2,504 research outputs found
Reassessment of the evidence for postcranial skeletal pneumaticity in Triassic archosaurs, and the early evolution of the avian respiratory system.
Uniquely among extant vertebrates, birds possess complex respiratory systems characterised by the combination of small, rigid lungs, extensive pulmonary air sacs that possess diverticula that invade (pneumatise) the postcranial skeleton, unidirectional ventilation of the lungs, and efficient crosscurrent gas exchange. Crocodilians, the only other living archosaurs, also possess unidirectional lung ventilation, but lack true air sacs and postcranial skeletal pneumaticity (PSP). PSP can be used to infer the presence of avian-like pulmonary air sacs in several extinct archosaur clades (non-avian theropod dinosaurs, sauropod dinosaurs and pterosaurs). However, the evolution of respiratory systems in other archosaurs, especially in the lineage leading to crocodilians, is poorly documented. Here, we use µCT-scanning to investigate the vertebral anatomy of Triassic archosaur taxa, from both the avian and crocodilian lineages as well as non-archosaurian diapsid outgroups. Our results confirm previous suggestions that unambiguous evidence of PSP (presence of internal pneumatic cavities linked to the exterior by foramina) is found only in bird-line (ornithodiran) archosaurs. We propose that pulmonary air sacs were present in the common ancestor of Ornithodira and may have been subsequently lost or reduced in some members of the clade (notably in ornithischian dinosaurs). The development of these avian-like respiratory features might have been linked to inferred increases in activity levels among ornithodirans. By contrast, no crocodile-line archosaur (pseudosuchian) exhibits evidence for unambiguous PSP, but many of these taxa possess the complex array of vertebral laminae and fossae that always accompany the presence of air sacs in ornithodirans. These laminae and fossae are likely homologous with those in ornithodirans, which suggests the need for further investigation of the hypothesis that a reduced, or non-invasive, system of pulmonary air sacs may be have been present in these taxa (and secondarily lost in extant crocodilians) and was potentially primitive for Archosauria as a whole
New information on the palate and lower jaw of Massospondylus (Dinosauria: Sauropodomorpha)
Additional anatomical details of the palate and lower jaw of the prosauropod dinosaur Massospondylus Owen are documented on the
basis of a previously undescribed skull from the upper Elliot Formation. The palate is generally similar to that of other early
sauropodomorphs, but can be shown to differ from those of Plateosaurus, Lufengosaurus and Thecodontosaurus in several respects. For
example, Massospondylus lacks the well-developed palatine boss seen in Plateosaurus and the pneumatic recess that is present on the
ectopterygoid of Thecodontosaurus. In addition, Massospondylus possesses an expanded medioventral premaxillary process that is much
larger than that of any other basal sauropodomorph.The Royal Society of London and the
Palaeontological Research Fund of the Natural History Museu
A revision of the non-avian dinosaurs ‘Eucercosaurus tanyspondylus’ and ‘Syngonosaurus macrocercus’ from the Cambridge Greensand, UK
The Cambridge Greensand Member (lower Cenomanian: Upper Cretaceous) has yielded a diverse fauna of terrestrial and marine tetrapods, whose remains are largely reworked from the underlying Gault Formation (upper Albian: Lower Cretaceous). Here, we re-describe two of the non-avian dinosaur taxa named from this unit, ‘Eucercosaurus tanyspondylus’ Seeley, 1879 and ‘Syngonosaurus macrocercus’ Seeley, 1879, both of which have been referred to as either ankylosaurs or ornithopods but whose validity has not been rigorously assessed for over a century. Both taxa are interpreted as the remains of iguanodontian dinosaurs but possess no clear diagnostic features. Nevertheless, although ‘Eucercosaurus’ and ‘Syngonosaurus’ are nomina dubia they do indicate that iguanodontians were common components of the Cambridge Greensand tetrapod fauna and, alongside ‘Trachodon cantabrigiensis’ Lydekker, 1888, represent an important datum for understanding iguanodontian distributions during the mid-Cretaceous
V3885 Sagittarius: a Comparison with a Range of Standard Model Accretion Disks
A analysis of standard model accretion disk synthetic
spectrum fits to combined and STIS spectra of V3885 Sagittarius, on an
absolute flux basis, selects a model that accurately represents the observed
SED. Calculation of the synthetic spectrum requires the following system
parameters. The cataclysmic variable secondary star period-mass relation
calibrated by Knigge in 2007 sets the secondary component mass. A mean white
dwarf (WD) mass from the same study, that is consistent with an
observationally-determined mass ratio, sets the adopted WD mass of
, and the WD radius follows from standard theoretical models. The
adopted inclination, i=65{\arcdeg}, is a literature consensus, and is
subsequently supported by analysis. The mass transfer rate
is the remaining parameter to set the accretion disk profile, and
the parallax constrains that parameter to
by a comparison
with observed spectra. The fit to the observed spectra adopts the contribution
of a K WD. The model thus provides realistic constraints on
and for a large system above the period gap.Comment: 41 pages, 7 figures, 9 tables. Astrophysical Journal (accepted
Numerical approximation of statistical solutions of scalar conservation laws
We propose efficient numerical algorithms for approximating statistical
solutions of scalar conservation laws. The proposed algorithms combine finite
volume spatio-temporal approximations with Monte Carlo and multi-level Monte
Carlo discretizations of the probability space. Both sets of methods are proved
to converge to the entropy statistical solution. We also prove that there is a
considerable gain in efficiency resulting from the multi-level Monte Carlo
method over the standard Monte Carlo method. Numerical experiments illustrating
the ability of both methods to accurately compute multi-point statistical
quantities of interest are also presented
Body mass estimates of an exceptionally complete Stegosaurus (Ornithischia: Thyreophora): comparing volumetric and linear bivariate mass estimation methods
© 2015 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. The file attached is the published version of the article
Expresión de las moléculas del Complejo Mayor de Histocompatibilidad clase II y moléculas co-estimuladoras en carcinomas orales in vitro
El descubrimiento de que el epitelio escamoso estratificado que
cubre la mucosa oral podia expresar moleculas del Complejo
Mayor de Histocompatibilidad clase II en varias condiciones
patologicas de tipo inflamatorio abrio la posibilidad de que los
queratinocitos orales sean celulas inmunologicamente activas,
las cuales pueden funcionar con .celulas presentadoras de
antigenos'ñ. Para una efectiva activacion de los linfocitos T,
las celulas presentadoras de antigenos requieren, ademas de
la expresion de moleculas del Complejo Mayor de Histocompatibilidad
clase II, senales co-estimuladoras. El proposito del
presente estudio fue determinar la expresion de moleculas del
Complejo Mayor de Histocompatibilidad clase II y las moleculas
co-estimuladoras CD40, CD80 y CD86 en queratinocitos bucales
normales y derivados de carcinomas de celulas escamosas. Usando
citometria de flujo en queratinocitos cultivados de mucosa
oral sana y siete lineas celulares derivadas de carcinomas orales,
fue confirmado que los queratinocitos expresan moleculas del
Complejo Mayor de Histocompatibilidad clase II despues de
estimulacion con IFN'Á in vitro. Todas las lineas celulares expresaron
constitutivamente CD40, por el contrario, CD80 y CD86
universalmente fueron negativos. La ausencia de estas ultimas
moleculas pudiera ser la causa por la cual los carcinomas orales
escapan de la vigilancia inmunologica y pueden crecer, invadir
y hacer metastasis pese al sistema inmunologico.Recognition in the 1980Es that keratinocytes can express class II
molecules of the Major Histocompatibility Complex (MHC) first
raised the possibility that these cells might have an immunological
function, and may even act as antigen presenting cells (APC).
For effective T lymphocyte activation, APC require, in addition
to MHC II, appropriate costimulatory signals. The aim of this
study was to determine the expression of MHC class II and the
co-stimulatory molecules CD40, CD80 and CD86 in keratinocytes
derived from healthy oral mucosa and oral carcinomas.
Using flow cytometry, it was confirmed that oral keratinocytes
.switch on'ñ expression of MHC class II molecules after stimulation
with IFN'Á in vitro. All keratinocyte lines expressed CD40
constitutively; by contrast, CD80 and CD86 were universally
absent. Loss of CD80 and CD86 may be one means whereby
tumours escape immunological surveillance.
Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Nova-like BB Doradus
We present an analysis of the Far Ultraviolet Spectroscopic Explorer
({\it{FUSE}}) spectra of the little-known southern nova-like BB Doradus. The
spectrum was obtained as part of our Cycle 8 {\it FUSE} survey of high
declination nova-like stars.
The FUSE spectrum of BB Dor, observed in a high state, is modeled with an
accretion disk with a very low inclination (possibly lower than 10deg).
Assuming an average WD mass of 0.8 solar leads to a mass accretion rate of
1.E-9 Solar mass/year and a distance of the order of 650 pc, consistent with
the extremely low galactic reddening in its direction. The spectrum presents
some broad and deep silicon and sulfur absorption lines, indicating that these
elements are over-abundant by 3 and 20 times solar, respectively
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