha/Fe] relative to single
DLAs matched in metallicity and redshift. In addition, we present follow-up
UVES data of J0034+1639, a sightline containing three DLAs, including a
metal-poor DLA with [Fe/H]=-2.82 (the third lowest [Fe/H] in DLAs identified to
date) at z=4.25. Lastly we study the dust-corrected [Zn/Fe], emphasizing that
near-IR coverage of X-Shooter provides unprecedented access to MgII, CaII and
TiII lines (at redshifts 3-4) to provide additional evidence for subsolar
[Zn/Fe] ratio in DLAs.Comment: Accepted to MNRAS. 19 pages plus Appendix material (102 pages total
The Mass of the Black Hole in the Quasar PG 2130+099
We present the results of a recent reverberation-mapping campaign undertaken
to improve measurements of the radius of the broad line region and the central
black hole mass of the quasar PG 2130+099. Cross correlation of the 5100
angstrom continuum and H-beta emission-line light curves yields a time lag of
22.9 (+4.4 - 4.3) days, corresponding to a central black hole mass MBH= 3.8
(+/- 1.5) x 10^7 Msun. This value supports the notion that previous
measurements yielded an incorrect lag. We re-analyzed previous datasets to
investigate the possible sources of the discrepancy and conclude that previous
measurement errors were apparently caused by a combination of undersampling of
the light curves and long-term secular changes in the H-beta emission-line
equivalent width. With our new measurements, PG 2130+099 is no longer an
outlier in either the R-L or the MBH-Sigma relationships.Comment: 21 pages, 7 figures; Accepted for publication in Ap
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