596 research outputs found
Detection of a period decrease in NN Ser with ULTRACAM: evidence for strong magnetic braking or an unseen companion?
We present results of high time resolution photometry of the eclipsing
pre-cataclysmic variable NN Ser. We observed 13 primary eclipses of NN Ser
using the high-speed CCD camera ULTRACAM and derived times of mid-eclipse, from
fitting of light curve models, with uncertainties as low as 0.06 s. The
observed rates of period change appear difficult to reconcile with any models
of orbital period change. If the observed period change reflects an angular
momentum loss, the average loss rate is consistent with the loss rates (via
magnetic stellar wind braking) used in standard models of close binary
evolution, which were derived from observations of much more massive cool
stars. Observations of low-mass stars such as NN Ser's secondary predict rates
of ~100 times lower than we observe. We show that magnetic activity-driven
changes in the quadrupole moment of the secondary star (Applegate, 1992) fail
to explain the period change by an order of magnitude on energetic grounds, but
that a light travel time effect caused by the presence of a third body in a
long (~ decades) orbit around the binary could account for the observed changes
in the timings of NN Ser's mid-eclipses. We conclude that we have either
observed a genuine angular momentum loss for NN Ser, in which case our
observations pose serious difficulties for the theory of close binary
evolution, or we have detected a previously unseen low-mass companion to the
binary.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
Barriers and facilitators to HIV and syphilis rapid diagnostic testing in antenatal care settings in low-income and middle-income countries: A systematic review
Background Testing and treatment during pregnancy is a well-established and cost-effective prevention strategy, which relies largely on use of rapid diagnostic tests (RDTs). Yet, in many low-income and-middle-income countries, the uptake of RDTs is suboptimal. A qualitative meta-synthesis was conducted to identify the barriers and enablers to use of HIV and syphilis RDTs among pregnant women in low-income and middle-income countries. Methods This review was conducted using PRISMA guidelines. Eligible studies included peer-reviewed publications, which used qualitative methods to explore HIV and syphilis RDT in antenatal care clinics in low-income and middle-income countries. Studies focusing on perspectives of pregnant women, healthcare workers and/or stakeholders were included. We used an inductive approach informed by a modified socioecological model to synthesise the data. Results 62 manuscripts met the eligibility criteria. For pregnant women, initial acceptance of the RDT and continuation in antenatal care depends on the perception that engaging in testing will be a beneficial experience for their baby and themselves, often influenced by the provision of services that are gender-sensitive, confidential, respectful, flexible and considers their well-being into the future. Local sociocultural beliefs about pregnancy and diseases, awareness of diseases and gender roles in society also influenced RDT acceptability among pregnant women. For healthcare workers, the ability to provide high-quality RDT care required ongoing training, accurate and easy to use tests, support from supervisors and communities, sufficient resources and staffing to provide services, and reliable salary. At the stakeholder level, well-developed guidelines and health system infrastructures were imperative to the delivery of RDT in antenatal clinics. Conclusion Our findings highlight clear gaps to the provision of sustainable and culturally acceptable maternal HIV and/or syphilis screening using RDTs. In addition, greater attention needs to be paid to community stakeholders in promoting the uptake of RDT in antenatal clinics. PROSPERO registration number CRD42018112190
The effect of starspots on eclipse timings of binary stars
We investigate the effects that starspots have on the light curves of
eclipsing binaries and in particular how they may affect the accurate
measurement of eclipse timings. Concentrating on systems containing a low-mass
main-sequence star and a white dwarf, we find that if starspots exhibit the
Wilson depression they can alter the times of primary eclipse ingress and
egress by several seconds for typical binary parameters and starspot
depressions. In addition, we find that the effect on the eclipse ingress/egress
times becomes more profound for lower orbital inclinations. We show how it is
possible, in principle, to determine estimates of both the binary inclination
and depth of the Wilson depression from light curve analysis
The effect of depressed starspots on the O-C diagrams of eclipsing systems is
also investigated. It is found that the presence of starspots will introduce a
`jitter' in the O-C residuals and can cause spurious orbital period changes to
be observed. Despite this, we show that the period can still be accurately
determined even for heavily spotted systems.Comment: 7 pages, 9 figures, accepted for publication in MNRA
Peaks above the Harrison-Zel'dovich spectrum due to the Quark-Gluon to Hadron Transition
The quark-gluon to hadron transition affects the evolution of cosmological
perturbations. If the phase transition is first order, the sound speed vanishes
during the transition, and density perturbations fall freely. This distorts the
primordial Harrison-Zel'dovich spectrum of density fluctuations below the
Hubble scale at the transition. Peaks are produced, which grow at most linearly
in wavenumber, both for the hadron-photon-lepton fluid and for cold dark
matter. For cold dark matter which is kinetically decoupled well before the QCD
transition clumps of masses below are produced.Comment: Extended version, including evolution of density perturbations for a
bag model and for a lattice QCD fit (3 new figures). Spectrum for bag model
(old figure) is available in astro-ph/9611186. 9 pages RevTeX, uses epsf.sty,
3 PS figure
Detection of Enhancement in Number Densities of Background Galaxies due to Magnification by Massive Galaxy Clusters
We present a detection of the enhancement in the number densities of
background galaxies induced from lensing magnification and use it to test the
Sunyaev-Zel'dovich effect (SZE) inferred masses in a sample of 19 galaxy
clusters with median redshift selected from the South Pole
Telescope SPT-SZ survey. Two background galaxy populations are selected for
this study through their photometric colours; they have median redshifts
(low- background) and
(high- background). Stacking these
populations, we detect the magnification bias effect at and
for the low- and high- backgrounds, respectively. We fit NFW
models simultaneously to all observed magnification bias profiles to estimate
the multiplicative factor that describes the ratio of the weak lensing
mass to the mass inferred from the SZE observable-mass relation. We further
quantify systematic uncertainties in resulting from the photometric
noise and bias, the cluster galaxy contamination and the estimations of the
background properties. The resulting for the combined background
populations with uncertainties is
, indicating good consistency
between the lensing and the SZE-inferred masses. We use our best-fit to
predict the weak lensing shear profiles and compare these predictions with
observations, showing agreement between the magnification and shear mass
constraints. This work demonstrates the promise of using the magnification as a
complementary method to estimate cluster masses in large surveys.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered
Isocyanoazulenes (CNAz) constitute a relatively new class of isocyanoarenes that offers rich structural and electronic diversification of the organic isocyanide ligand platform. This article considers a series of 2-isocyano-1,3-X2-azulene ligands (X = H, Me, CO2Et, Br, and CN) and the corresponding zero-valent complexes thereof, [(OC)5Cr(2-isocyano-1,3-X2-azulene)]. Air- and thermally stable, X-ray structurally characterized 2-isocyano-1,3-dimethylazulene may be viewed as a non-benzenoid aromatic congener of 2,6-dimethyphenyl isocyanide (2,6-xylyl isocyanide), a longtime “workhorse” aryl isocyanide ligand in coordination chemistry. Single crystal X-ray crystallographic {Cr–CNAz bond distances}, cyclic voltametric {E1/2(Cr0/1+)}, 13C NMR {δ(13CN), δ(13CO)}, UV-vis {dπ(Cr) → pπ*(CNAz) Metal-to-Ligand Charge Transfer}, and FTIR {νN≡C, νC≡O, kC≡O} analyses of the [(OC)5Cr(2-isocyano-1,3-X2-azulene)] complexes provided a multifaceted, quantitative assessment of the π-acceptor/σ-donor characteristics of the above five 2-isocyanoazulenes. In particular, the following inverse linear relationships were documented: δ(13COtrans) vs. δ(13CN), δ(13COcis) vs. δ(13CN), and δ(13COtrans) vs. kC≡O,trans force constant. Remarkably, the net electron withdrawing capability of the 2-isocyano-1,3-dicyanoazulene ligand rivals those of perfluorinated isocyanides CNC6F5 and CNC2F3
Can a Large Neutron Excess Help Solve the Baryon Loading Problem in Gamma-Ray Burst Fireballs?
We point out that the baryon-loading problem in Gamma-Ray Burst (GRB) models
can be amelioriated if a significant fraction of the baryons which inertially
confine the fireball are converted to neutrons. A high neutron fraction in some
circumstances can result in a reduced transfer of energy from relativistic
light particles in the fireball to baryons. The energy needed to produce the
required relativistic flow in the GRB is consequently reduced, in some cases by
orders of magnitude. This could be relevant to GRB models because a high
neutron-to-proton ratio has been calculated in neutron star-merger fireball
environments. Significant neutron excess also could occur near compact objects
with high neutrino fluxes.Comment: 5 pages, 2 figures, to appear in Phys. Rev. Let
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
The planets around NN Serpentis : still there
We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the William Herschel Telescope and New Technology Telescope, the RISE camera on the Liverpool Telescope and HAWK-I on the Very Large Telescope to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25 yr. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36 s that has set in since 2010 compared to the previous 8 yr of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9 ± 0.5 and 15.3 ± 0.3 yr, and masses of 2.3 ± 0.5 and 7.3 ± 0.3 MJ. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07 s relative to the best-fitting model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems
School librarians as literacy educators within a complex role
Librarians in schools are expected to play an important role as literacy educators, and have a positive impact on young people’s literacy learning. However in the context of their diverse workload, relatively little is known about how this aspect of their role sits within its competing demands, and the exact scope of the literacy educator requirements. Using a hybrid approach to content analysis, this article analyses 40 recent job description documents to identify the nature and prevalence of different aspects of the role, and to explore the literacy educator aspect of this profession. Findings suggest that while the literacy educator aspect is one of the most common role requirements, it sits within a complex workload, and the literacy educator aspect is itself multi-faceted and demanding
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