-Knowledge of the propagation media is a key step toward a successful transceiver design. Such information is typically gathered by conducting physical experiments, measuring and processing the corresponding data to obtain channel characteristics. In case of medical implants, this could be extremely difficult, if not impossible. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe RF propagation from medical implants inside a human body. This virtual environment allows for more natural interaction between experts with different backgrounds, such as engineering and medical sciences. Here, we show how this platform has been used to determine a statistical path loss model for medical implant communication systems.
We investigate the influence of geometrical confinement on the breakup of long fluid threads in the absence of imposed flow using a lattice Boltzmann model. Our simulations primarily focus on the case of threads centered coaxially in a tube filled with another Newtonian fluid and subjected to both impulsive and random perturbations. We observe a significant slowing down of the rate of thread breakup ("kinetic stabilization") over a wide range of the confinement, Lambda= R(tube)/R(thread) < or =10 and find that the relative surface energies of the liquid components influence this effect. For Lambda<2.3, there is a transition in the late-stage morphology between spherical droplets and tube "plugs." Unstable distorted droplets ("capsules") form as transient structures for intermediate confinement (Lambda approximately equal 2.1-2.5). Surprisingly, the thread breakup process for more confined threads (Lambda< or =1.9 ) is found to be sensitive to the nature of the initial thread perturbation. Localized impulsive perturbations ("taps") cause a "bulging" of the fluid at the wall, followed by thread breakup through the propagation of a wave-like disturbance ("end-pinch instability") initiating from the thread rupture point. Random impulses along the thread, modeling thermal fluctuations, lead to a complex breakup process involving a competition between the Raleigh and end-pinch instabilities. We also briefly compare our tube simulations to threads confined between parallel plates and to multiple interacting threads under confinement.
We investigate the stability of a polymer thread imbedded in a matrix that is confined
between two parallel plates. Utilizing a combination of experiments, numerical simulations (lattice−Boltzmann), and surface area calculations, we find substantial deviations from the classical results when
the diameter of the thread (D
0) is comparable to the height (H) of the matrix. We find three regimes as
a function of H/D
0: For H/D
0
≳ 3, the thread breaks up into droplets through a finite wavelength
axisymmetric capillary instability as described by Rayleigh and Tomotika. For 1.3 ≲ H/D
0 ≲ 3, the effects
of the confinement are felt; the shape becomes nonaxisymmetric, the early-stage growth rate decreases,
and the wavelength increases. For sufficiently low H/D
0, we observe that the thread is stable with respect
to the capillary instability over the experimental time scales. The simulations qualitatively agree with
the experiments and reveal that while the shape of the growing bulges is nonaxisymmetic, the narrowing
necks are circular. A simple surface area consideration then shows that as the wall-induced asymmetry
of the fluctuation increases, the minimally unstable wavelength increases and eventually diverges.
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