3,594 research outputs found
The Circumstellar Environment of High Mass Protostellar Objects. III Evidence of Infall?
The results are presented of a molecular line survey to search for the
spectral signature of infall towards 77 850 micron continuum sources believed
to be candidate high mass protostellar objects. Up to six different
transitions, HCO+ 1-0, 3-2 and 4-3, H2CO 2_12-1_11, N2H+ and H13CO+ 3-2, were
observed towards each source. Towards the peak of the 850 micron emission, N2H+
was typically strong, with a peak antenna temperature of ~1.5K, with a typical
linewidth of ~2km/s. The good agreement between the velocity and velocity width
of the N2H+ and H13CO+ emission suggests that both species are tracing similar
material in the sources. With respect to the velocity of the N2H+, there is a
statistically significant excess of blue asymmetric line profiles in both the
HCO+ 1-0 and H2CO transitions. This excess reaches levels similar to that seen
towards samples of low mass protostars, and suggests that the material around
these high mass sources is infalling. We identify 22 promising candidate infall
sources which show at least one blue asymmetric line profile and no red
asymmetric profiles. The infall velocity is estimated to be in the range of 0.1
km/s to 1 km/s with an implied mass accretion rate of between 2x10^{-4} Msol/yr
and 10^{-3}Msol/yr.Comment: Accepted for publication in Astronomy and Astrophysics. Higher
resolution versions of Figures 1 and 2 are available from
http://www.jb.man.ac.uk/~gaf/Papers.htm
Longitudinal residual strain and stress-strain relationship in rat small intestine
BACKGROUND: To obtain a more detailed description of the stress-free state of the intestinal wall, longitudinal residual strain measurements are needed. Furthermore, data on longitudinal stress-strain relations in visceral organs are scarce. The present study aims to investigate the longitudinal residual strain and the longitudinal stress-strain relationship in the rat small intestine. METHODS: The longitudinal zero-stress state was obtained by cutting tissue strips parallel to the longitudinal axis of the intestine. The longitudinal residual stress was characterized by a bending angle (unit: degrees per unit length and positive when bending outwards). Residual strain was computed from the change in dimensions between the zero-stress state and the no-load state. Longitudinal stresses and strains were computed from stretch experiments in the distal ileum at luminal pressures ranging from 0–4 cmH(2)O. RESULTS: Large morphometric variations were found between the duodenum and ileum with the largest wall thickness and wall area in the duodenum and the largest inner circumference and luminal area in the distal ileum (p < 0.001). The bending angle did not differ between the duodenum and ileum (p > 0.5). The longitudinal residual strain was tensile at the serosal surface and compressive at the mucosal surface. Hence, the neutral axis was approximately in the mid-wall. The longitudinal residual strain and the bending angle was not uniform around the intestinal circumference and had the highest values on the mesenteric sides (p < 0.001). The stress-strain curves fitted well to the mono-exponential function with determination coefficients above 0.96. The α constant increased with the pressure, indicating the intestinal wall became stiffer in longitudinal direction when pressurized. CONCLUSION: Large longitudinal residual strains reside in the small intestine and showed circumferential variation. This indicates that the tissue is not uniform and cannot be treated as a homogenous material. The longitudinal stiffness of the intestinal wall increased with luminal pressure. Longitudinal residual strains must be taken into account in studies of gastrointestinal biomechanical properties
Asynchronous Probabilistic Couplings in Higher-Order Separation Logic
Probabilistic couplings are the foundation for many probabilistic relational
program logics and arise when relating random sampling statements across two
programs. In relational program logics, this manifests as dedicated coupling
rules that, e.g., say we may reason as if two sampling statements return the
same value. However, this approach fundamentally requires aligning or
"synchronizing" the sampling statements of the two programs which is not always
possible.
In this paper, we develop Clutch, a higher-order probabilistic relational
separation logic that addresses this issue by supporting asynchronous
probabilistic couplings. We use Clutch to develop a logical step-indexed
logical relational to reason about contextual refinement and equivalence of
higher-order programs written in a rich language with higher-order local state
and impredicative polymorphism. Finally, we demonstrate the usefulness of our
approach on a number of case studies.
All the results that appear in the paper have been formalized in the Coq
proof assistant using the Coquelicot library and the Iris separation logic
framework
Molecular line profiles as diagnostics of protostellar collapse: modelling the `blue asymmetry' in inside-out infall
The evolution of star-forming core analogues undergoing inside-out collapse
is studied with a multi-point chemodynamical model which self-consistently
computes the abundance distribution of chemical species in the core. For
several collapse periods the output chemistry of infall tracer species such as
HCO+, CS, and N2H+, is then coupled to an accelerated Lambda-iteration
radiative transfer code, which predicts the emerging molecular line profiles
using two different input gas/dust temperature distributions. We investigate
the sensitivity of the predicted spectral line profiles and line asymmetry
ratios to the core temperature distribution, the time-dependent model
chemistry, as well as to ad hoc abundance distributions. The line asymmetry is
found to be strongly dependent on the adopted chemical abundance distribution.
In general, models with a warm central region show higher values of blue
asymmetry in optically thick HCO+ and CS lines than models with a starless core
temperature profile. We find that in the formal context of Shu-type inside-out
infall, and in the absence of rotation or outflows, the relative blue asymmetry
of certain HCO+ and CS transitions is a function of time and, subject to the
foregoing caveats, can act as a collapse chronometer. The sensitivity of
simulated HCO+ line profiles to linear radial variations, subsonic or
supersonic, of the internal turbulence field is investigated in the separate
case of static cores.Comment: Accepted to MNRAS; 20 pages, 13 fig
Does Infall End Before the Class I Stage?
We have observed HCO+ J=3-2 toward 16 Class I sources and 18 Class 0 sources,
many of which were selected from Mardones et al. (1997). Eight sources have
profiles significantly skewed to the blue relative to optically thin lines. We
suggest six sources as new infall candidates. We find an equal "blue excess"
among Class 0 and Class I sources after combining this sample with that of
Gregersen et al. (1997). We used a Monte Carlo code to simulate the temporal
evolution of line profiles of optically thick lines of HCO+, CS and H2CO in a
collapsing cloud and found that HCO+ had the strongest asymmetry at late times.
If a blue-peaked line profile implies infall, then the dividing line between
the two classes does not trace the end of the infall stage.Comment: 21 pages, 8 figures, accepted by ApJ for April 20, 2000, added
acknowledgmen
THE POTENTIAL EFFECT OF MINI-TRAMPOLINE STIFFNESS ON TAKE-OFF BEHAVIOUR OF GYMNASTS – A METHODOLOGICAL STUDY
The purpose of this study was to compare two mini-trampolines with different spring constant in regard to their effect on take-off mechanics. It was expected that the softer (36 springs) trampoline would lead to a longer contact time and a higher take-off impulse. To assess reaction forces during jumps a flexible force insole was used simultaneously with the measurement of run-in velocity by timing gates. Results showed no significant differences in contact mechanics or contact time indicating that the difference between these two trampolines is only marginal. Therefore, this study provides mainly a novel measurement approach to assess the effect of equipment changes in trampolining. Future studies are warranted to assess the athlete-equipment interaction in greater detail
Volumetric measurements of weak current-induced magnetic fields in the human brain at high resolution
PURPOSE
Clinical use of transcranial electrical stimulation (TES) requires accurate knowledge of the injected current distribution in the brain. MR current density imaging (MRCDI) uses measurements of the TES-induced magnetic fields to provide this information. However, sufficient sensitivity and image quality in humans in vivo has only been documented for single-slice imaging.
METHODS
A recently developed, optimally spoiled, acquisition-weighted, gradient echo-based 2D-MRCDI method has now been advanced for volume coverage with densely or sparsely distributed slices: The 3D rectilinear sampling (3D-DENSE) and simultaneous multislice acquisition (SMS-SPARSE) were optimized and verified by cable-loop experiments and tested with 1-mA TES experiments for two common electrode montages.
RESULTS
Comparisons between the volumetric methods against the 2D-MRCDI showed that relatively long acquisition times of 3D-DENSE using a single slab with six slices hindered the expected sensitivity improvement in the current-induced field measurements but improved sensitivity by 61% in the Laplacian of the field, on which some MRCDI reconstruction methods rely. Also, SMS-SPARSE acquisition of three slices, with a factor 2 CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) acceleration, performed best against the 2D-MRCDI with sensitivity improvements for the and Laplacian noise floors of 56% and 78% (baseline without current flow) as well as 43% and 55% (current injection into head). SMS-SPARSE reached a sensitivity of 67 pT for three distant slices at 2 × 2 × 3 mm resolution in 10 min of total scan time, and consistently improved image quality.
CONCLUSION
Volumetric MRCDI measurements with high sensitivity and image quality are well suited to characterize the TES field distribution in the human brain
International genome-wide meta-analysis identifies new primary biliary cirrhosis risk loci and targetable pathogenic pathways
Primary biliary cirrhosis (PBC) is a classical autoimmune liver disease for which effective immunomodulatory therapy is lacking. Here we perform meta-analyses of discovery data sets from genome-wide association studies of European subjects (n=2,764 cases and 10,475 controls) followed by validation genotyping in an independent cohort (n=3,716 cases and 4,261 controls). We discover and validate six previously unknown risk loci for PBC (Pcombined10(-8)) and used pathway analysis to identify JAK-STAT/IL12/IL27 signalling and cytokine-cytokine pathways, for which relevant therapies exist
Water emission in NGC1333-IRAS4: The physical structure of the envelope
We report ISO-LWS far infrared observations of CO, water and oxygen lines
towards the protobinary system IRAS4 in the NGC1333 cloud. We detected several
water, OH, CO rotational lines, and two [OI] and [CII] fine structure lines.
Given the relatively poor spectral and spatial resolution of these
observations, assessing the origin of the observed emission is not
straightforward. In this paper, we focus on the water line emission and explore
the hypothesis that it originates in the envelopes that surround the two
protostars, IRAS4 A and B, thanks to an accurate model. The model reproduces
quite well the observed water line fluxes, predicting a density profile, mass
accretion rate, central mass, and water abundance profile in agreement with
previous works. We hence conclude that the emission from the envelopes is a
viable explanation for the observed water emission, although we cannot totally
rule out the alternative that the observed water emission originates in the
outflow
- …