5,020 research outputs found
Estimation of elastic and viscous properties of the left ventricle based on annulus plane harmonic behavior
Assessment of left ventricular (LV) function
with an emphasis on contractility has been a challenge
in cardiac mechanics during the recent decades. The LV
function is usually described by the LV pressurevolume
(P-V) diagram. The standard P-V diagrams are
easy to interpret but difficult to obtain and require
invasive instrumentation for measuring the
corresponding volume and pressure data. In the present
study, we introduce a technique that can estimate the
viscoelastic properties of the LV based on harmonic
behavior of the ventricular chamber and it can be
applied non-invasively as well. The estimation technique
is based on modeling the actual long axis displacement
of the mitral annulus plane toward the cardiac base as a
linear damped oscillator with time-varying coefficients.
The time-varying parameters of the model were
estimated by a standard Recursive Linear Least
Squares (RLLS) technique. LV stiffness at end-systole
and end diastole was in the range of 61.86-136.00
dyne/g.cm and 1.25-21.02 dyne/g.cm, respectively. The
only input used in this model was the long axis
displacement of the annulus plane, which can also be
obtained non-invasively using tissue Doppler or MR
imaging
Compact Toroidal Ion Trap Design and Optimization
We present the design of a new type of compact toroidal, or "halo", ion trap.
Such traps may be useful for mass spectrometry, studying small Coulomb cluster
rings, quantum information applications, or other quantum simulations where a
ring topology is of interest. We present results from a Monte Carlo
optimization of the trap design parameters using finite-element analysis
simulations that minimizes higher-order anharmonic terms in the trapping
pseudopotential, while maintaining complete control over ion placement at the
pseudopotential node in 3D using static bias fields. These simulations are
based on a practical electrode design using readily-available parts, yet can be
easily scaled to any size trap with similar electrode spacings. We also derive
the conditions for a crystal phase transition for two ions in the compact halo
trap, the first non-trivial phase transition for Coulomb crystals in this
geometry.Comment: 8 pages, 9 figure
Patient-specific CFD simulation of intraventricular haemodynamics based on 3D ultrasound imaging
Background: The goal of this paper is to present a computational fluid dynamic (CFD) model with moving boundaries to study the intraventricular flows in a patient-specific framework. Starting from the segmentation of real-time transesophageal echocardiographic images, a CFD model including the complete left ventricle and the moving 3D mitral valve was realized. Their motion, known as a function of time from the segmented ultrasound images, was imposed as a boundary condition in an Arbitrary Lagrangian-Eulerian framework.
Results: The model allowed for a realistic description of the displacement of the structures of interest and for an effective analysis of the intraventricular flows throughout the cardiac cycle. The model provides detailed intraventricular flow features, and highlights the importance of the 3D valve apparatus for the vortex dynamics and apical flow.
Conclusions: The proposed method could describe the haemodynamics of the left ventricle during the cardiac cycle. The methodology might therefore be of particular importance in patient treatment planning to assess the impact of mitral valve treatment on intraventricular flow dynamics
Patient-specific computational fluid dynamic simulation of intraventricular hemodynamics : introducing mitral valve motion as prescribed boundary condition
Assessment of myocardial injury after reperfused infarction by T1ρ cardiovascular magnetic resonance.
BackgroundThe evolution of T1ρ and of other endogenous contrast methods (T2, T1) in the first month after reperfused myocardial infarction (MI) is uncertain. We conducted a study of reperfused MI in pigs to serially monitor T1ρ, T2 and T1 relaxation, scar size and transmurality at 1 and 4 weeks post-MI.MethodsTen Yorkshire swine underwent 90 min of occlusion of the circumflex artery and reperfusion. T1ρ, T2 and native T1 maps and late gadolinium enhanced (LGE) cardiovascular magnetic resonance (CMR) data were collected at 1 week (n = 10) and 4 weeks (n = 5). Semi-automatic FWHM (full width half maximum) thresholding was used to assess scar size and transmurality and compared to histology. Relaxation times and contrast-to-noise ratio were compared in healthy and remote myocardium at 1 and 4 weeks. Linear regression and Bland-Altman was performed to compare infarct size and transmurality.ResultsRelaxation time differences between infarcted and remote myocardial tissue were ∆T1 (infarct-remote) = 421.3 ± 108.8 (1 week) and 480.0 ± 33.2 ms (4 week), ∆T1ρ = 68.1 ± 11.6 and 74.3 ± 14.2, and ∆T2 = 51.0 ± 10.1 and 59.2 ± 11.4 ms. Contrast-to-noise ratio was CNRT1 = 7.0 ± 3.5 (1 week) and 6.9 ± 2.4 (4 week), CNRT1ρ = 12.0 ± 6.2 and 12.3 ± 3.2, and CNRT2 = 8.0 ± 3.6 and 10.3 ± 5.8. Infarct size was not significantly different for T1ρ, T1 and T2 compared to LGE (p = 0.14) and significantly decreased from 1 to 4 weeks (p < 0.01). Individual infarct size changes were ∆T1ρ = -3.8%, ∆T1 = -3.5% and ∆LGE = -2.8% from 1 - 4 weeks, but there was no observed change in infarct size for T2 or histologically.ConclusionsT1ρ was highly correlated with alterations left ventricle (LV) pathology at 1 and 4 weeks post-MI and therefore it may be a useful method endogenous contrast imaging of infarction
Robust Parafoil Terminal Guidance Using Massively Parallel Processing
Terminal guidance of autonomous parafoils is a difficult problem in which wind uncertainty and system underactuation are major challenges. Existing strategies almost exclusively use impact error as the criterion for optimality. Practical airdrop systems, however, must also include other criteria that maybe even more important than impact error for some missions, such as ground speed at impact or constraints imposed by drop zones with restrictions on flight patterns. Furthermore, existing guidance schemes determine terminal trajectories using deterministic wind information and may result in a solution that works in ideal wind but may be sensitive to variations. The work described here develops a guidance strategy that uses massively parallel Monte Carlo simulation performed on a graphics processing unit to rank candidate trajectories in terms of robustness to wind uncertainty. The result is robust guidance, as opposed to optimal guidance. Through simulation results, the proposed path planning scheme proves more robust in realistic dynamic wind environments compared with previous optimal trajectory planners that assume perfect knowledge of a constant wind
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