scholarly journals Numerical analysis of the biomechanical effects on micro-vessels by ultrasound-driven cavitation

2021 ◽  
Vol 23 (1) ◽  
Author(s):  
Wenyi Liu ◽  
Jiwen Hu ◽  
Yatao Liu ◽  
Weirui Liu ◽  
Xuekun Chen
Keyword(s):  
Vessel Wall ◽  
Strong Dependence ◽  
Maximum Shear Stress ◽  
Bubble Radius ◽  
Excitation Frequency ◽  
Maximum Value ◽  
Coupling System ◽  
Inner Vessel ◽  
Microvessel Wall ◽  
Insight Into

Purpose: The goal of this study was to evaluate the biomechanical effects such as sonoporation or permeability, produced by ultrasound- driven microbubbles (UDM) within microvessels with various parameters. Methods: In this study, a bubble-fluid-solid coupling system was established through combination of finite element method. The stress, strain and permeability of the vessel wall were theoretically simulated for different ultrasound frequencies, vessel radius and vessel thickness. Results: the bubble oscillation induces the vessel wall dilation and invagination under a pressure of 0.1 MPa. The stress distribution over the microvessel wall was heterogeneous and the maximum value of the midpoint on the inner vessel wall could reach 0.7 MPa as a frequency ranges from 1 to 3 MHz, and a vessel radius and an initial microbubble radius fall within the range of 3.5–13 μm and 1–4 μm, respectively. With the same conditions, the maximum shear stress was equal to 1.2 kPa and occurred at a distance of ±5 μm from the midpoint of 10 μm and the maximum value of permeability was 3.033 × 10–13. Conclusions: Results of the study revealed a strong dependence of biomechanical effects on the excitation frequency, initial bubble radius, and vessel radius. Numerical simulations could provide insight into understanding the mechanism behind bubble-vessel interactions by UDM, which may explore the potential for further improvements to medical applications.

scholarly journals New Insights on the Mechanism of Fatty Acids as Buccal Permeation Enhancers

Pharmaceutics ◽  
2018 ◽  
Vol 10 (4) ◽  
pp. 201 ◽  
Author(s):  
Cristina Padula ◽  
Silvia Pescina ◽  
Sara Nicoli ◽  
Patrizia Santi
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Fluorescein Isothiocyanate ◽  
Penetration Enhancers ◽  
Systemic Delivery ◽  
Permeation Enhancers ◽  
Maximum Value ◽  
The Relationship ◽  
Insight Into ◽  
The Ideal

Buccal mucosa has recently received much attention as a potential route for systemic delivery of drugs, including biologics and vaccines. The aim of this work was to gain insight into the mechanism of fatty acids as buccal permeation enhancers, by studying the effect of a series of medium and long chain fatty acids on the permeation of a model high molecular weight and hydrophilic molecule, fluorescein isothiocyanate labelled dextran (FD-4, m.w. 4 kDa) across porcine esophageal epithelium. A parabolic relationship between fatty acid lipophilicity and enhancement was obtained, regardless of the presence and number of double bonds. The relationship, which resembles the well-known relationship between permeability and lipophilicity of transdermal delivery, presents a maximum value in correspondence of C10 (logP approx. 4). This is probably the ideal lipophilicity for the fatty acid to interact with the lipid domains of the mucosa. When the same analysis was performed on skin data, the same trend was observed, although the maximum value was reached for C12 (logP approx. 5), in agreement with the higher lipophilicity of the skin. The results obtained in the present work represent a significant advancement in the understanding of the mechanisms of action of fatty acids as buccal penetration enhancers.

scholarly journals The effect of vascular diseases on bioimpedance measurements: mathematical modeling

2018 ◽  
Vol 5 (6) ◽  
Author(s):  
Yomna H. Shash ◽  
Mohamed A. A. Eldosoky ◽  
Mohamed T. Elwakad
Keyword(s):  
Mathematical Models ◽  
Vessel Wall ◽  
Vascular Diseases ◽  
Impedance Analysis ◽  
Wide Field ◽  
Vascular Disorders ◽  
Non Invasive ◽  
Novel Method ◽  
Inner Vessel ◽  
Arteries And Veins

Introduction: The non-invasive nature of bioimpedance technique is the reason for the adoption of this technique in the wide field of bio-research. This technique is useful in the analysis of a variety of diseases and has many advantages. Cardiovascular diseases are the most dangerous diseases leading to death in many regions of the world. Vascular diseases are disorders that affect the arteries and veins. Most often, vascular diseases have greater impacts on the blood flow, either by narrowing or blocking the vessel lumen or by weakening the vessel wall. The most common vascular diseases are atherosclerosis, wall swelling (aneurysm), and occlusion. Atherosclerosis is a disease caused by the deposition of plaques on the inner vessel wall, while a mural aneurysm is formed as a result of wall weakness. The main objective of this study was to investigate the effects of vascular diseases on vessel impedance. Furthermore, this study aimed to develop the measurement of vessel abnormalities as a novel method based on the bioimpedance phenomenon. Methods: Mathematical models were presented to describe the impedance of vessels in different vascular cases. In addition, a 3D model of blood vessels was simulated by COMSOL MULTIPHYSICS.5, and the impedance was measured at each vascular condition. Results: The simulation results clarify that the vascular disorders (stenosis, blockage or aneurysm) have significant impact on the vessel impedance, and thus they can be detected by using the bio-impedance analysis. Moreover, using frequencies in KHz range is preferred in detecting vascular diseases since it has the ability to differentiate between the healthy and diseased blood vessel. Finally, the results can be improved by selecting an appropriate electrodes configuration for analysis. Conclusion: From this work, it can be concluded that bioimpedance analysis (BIA) has the ability to detect vascular diseases. Furthermore, the proposed mathematical models are successful at describing different cases of vascular disorders.

Fundamentals of Microwave-Material Interactions and Sintering

1988 ◽  
Vol 124 ◽  
Author(s):  
Wayne R. Tinga
Keyword(s):  
Strong Dependence ◽  
Internal Heat ◽  
Temperature Limit ◽  
Small Samples ◽  
Material Transport ◽  
Material Particle ◽  
Heating Uniformity ◽  
Materials Used ◽  
Insight Into ◽  
Process Material

ABSTRACTBasic interaction mechanisms are shown to depend strongly on the dielectric and magnetic properties of a process material. This causes a strong dependence of power absorption on frequency, material particle size, shape, temperature, and density. Sintering dynamics cause the microstructure of the treated material to change resulting in a change in microwave (1W) heating uniformity and rate. The concept of dielectric mixtures is introduced to predict the dielectric and heating properties of a host material with its inclusions in the form of shells, ellipsoids, spheres, disks and needles. Simplified models are described to give a process designer some insight into the behavior of MW sintering. Microwave power, by its very nature, gives better heating control and efficiency and provides internal heat to aid the material transport during sintering. No inherent temperature limit exists for MW sintering although refractory materials used to contain the process material create an artificial upper limit. It is shown that very high (1500–2000°C) temperatures in small samples can be readily achieved using commercial microwave ovens if appropriate MW transparent sample holders are used.

Dripping instability of a two-dimensional liquid film under an inclined plate

2021 ◽  
Vol 932 ◽  
Author(s):  
Guangzhao Zhou ◽  
Andrea Prosperetti
Keyword(s):  
Liquid Film ◽  
Initial Conditions ◽  
Strong Dependence ◽  
Bond Number ◽  
Quasi Equilibrium ◽  
Two Dimensional ◽  
Inclined Plate ◽  
Maximum Value ◽  
Critical Curvature ◽  
Rayleigh Taylor Instability

It is known that the dripping of a liquid film on the underside of a plate can be suppressed by tilting the plate so as to cause a sufficiently strong flow. This paper uses two-dimensional numerical simulations in a closed-flow framework to study several aspects of this phenomenon. It is shown that, in quasi-equilibrium conditions, the onset of dripping is closely associated with the curvature of the wave crests approaching a well-defined maximum value. When dynamic effects become significant, this connection between curvature and dripping weakens, although the critical curvature remains a useful reference point as it is intimately related to the short length scales promoted by the Rayleigh–Taylor instability. In the absence of flow, when the film is on the underside of a horizontal plate, the concept of a limit curvature is relevant only for small liquid volumes close to a critical value. Otherwise, the drops that form have a smaller curvature and a large volume. The paper also illustrates the peculiarly strong dependence of the dripping transition on the initial conditions of the simulations. This feature prevents the development of phase maps dependent only on the governing parameters (Reynolds number, Bond number, etc.) similar to those available for film flow on the upper side of an inclined plate.

What Constitutes a Smart City?

2019 ◽  
pp. 1-29
Author(s):  
Sekhar Kondepudi ◽  
Ramita Kondepudi
Keyword(s):  
Detailed Analysis ◽  
Smart City ◽  
Strong Dependence ◽  
Common Theme ◽  
Standard Definition ◽  
Definition Of ◽  
Holistic Description ◽  
Insight Into

This chapter provides an insight into what is meant by a Smart City and the underlying factors that make a city smart. The authors answer the question of “what constitutes a smart city” by presenting a multi-faceted approach including a detailed analysis of classical smart city definitions, attributes of a smart city, industry viewpoints and efforts by standards developing organizations. Through this approach, a common theme is established which best describes a smart city. The content of this chapter can therefore form the basis of developing a standard definition of a global smart city, and subsequently can be used to develop a framework to measure the performance of a smart city. The authors also propose a definition which in their view provides a reasonably holistic description of a smart city. However, they recognize that a smart city may mean different things to different stakeholders, and therefore has a strong dependence on the “lens” through which a smart city is viewed.

What Constitutes a Smart City?

2018 ◽  
pp. 1-29
Author(s):  
Sekhar Kondepudi ◽  
Ramita Kondepudi
Keyword(s):  
Detailed Analysis ◽  
Smart City ◽  
Strong Dependence ◽  
Common Theme ◽  
Standard Definition ◽  
Definition Of ◽  
Holistic Description ◽  
Insight Into

This chapter provides an insight into what is meant by a Smart City and the underlying factors that make a city smart. The authors answer the question of “what constitutes a smart city” by presenting a multi-faceted approach including a detailed analysis of classical smart city definitions, attributes of a smart city, industry viewpoints and efforts by standards developing organizations. Through this approach, a common theme is established which best describes a smart city. The content of this chapter can therefore form the basis of developing a standard definition of a global smart city, and subsequently can be used to develop a framework to measure the performance of a smart city. The authors also propose a definition which in their view provides a reasonably holistic description of a smart city. However, they recognize that a smart city may mean different things to different stakeholders, and therefore has a strong dependence on the “lens” through which a smart city is viewed.

Elevation of inflammatory S100A8/S100A9 complexes in intracranial aneurysms

2020 ◽  
Vol 12 (11) ◽  
pp. 1117-1121
Author(s):  
Antonius Mattheus de Korte ◽  
René Aquarius ◽  
Thomas Vogl ◽  
Johannes Roth ◽  
Ronald H M A Bartels ◽  
...  
Keyword(s):  
Vessel Wall ◽  
Primary Outcome ◽  
Control Group ◽  
Healthy Controls ◽  
Activated Macrophages ◽  
Related Factors ◽  
Aneurysm Wall ◽  
Healthy Control ◽  
Insight Into

BackgroundInflammation-related factors might give further insight into the pathophysiology of vessel wall inflammation and intracranial aneurysm (IA) rupture. One of these factors is the protein complex S100A8/A9, which is released by neutrophils, monocytes, and activated macrophages and is known for its role in cardiovascular disease.ObjectiveTo determine if venous S100A8/A9 levels in patients with a ruptured IA (rIA) or unruptured IA (uIA) are elevated compared with a control group. Second, to assess differences between venous and intra-aneurysmal S100A8/A9 levels of rIA and uIA patients.MethodsA prospective case study was performed between June 2016 and May 2017 in patients harboring a ruptured or unruptured saccular IA. Primary outcome measures were individual S100A8/A9 serum concentrations as measured in venous and intra-aneurysmal blood samples during endovascular treatment. Venous serum S100A8/A9 concentrations from a healthy control group served as a reference.ResultsWe included 16 patients with either a rIA or uIA and 47 healthy controls. Venous S100A8/A9 concentrations were higher in aneurysm patients (rIA and uIA) than those of healthy controls (P≤0.001). S100A8/A9 concentrations were higher in intra-aneurysmal samples than in venous samples of rIA patients (P=0.011). This difference was not found in uIA patients (P=0.054). Intra-aneurysmal S100A8/A9 levels were higher in rIAs than in uIAs (P=0.04).ConclusionsVenous S100A8/A9 levels are elevated in patients with both rIAs and uIAs compared with healthy controls and likely represents aneurysm wall inflammation. S100A8/A9 causes macrophage-induced inflammation and degeneration of the vessel wall which might explain higher intra-aneurysmal S100A8/A9 levels found in rIAs than in uIAs.

Off-Axis Torsion Tests on Tubular Specimens of Steel

2001 ◽  
Vol 123 (3) ◽  
pp. 268-273 ◽  
Author(s):  
Takenobu Takeda ◽  
Zhongchun Chen
Keyword(s):  
Shear Stress ◽  
Yield Stress ◽  
Maximum Shear Stress ◽  
Torsion Test ◽  
Combined Loading ◽  
Anisotropic Hardening ◽  
Principal Stresses ◽  
Maximum Value ◽  
The Difference ◽  
Tubular Specimens

In order to analyze the anisotropic hardening behavior of metals, an off-axis torsion test by combined loading is developed. In this test, the maximum shear stress direction φ can be changed from 0 deg to 90 deg while the ratio of maximum and minimum principal stresses is kept at −1. With increasing angle φ, the yield stress of the torsional-prestrained steel decreases; the difference between the directions of the maximum shear stress and principal shear strain increment rises to a maximum value and then decreases. It is experimentally verified that anisotropy is more severe when a smaller offset strain is used in defining the yield stress.

THz-induced luminescence in ZnO nanocrystals with strong dependence on the excitation frequency

2016 ◽  
Author(s):  
Masaya Nagai ◽  
Shingo Aono ◽  
Masaaki Ashida ◽  
Keigo Kawase ◽  
Akinori Irizawa ◽  
...  
Keyword(s):  
Strong Dependence ◽  
Excitation Frequency ◽  
Zno Nanocrystals

More Insight into the VHF-Glow-Discharge by Plasma Impedance Measurements

1994 ◽  
Vol 336 ◽  
Author(s):  
U. Kroll ◽  
Y. Ziegler ◽  
J. Meier ◽  
H. Keppner ◽  
A. Shah
Keyword(s):  
Room Temperature ◽  
Hydrogen Plasma ◽  
Excitation Frequency ◽  
Sheath Thickness ◽  
Parallel Plate Capacitor ◽  
Peak Voltage ◽  
Impedance Measurements ◽  
Plasma Impedance ◽  
Plasma Excitation ◽  
Insight Into

ABSTRACTWe performed plasma impedance measurements at room temperature for a hydrogen plasma using an impedance analyser. The plasma excitation frequency range spans from 40 to 70 MHz. Both the real and imaginary part of the impedance decrease monotonously with increasing frequency. These measurements are in agreement with prior experimental observations [1], that the required peak-to-peak voltage between the electrodes is reduced at higher excitation frequencies. Using a simple equivalent circuit for the plasma this effect can be mainly attributed to the increased sheath capacitance. Furthermore, by modelling the sheath with a simple parallel plate capacitor, its thickness could be estimated: it decreases from 2 MM at 40 MHz to about 1.4 MM at 70 MHz plasma excitation frequency. Finally, a possible link between the decreasing sheath thickness on the increase of deposition rate is discussed.

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