24,468 research outputs found
Blood ties: ABO is a trans-species polymorphism in primates
The ABO histo-blood group, the critical determinant of transfusion
incompatibility, was the first genetic polymorphism discovered in humans.
Remarkably, ABO antigens are also polymorphic in many other primates, with the
same two amino acid changes responsible for A and B specificity in all species
sequenced to date. Whether this recurrence of A and B antigens is the result of
an ancient polymorphism maintained across species or due to numerous, more
recent instances of convergent evolution has been debated for decades, with a
current consensus in support of convergent evolution. We show instead that
genetic variation data in humans and gibbons as well as in Old World Monkeys
are inconsistent with a model of convergent evolution and support the
hypothesis of an ancient, multi-allelic polymorphism of which some alleles are
shared by descent among species. These results demonstrate that the ABO
polymorphism is a trans-species polymorphism among distantly related species
and has remained under balancing selection for tens of millions of years, to
date, the only such example in Hominoids and Old World Monkeys outside of the
Major Histocompatibility Complex.Comment: 45 pages, 4 Figures, 4 Supplementary Figures, 5 Supplementary Table
A New Multi-Dimensional General Relativistic Neutrino Hydrodynamics Code for Core-Collapse Supernovae II. Relativistic Explosion Models of Core-Collapse Supernovae
We present the first two-dimensional general relativistic (GR) simulations of
stellar core collapse and explosion with the CoCoNuT hydrodynamics code in
combination with the VERTEX solver for energy-dependent, three-flavor neutrino
transport, using the extended conformal flatness condition for approximating
the spacetime metric and a ray-by-ray-plus ansatz to tackle the
multi-dimensionality of the transport. For both of the investigated 11.2 and 15
solar mass progenitors we obtain successful, though seemingly marginal,
neutrino-driven supernova explosions. This outcome and the time evolution of
the models basically agree with results previously obtained with the PROMETHEUS
hydro solver including an approximative treatment of relativistic effects by a
modified Newtonian potential. However, GR models exhibit subtle differences in
the neutrinospheric conditions compared to Newtonian and pseudo-Newtonian
simulations. These differences lead to significantly higher luminosities and
mean energies of the radiated electron neutrinos and antineutrinos and
therefore to larger energy-deposition rates and heating efficiencies in the
gain layer with favorable consequences for strong non-radial mass motions and
ultimately for an explosion. Moreover, energy transfer to the stellar medium
around the neutrinospheres through nucleon recoil in scattering reactions of
heavy-lepton neutrinos also enhances the mentioned effects. Together with
previous pseudo-Newtonian models the presented relativistic calculations
suggest that the treatment of gravity and energy-exchanging neutrino
interactions can make differences of even 50-100% in some quantities and is
likely to contribute to a finally successful explosion mechanism on no minor
level than hydrodynamical differences between different dimensions.Comment: 24 pages, 18 figures; improved figures, revised discussion about the
impact of neutrino rates, and other minor changes; accepted for publication
in Ap
Risk, commercialism and social purpose: Repositioning the English housing association sector
Originally seen as the ‘third arm’ of UK housing policy, the independent, not-for-profit housing association sector had long been seen as effective in ‘filling the gap’ where the state or market were unable to provide for households in need. Since the 1980s in particular, successive governments had viewed housing associations in favourable terms as efficient, semi-autonomous social businesses, capable of leveraging significant private funding. By 2015, in contrast, central government had come to perceive the sector as inefficient, bureaucratic and wasteful of public subsidy. Making use of institutional theory, this paper considers this paradigm shift and examines the organisational responses to an increasingly challenging operating environment. By focusing, in particular, on large London housing associations, the paper analyses their strategic decision-making to address the opportunities and threats presented. The paper argues that in facing an era of minimal subsidy, low security and high risk, the 2015 reforms represent a critical juncture for the sector. Housing organisations face a stark dilemma about whether to continue a strategy of ‘profit for purpose’ or to embrace an unambiguously commercial ethos. The article contends that the trajectory of decision-making (although not unidirectional) leads ultimately towards an increased exposure to risk and vulnerability to changes in the housing market. More fundamentally, the attempt to reconcile social and commercial logics is likely to have wider consequences for the legitimacy of the sector
The influence of reconstruction criteria on the sensitive probes of the symmetry potential
Different criteria of constructing clusters and tracing back
resonances from the intermediate-energy neutron-rich HICs are discussed by
employing the updated UrQMD transport model. It is found that both the
phase-space and the coordinate-density criteria affect the single and the
double neutron/proton ratios of free nucleons at small transverse momenta, but
the influence becomes invisible at large transverse momenta. The effect of
different methods of reconstructing freeze-out s on the
ratio is strong in a large kinetic energy region.Comment: 8 pages, 7 fig
The Circumgalactic Medium of Submillimeter Galaxies. II. Unobscured QSOs within Dusty Starbursts and QSO Sightlines with Impact Parameters below 100 Kiloparsec
We present Atacama Large Millimeter/submillimeter Array (ALMA) 870um
observations of 29 bright Herschel sources near high-redshift QSOs. The
observations confirm that 20 of the Herschel sources are submillimeter-bright
galaxies (SMGs) and identify 16 new SMG-QSO pairs that are useful to studies of
the circumgalactic medium (CGM) of SMGs. Eight out of the 20 SMGs are blends of
multiple 870um sources. The angular separations for six of the Herschel-QSO
pairs are less than 10", comparable to the sizes of the Herschel beam and the
ALMA primary beam. We find that four of these six "pairs" are actually QSOs
hosted by SMGs. No additional submillimeter companions are detected around
these QSOs and the rest-frame ultraviolet spectra of the QSOs show no evidence
of significant reddening. Black hole accretion and star formation contribute
almost equally in bolometric luminosity in these galaxies. The SMGs hosting
QSOs show similar source sizes, dust surface densities, and SFR surface
densities as other SMGs in the sample. We find that the black holes are growing
3 faster than the galaxies when compared to the present-day
black-hole-galaxy mass ratio, suggesting a QSO duty cycle of 30% in
SMGs at z ~ 3. The remaining two Herschel-detected QSOs are undetected at 870um
but each has an SMG "companion" only 9" and 12" away (71 and 95 kpc at z = 3).
They could be either merging or projected pairs. If the former, they would
represent a rare class of "wet-dry" mergers. If the latter, the QSOs would, for
the first time, probe the CGM of SMGs at impact parameters below 100 kpc.Comment: ApJ accepte
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