519 research outputs found
Numerical Modeling of Pulse Wave Propagation in a Stenosed Artery using Two-Way Coupled Fluid Structure Interaction (FSI)
As the heart beats, it creates fluctuation in blood pressure leading to a
pulse wave that propagates by displacing the arterial wall. These waves travel
through the arterial tree and carry information about the medium that they
propagate through as well as information of the geometry of the arterial tree.
Pulse wave velocity (PWV) can be used as a non-invasive diagnostic tool to
study the functioning of cardiovascular system. A stenosis in an artery can
dampen the pulse wave leading to changes in the propagating pulse. Hence, PWV
analysis can be performed to detect a stenosed region in arteries. This paper
presents a numerical study of pulse wave propagation in a stenosed artery by
means of two-way coupled fluid structure interaction (FSI). The computational
model was validated by the comparison of the simulated PWV results with
theoretical values for a healthy artery. Propagation of the pulse waves in the
stenosed artery was compared with healthy case using spatiotemporal maps of
wall displacements. The analysis for PWV showed significance differences
between the healthy and stenosed arteries including damping of propagating
waves and generation of high wall displacements downstream the stenosis caused
by flow instabilities. This approach can be used to develop patient-specific
models that are capable of predicting PWV signatures associated with stenosis
changes. The knowledge gained from these models may increase utility of this
approach for managing patients at risk of stenosis occurrence
Interstitial cell network volume is reduced in the terminal bowel of ageing mice
Ageing is associated with impaired neuromuscular function of the terminal gastrointestinal (GI) tract, which can result in chronic constipation, faecal impaction and incontinence. Interstitial cells of cajal (ICC) play an important role in regulation of intestinal smooth muscle contraction. However, changes in ICC volume with age in the terminal GI tract (the anal canal including the anal sphincter region and rectum)have not been studied. Here, the distribution, morphology and network volume of ICC in the terminal GI tract of 3âto 4âmonthâold and 26âto 28âmonthâold C57BL/6mice were investigated. ICC were identified by immunofluorescence labelling of wholemount preparations with an antibody against câKit. ICC network volume was measured by softwareâbased 3D volume rendering of confocal Z stacks. A significant reduction in ICC network volume per unit volume of muscle was measured in aged animals. No ageâassociated change in ICC morphology was detected. The thickness of the circular muscle layer of the anal sphincter region and rectum increased with age, while that in the distal colon decreased. These results suggest that ageing is associated with a reduction in the network volume of ICC in the terminal GI tract, which may influence the normal function of these regions
The Influence of the Aortic Root Geometry on Flow Characteristics of a Bileaflet Mechanical Heart Valve
Bileaflet mechanical heart valves have one of the most successful valve
designs for more than 30 years. These valves are often used for aortic valve
replacement, where the geometry of the aortic root sinuses may vary due to
valvular disease and affect valve performance. Common geometrical sinus changes
may be due to valve stenosis and insufficiency. In the current study, the
effect of these geometrical changes on the mean flow and velocity fluctuations
downstream of the valve and aortic sinuses were investigated. The study focused
on the fully-open leaflet position where blood velocities are close to their
maximum. Simulation results were validated using previous experimental laser
Doppler anemometry (LDA) measurements. Results showed that as the stenosis and
insufficiency increased there were more flow separation and increased local
mean velocity downstream of the leaflets. In addition, the detected elevated
velocity fluctuations were associated with higher Reynolds shear stresses
levels, which may increase the chances of blood damage and platelet activation
and may lead to increased risk of blood clot formation
Towards portable muography with small-area, gas-tight glass Resistive Plate Chambers
Imaging techniques that use atmospheric muons, collectively named under the
neologism "muography", have seen a tremendous growth in recent times, mainly
due to their diverse range of applications. The most well-known ones include
but are not limited to: volcanology, archaeology, civil engineering, nuclear
reactor monitoring, nuclear waste characterization, underground mapping, etc.
These methods are based on the attenuation or deviation of muons to image large
and/or dense objects where conventional techniques cannot work or their use
becomes challenging.
In this context, we have constructed a muography telescope based on "mini
glass-RPC planes" following a design similar to the glass-RPC detectors
developed by the CALICE Collaboration and used by the TOMUVOL experiment in the
context of volcano radiography, but with smaller active area (16 16
cm). The compact size makes it an attractive choice with respect to other
detectors previously employed for imaging on similar scales. An important
innovation in this design is that the detectors are sealed. This makes the
detector more portable and solves the usual safety and logistic issues for gas
detectors operated underground and/or inside small rooms. This paper provides
an overview on our guiding principles, the detector development and our
operational experiences. Drawing on the lessons learnt from the first
prototype, we also discuss our future direction for an improved second
prototype, focusing primarily on a recently adopted serigraphy technique for
the resistive coating of the glass plates.Comment: 8 pages, 7 figures, XV Workshop on Resistive Plate Chambers and
Related Detectors (RPC2020
Globular cluster population of the HST frontier fields galaxy J07173724+3744224
We present the first measurement of the globular cluster population
surrounding the elliptical galaxy J07173724+3744224 (z=0.1546). This galaxy is
located in the foreground in the field-of-view of the Hubble Space Telescope
(HST) Frontier Fields observations of galaxy cluster MACS J0717.5+3745
(z=0.5458). Based on deep HST ACS F435W, F606W, and F814W images, we find a
total globular cluster population of N_tot = 3441 +/- 1416. Applying the
appropriate extinction correction and filter transformation from ACS F814W to
the Johnson V-band, we determine that the host galaxy has an absolute magnitude
of M_V = -22.2. The specific frequency was found to be S_N = 4.5 +/- 1.8. The
radial profile of the globular cluster system was best fit using a powerlaw of
the form , with the globular cluster population found to
be more extended than the halo light of the host galaxy (). The F435W-F814W colour distribution suggests a bimodal population,
with red globular clusters 1-3x more abundant than blue clusters. These results
are consistent with the host elliptical galaxy J07173724+3744224 having formed
its red metal-rich GCs in situ, with the blue metal-poor globular clusters
accreted from low-mass galaxies.Comment: 21 pages, 14 figures, 2 tables, revised following peer-review,
accepted for publication in MNRA
Evaluation of Acoustic Parameters for Angulimala Sutta using Voiced to Unvoiced Ration and Vowel Distribution
Pirith is believed as a protective doctrine preached by the Load Buddha in Pali language. The aim of this study is to analyze acoustic properties of Pirith using computer-aided methods and identify special characteristics and patterns. In this study, two methods were used to identify special characteristics of Angulimala Sutta. First method calculates voiced to unvoiced ratio using zero crossing rate and energy content associated with the acoustic signal while second method recognizes vowel distribution using first and second formant frequencies. Results of the first method indicates approximately 96% of frames are voiced while the second method suggests approximately 72% of vowels concentrate in the square region of F1,0~1500 Hz and demonstrating when chanting the Angulimala sutta most of the time the tongue height is low positioned in back levels while lips shaped unrounded. KEYWORDS: Formant frequencies, Voiced to unvoiced ratio, Zero-Crossing rate, Vowel distributio
Star formation in low-redshift cluster dwarf galaxies
Evolution of galaxies in dense environments can be affected by close encounters with neighbouring galaxies and interactions with the intracluster medium. Dwarf galaxies (dGs) are important as their low mass makes them more susceptible to these effects than giant systems. Combined luminosity functions (LFs) in the r and u band of 15 galaxy clusters were constructed using archival data from the CanadaâFranceâHawaii Telescope. LFs were measured as a function of clustercentric radius from stacked cluster data. Marginal evidence was found for an increase in the faint-end slope of the u-band LF relative to the r-band with increasing clustercentric radius. The dwarf-to-giant ratio (DGR) was found to increase toward the cluster outskirts, with the u-band DGR increasing faster with clustercentric radius compared to the r-band. The dG blue fraction was found to be âŒ2 times larger than the giant galaxy blue fraction over all clustercentric distance (âŒ5Ï level). The central concentration (C) was used as a proxy to distinguish nucleated versus non-nucleated dGs. The ratio of high-C to low-C dGs was found to be âŒ2 times greater in the inner cluster region compared to the outskirts (2.8Ï level). The faint-end slope of the r-band LF for the cluster outskirts (0.6 †r/r200 \u3c 1.0) is steeper than the Sloan Digital Sky Survey field LF, while the u-band LF is marginally steeper at the 2.5Ï level. Decrease in the faint-end slope of the r- and u-band cluster LFs towards the cluster centre is consistent with quenching of star formation via ram pressure stripping and galaxyâgalaxy interactions
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