The effect of stenosis rate and Reynolds number on local flow characteristics and plaque formation around the atherosclerotic stenosis

Purpose: Atherosclerosis causes plaque to build-up in arteries. Effect of the specific local hemodynamic environment around an atherosclerotic plaque on the thrombosis formation does not remain quite clear but is believed to be crucial. The aim of this study is to uncover the flow effects on plaques formation. Methods: To study the mechanically regulated plaque formation, the flow fields in artery blood vessels with different stenosis rates at various Reynolds numbers were simulated numerically with the two-dimensional axisymmetric models, and the hemodynamic characteristics around the plaque were scaled with stenosis rate and Reynolds number. Results: The results showed that increases of both Reynolds number and stenosis rate facilitated the occurrence of flow separation phenomenon, extended recirculation zone, and upregulated the maximum normalized wall shear stress near the plaque throat section while downregulated the minimal normalized wall shear stress at the front shoulder of plaque, as it should be; in the atherosclerotic plaque leeside of the recirculation zone, an obvious catch bond region of wall shear stress might exist especially under low Reynolds number with stenosis rate smaller than 30%. This catch bond region in the plaque leeside might be responsible for the LBF (low blood flow)-enhanced formation of the atherosclerotic plaque. Conclusions: This work may provide a novel insight into understanding the biomechanical effects behind the formation and damage of atherosclerotic plaques and propose a new strategy for preventing atherosclerotic diseases.

Dual absorption spectral changes by light-triggered shuttling in bistable [2]rotaxanes with non-destructive readout

The photochromic [2]rotaxanes have dual spectral variation characteristics: the spectral changes of the azobenzene (AB) unit and the charge-transfer band. By employing the CT bond region as output signal, non-destructive readout of optical information could be achieved.

Mechanical Performance Analysis of Composite Scarf Joints with Debond Flaw

The adhesive structural mechanical performance is influenced by debond flaw. This paper presents a research on the effect of flaws on the mechanical performance of composite scarf joints. The experimental results show that the load-carrying capacity of composite scarf joints changed along with the location of the debond flaw. The location of the flaw in the bondline influences the failure mode. Additionally, the finite element method was employed to obtain the failure mode of the composite scarf joint. The adhesively bonded joints were modeled using ABAQUS software. The computational results show that flaws located at the edge of the bond region result in more pronounced load reduction than which located at the middle of bond region.

Microstructural Changes of FSX-414 Superalloy during TLP Bonding

The as-cast FSX-414 Co-based superalloy samples were solution treated at 1150oC for 4h and then aged at 980oC for 4h. Specimens for joining were cut from the as-cast ingot and TLP bonding carried out at the same conditions as for the solution and solution+aging treatment, using MBF-30 interlayer. Microstructures were studied for as-cast, heat treated and TLP bonded specimens. These studies showed that the ununiform distributed carbides of MC type in the as-cast specimens replaced by M23C6 type carbides with uniform distribution in the heat treated microstructure. Due to complete isothermal solidification, no eutectic structure in the bond region were wasobserved, but some intermetallics in the diffusion affected zone (DAZ) were observed. Microhardness tests were used to compare the hardness of age hardened specimens with bonded specimens at the same heat treatment condition. Hardness profile also showed a peak in DAZ region in spite of complete isothermal solidification.

Demonstration of catch bonds between an integrin and its ligand

Binding of integrins to ligands provides anchorage and signals for the cell, making them prime candidates for mechanosensing molecules. How force regulates integrin–ligand dissociation is unclear. We used atomic force microscopy to measure the force-dependent lifetimes of single bonds between a fibronectin fragment and an integrin α5β1-Fc fusion protein or membrane α5β1. Force prolonged bond lifetimes in the 10–30-pN range, a counterintuitive behavior called catch bonds. Changing cations from Ca2+/Mg2+ to Mg2+/EGTA and to Mn2+ caused longer lifetime in the same 10–30-pN catch bond region. A truncated α5β1 construct containing the headpiece but not the legs formed longer-lived catch bonds that were not affected by cation changes at forces <30 pN. Binding of monoclonal antibodies that induce the active conformation of the integrin headpiece shifted catch bonds to a lower force range. Thus, catch bond formation appears to involve force-assisted activation of the headpiece but not integrin extension.

AN INTENSITY TESTING MODEL AND EXAMINATION OF GOLD–SILICON WAFER BONDING

A bonding intensity testing method, called Press-arm model, has been successfully designed and verified by Ansys finite element analysis. The gold–silicon bonding strength [σ2] = 238 MPa has been measured by the Press-arm model. We can probably determine the [σ2] value and compare the bonding strengths by the Press-arm length l. The model can also be used in other type of bonding. The bond region is sufficiently stronger than the silicon substrate. A substrate- Si/Cr/Au/poly - Si/Au and a silicon substrate is bonded at 380–450°C. It occurs as soon as the dissolving of the SiO 2 layer by silicidation of the Cr barrier layer. To avoid gold contamination to the silicon die, an excess annealing temperature (about 20°C higher than Au – Si eutectic horizontal) is used. The bonding surface with brick pattern is in favor of Au – Si bonding.