Chekema Prince

Energy harvesting from base excitation of ionic polymer metal composites in fluid environments

In this paper, we analytically and experimentally study the energy harvesting capability of submerged ionic polymer metal composites?(IPMCs). We consider base excitation of an IPMC strip that is shunted with an electric impedance and immersed in a fluid environment. We develop a modeling framework to predict the energy scavenged from the IPMC vibration as a function of the excitation frequency range, the constitutive and geometric properties of the IPMC, and the electric shunting load. The mechanical vibration of the IPMC strip is modeled through Kirchhoff?Love plate theory. The effect of the encompassing fluid on the IPMC vibration is described by using a linearized solution of the Navier?Stokes equations, that is traditionally considered in modeling atomic force microscope cantilevers. The dynamic chemo-electric response of the IPMC is described through the Poisson?Nernst?Planck model, in which the effect of mechanical deformations of the backbone polymer is accounted for. We present a closed-form solution for the current flowing through the IPMC strip as a function of the voltage across its electrodes and its deformation. We use modal analysis to establish a handleable expression for the power harvested from the vibrating IPMC and to optimize the shunting impedance for maximum energy harvesting. We validate theoretical findings through experiments conducted on IPMC strips vibrating in aqueous environments.

Functional assessment of the kidney from magnetic resonance and computed tomography renography: Impulse retention approach to a multicompartment model

A three‐compartment model is proposed for analyzing magnetic resonance renography (MRR) and computed tomography renography (CTR) data to derive clinically useful parameters such as glomerular filtration rate (GFR) and renal plasma flow (RPF). The model fits the convolution of the measured input and the predefined impulse retention functions to the measured tissue curves. A MRR study of 10 patients showed that relative root mean square errors by the model were significantly lower than errors for a previously reported three‐compartmental model (11.6% ± 4.9 vs 15.5% ± 4.1; P < 0.001). GFR estimates correlated well with reference values by 99mTc‐DTPA scintigraphy (correlation coefficient r = 0.82), and for RPF, r = 0.80. Parameter‐sensitivity analysis and Monte Carlo simulation indicated that model parameters could be reliably identified. When the model was applied to CTR in five pigs, expected increases in RPF and GFR due to acetylcholine were detected with greater consistency than with the previous model. These results support the reliability and validity of the new model in computing GFR, RPF, and renal mean transit times from MR and CT data. Magn Reson Med 59:278–288, 2008.

Quantitative determination of Gd-DTPA concentration in T1-weighted MR renography studies.

A method for calculating contrast agent concentration from MR signal intensity (SI) was developed and validated for T1‐weighted MR renography (MRR) studies. This method is based on reference measurements of SI and relaxation time T1 in a Gd‐DTPA‐doped water phantom. The same form of SI vs. T1 dependence was observed in human tissues. Contrast concentrations calculated by the proposed method showed no bias between 0 and 1 mM, and agreed better with the reference values derived from direct T1 measurements than the concentrations calculated using the relative signal method. Phantom‐based conversion was used to determine the contrast concentrations in kidney tissues of nine patients who underwent dynamic Gd‐DTPA‐enhanced 3D MRR at 1.5T and 99mTc‐DTPA radionuclide renography (RR). The concentrations of both contrast agents were found to be close in magnitude and showed similar uptake and washout behavior. As shown by Monte Carlo simulations, errors in concentration due to SI noise were below 10% for SNR = 20, while a 10% error in precontrast T1 values resulted in a 12–17% error for concentrations between 0.1 and 1 mM. The proposed method is expected to be particularly useful for assessing regions with highly concentrated contrast. Magn Reson Med 57:1012–1018, 2007.

Temporally-resolved hydrodynamics in the vicinity of a vibrating ionic polymer metal composite

In this paper, we study the hydrodynamics induced by an ionic polymer metal composite (IPMC) cantilever vibrating in a quiescent fluid. Time-resolved particle image velocimetry is used to measure the velocity field in the vicinity of the vibrating IPMC strip and a control volume analysis is utilized to estimate the thrust production per unit IPMC width. The governing fluid dynamics dimensionless parameters are varied parametrically to ascertain the influence of the Reynolds number, the peak tip displacement to IPMC length ratio, and the IPMC aspect ratio. It is found that the Reynolds number is the dominant parameter in determining the thrust produced by the IPMC, while the relative tip displacement and aspect ratio play secondary roles. An increase in the relative tip displacement has a minimal effect on the produced thrust, while an increase in the aspect ratio results in a mild decrease in thrust production. It is further found that estimating the thrust from the mean velocity field significantly under...

A Numerical Study of the Impact of Wavy Walls on Steady Fluid Flow Through a Curved Tube

In this paper, we discuss the impact of a wavy-walled pipe cross-section on steady flow in a curved tube at moderate Dean numbers and small tube radius-to-radius-of-curvature ratios. Parameters investigated include the protrusion height, the number of protrusions around the tube circumference, and the pipe curvature. This work extends a previous analytical investigation that employed a double perturbation expansion to elucidate the flow field as a function of these parameters. Due to the rapid growth in the solution complexity as the number of terms in each expansion increases, the analytical work is relegated to small wall perturbations and low Dean numbers. These barriers are removed in the present study by numerically solving the Navier–Stokes equations at Dean numbers up to 2500. The impact on the axial and secondary flow structures are emphasized, along with the resulting wall shear stress distributions.

Enhanced muscle blood flow with intermittent pneumatic compression of the lower leg during plantar flexion exercise and recovery.

This study tested the hypothesis that intermittent compression of the lower limb would increase blood flow during exercise and postexercise recovery. Data were collected from 12 healthy individuals (8 men) who performed 3 min of standing plantar flexion exercise. The following three conditions were tested: no applied compression (NoComp), compression during the exercise period only (ExComp), and compression during 2 min of standing postexercise recovery. Doppler ultrasound was used to determine superficial femoral artery (SFA) blood flow responses. Mean arterial pressure (MAP) and cardiac stroke volume (SV) were assessed using finger photoplethysmography, with vascular conductance (VC) calculated as VC = SFA flow/MAP. Compared with the NoComp condition, compression resulted in increased MAP during exercise [+3.5 ± 4.1 mmHg (mean ± SD)] but not during postexercise recovery (+1.6 ± 5.9 mmHg). SV increased with compression during both exercise (+4.8 ± 5.1 ml) and recovery (+8.0 ± 6.6 ml) compared with NoComp. There was a greater increase in SFA flow with compression during exercise (+52.1 ± 57.2 ml/min) and during recovery (+58.6 ± 56.7 ml/min). VC immediately following exercise was also significantly greater in the ExComp condition compared with the NoComp condition (+0.57 ± 0.42 ml·min-1·mmHg-1), suggesting the observed increase in blood flow during exercise was in part because of changes in VC. Results from this study support the hypothesis that intermittent compression applied during exercise and recovery from exercise results in increased limb blood flow, potentially contributing to changes in exercise performance and recovery. NEW & NOTEWORTHY Blood flow to working skeletal muscle is achieved in part through the rhythmic actions of the skeletal muscle pump. This study demonstrated that the application of intermittent pneumatic compression during the diastolic phase of the cardiac cycle, to mimic the mechanical actions of the muscle pump, accentuates muscle blood flow during exercise and elevates blood flow during the postexercise recovery period. Intermittent compression during and after exercise might have implications for exercise performance and recovery.

Flow in the Vascular System Post Stent Implantation: Examining the Near-Stent Flow Physics

As a simplified stent model, fully-developed flow of an incompressible, Newtonian fluid through a curved tube with axially aligned wall protuberances is investigated to define the impact of stent implantation on hemodynamic behavior in curved vessels. According to previous research local hemodynamics tends to trigger biochemical pathways that result in the inception and progression of in-stent restenosis (ISR) and ultimately lead to stent failure. In this manuscript, we focus on hemodynamic changes due to stent strut protrusion into the vessel lumen as a facilitator of ISR. We investigate a range of physiologically relevant stent strut heights and flow parameters using computational fluid dynamics (CFD).Copyright

Secondary Flow Structure Induced by Physiologically Relevant Waveform in a Curved Tube

The complex geometry of the vascular system can induce the development of complex primary and secondary flow regimes within blood vessels. Recent literature has focused on the impact of these complex flow regimes on endothelial cells (EC), which line blood vessels, and their role on the progression of vascular disease. One such disease, atherosclerosis has been linked to the reaction of ECs to flow conditions. Atherosclerosis is often treated by stent implantation to return the vessel lumen to its native diameter. It is hypothesized that stent struts may alter the development of secondary flow within the vessel and cause re-stenosis and/or thrombosis distal to the stent.© 2009 ASME