184 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
Enhanced tunability of magnetron sputtered Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3] thin films on c-plane sapphire substrates
Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1 to 20 GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200 kV/cm and total device Q of more than 15 (up to 20 GHz) were achieved following postdeposition annealing at 900°C
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
Casimir force in the presence of a magnetodielectric medium
In this article we investigate the Casimir effect in the presence of a medium
by quantizing the Electromagnetic (EM) field in the presence of a
magnetodielectric medium by using the path integral formalism. For a given
medium with definite electric and magnetic susceptibilities, explicit
expressions for the Casimir force are obtained which are in agree with the
original Casimir force between two conducting parallel plates immersed in the
quantum electromagnetic vacuum.Comment: 8 pages, 1 figur
Finite temperature Cherenkov radiation in the presence of a magnetodielectric medium
A canonical approach to Cherenkov radiation in the presence of a
magnetodielectric medium is presented in classical, nonrelativistic and
relativistic quantum regimes. The equations of motion for the canonical
variables are solved explicitly for both positive and negative times. Maxwell
and related constitute equations are obtained. In the large-time limit, the
vector potential operator is found and expressed in terms of the medium
operators. The energy loss of a charged particle, emitted in the form of
radiation, in finite temperature is calculated. A Dirac equation concerning the
relativistic motion of the particle in presence of the magnetodielectric medium
is derived and the relativistic Cherenkov radiation at zero and finite
temperature is investigated. Finally, it is shown that the Cherenkov radiation
in nonrelativistic and relativistic quantum regimes, unlike its classical
counterpart, introduces automatically a cutoff for higher frequencies beyond
which the power of radiation emission is zero.Comment: To be appear in PR
Exercise training and weight loss, not always a happy marriage: single blind exercise trials in females with diverse BMI
Individuals show high variability in body weight responses to exercise training. Expectations and motivation towards effects of exercise on body weight might influence eating behaviour and could conceal regulatory mechanisms. We conducted two single-blind exercise trials (4 weeks (study 1) and 8 weeks (study 2)) with concealed objectives and exclusion of individuals with weight loss intention. Circuit exercise training programs (3 times a week (45-90 min), intensity 50-90% VO2peak, for 4 and 8 weeks) were conducted. 34 females finished the 4 weeks intervention and 36 females the 8 weeks intervention. Overweight/obese (OV/OB) and lean (L) female participants´ weight/body composition responses were assessed and fasting and postprandial appetite hormone levels (PYY, insulin, amylin, leptin, ghrelin) were measured pre and post intervention for understanding potential contribution to individuals’ body weight response to exercise training (study 2). Exercise training in both studies did not lead to a significant reduction of weight/BMI in the participants’ groups, however, lean participants gained muscle mass. Appetite hormones levels were significantly (p<0.05) altered in the OV/OB group affecting fasting (-24%) and postprandial amylin (-14%) levels. Investigation of individuals’ BMI responses using multiple regression analysis revealed that levels of fasting leptin, postprandial amylin increase, and BMI were significant predictors of BMI change explaining about 43% of the variance. In conclusion, tested exercise training did not lead to weight loss in female participants, while a considerable proportion of variance in body weight response to training could be explained by individuals’ appetite hormone levels and BMI
Taylor-like vortices in the shear-banding flow of giant micelles
Using flow visualizations in Couette geometry, we demonstrate the existence
of Taylor-like vortices in the shear-banding flow of a giant micelles system.
We show that vortices stacked along the vorticity direction develop
concomitantly with interfacial undulations. These cellular structures are
mainly localized in the induced band and their dynamics is fully correlated
with that of the interface. As the control parameter increases, we observe a
transition from a steady vortex flow to a state where pairs of vortices are
continuously created and destroyed. Normal stress effects are discussed as
potential mechanisms driving the three-dimensional flow.Comment: 5 pages, 4 figure
A biology-driven approach identifies the hypoxia gene signature as a predictor of the outcome of neuroblastoma patients
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