817 research outputs found
Post-traumatic, intrapulmonary arteriovenous fi stula: Diagnosis by trans-oesophageal echocardiography
Image in Cardiolog
Talking quiescence: a rigorous theory that supports parallel composition, action hiding and determinisation
The notion of quiescence - the absence of outputs - is vital in both
behavioural modelling and testing theory. Although the need for quiescence was
already recognised in the 90s, it has only been treated as a second-class
citizen thus far. This paper moves quiescence into the foreground and
introduces the notion of quiescent transition systems (QTSs): an extension of
regular input-output transition systems (IOTSs) in which quiescence is
represented explicitly, via quiescent transitions. Four carefully crafted rules
on the use of quiescent transitions ensure that our QTSs naturally capture
quiescent behaviour.
We present the building blocks for a comprehensive theory on QTSs supporting
parallel composition, action hiding and determinisation. In particular, we
prove that these operations preserve all the aforementioned rules.
Additionally, we provide a way to transform existing IOTSs into QTSs, allowing
even IOTSs as input that already contain some quiescent transitions. As an
important application, we show how our QTS framework simplifies the fundamental
model-based testing theory formalised around ioco.Comment: In Proceedings MBT 2012, arXiv:1202.582
Quantized vortices and collective oscillations of a trapped Bose condensed gas
Using a sum rule approach we calculate the frequency shifts of the quadrupole
oscillations of a harmonically trapped Bose gas due to the presence of a
quantized vortex. Analytic results are obtained for positive scattering lengths
and large N where the shift relative to excitations of opposite angular
momentum is found to be proportional to the quantum circulation of the vortex
and to decrease as N^{-2/5}. Results are also given for smaller values of N
covering the transition between the ideal gas and the Thomas-Fermi limit. For
negative scattering lengths we predict a macroscopic instability of the vortex.
The splitting of the collective frequencies in toroidal configurations is also
discussed.Comment: Rextex, 4 pages, 1 postscript figur
Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica – Part 3: Insights from Oligocene–Miocene TEX86-based sea surface temperature reconstructions
The volume of the Antarctic continental ice
sheet(s) varied substantially during the Oligocene and
Miocene ( 34–5 Ma) from smaller to substantially larger
than today, both on million-year and on orbital timescales.
However, reproduction through physical modeling of a dynamic
response of the ice sheets to climate forcing remains
problematic, suggesting the existence of complex feedback
mechanisms between the cryosphere, ocean, and atmosphere
systems. There is therefore an urgent need to improve the
models for better predictions of these systems, including resulting
potential future sea level change. To assess the interactions
between the cryosphere, ocean, and atmosphere,
knowledge of ancient sea surface conditions close to the
Antarctic margin is essential. Here, we present a new TEX86-
based sea surface water paleotemperature record measured
on Oligocene sediments from Integrated Ocean Drilling
Program (IODP) Site U1356, offshore Wilkes Land, East
Antarctica. The new data are presented along with previously
published Miocene temperatures from the same site.
Together the data cover the interval between 34 and
11 Ma and encompasses two hiatuses. This record allows us
to accurately reconstruct the magnitude of sea surface temperature
(SST) variability and trends on both million-year
and glacial–interglacial timescales.Julian D. Hartman, Francesca Sangiorgi,
Henk Brinkhuis, and Peter K. Bijl acknowledge the NWO Netherlands
Polar Program project number 866.10.110. Stefan Schouten
was supported by the Netherlands Earth System Science Centre
(NESSC), funded by the Dutch Ministry of Education, Culture
and Science (OCW). Peter K. Bijl and Francien Peterse received
funding through NWO-ALW VENI grant nos. 863.13.002 and
863.13.016, respectively. Carlota Escutia and Ariadna Salabarnada
thank the Spanish Ministerio de Econimía y Competitividad for
grant CTM2014-60451-C2-1-P. We thank Alexander Ebbing
and Anja Bruls for GDGT sample preparation during their MSc
research. This research used samples from the Integrated Ocean
Drilling Program (IODP). IODP was sponsored by the US National
Science Foundation and participating countries under management
of Joined Oceanographic Institutions Inc
Is disturbed clearance of apoptotic keratinocytes responsible for UVB-induced inflammatory skin lesions in systemic lupus erythematosus?
Apoptotic cells are thought to play an essential role in the pathogenesis of systemic lupus erythematosus (SLE). We hypothesise that delayed or altered clearance of apoptotic cells after UV irradiation will lead to inflammation in the skin of SLE patients. Fifteen SLE patients and 13 controls were irradiated with two minimal erythemal doses (MEDs) of ultraviolet B light (UVB). Subsequently, skin biopsies were analysed (immuno)histologically, over 10 days, for numbers of apoptotic cells, T cells, macrophages, and deposition of immunoglobulin and complement. Additionally, to compare results with cutaneous lesions of SLE patients, 20 biopsies of lupus erythematosus (LE) skin lesions were analysed morphologically for apoptotic cells and infiltrate. Clearance rate of apoptotic cells after irradiation did not differ between patients and controls. Influx of macrophages in dermal and epidermal layers was significantly increased in patients compared with controls. Five out of 15 patients developed a dermal infiltrate that was associated with increased epidermal influx of T cells and macrophages but not with numbers of apoptotic cells or epidermal deposition of immunoglobulins. Macrophages were ingesting multiple apoptotic bodies. Inflammatory lesions in these patients were localised near accumulations of apoptotic keratinocytes similar as was seen in the majority of LE skin lesions. In vivo clearance rate of apoptotic cells is comparable between SLE patients and controls. However, the presence of inflammatory lesions in the vicinity of apoptotic cells, as observed both in UVB-induced and in LE skin lesions in SLE patients, suggests that these lesions result from an inflammatory clearance of apoptotic cells
Methodology for evaluating thermal track buckling in dual gauge tracks with continuous welded rail
In the National Spanish railway network, two types of track gauge with continuous welded rails are currently in use: the Iberian wide gauge (1668 mm) and the standard gauge (1435 mm). In order to improve links and freight traffic between different lines and with the rest of Europe, a dual gauge track with three rails was developed. This solution modifies the classical track configuration, so it is necessary to develop new methodologies and studies to understand its behavior. Among other loads applied on a continuous welded rail track, a considerable rise in temperature induces compressive stresses in the three rails that can lead to lateral track buckling. Moreover, on dual gauge tracks, the addition of the third rail increases the axial compression, which may lead to track instability. For this reason, a three-dimensional continuous welded rail model is developed in this study to be used for dual gauge track buckling analysis on straight tracks subjected to temperature load. The continuous welded rail dual gauge track model consists of beam, solid and spring elements, in which a non-linear behaviour of the ballast is considered. The results obtained may be used to predict the buckling capacity of the continuous welded rail on dual gauge tracks with respect to different parameters such as lateral resist-ance, lateral imperfections, sleeper spacing or torsional stiffness.Villalba Sanchis, I.; Insa Franco, R.; Salvador Zuriaga, P.; Martínez Fernández, P. (2017). Methodology for evaluating thermal track buckling in dual gauge tracks with continuous welded rail. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. 231(3):269-279. doi:10.1177/0954409715626957S269279231
The physics of water and wax in the pores of a working Gas-to-Liquids catalyst
The so-called Fischer-Tropsch catalysis allows to convert natural gas into liquid products and is the underlying mechanism of commercially used "Gas-to-Liquids" plants. The actual reaction takes place in millimetre sized porous pellets in which active metallic particles are dispersed as catalysts. Due to the reaction the pores of the pellets will become filled with the reaction products ("wax" and water), but it is uncertain if the fluid in the pores can be understood as a single liquid phase, a liquid-gas mixture, or multiple continuous phases. The answer to this question is important for a thorough understanding of the transport processes inside the reactor and can be utilized to improve its eciency. In this project, a theoretical analysis of the behaviour inside the pores is performed. It is concluded that a liquid water phase might well exist next to the wax phase. However, the analysis is based on very limited experimental data of unknown quality. Therefore, we propose a number of possible experiments to validate the theoretical concepts
Spin Excitations and Sum Rules in the Heisenberg Antiferromagnet
Various bounds for the energy of collective excitations in the Heisenberg
antiferromagnet are presented and discussed using the formalism of sum rules.
We show that the Feynman approximation significantly overestimates (by about
30\% in the square lattice) the spin velocity due to the non
negligible contribution of multi magnons to the energy weighted sum rule. We
also discuss a different, Goldstone type bound depending explicitly on the
order parameter (staggered magnetization). This bound is shown to be
proportional to the dispersion of classical spin wave theory with a
q-independent normalization factor. Rigorous bounds for the excitation energies
in the anisotropic Heisenberg model are also presented.Comment: 26 pages, Plain TeX including 1 PostScript figure, UTF-307-10/9
Real-time pion propagation in finite-temperature QCD
We argue that in QCD near the chiral limit, at all temperatures below the
chiral phase transition, the dispersion relation of soft pions can be expressed
entirely in terms of three temperature-dependent quantities: the pion screening
mass, a pion decay constant, and the axial isospin susceptibility. The
definitions of these quantities are given in terms of equal-time (static)
correlation functions. Thus, all three quantities can be determined directly by
lattice methods. The precise meaning of the Gell-Mann--Oakes--Renner relation
at finite temperature is given.Comment: 25 pages, 2 figures; v2: discussion on the region of applicability
expanded, to be published in PR
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